The mandate of EUMETSAT is providing space observations for operational meteorology and climate monitoring. EUMETSAT operates geostationary and sun-synchronous polar orbiting satellites through mandatory programmes. Optional programmes provide further observations for altimetry and oceanography. EUMETSAT makes available data from partner agencies’ satellites to the user community through third party programmes. The current fleet of operational geostationary spacecraft comprises Meteosat-7, which is the last satellite of the first generation and the four satellites of the Second Generation of Meteosat (MSG), Meteosat-8, Meteosat-9, Meteosat-10 and Meteosat-11. The EUMETSAT Polar System (EPS) provides data from sun-synchronous polar orbit with currently two satellites: Metop-B, the second of a series of three satellites, launched in September 2012 and currently the prime satellite, and Metop-A, the first of the series, in orbit since October 2006. These satellites are part of the Initial Joint Polar System (IJPS) together with the US. EUMETSAT’s first optional programme continues to provide data from the Jason-2 satellite since summer 2008. The follow on satellite Jason-3 was successfully launched and commissioned in 2016 and is now providing the reference altimetry mission. To assure continuity in the mandatory missions the development of Meteosat Third Generation (MTG) is ongoing. The EPS-SG EPS Second generation) programme is now under full development. In the frame of the Copernicus Programme EUMETSAT operates the Sentinel-3A satellite, which was launched in February 2016. EUMETSAT is providing operational marine products from the Sentinel-3A satellite. Sentinel-3B, is scheduled to be launched early 2018.

The Meteosat Third Generation (MTG) series of future European geostationary meteorological satellites consists of two types of satellites, the imaging satellites (MTG-I) and the sounding satellites (MTG-S). The Infrared Sounder (IRS) is one of the two instruments hosted on board the MTG-S satellites. The scope of the IRS mission is to provide the user community with information on time evolution of humidity and temperature distribution, as function of latitude, longitude and altitude. Regarding time and space sampling, the entire Earth disk will be covered, with particular focus on Europe, which will be revisited every 30 minutes. This paper presents a synthetic overview of the mission and the instrument, and will go through the level 1 processing chain which takes instrument raw data to obtain spectrally and radiometrically calibrated and geolocalised radiances, called level 1b products. A discussion will be presented around the radiances uniformisation in space, spectral range and time and its impact for the users community.

In the EarthCARE mission the BBR (Broad Band Radiometer) has the role of measuring the net earth radiance (i.e. total reflected-solar and thermally-emitted radiances), from the same earth scene as viewed by the other instruments (aerosol lidar, cloud radar and spectral imager). It does this measurement at 10km scene size and in 3 view angles. It is an imaging radiometer in that it uses micro-bolometer linear-array detector (pushbroom orientation), to over-sample these required scenes, with the samples being binned on-ground to produce the 10km radiance data. For the measurements of total earth radiance, the BBR is based on the heritage of Earth Radiation Budget (ERB) instruments. The ground calibration methods of this type of sensor is technically very similar to other EO instruments that measure in the thermalIR, but with added challenges: (1) The thermal-IR measurement has to have a much wider spectral range than normal thermal-IR channels to cover the whole earth-emission spectrum i.e. ~4 to >50microns; (2) The 2nd channel (reflected solar radiance) must also have a broad response to cover almost the whole solar spectrum, i.e. ~0.3 to 4microns. And this solar channel must be measured on the same radiometric calibration as the thermal channel, which in practice is best done by using the same radiometer for both channels. The radiometer is designed to be very broad-band i.e. 0.3 to 50microns (i.e. more than two decades), to cover both ranges, and a switchable spectral filter (short-pass cutoff at 4μm) is used to separate the channels. The on-ground measurements which are required to link the calibration of these channels will be described. A calibration of absolute responsivity in each of the two bands is needed; in the thermal-IR channel this is by the normal method of using a calibrated blackbody test source, and in the solar channel it is by means of a narrow-band (laser) and a reference radiometer (from NPL). A calibration of relative spectral response is also needed, across this wide range, for the purpose of linking the two channels, and for converting the narrow-band solar channel measurement to broad-band.

Remote sensing of pollutants are enabled from a satellite in a geostationary orbit containing an imaging spectrometer encompassing the wavelength ranges of 290 - 490 nm and 540 - 740 nm. As the first of NASA's Earth Venture Instrument Program, the Tropospheric Emissions: Monitoring of Pollution (TEMPO) program will utilize this instrument to measure hourly air quality over a large portion of North America. The focal plane subsystem (FPS) contains two custom designed and critically aligned full frame transfer charge coupled devices (active area: 1028 x 2048, 18 μm) within a focal plane array package designed for radiation tolerance and space charging rejection. In addition, the FPS contains custom distributed focal plane electronics that provide all necessary clocks and biases to the sensors, receives all analog data from the sensors and performs 14 bit analog to digital conversion for upstream processing. Finally, the FPS encompasses custom low noise cables connecting the focal plane array and associated electronics. This paper discusses the design and performance of this novel focal plane subsystem with particular emphasis on the optical performance achieved including alignment, quantum efficiency, and modulation transfer function.

The Landsat 9 mission will continue the legacy of Earth remote sensing that started in 1972. The Operational Land Imager 2 (OLI 2) is one of two instruments on the Landsat 9 satellite. The OLI 2 instrument is essentially a copy of the OLI instrument flying on Landsat 8. A key element of the OLI 2 instrument is the focal plane subsystem, or FPS, which consists of the focal plane array (FPA), the focal plane electronics (FPE) box, and low-thermal conductivity cables. This paper presents design details of the OLI 2 FPS. The FPA contains 14 critically-aligned focal plane modules (FPM). Each module contains 6 visible/near-IR (VNIR) detector arrays and three short-wave infrared (SWIR) arrays. A complex multi-spectral optical filter is contained in each module. Redundant pixels for each array provide exceptional operability. Spare detector modules from OLI were recharacterized after six years of storage. Radiometric test results are presented and compared with data recorded in 2010. Thermal, optical, mechanical and structural features of the FPA will be described. Special attention is paid to the thermal design of the FPA since thermal stability is crucial to ensuring low-noise and low-drift operation of the detectors which operate at -63°C. The OLI 2 FPE provides power, timing, and control to the focal plane modules. It also digitizes the video data and formats it for the solid-state recorder. Design improvements to the FPA-FPE cables will be discussed and characterization data will be presented. The paper will conclude with the status of the flight hardware assembly and testing.

Revisiting time and global coverage are two major requirements for most of the remote sensing satellites. Constellation of satellites can get the benefit of short revisit time and global coverage. Typically, remote sensing satellites prefer to choose Sun Synchronous Orbit (SSO) because of fixed revisiting time and Sun beta angle. The system design and mission operation will be simple and straightforward. However, if we focus on providing remote sensing and store-and-forward communication services for low latitude countries, Sun Synchronous Orbit will not be the best choice because we need more satellites to cover the communication service gap in low latitude region. Sometimes the design drivers for remote sensing payloads are conflicted with the communication payloads. For example, lower orbit altitude is better for remote sensing payload performance, but the communication service zone will be smaller and we need more satellites to provide all time communication service. The current studies focus on how to provide remote sensing and communication services for low latitude countries. A cost effective approach for the mission, i.e. constellation of microsatellites, will be evaluated in this paper.

NASA’s Sustainable Land Imaging (SLI) program, managed through the Earth Science Technology Office, aims to develop technologies that will provide future Landsat-like measurements. SLI aims to develop a new generation of smaller, more capable, less costly payloads that meet or exceed current imaging capabilities. One projects funded by this program is Ball’s Compact Hyperspectral Prism Spectrometer (CHPS), a visible-to-shortwave imaging spectrometer that provides legacy Landsat data products as well as hyperspectral coverage suitable for a broad range of land science products. CHPS exhibits extremely low straylight and accommodates full aperture, full optical path calibration needed to ensure the high radiometric accuracy demanded by SLI measurement objectives. Low polarization sensitivity in visible to near-infrared bands facilitates coastal water science as first demonstrated by the exceptional performance of the Operational Land Imager. Our goal is to mature CHPS imaging spectrometer technology for infusion into the SLI program. Our effort builds on technology development initiated by Ball IRAD investment and includes laboratory and airborne demonstration, data distribution to science collaborators, and maturation of technology for spaceborne demonstration. CHPS is a three year program with expected exiting technology readiness of TRL-6. The 2013 NRC report Landsat and Beyond: Sustaining and Enhancing the Nations Land Imaging Program recommended that the nation should “maintain a sustained, space-based, land-imaging program, while ensuring the continuity of 42-years of multispectral information.” We are confident that CHPS provides a path to achieve this goal while enabling new science measurements and significantly reducing the cost, size, and volume of the VSWIR instrument.

The CubeSat Infrared Atmospheric Sounder (CIRAS) is a NASA Earth Science Technology Office (ESTO) sponsored mission to demonstrate key technologies used in very high spectral resolution infrared remote sensing of Earth’s atmosphere from space. CIRAS was awarded under the ESTO In-flight Validation of Earth Science Technologies (InVEST) program in 2015 and is currently under development at NASA JPL with key subsystems being developed by industry. CIRAS incorporates key new instrument technologies including a 2D array of High Operating Temperature Barrier Infrared Detector (HOT-BIRD) material, selected for its high uniformity, low cost, low noise and higher operating temperatures than traditional materials. The second key technology is an MWIR Grating Spectrometer (MGS) designed to provide imaging spectroscopy for atmospheric sounding in a CubeSat volume. The MGS is under development by Ball Aerospace with the grating and slit developed by JPL. The third key technology is a blackbody fabricated with JPL’s black silicon to have very high emissivity in a flat plate construction. JPL will also develop the mechanical, electronic and thermal subsystems for CIRAS, while the spacecraft will be a 6U CubeSat developed by Blue Canyon Technologies. This paper provides an overview of the design and acquisition approach, and provides a status of the current development.

The Snow and Water Imaging Spectrometer (SWIS) is a fast, high-uniformity, low-polarization sensitivity imaging spectrometer and telescope system designed for integration on a 6U CubeSat platform. Operating in the 350-1700 nm spectral region with 5.7 nm sampling, SWIS is capable of simultaneously addressing the demanding needs of coastal ocean science and snow and ice monitoring. New key technologies that facilitate the development of this instrument include a linear variable anti-reflection (LVAR) detector coating for stray light management, and a single drive on-board calibration mechanism utilizing a transmissive diffuser for solar calibration. We provide an overview of the SWIS instrument design and potential science applications and describe the instrument assembly and alignment, supported by laboratory measurements.

The increasing number of Earth Observation missions launched over the last decade has stimulated the development of a large number of satellite instruments able to acquire and deliver rich imageries suitable to support many different applications. Recent advances in electronics, optical manufacturing and remote sensing are now enabling the conception of smaller instruments that could enable new mission concepts at lower costs such as the adoption of satellite constellations for improved temporal resolution. In this paper we present the development of an innovative optical payload named STREEGO suitable for Earth Observation from Low Earth Orbit (LEO) microsatellites. STREEGO is an athermal, fully reflective telescope based on a three mirror anastigmat (TMA) design which features a 200 mm aperture, a focal length of 1.2 m and an across-track Field of View (FoV) of about 2°. Leveraging on a large format two-dimensional CMOS sensor with a pixel size of 5.5 μm, it delivers a nominal modulation transfer function (MTF) of 64% at Nyquist frequency and a ground sampling distance of 2.75 m from an altitude of 600 km. In the design of the instrument detailed stray-light and tolerance analyses were performed and a worst-case thermal model was also developed to ensure that optimal image quality is achieved under operational conditions. After preliminary tests on a Demonstrator Model (DM), an Engineering Model (EM) of the payload with a mass of 20 kg including its electronics and mounting interfaces has been integrated and tested in laboratory and it is now ready to start an environmental test campaign to increase its Technology Readiness Level (TRL). The qualification of the instrument and the results achieved are presented in detail.

Small satellites (“SmallSats”) are a growing segment of the Earth imaging and remote sensing market. Designed to be relatively low cost and with performance tailored to specific end-use applications, they are driving changes in optical telescope assembly (OTA) requirements. OTAs implemented in silicon carbide (SiC) provide performance advantages for space applications but have been predominately limited to large programs. A new generation of lightweight and thermally-stable designs is becoming commercially available, expanding the application of SiC to small satellites. This paper reviews the cost and technical advantages of an OTA designed using SiC for small satellite platforms. Taking into account faceplate fabrication quilting and surface distortion after gravity release, an optimized open-back SiC design with a lightweighting of 70% for a 125-mm SmallSat-class primary mirror has an estimated mass area density of 2.8 kg/m² and an aspect ratio of 40:1. In addition, the thermally-induced surface error of such optimized designs is estimated at λ/150 RMS per watt of absorbed power. Cost advantages of SiC include reductions in launch mass, thermal-management infrastructure, and manufacturing time based on allowable assembly tolerances.

The airborne Portable Remote Imaging Spectrometer (PRISM) instrument is based on a fast (F/1.8) Dyson spectrometer operating at 350-1050 nm and a two-mirror telescope combined with a Teledyne HyViSI 6604A detector array. Raw PRISM data contain electronic and optical artifacts that must be removed prior to radiometric calibration. We provide an overview of the process transforming raw digital numbers to calibrated radiance values. Electronic panel artifacts are first corrected using empirical relationships developed from laboratory data. The instrument spectral response functions (SRF) are reconstructed using a measurement-based optimization technique. Removal of SRF effects from the data improves retrieval of true spectra, particularly in the typically low-signal near-ultraviolet and near-infrared regions. As a final step, radiometric calibration is performed using corrected measurements of an object of known radiance. Implementation of the complete calibration procedure maximizes data quality in preparation for subsequent processing steps, such as atmospheric removal and spectral signature classification.

Pacific Advanced Technology (PAT) has developed an infrared hyperspectral camera based on diffractive optic arrays. This approach to hyperspectral imaging has been demonstrated in all three infrared bands SWIR, MWIR and LWIR. The hyperspectral optical system has been integrated into the cold-shield of the sensor enabling the small size and weight of this infrared hyperspectral sensor. This new and innovative approach to an infrared hyperspectral imaging spectrometer uses micro-optics that are made up of an area array of diffractive optical elements where each element is tuned to image a different spectral region on a common focal plane array. The lenslet array is embedded in the cold-shield of the sensor and actuated with a miniature piezo-electric motor. This approach enables rapid infrared spectral imaging with multiple spectral images collected and processed simultaneously each frame of the camera. This paper will present our optical mechanical design approach which results in an infrared hyper-spectral imaging system that is small enough for a payload on a small satellite, mini-UAV, commercial quadcopter or man portable. Also, an application of how this spectral imaging technology can easily be used to quantify the mass and volume flow rates of hydrocarbon gases. The diffractive optical elements used in the lenslet array are blazed gratings where each lenslet is tuned for a different spectral bandpass. The lenslets are configured in an area array placed a few millimeters above the focal plane and embedded in the cold-shield to reduce the background signal normally associated with the optics. The detector array is divided into sub-images covered by each lenslet. We have developed various systems using a different number of lenslets in the area array. Depending on the size of the focal plane and the diameter of the lenslet array will determine the number of simultaneous different spectral images collected each frame of the camera. A 2 x 2 lenslet array will image four different spectral images of the scene each frame and when coupled with a 512 x 512 focal plane array will give spatial resolution of 256 x 256 pixel each spectral image. Another system that we developed uses a 4 x 4 lenslet array on a 1024 x 1024 pixel element focal plane array which gives 16 spectral images of 256 x 256 pixel resolution each frame. This system spans the SWIR and MWIR bands with a single optical array and focal plane array.

We report an innovative simple alignment method for a VNIR spectrometer in the wavelength region of 400–900 nm; this device is later combined with fore-optics (a telescope) to form a f/2.5 hyperspectral imaging spectrometer with a field of view of ±7.68°. The detector at the final image plane is a 640×480 charge-coupled device with a 24 μm pixel size. We first assembled the fore-optics and the spectrometer separately and then combined them via a slit co-located on the image plane of the fore-optics and the object plane of the spectrometer. The spectrometer was assembled in three steps. In the initial step, the optics was simply assembled with an optical axis guiding He-Ne laser. In the second step, we located a pin-hole on the slit plane and a Shack-Hartmann sensor on the detector plane. The wavefront errors over the full field were scanned simply by moving the point source along the slit direction while the Shack-Hartmann sensor was constantly conjugated to the pin-hole position by a motorized stage. Optimal alignment was then performed based on the reverse sensitivity method. In the final stage, the pin-hole and the Shack-Hartmann sensor were exchanged with an equispaced 10 pin-hole slit called a field identifier and a detector. The light source was also changed from the laser (single wavelength source) to a krypton lamp (discrete multi-wavelength source). We were then easily able to calculate the distortion and keystone on the detector plane without any scanning or moving optical components; rather, we merely calculated the spectral centroids of the 10 pin-holes on the detector. We then tuned the clocking angles of the convex grating and the detector to minimize the distortion and keystone. The final assembly was tested and found to have an RMS WFE < 90 nm over the entire field of view, a keystone of 0.08 pixels, a smile of 1.13 pixels and a spectral resolution of 4.32 nm.

Prior work has demonstrated that curved focal plan arrays (FPA) enable lenses for traditional cameras with improved image quality and fewer elements as compared to existing flat image planes. There is an increasing interest in the development of curved focal planes for other imaging applications using a variety of surface contours. In this work, the potential performance improvements of a hyperspectral imaging system (HSI) with a curved FPA are explored using Corning’s existing hyperspectral designs. We evaluated the effect of curved FPAs for spectrometers from the free-space and monolithic Offner class as well as the Dyson form. While these designs are already optimized with aspheric mirrors, the addition of the curved FPA provided additional performance improvements. Surface types considered for the FPA include aspheric, toroidal, anamorphic and free-forms. All of these FPA surface types are manufacturable. The surfaces providing optimum performance offer guidelines for future curved FPA development. We found that multiple design parameters, such as size, weight, f-number, field of view and relative cost can be improved compared with current state-of-the-art flat FPAs. A free-space Offner spectrometer, for example, can be reduced 30% in size, or improved by 20% in f-number.

For imaging spectrometers beside the polarization sensitivity and efficiency the imaging quality of the diffraction grating is essential. Low aberration imaging quality of the grating is required not to limit the overall imaging quality of the instrument. The wavefront aberration of an optical grating is a combination of the substrate wavefront and the grating wavefront. During the manufacturing process of the grating substrate different processes can be applied in order to minimize the wavefront aberrations. The imaging performance of the grating is also optimized due to the recording setup of the holography and a special technique to apply blazed profiles also in photoresist of curved substrates. This technology of holographically manufactured gratings is used for transmission and reflection gratings on different types of substrates like prisms, convex and concave spherical and aspherical surface shapes, free-form elements. All the manufactured gratings are monolithic and can be coated with high reflection and anti-reflection coatings. Prism substrates were used to manufacture monolithic GRISM elements for the UV to IR spectral range preferably working in transmission. Besides of transmission gratings, numerous spectrometer setups (e.g. Offner, Rowland circle, Czerny-Turner system layout) working on the optical design principles of reflection gratings. The present approach can be applied to manufacture high quality reflection gratings for the EUV to the IR. In this paper we report our latest results on manufacturing lowest wavefront aberration gratings based on holographic processes in order to enable at least diffraction limited complex spectrometric setups over certain wavelength ranges. Beside the results of low aberration gratings the latest achievements on improving efficiency together with less polarization sensitivity and multi-band performance of diffractive gratings will be shown.

The Radiometric Calibration Test Site (RadCaTS) is an automated facility developed by the Remote Sensing Group (RSG) at the University of Arizona to provide radiometric calibration data for airborne and satellite sensors. RadCaTS uses stationary ground-viewing radiometers (GVRs) to spatially sample the surface reflectance of the site. The number and location of the GVRs is based on previous spatial, spectral, and temporal analyses of Railroad Valley. With the increase in high-resolution satellite sensors, there is renewed interest in examining the spatial uniformity the 1-km² RadCaTS area at scales smaller than a typical 30-m sensor. RadCaTS is one of the four instrumented sites currently in the CEOS WGCV Radiometric Calibration Network (RadCalNet), which aims to harmonize the post-launch radiometric calibration of satellite sensors through the use of a global network of automated calibration sites. A better understanding of the RadCaTS spatial uniformity as a function of pixel size will also benefit the RadCalNet work. RSG has recently acquired a commercially-available small unmanned airborne system (sUAS) system, with which preliminary spatial homogeneity measurements of the 1-km² RadCaTS area were made. This work describes an initial assessment of the airborne platform and integrated camera for spatial studies of RadCaTS using data that were collected in 2016 and 2017.

A small portable transfer radiometer has been developed as part of an effort to ensure the quality of upwelling radiance at automated test sites used for vicarious calibration in the solar reflective. The test sites, such as the one located at Railroad Valley, are used to predict top-of-atmosphere reflectance relying on ground-based measurements of the atmosphere and surface. The portable transfer radiometer is designed for one-person operation for on-site field calibration the instrumentation used to determine ground-leaving radiance. The current work describes the laboratorybased calibration of the transfer radiometer highlighting the expected accuracy and SI-traceability. Results from recent field deployments of the transfer radiometer are presented to show how the sensor is to be used for 1) evaluating the health of the automated site radiometers, 2) characterizing the surface being measured at the automated test sites, and 3) assessing the error budget for top-of-atmosphere reflectance prediction the test site characterization. Additionally, results from using the transfer radiometer for a radiance-based calibration of the Operational Land Imager are presented.

The Moderate Resolution Imaging Spectroradiometer (MODIS) instruments have successfully operated for more than 17 and 15 years, respectively, on-board the NASA’s Earth Observing System (EOS) Terra and Aqua spacecraft. MODIS level 1B (L1B) data products include top of the atmosphere (TOA) reflectance factors for the reflective solar bands (RSB) and radiances for both the RSB and the thermal emissive bands (TEB), and their associated uncertainty indices (UI) at a pixel-by-pixel level. This paper provides a brief review of MODIS L1B calibration algorithms, including improvements made in recent years. It presents an update of sensor calibration uncertainty assessments with a focus on several new contributors resulting from changes in sensor characteristics and on-orbit calibration approaches and the impact due to these changes on the L1B data quality. Also discussed in this paper are potential changes that could be made to continue improving the quality of MODIS L1B uncertainty product.

The MODerate-resolution Imaging Spectroradiometer (MODIS) is one of the primary instruments in the National Aeronautics and Space Administration (NASA) Earth Observing System (EOS). The first MODIS instrument was launched in December 1999 on-board the Terra spacecraft. A follow on MODIS was launched on an afternoon orbit in 2002 and is aboard the Aqua spacecraft. Both MODIS instruments are very akin, has 36 bands, among which bands 20 to 25 are Middle Wave Infrared (MWIR) bands covering a wavelength range from approximately 3.750 μm to 4.515 μm. It was found that there was severe contamination in these bands early in mission but the effect has not been characterized and mitigated at the time. The crosstalk effect induces strong striping in the Earth View (EV) images and causes significant retrieval errors in the EV Brightness Temperature (BT) in these bands. An algorithm using a linear approximation derived from on-orbit lunar observations has been developed to correct the crosstalk effect and successfully applied to mitigate the effect in both Terra and Aqua MODIS Long Wave Infrared (LWIR) Photovoltaic (PV) bands. In this paper, the crosstalk effect in the Aqua MWIR bands is investigated and characterized by deriving the crosstalk coefficients using the scheduled Aqua MODIS lunar observations for the MWIR bands. It is shown that there are strong crosstalk contaminations among the five MWIR bands and they also have significant crosstalk contaminations from Short Wave Infrared (SWIR) bands. The crosstalk correction algorithm previously developed is applied to correct the crosstalk effect in these bands. It is demonstrated that the crosstalk correction successfully reduces the striping in the EV images and improves the accuracy of the EV BT in the five bands as was done similarly for LWIR PV bands. The crosstalk correction algorithm should thus be applied to improve both the image quality and radiometric accuracy of the Aqua MODIS MWIR bands Level 1B (L1B) products.

Observations in the Terra MODIS PVLWIR bands 27 – 30 are known to be influenced by electronic crosstalk from those bands as senders and into those same bands as receivers. The magnitude of this crosstalk affecting L1B radiances has been steadily increasing throughout the mission lifetime, and has resulted in several detectors within these bands to be unusable for making L2 and L3 science products. In recent years, the crosstalk contamination has been recognized as compromising the climate quality status of several MODIS L2 and L3 science products that depend on the PVLWIR bands. In response, the MODIS Characterization Support Team (MCST) has undertaken an effort to generate a crosstalk correction algorithm in the operational L1B radiance algorithm. The correction algorithm has been tested and established and crosstalk corrected L1B radiances have been tested in several Terra MODIS L2 science product algorithms, including MOD35 (Cloud Mask), MOD06 (Cloud Fraction, Cloud Particle Phase, Cloud Top Properties), and MOD07 (Water Vapor Profiles). Comparisons of Terra MODIS to Aqua MODIS and Terra MODIS to MetOp-A IASI show that long-term trends in Collection 6 L1B radiances and the associated L2 and L3 science products are greatly improved by the crosstalk correction. The crosstalk correction is slated for implementation into Collect 6.1 of MODIS processing.

The DC restore (DCR) process of MODIS instrument maintains the output of a detector at focal plane assembly (FPA) within the dynamic range of subsequent analog-to-digital converter, by adding a specific offset voltage to the output. The DCR offset value is adjusted per scan, based on the comparison of the detector response in digital number (DN) collected from the blackbody (BB) view with target DN saved as an on-board look-up table. In this work, the MODIS DCR mechanism is revisited, with the trends of DCR offset being provided for thermal emissive bands (TEB). Noticeable changes have been occasionally found which coincide with significant detector gain change due to various instrumental events such as safe-mode anomaly or FPA temperature fluctuation. In general, MODIS DCR functionality has been effective and the change of DCR offset has no impact to the quality of MODIS data. One exception is the Earth view (EV) data saturation of Aqua MODIS LWIR bands 33, 35 ad 36 during BB warm-up cool-down (WUCD) cycle which has been observed since 2008. The BB view of their detectors saturate when the BB temperature is above certain threshold so the DCR cannot work as designed. Therefore, the dark signal DN fluctuates with the cold FPA (CFPA) temperature and saturate for a few hours per WUCD cycle, which also saturate the EV data sector within the scan. The CFPA temperature fluctuation peaked in 2012 and has been reduced in recent years and the saturation phenomenon has been easing accordingly. This study demonstrates the importance of DCR to data generation.

The Atmospheric Infrared Sounder (AIRS) on the EOS Aqua Spacecraft was launched on May 4, 2002 and is currently fully operational. AIRS, in addition to the infrared system comprised of 2378 channels with wavelengths ranging from 3.7-15.4 um, has 4 Visible/Near-Infrared channels and an on-board calibration source utilizing 3 independent lamps to characterize the change in the visible response over time. One of the key measurements related to climate change is the measurement of the Reflected Short-Wave Solar radiation (RSW). The AIRS visible light channels can be used to accurately measure the stability of the RSW. We describe our experience from 15 years of AIRS data with using internal calibration lamps, vicarious calibration, MODIS cross-calibration, and Deep Convective Clouds (DCCs) for the calibration and stabilization of the AIRS visible light data. The result is the DCC stabilized anomaly trend of the RSW measured with AIRS.

The Clouds and the Earth’s Radiant Energy System (CERES) scanning radiometer is designed to measure the solar radiation reflected by the Earth and thermal radiation emitted by the Earth. Five CERES instruments are currently in service; two aboard the Terra spacecraft, launched in 1999; two aboard the Aqua spacecraft, launched in 2002; and one instrument about the NPP spacecraft, launched in 2011. Verifying the pointing accuracy of the CERES instruments is required to assure that all earth viewing data is correctly geolocated. The CERES team has developed an on-orbit technique for assessing the pointing accuracy of the CERES sensors that relies on a rapid gradient change of measurements taken over a well-defined and known Earth target, such as a coastline, where a strong contrast in brightness and temperature exists. The computed coastline is then compared with World Bank II map to verify the accuracy of the measurement location. This paper briefly restates the algorithm used in the study, describes collection of coastline data, and summarizes the results of the study the CERES FM1, FM2, FM3, and FM5 instruments.

GOES-16, which was launched on 19 November 2017, is the first of the next generation of geostationary weather satellites of NOAA. The Advanced Baseline Imager (ABI) is the primary instrument and mission critical payload onboard imaging the Earth with 16 different spectral bands covering 6 visible/near-infrared (VNIR) bands and 10 infrared (IR) bands. Although the GOES-16 ABI data are currently experimental and undergoing testing, in this study we focus on reporting some preliminary assessment results of the ABI radiometric calibration performance during the post-launch test (PLT) and post-launch product tests (PLPT) period. Our results show that the ABI IR full-disk (FD) images mean brightness temperature (Tb) bias with respect to S-NPP/CrIS and Metop-B/IASI of less than 0.3K. Diurnal variation is very small with a jump of less than 0.15K occurring twice a day around satellite local noon and midnight. The ABI VNIR radiometric calibration has a mean reflectance difference to SNPP/VIIRS of less than 5% for all the 6 VNIR bands except for B02 (0.64µm), which was about 8% brighter than corresponding VIIRS data during the PLT period. It may be noted that calibration of the VNIR bands experienced instabilities associated with ground system (GS) software patch testing and data receiving site failover testing, which can be reflected with the time-series monitoring from different earth and space-based invariant targets. Validations and investigations are still ongoing to improve the ABI imagery and data quality.

The first satellite of the Geostationary Operational Environmental Satellite-R series (GOES-R), the next generation of NOAA geostationary environmental satellites, was launched November 19, 2016. This satellite, GOES-16, carries six instruments dedicated to the study of the Earth’s weather (ABI), lightning mapping (GLM), solar observations (EXIS and SUVI), and space weather monitoring (SEISS and MAG). Each of these six instruments are in the process of going through a series of specialized calibration plans to achieve their product quality requirements. In this review paper we will describe the overall status of the on-orbit calibration program, the path forward to Full product validation status, and any changes that may occur for the cal/val plans for GOES-S, which is planned for launch in early 2018.

The Advanced Baseline Imager (ABI) onboard the GOES-16 satellite, which was launched on 19 November 2016, is the first next-generation geostationary weather instrument in the west hemisphere. It has 16 spectral solar reflective and emissive bands located in three focal plane modules (FPM): one visible and near infrared (VNIR) FPM, one midwave infrared (MWIR), and one longwave infrared (LWIR) FPM. All the ABI bands are geometeorically calibrated with new techniques of Kalman filtering and Global Positioning System (GPS) to determine the accurate spacecraft attitude and orbit configuration to meet the challenging image navigation and registration (INR) requirements of ABI data. This study is to validate the ABI navigation and band-to-band registration (BBR) accuracies using the spectrally matched pixels of the Suomi National Polar-orbiting Partnership (SNPP) Visible Infrared Imaging Radiometer Suite (VIIRS) M-band data and the ABI images from the Simultaneous Nadir Observation (SNO) images. The preliminary results showed that during the ABI post-launch product test (PLPT) period, the ABI BBR errors at the y-direction (along the VIIRS track direction) is smaller than at the x-direction (along the VIIRS scan direction). Variations in the ABI BBR calibration residuals and navigation difference to VIIRS can be observed. Note that ABI is not operational yet and the data is experimental and still under testing. Effort is still ongoing to improve the ABI data quality.

Launched on March 6th, 2017 from Kourou, Sentinel 2B has passed the phase of commissioning. Sentinel 2B will work together with Sentinel 2A launched in June 2015. The building and implementation of the satellite has been made under the responsibility of ESA, for the European Commission. The subset of Image Quality commissioning was delegated by ESA to CNES, referring to the experience of the French Space Agency on previous imagers. This phase lasted 4 months after the launch, a little longer than the formal In Orbit Calibration period conducted by ESA, some Image Quality parameters requiring several months before converging to a stable state. This paper presents the status of the satellite, from an IQ prospective, just before it entered its operational phase. The radiometric and geometric performances are listed, including: the absolute radiometric calibration, the equalization, the SNR, the absolute and the multi-temporal location accuracy. The performances of both satellites Sentinel and Sentinel 2B working together, will be addressed. A particular focus will be done on multi-temporal location performances, homogeneity of radiometric inter calibrations. The accomplishment of the Global Reference Image over Europe is evoked as well. The IQ commissioning phase ended on June 2017. From this date, the monitoring of IQ parameters is under the responsibility of ESA/ESRIN. Nevertheless, CNES continues to support ESA to survey the accuracy of S2A and S2B performances. The article ends by dealing with the prospective offered by the couple Sentinel 2A + Sentinel 2B.

First, the emission wavelengths from visible to short-wave infrared are generated by Light Emitting Diodes (LEDs) and phosphors which spectrally down convert the higher energy photons from the LED to a lower energy photon distribution. This process is analogous to the commercial lighting industry where blue LEDs are down converted into a distribution that resembles variations of white light. Second, several formats of carbon materials have been combined together into a multi-layer structure so that a highly uniform temperature interface feeds a high emissivity surface of vertically aligned carbon nanotubes. Finally, both of these technologies give rise to a thin profile, layered structure which can be easily mounted on a paddle for movement in and out of the optical path.

The quick advance in remote sensing technologies established the potential to gather accurate and reliable information about the Earth surface using high resolution satellite images. Remote sensing satellite images of less than one-meter pixel size are currently used in large-scale mapping. Rigorous photogrammetric equations are usually used to describe the relationship between the image coordinates and ground coordinates. These equations require the knowledge of the exterior and interior orientation parameters of the image that might not be available. On the other hand, the parallel projection transformation could be used to represent the mathematical relationship between the image-space and objectspace coordinate systems and provides the required accuracy for large-scale mapping using fewer ground control features. This article investigates the differences between point-based and line-based parallel projection transformation models in rectifying satellite images with different resolutions. The point-based parallel projection transformation model and its extended form are presented and the corresponding line-based forms are developed. Results showed that the RMS computed using the point- or line-based transformation models are equivalent and satisfy the requirement for large-scale mapping. The differences between the transformation parameters computed using the point- and line-based transformation models are insignificant. The results showed high correlation between the differences in the ground elevation and the RMS.

Currently, most mapping tasks are carried out using remote sensing data such as satellite imageries and LIDAR point clouds. This paper presents the integration of a QuickBird imagery set (both pan and multispectral) and LIDAR DEM generated from a LIDAR point cloud for mapping the coastline. A number of image processing techniques were applied to pan image to generate a coastline. Then a supervised classification is performed on the multispectral image followed by a raster to vector conversion to extract another shoreline. A third line was created from the LIDAR data using a set of processing algorithms. The three lines are weighted and pixels belonging to all of them are grouped to fit a final coastline. In order to evaluate the results, we manually extracted the corresponding line from the pan image and compared points belonging to both lines. Differences averaged about 1.37 meters.

The Havemann-Taylor Fast Radiative Transfer Code (HT-FRTC) is a principal component based fast radiative transfer code that can be used across the whole electromagnetic spectrum to calculate transmittance, radiance and flux spectra. The principal components cover the spectrum at a very high spectral resolution, which allows very fast line-by-line, hyperspectral and broadband simulations for satellite-based, airborne and ground-based sensors. The principal components are derived during a code training phase from line-by-line simulations for a diverse set of atmospheric and surface conditions. The derived principal components are sensor independent, i.e. no extra training is required to include additional sensors. During the training phase, predictors that are required by the fast radiative transfer code to determine the principal component scores from the monochromatic radiances (or fluxes, transmittances) are also derived. These predictors are calculated for each training profile at a small number of frequencies, which are selected by a k-means cluster algorithm during the training phase. The predictors are calculated using Gaussian Processes, which is more accurate than a linear regression algorithm. The HT-FRTC code is an integral part of the Met Office’s Tactical Decision aids such as Neon and IRVIS and as such plays an important part in the prediction of environmental impacts on various sensors such as IR cameras and night-vision goggles. Moreover, the HT-FRTC has been incorporated into a onedimensional variation (1D-Var) retrieval system that also works solely in principal component space. This keeps the dimensions of the matrices involved small which is important for computational efficiency.

The BRDF describes optical scatter off realistic surfaces. The microfacet BRDF model assumes geometric optics but is computationally simple compared to wave optics models. In this work, MERL BRDF data is fitted to the original Cook-Torrance microfacet model, and a modified Cook-Torrance model using the polarization factor in place of the mathematically problematic cross section conversion and geometric attenuation terms. The results provide experimental evidence that this modified Cook-Torrance model leads to improved fits, particularly for large incident and scattered angles. These results are expected to lead to more accurate BRDF modeling for remote sensing.

The bidirectional reflectance distribution function (BRDF) describes optical scatter from surfaces by relating the incident irradiance to the exiting radiance over the entire hemisphere. Laboratory verification of BRDF models and experimentally populated BRDF databases are hampered by sparsity of monochromatic sources and ability to statistically control the surface features. Numerical methods are able to control surface features, have wavelength agility, and via Fourier methods of wave propagation, may be used to fill the knowledge gap. Monte-Carlo techniques, adapted from turbulence simulations, generate Gaussian distributed and correlated surfaces with an area of 1 cm² , RMS surface height of 2.5 μm, and correlation length of 100 μm. The surface is centered inside a Kirchhoff absorbing boundary with an area of 16 cm² to prevent wrap around aliasing in the far field. These surfaces are uniformly illuminated at normal incidence with a unit amplitude plane-wave varying in wavelength from 3 μm to 5 μm. The resultant scatter is propagated to a detector in the far field utilizing multi-step Fresnel Convolution and observed at angles from −2 μrad to 2 μrad. The far field scatter is compared to both a physical wave optics BRDF model (Modified Beckmann Kirchhoff) and two microfacet BRDF Models (Priest, and Cook-Torrance). Modified Beckmann Kirchhoff, which accounts for diffraction, is consistent with simulated scatter for multiple wavelengths for RMS surface heights greater than λ/2. The microfacet models, which assume geometric optics, are less consistent across wavelengths. Both model types over predict far field scatter width for RMS surface heights less than λ/2.

The Sentinel 4 instrument is an imaging spectrometer, developed by Airbus under ESA contract in the frame of the joint European Union (EU)/ESA COPERNICUS program with the objective of monitoring trace gas concentrations. Sentinel 4 will provide accurate measurements of key atmospheric constituents such as ozone, nitrogen dioxide, sulfur dioxide, formaldehyde, as well as aerosol and cloud properties. Sentinel 4 is unique in being the first geostationary UVN mission. The SENTINEL 4 space segment will be integrated on EUMETSAT's Meteosat Third Generation Sounder satellite (MTG-S). Sentinel 4 will provide coverage of Europe and adjacent regions. The Sentinel 4 instrument comprises as a major element two Focal Plane Subsystems (FPS) covering the wavelength ranges 305 nm to 500 nm (UVVIS) and 750 nm to 775 nm (NIR) respectively. The paper describes the Focal Plane Subsystems, comprising the detectors, the optical bench and the control electronics. Further the design and development approach will be presented as well as first measurement results of FPS Qualification Model.

The Sentinel-4 UVN Instrument is a dispersive imaging spectrometer covering the UV-VIS and the NIR wavelength. It is developed and built under an ESA contract by an industrial consortium led by Airbus Defence and Space. It will be accommodated on board of the MTG-S (Meteosat Third Generation - Sounder) satellite that will be placed in a geostationary orbit over Europe sampling data for generating two-dimensional maps of a number of atmospheric trace gases. The incoming light is dispersed by reflective gratings and detected by the two (UVVIS and NIR) CCDs mounted inside the focal plane assemblies. Both CCD detectors acquire spectral channels and spatial sampling in two orthogonal directions and will be operated at about 215 K mainly to minimize random telegraph signal effects and to reduce dark current. Stringent detector temperature as well as alignment stability requirements of less than ±0.1 K per day respectively of less than 2 micrometers/2 arcseconds from ground to orbit are driving the FPA thermo-mechanical design. A specific FPA design feature is the redundant LED-calibration system for bad pixel detection as well as pixel gain and linearity monitoring. This paper reports on the design and qualification of the Focal Plane Assemblies with emphasis on thermo-mechanical as well as alignment stability verification.

The Sentinel-4 instrument is an imaging spectrometer, developed by Airbus under ESA contract in the frame of the joint European Union (EU)/ESA COPERNICUS program. SENTINEL-4 will provide accurate measurements of trace gases from geostationary orbit, including key atmospheric constituents such as ozone, nitrogen dioxide, sulfur dioxide, formaldehyde, as well as aerosol and cloud properties. Key to achieving these atmospheric measurements are the two CCD detectors, covering the wavelengths in the ranges 305 nm to 500 nm (UVVIS) and 750 to 775 nm (NIR) respectively. The paper describes the architecture, and operation of these two CCD detectors, which have an unusually high full-well capacity and a very specific architecture and read-out sequence to match the requirements of the Sentinel- 4 instrument. The key performance aspects and their verification through measurement are presented, with a focus on an unusual, bi-modal dark signal generation rate observed during test.

The detectors of the Sentinel 4 multi spectral imager are operated in flight at 215K while the analog electronics is operated at ambient temperature. The detector is cooled by means of a radiator. For thermal reasons no active component has been allowed in the cooled area closest to the detector as the passive radiator is restricted in its size. For thermal decoupling of detector and electronics a long distance between detector and electronics is considered ideal as thermal conductivity decreases with the length of the connection. In contradiction a short connection between detector and electronics is ideal for the electronic signals. Only a short connection ensures the signal integrity of both the weak detector output signal but similarly also the clock signals for driving the detector. From a mechanical and thermal point of view the connection requires a certain minimum length. The selected solution serves all these needs but had to approach the limits of what is electrically, mechanically and thermally feasible. In addition, shielding from internal (self distortion) and external distorting signals has to be realized for the connection between FEE(Front End Electronics) and detectors. At the time of the design of the flex it was not defined whether the mechanical structure between FEE and FPA (Focal Plane Assembly) would act as a shielding structure. The physical separation between CCD detector and the Front-end Electronics, the adverse EMI environment in which the instrument will be operated in (the location of the instrument on the satellite is in vicinity to a down-link K-band communication antenna of the S/C) require at least the video output signals to be shielded. Both detectors (a NIR and a UVVIS detector) are sensitive to contamination and difficult to be cleaned in case of any contamination. This brings up extreme cleanliness requirements for the detector in manufacturing and assembly. Effectively the detector has to be kept in an ISO 5 environment and additionally humidity has to be avoided - which does not comply with the usual clean-room atmosphere. This paper describes how in Sentinel 4 the given challenges have been overcome, how the limited load drive capability of the detector component has been considered on a flex length of about 20 cm (7.87 in) and how EMC shielding of the highly sensitive analog signals of the detector has been realized. Also covered are design/manufacturing aspects and a glance on testing results is provided

The Sentinel-4 payload is a multi-spectral camera system, designed to monitor atmospheric conditions over Europe from a geostationary orbit. The German Aerospace Center, DLR Berlin, conducted the verification campaign of the Focal Plane Subsystem (FPS) during the second half of 2016. The FPS consists, of two Focal Plane Assemblies (FPAs), two Front End Electronics (FEEs), one Front End Support Electronic (FSE) and one Instrument Control Unit (ICU). The FPAs are designed for two spectral ranges: UV-VIS (305 nm - 500 nm) and NIR (750 nm - 775 nm). In this publication, we will present in detail the set-up of the verification campaign of the Sentinel-4 Qualification Model (QM). This set up will also be used for the upcoming Flight Model (FM) verification, planned for early 2018. The FPAs have to be operated at 215 K ± 5 K, making it necessary to exploit a thermal vacuum chamber (TVC) for the test accomplishment. The test campaign consists mainly of radiometric tests. This publication focuses on the challenge to remotely illuminate both Sentinel-4 detectors as well as a reference detector homogeneously over a distance of approximately 1 m from outside the TVC. Selected test analyses and results will be presented.

The future ESA Earth Observation Sentinel-4/UVN is a high resolution spectrometer intended to fly on board a Meteosat Third Generation Sounder (MTG-S) platform, placed in a geostationary orbit. The main objective of this optical mission is to continuously monitor the air quality over Europe in near-real time. The Sentinel-4/UVN instrument operates in three wavelength bands: Ultraviolet (UV: 305-400 nm), Visible (VIS: 400- 500 nm) and Near-infrared (NIR: 750-775 nm). Two dedicated CCD detector have been developed to be used in the Focal Plane Subsystems (FPS), one for the combined UV and VIS band, the other covering the NIR band. Being a high resolution spectrometer with challenging radiometric accuracy requirements, both on spectral and spatial dimensions, an effect such the Random Telegraph Signal (RTS) can represent a relevant contribution for the complete system accuracy. In this work we analyze the RTS effect on data acquired during the FPS testing campaign with qualification models for the Sentinel-4/UVN detectors. This test campaign has been performed in late 2016. The strategy for the impact assessment of RTS is to measure the effect at room temperature and then to extrapolate the results to the at instrument operational temperature. This way, very-long lasting data acquisitions could be avoided since the RTS frequency is much lower at cryogenic temperatures. A reliable technique for RTS effect detection has been developed in order to characterize the signal levels amplitude and occurrence frequencies (flipping rate). We demonstrate the residual impact of the RTS on the global In-Orbit Sentinel-4/UVN instrument performance and products accuracy.

First launched in 1972, the Landsat satellite sensors have provided the longest continuous record of high quality images of the Earth’s surface that are used in both civilian and military applications. Extraction of quantitative information (e.g., surface reflectance) from the Landsat image data is only possible through an accurate absolute radiometric calibration. Typically, this calibration has been performed as a radiance-based cross-calibration between sensors. However, to convert radiance to reflectance, an accurate estimate of solar exoatmospheric irradiance is critical; and there are several solar models currently available which estimate exoatmospheric irradiance with varying levels of accuracy. Because of these inconsistencies in solar models, a TOA reflectance-based approach, independent of exoatmospheric irradiance, has been developed to provide a consistent cross-calibration of the Landsat series (from Landsat 8 OLI to Landsat 4 MSS), based on analysis of coincident and near-coincident scene pairs acquired with each sensor. The methodology uses Landsat-8 OLI reflectance measurements as the starting point (reference), as they are estimated with a 3% uncertainty (compared to the 5% uncertainty associated with radiance measurements). A set of radiometric calibration coefficients has been estimated based on the equations presented in this paper, which allows direct conversion of the digital numbers from the image data to TOA reflectance. The results obtained from application of these coefficients show significant improvement in consistency of reflectance measurements among the Landsat sensors.

Landsat data in the U.S. Geological Survey (USGS) archive are being reprocessed to generate a tiered collection of consistently geolocated and radiometrically calibrated products that are suitable for time series analyses. With the implementation of the collection management, no major updates will be made to calibration of the Landsat sensors within a collection. Only calibration parameters needed to maintain the established calibration trends without an effect on derived environmental records will be regularly updated, while all other changes will be deferred to a new collection. This first collection, Collection 1, incorporates various radiometric calibration updates to all Landsat sensors including absolute and relative gains for Landsat 8 Operational Land Imager (OLI), stray light correction for Landsat 8 Thermal Infrared Sensor (TIRS), absolute gains for Landsat 4 and 5 Thematic Mappers (TM), recalibration of Landsat 1-5 Multispectral Scanners (MSS) to ensure radiometric consistency among different formats of archived MSS data, and a transfer of Landsat 8 OLI reflectance based calibration to all previous Landsat sensors. While all OLI/TIRS, ETM+ and majority of TM data have already been reprocessed to Collection 1, a completion of MSS and remaining TM data reprocessing is expected by the end of this year. It is important to note that, although still available for download from the USGS web pages, the products generated using the Pre-Collection processing do not benefit from the latest radiometric calibration updates. In this paper, we are assessing radiometry of solar reflective bands in Landsat Collection 1 products through analysis of trends in on-board calibrator and pseudo invariant site (PICS) responses.

The Operational Land Imager (OLI) and Thermal Infrared Sensor (TIRS) routinely acquire earth science datasets, which are processed to orthorectified geometrically registered products by the USGS Landsat Product Generation System (LPGS). This paper will discuss the radiometric response uniformity of these products and its stability over time. Highlighted is the data analysis methodology that enables assessment of each focal plane’s sensor chip arrays’ (or modules’) response variability at levels under 0.5%. Specifically, the technique takes advantage of the overlapping FOV’s of the adjacent sensor chips. The analysis enables tracking the stability of the chip-to-chip response variation over the mission lifetime, and detection of residual non-linearity.

The Landsat 8 Operational Land Imager (OLI) is an optical multispectral push-broom sensor with a focal plane consisting of over 7000 detectors per spectral band. Each of the individual imaging detectors contributes one column of pixels to an image. Any difference in the response between neighboring detectors may result in a visible stripe or band in the imagery. An accurate estimate of each detector’s relative gain is needed to account for any differences between detector responses. This paper describes a procedure for estimating relative gains which uses normally acquired Earth viewing statistics.

The Thermal Infrared Sensor (TIRS) instrument is the thermal-band imager on the Landsat-8 platform. The initial onorbit calibration estimates of the two TIRS spectral bands indicated large average radiometric calibration errors, -0.29 and -0.51 W/m² sr μm or -2.1K and -4.4K at 300K in Bands 10 and 11, respectively, as well as high variability in the errors, 0.87K and 1.67K (1-σ), respectively. The average error was corrected in operational processing in January 2014, though, this adjustment did not improve the variability. The source of the variability was determined to be stray light from far outside the field of view of the telescope. An algorithm for modeling the stray light effect was developed and implemented in the Landsat-8 processing system in February 2017. The new process has improved the overall calibration of the two TIRS bands, reducing the residual variability in the calibration from 0.87K to 0.51K at 300K for Band 10 and from 1.67K to 0.84K at 300K for Band 11. There are residual average lifetime bias errors in each band: 0.04 W/m² sr μm (0.30K) and -0.04 W/m² sr μm (-0.29K), for Bands 10 and 11, respectively.

This paper deals with a calibration algorithm to be used with data from the Thermal Infrared Sensor (TIRS) on board Landsat 8. Some non-uniform banding calibration errors have been observed in TIRS data since it was launched in 2013. Investigations have shown that this artifact is due to out-of-field radiance that scatters onto the TIRS focal plane. A calibration algorithm which utilizes TIRS image data itself to correct the stray light error has been proposed and implemented. Preliminary experiments have indicated this methodology reduces stray light artifacts significantly. However, there are some cases in which the TIRS TIRS method may not optimally mitigate stray light. These are special cases where there is a large temperature contrast between the edge of the TIRS image and of out-of-field radiance. This paper outlines an alternative approach with near-coincident image data from an external satellite sensor and compares the correction results with the current operational method, in general, and for some of the out-of-field special cases.

We present system-level responsivity calibration results of the visible and near infrared channels of JPSS-1 VIIRS in the reflective solar band (RSB) from bands M1( 412 nm) to M7 (865 nm). A monochromator-based method based on the Spectral Measurement Assembly (SpMA), and a laser-based calibration method based on Travelling-Spectral Irradiance and Radiance responsivity Calibrations using Uniform Sources (T-SIRCUS) were applied with different illumination methods to obtain the relative and absolute spectral responses (RSR and ASR). The spectral features of RSR for each band are verified by comparing to the component-level spectral transmittance of the VIIRS bandpass filters. Variation of RSR results of a single pixel/detector with respect to the band-averaged for each band is also investigated. Utilization of RSR results from SpMA and T-SIRCUS with different illumination methods as well as the component transmittance results enables us to recognize optical and electrical cross-talk from out-of-band, which is estimated at about 3 %. We also attempted to use the ASRs from T-SIRCUS to validate the gain coefficients derived from an independent radiometric calibration test using a broadband source. Three spectral shapes of flat spectral radiance, Tungsten lamp, and solar emission are used to simulate different scenarios for baseline, pre-launch calibration, and on-orbit calibration to verify the radiometric coefficients with the more accurate NIST-traceable calibration.

The Joint Polar Satellite System 2 (JPSS-2) Visible Infrared Imaging Radiometer Suite (VIIRS) includes one spectral band centered in a strong atmospheric absorption region. As much of the pre-launch calibration is performed under laboratory ambient conditions, accurately accounting for the absorption, and thereby ensuring the transfer of the sensor calibration to on-orbit operations, is necessary to generate science quality data products. This work is focused on the response versus scan angle (RVS) measurements, which characterize the relative scan angle dependent reflectance of the JPSS-2 VIIRS instrument optics. The spectral band of interest, centered around 1378 nm, is within a spectral region strongly effected by water vapor absorption. The methodology used to model the absolute humidity and the atmospheric transmittance under the laboratory conditions is detailed. The application of this transmittance to the RVS determination is then described including an uncertainty estimate; a comparison to the pre-launch measurements from earlier sensor builds is also performed.

The Visible Infrared Imaging Radiometer Suite (VIIRS) is a scanning radiometercontaining 22 spectral bands that is currently collecting data aboard the Suomi-NPP satellite. A second flight unit is set to launch aboard the JPSS-1 satellite in the 4th quarter of 2017 followed by a third one aboard JPSS-2 in 2022. The VIIRS sensor is designed to obtain high quality data products over a variety of conditions including high contrast scenes like bright clouds over ocean for example. In the pre-launch test program the vendor, Raytheon, made measurements to determine the contamination from Near Field Response (NFR), which is scattered light from bright targets, to characterize these features and compare them against the structured scene requirement. As of now prelaunch testing has been completed on the first three VIIRS flight units, S-NPP, JPSS-1 and JPSS-2, with independent analyses performed by the NASA VCST team. We present this NFR characterization including derivation of the Harvey-Shack coefficients and impacts from other contamination such as retro reflections off the dewar to the cold focal planes.

The Visible/Infrared Imaging Radiometer Suite (VIIRS) is a key sensor on the Suomi National Polar-orbiting Partnership (NPP) satellite as well as the upcoming Joint Polar Satellite System (JPSS). VIIRS collects Earth radiometric and imagery data in 22 spectral bands from 0.4 to 12.5 μm. Radiometric calibration of the reflective bands in the 0.4 to 2.5 μm wavelength range is performed by measuring the sunlight reflectance from Spectralon®. Reflected sun light is directly proportional to the Bidirectional Reflectance Distribution Function (BRDF) of the Spectralon. This paper presents the BRDF measurements of the Spectralon for JPSS J2 in the 0.4 – 1.63 μm wavelength using PASCAL (Polarization And Scatter Characterization Analysis of Lambertian materials) with an uncertainty better than 1.2%. PASCAL makes absolute measurements of the BRDF in an analogous fashion to the National Institute of Standards and Technology (NIST) Spectral Tri-function Automated Reflectance Reflectometer (STARR) facility. Unique additional features of this instrument include the ability to vary the sample elevation and roll / clock the sample about its normal, allowing measurement of BRDF in the as used geometry. Comparison of BRDF in the as used configuration for NPP, J1, and J2 shows variation of up to 3%. The sign of the change from panel to panel depends on the angle of incidence and view angle. The results demonstrate lot to lot variability in Spectralon and emphasize the necessity of characterizing each panel. A pattern in the BRDF variation is also presented.

Satellite instruments operating in the reflective solar wavelength region require accurate and precise determination of the Bidirectional Reflectance Distribution Functions (BRDFs) of the laboratory and flight diffusers used in their pre-flight and on-orbit calibrations. This paper advances that initial work and presents a comparison of spectral Bidirectional Reflectance Distribution Function (BRDF) and Directional Hemispherical Reflectance (DHR) of Spectralon*, a common material for laboratory and onorbit flight diffusers. A new measurement setup for BRDF measurements from 900 nm to 2500 nm located at NASA Goddard Space Flight Center (GSFC) is described. The GSFC setup employs an extended indium gallium arsenide detector, bandpass filters, and a supercontinuum light source. Comparisons of the GSFC BRDF measurements in the shortwave infrared (SWIR) with those made by the National Institute of Standards and Technology (NIST) Spectral Tri-function Automated Reference Reflectometer (STARR) are presented. The Spectralon sample used in this study was 2 inch diameter, 99% white pressed and sintered Polytetrafluoroethylene (PTFE) target. The NASA/NIST BRDF comparison measurements were made at an incident angle of 0° and viewing angle of 45° . Additional BRDF data not compared to NIST were measured at additional incident and viewing angle geometries and are not presented here. The total combined uncertainty for the measurement of BRDF in the SWIR range made by the GSFC scatterometer is less than 1% (k = 1). This study is in support of the calibration of the Radiation Budget Instrument (RBI) and Visible Infrared Imaging Radiometer Suit (VIIRS) instruments of the Joint Polar Satellite System (JPSS) and other current and future NASA remote sensing missions operating across the reflected solar wavelength region.

CubeSats offer a low cost platform for remote sensing and in-situ measurements in space. Not only is the cost of the spacecraft low, but also the cost of the launch since typically CubeSats are secondary payloads to the primary satellite being launched. Despite the low available volume, mass and power and a typically less than ideal orbit, the platform can be ideal for demonstrating technology and even achieving certain science quality measurements. In this talk we discuss the CubeSat Infrared Atmospheric Sounder (CIRAS) a new project at NASA JPL designed to demonstrate key technologies for hyperspectral infrared measurements of atmospheric temperature and water vapor from space.

The Suomi NPP VIIRS thermal emissive bands (TEB) have been performing very well since data became available on January 20, 2012. The longwave infrared bands at 11 and 12 um (M15 and M16) are primarily used for sea surface temperature (SST) retrievals. A long standing anomaly has been observed during the quarterly warm-up-cool-down (WUCD) events. During such event daytime SST product becomes anomalous with a warm bias shown as a spike in the SST time series on the order of 0.2 K. A previous study (CAO et al. 2017) suggested that the VIIRS TEB calibration anomaly during WUCD is due to a flawed theoretical assumption in the calibration equation and proposed an Ltrace method to address the issue. This paper complements that study and presents operational implementation and validation of the Ltrace method for M15 and M16. The Ltrace method applies bias correction during WUCD only. It requires a simple code change and one-time calibration parameter look-up-table update. The method was evaluated using colocated CrIS observations and the SST algorithm. Our results indicate that the method can effectively reduce WUCD calibration anomaly in M15, with residual bias of ~0.02 K after the correction. It works less effectively for M16, with residual bias of ~0.04 K. The Ltrace method may over-correct WUCD calibration biases, especially for M16. However, the residual WUCD biases are small in both bands. Evaluation results using the SST algorithm show that the method can effectively remove SST anomaly during WUCD events.

The Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi National Polar-orbiting Partnership (SNPP) spacecraft has been on orbit for more than five years. Pronounced striping in Earth view (EV) images and obvious discontinuity in the EV brightness temperature (BT) of the thermal emissive bands (TEB) during the blackbody (BB) warm-up cool-down (WUCD) calibration have been found since launch but the root-cause of the phenomena has not yet been identified. Meanwhile, recent studies of the MODerate-resolution Imaging Spectroradiometer (MODIS) long-wave infrared (LWIR) photovoltaic (PV) bands demonstrate that crosstalk effect induces the same erroneous features. In this paper, it is shown that there is, indeed, a remarkable crosstalk contamination in SNPP VIIRS TEB. The crosstalk effect is quantitatively characterized by deriving the crosstalk coefficients from the scheduled lunar observations and the established lunar imagery analysis. Among all SNPP VIIRS TEB, band M14 is shown to have the largest crosstalk contamination from Band M15, while bands M13, M15, M16, and I5 have pronounced crosstalk effect as well. The crosstalk effect is distinctively different for the odd and even detectors within each affected band during to the pattern of the placement of the odd and the even detectors of the band on the focal plane assembly (FPA). The crosstalk coefficients are applied to mitigate the crosstalk effect and the improvements to both the BB calibration and EV retrieval are presented and addressed.

The 16 thermal emissive bands (TEB) of MODIS instruments on-board Terra and Aqua satellites are located at two cold focal plane assemblies (CFPA), which are cryogenically cooled by a passive radiative cooler. The CFPA temperatures are controlled at a nominal value of 83 K. For Aqua MODIS, the cooler margin has gradually decreased since launch, which deteriorates the CFPA temperature control. Since 2006, Aqua CFPA temperature has deviated from its 83 K baseline and been fluctuating with the instrument temperature seasonally, daily and per orbit. The magnitude of the fluctuation steadily increased until reached its peak at 0.7 K in 2013 and has been decreasing. The gains of TEB detectors, especially those of the photoconductive bands 31-36, change with the CFPA temperature by up to 8%, as is demonstrated by both pre-launch calibration and on-orbit monitoring. In this paper, the CFPA temperature and its related telemetries are provided. The impact of the fluctuation to TEB radiometric calibration is also assessed. Overall, because the calibration is normally performed on a scan-by-scan basis based on the observation of an onboard blackbody (BB), the detector gain change can be retrieved nearly real time. Therefore, the impact is not significant overall. However, for bands 33, 35 and 36, their detectors saturate when observing BB at BB temperature above certain saturation limits during quarterly held BB warmup-cooldown activities. Since there is no valid scan-by-scan calibration during these periods, a special treatment has to be applied to calibrate these bands to reflect the detector gain fluctuation.

Monitoring of VIIRS ocean clear-sky brightness temperatures against CRTM Simulations has been initially implemented in the NOAA Integrated Calibration/Validation System (ICVS) for VIIRS calibration and validation. The initial system builds upon the heritage Monitoring of IR Clear-sky Radiances over Ocean for SST (MICROS). Substantial effort was made to further minimize the observation minus simulation biases. Preliminary results show that both mean biases and standard deviation are significantly improved in ICVS, compared to MICROS. The long term stability has also improved and shows a close cross-sensor consistency between VIIRS and MODIS. The current monitoring system is ready for J1 VIIRS test.

We present improvements to the on-orbit calibration of the day-night band (DNB) of the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi National Polar-orbiting Partnership (SNPP) satellite. Most important among the improvements is the expansion of the “sweet spot” from 4 o to 7.8o to increase the number of the fully illuminated scans for calcuation. This allows for the completion of the on-orbit calibration using the solar diffuser (SD) within one orbit instead multiple orbits as required in the current standard approach. The bidirectional reflectance factor (BRF) of the SD and the vignetting function (VF) describing the transmission of the attenuation screen in front of the SD port are also examined and improved. Additional enhancements include the analysis of the out-of-band (OOB) contribution of the relative spectral response (RSR) and the adaptation of the previously improved SD degradation. The result shows that the improved DNB calibration coefficients are more stable, smooth and less noisy.

We describe the methodology for predicting the S-NPP VIIRS Day-Night-Band (DNB) detector gains and dark offsets. During the first 5 years of operation, the DNB has shown recognizable patterns in these calibration parameters. These patterns can be decomposed into two distinctive components: degradation and oscillation. We fit the historical data using a periodic function of time superimposed on an exponential function of time to capture both sources of the variation. The results of the fit showed good agreement with the measured data, indicating that the functions may be useful as a forward model for predicting these calibration parameters for calibration updates. As a test, predictions made in April, 2016 were examined against newly obtained measurement data at monthly intervals. Through April, 2017, the prediction errors have been smaller than 1.5% in the gains and 0.5% in the offsets, with the largest errors observed in the end-of-scan aggregation modes of the high-gain stage. The oscillatory features seen in the measured gains will be analyzed to isolate possible causes and to determine the relevance of its inclusion in the model. Comparisons with the results using the existing predictions of the gain and offset Look-Up-Tables (LUTs) will also be presented.

Over five years of the Suomi National Polar orbiting Partnership (S-NPP) Visible Infrared Imaging Radiometer Suite (VIIRS) Sensor Data Records (SDR) production, there were mutual demands of the lifetime VIIRS SDR reprocessing to alleviate operational changes and user oriented suggestions. Meanwhile, the NOAA Ocean Color (OC) team through its independent effort has achieved the robust calibration of the S-NPP VIIR Reflective Solar Bands (RSBs) – including improved radiometric accuracies, minimized annual oscillations and mitigated growing bias for long-term radiometric stability. The baseline VIIRS reprocessing is performed using the RSBAutoCal LUTs with an option of using OC calibration for their mission-long reprocessing to provide enhanced radiometric accuracy for OC Environmental Data Records (EDR) products. The SDR reprocessing team has applied the most recent calibration coefficients LUTs from the RSBAutoCal processing unit as a baseline product with a new field called ‘RadiometricBaisCorrection,’ which holds conversion factor from baseline to OC’s suggested calibration. This paper briefly summarizes the efforts of the SDR reprocessing team, the related entire life reprocessing issues and the initial results in the RSBs. It will show that the quality and accuracy of the SDR reprocessed with the new LUTs are significantly improved. It will also demonstrate the remarkable improvements of the VIIRS EDR for various applications and higher-level science products by using the reprocessed SDR as their inputs.

The Suomi National Polar-orbiting Partnership (SNPP) Visible Infrared Imaging Radiometer Suite (VIIRS) has been on orbit for more than five years. Through independent efforts by the NOAA Ocean Color (OC) Team, the radiometric calibration of reflective solar bands (RSBs) recently has reached a mature stage. Numerous improvements have been made in the standard RSB calibration methodology for the sensor data records (SDR), which is the starting point for the higher-level environmental data records (EDR) and science products. These improvements have helped the EDR ocean color products that demand stringent accuracy to reach maturity. The success of the OC EDR performance has further led to the institutional decision to use the calibration results generated by the OC Team, in the form of the lookup-tables (LUTs), as an official input for the operational SDR reprocessing, which are to be the official release to all users. The OC LUTs delivered for the operational SDR reprocessing is the latest update containing further improvements over the current LUTs used for the OC reprocessing and forward processing. This presentation will address the following topics: the inadequacies in the current operational forward SDR generated by the Interface Data Processing Segment (IDPS), the RSB calibration improvements made by the NOAA OC Team, the success of the RSB SDR reprocessing for ocean color EDR using the improved RSB LUTs, and finally, the use of the OC LUTs as the official LUTs for VIIRS RSB SDR operational reprocessing.

The Visible Infrared Imaging Radiometer Suite (VIIRS) aboard the Suomi National Polar-orbiting Partnership satellite has 14 reflective solar bands (RSBs) covering a spectral range from 410 nm to 2250 nm. We provide an overview of the noise characterization of the VIIRS RSB from pre-launch through more than five years of on-orbit operation. On orbit, the noise is measured as the variation in the signal level observed at the sunlit solar diffuser (SD) within each instrument scan. The SD signal level changes from scan to scan as the solar angle changes during the SD illumination time period of each orbit, allowing us to establish a functional dependence of the noise on signal level. The signal-to-noise ratio (SNR) for all RSB has been slowly decreasing on-orbit, but remains above specification performance values (given at fixed typical radiance for each band) and is projected to remain above specification for at least ten more years based on the current trends in the performance of the electronic and optical sub-systems. We show a comparison to pre-launch measurements, and also discuss the importance of data quantization and sample aggregation in the interpretation of the SNR values.

We present a new variant to the on-orbit calibration methodology for the reflective solar bands (RSBs) of SNPP VIIRS using solar diffuser (SD). Instead of following the standard method using full solar illumination through SD port that occurs during terminator crossing, we use light scattered off Earth scenes coming through the nadir port as the source of illumination for the SD. We describe the methodology, present the result, and compare with standard result. The scattered light signal for each orbit is summed up and a 16-day average is taken to build up the calibration coefficient trend. The preliminary result for SNPP VIIRS Bands M1 through M7 shows the scatter light-based approach to be viable, with its calibration coefficient result very well match the standard RSB calibration result over the entire mission to date. The preliminary result does show more variation, on the level of 2%. The methodology is applicable to other instruments employing a similar SD-based calibration strategy. Specifically for the twin MODIS in which the on-orbit RSB calibration is effectively identical, this approach is directly applicable as is.

The NASA Ocean Color calibration team continued to reanalyze and improve on their approach to the on-orbit calibration of the Visible Infrared Imaging Radiometer Suite (VIIRS), aboard the Suomi National Polar-orbiting Partnership (NPP) satellite, now five years into its Earth Observation mission. As the calibration was adjusted for changes in ocean band responsitivity with time, the team also observed the variance and autocorrelation properties of calibration trend fit residuals, which appeared to have a standard deviation within a few tenths of a percent. Autocorrelation was observed to be different between bands at the blue end of the spectrum and bands at the red/NIR end, which are affected by significant changes in responsitivity stemming from mirror contamination. This residual information offered insight into the effect of small calibration biases, which can cause significant trend uncertainties in regional time series of surface reflectance and derived products. This work involves modeling spurious trends that are inherent to the calibration over time and that also arise between reprocessing efforts because of extrapolation of the time-dependent calibration table. Uncertainty in calibration trends was estimated using models of instrument and calibration system trend artifacts and correlated noise models using Monte Carlo techniques. Combined table reprocessing and extrapolation biases are presented for the first time. Calibration trend uncertainty is then propagated through to ocean color remote sensing reflectance and chlorophyll-a concentration time series. The results quantify the smallest trend observable in these oceanic parameters. This quantification furthers our understanding of uncertainty in measuring regional and global biospheric trends in the ocean using VIIRS, and better defines the roles of records in climate research.

The NASA Ocean Biology Processing Group (OBPG) has continued monitoring the SNPP VIIRS on-orbit calibration since the derivation of the calibration for Reprocessing 2014.0 of the VIIRS ocean color data set. This paper examines four changes to the on-orbit calibration data processing scheme: the prelaunch counts-toradiance conversion; residual solar beta-angle effects in the solar calibration time series; the impact of additional lunar observations on the solar/lunar time series comparisons; and the necessity of putting calibration epochs into fits of the radiometric time series. Updating the prelaunch counts-to-radiance conversion from a linear function of instrument counts to a temperature-dependent, quadratic function of counts had the primary effect of reducing the observational scatter in the lunar calibration time series. The RMS errors due to residual solar beta angle effects are 0.1% for bands M1 (412 nm), M2 (445 nm), and M5 (672 nm) and less for the other bands. The additional lunar observations show that the slopes of the differences in the lunar and solar radiometric trends change nonlinearly over time. VIIRS bands M1–M11 all show changes in radiometric response trends between late 2014 and early 2015, which can be mitigated with an epoch boundary in the fits to the radiometric response on 1 January 2015. The updated solar calibration time series show RMS residuals per band of 0.05–0.22%. The updated lunar calibration time series shows RMS residuals per band of 0.08–0.27%. The solar and lunar time series show RMS differences of 0.10–0.20%.

The Visible Infrared Imaging Radiometer Suite (VIIRS) is currently operating onboard the Suomi National Polarorbiting Partnership (S-NPP) spacecraft. VIIRS records Earth imagery with spectral bands ranging from 0.4 to 12.2 micrometers at a combination of resolutions. Five imaging bands (I1-5) have a 375 m spatial resolution at nadir, which is half of the 750 m resolution of the 16 moderate resolution bands (M1-16). These bands are mounted according to their wavelengths at three separate Focal Plane Assemblies (FPA). The proper spatial registration among imaging bands is required to create multi-spectral images and analyses. Measurement of the band-to-band registration (BBR) is a determination of how well these bands are coincident. Using an external target such as the moon has proven to be a valid method and has been thoroughly investigated using VIIRS raw data record (RDR). Calibrated VIIRS radiometric data has been investigated using normalized mutual information (NMI) for BBR and shown stable results, by focusing on high-contrast shoreline sites. However, these results focus on a relatively small number of observations. We have previously reported analyses using earth-scene targets to determine BBR for MODIS instruments. This approach focuses on an African Desert site with high contrast spots generated through agricultural pivot irrigation. Using the near-daily observations provided by the VIIRS instrument, we investigate a large data set and track the BBR stability over the VIIRS mission. We discuss our results and compare them with prelaunch measurements and design specifications.

We update the effort in the radiometric evaluation of the two different versions of the calibrated sensor data records (SDRs) for the SNPP VIIRS reflective solar bands (RSBs) through direct comparison analysis with Aqua MODIS. The two SDR versions of interest are the official version generated by the Interface Data Process Segment (IDPS) system and the independent version calibrated by the NOAA Ocean Color (OC) Team. The key finding is the continual drift in the IDPS-generated radiance data for five short-wavelength RSBs (443 nm to 1238 nm), contrasting the multi-year stable result for the OC version. SNPP VIIRS M1 (410 nm) versus Aqua MODIS B8 (412 nm) continues to show drift for the IDPS-based and the OC-based comparison time series, pointing to the continual and worsening inaccuracy in Aqua MODIS B8 radiometric data that had been established by preceding studies in the previous year. The SNPP VIIRS M7 (862 nm) versus Aqua MODIS B2 (859 nm) comparison exhibits recent discontinuity in both IDPS-based and OC-based time series - the discontinuity for IDPS-generated SNPP VIIRS M7 is estimated at 0.5% upward near early October 2016, and for Aqua MODIS B2 it is 1.7% upward near mid-July 2016. The other important first-time result is the SNPP VIIRS M11 (2257 nm) versus Aqua MODIS B7 (2130 nm) comparison time series using the land-based snowy scenes of Antarctica, which demonstrates multi-year stability of SNPP VIIRS M11 and the agreement between the IDPS and the OC version of the VIIRS SDRs at this spectral range.

The inter-comparison of the reflective solar bands between the instruments onboard a geostationary orbit satellite and onboard a low Earth orbit satellite is very helpful to assess their calibration consistency. GOES-R was launched on November 19, 2016 and Himawari 8 was launched October 7, 2014. Unlike the previous GOES instruments, the Advanced Baseline Imager on GOES-16 (GOES-R became GOES-16 after November 29 when it reached orbit) and the Advanced Himawari Imager (AHI) on Himawari 8 have onboard calibrators for the reflective solar bands. The assessment of calibration is important for their product quality enhancement. MODIS and VIIRS, with their stringent calibration requirements and excellent on-orbit calibration performance, provide good references. The simultaneous nadir overpass (SNO) and ray-matching are widely used inter-comparison methods for reflective solar bands. In this work, the inter-comparisons are performed over a pseudo-invariant target. The use of stable and uniform calibration sites provides comparison with appropriate reflectance level, accurate adjustment for band spectral coverage difference, reduction of impact from pixel mismatching, and consistency of BRDF and atmospheric correction. The site in this work is a desert site in Australia (latitude -29.0 South; longitude 139.8 East). Due to the difference in solar and view angles, two corrections are applied to have comparable measurements. The first is the atmospheric scattering correction. The satellite sensor measurements are top of atmosphere reflectance. The scattering, especially Rayleigh scattering, should be removed allowing the ground reflectance to be derived. Secondly, the angle differences magnify the BRDF effect. The ground reflectance should be corrected to have comparable measurements. The atmospheric correction is performed using a vector version of the Second Simulation of a Satellite Signal in the Solar Spectrum modeling and BRDF correction is performed using a semi-empirical model. AHI band 1 (0.47μm) shows good matching with VIIRS band M3 with difference of 0.15%. AHI band 5 (1.69μm) shows largest difference in comparison with VIIRS M10.

The Cross-track Infrared Sounder (CrIS) onboard Suomi NPP (SNPP) and JPSS series has high radiometric accuracy, which can be used for validating some infrared bands of Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the same platform. The collocated CrIS and VIIRS sensor data record (SDR) along with the VIIRS cloud mask product from 19 to 21 September 2016 (during a period of blackbody warm-up cool-down, or WUCD) are used for inter-comparisons. This study addresses the questions on how the sub-pixel cloud presence and the local zenith angle impact the radiometric differences between CrIS and VIIRS. Both VIIRS brightness temperature (BT) bias and standard deviation for I5, M13, M15 and M15 whose spectral response functions (SRFs) have the full coverages over the CrIS spectral regions, are analyzed over the clear and cloudy skies, respectively. Results show good agreement between VIIRS and CrIS, cloud presence has substantial impact on STD, and also impact on BIAS, local zenith angle has also substantial impact on STD, but impact on bias is small. Both bias and STD are large in DCC (deep convective cloud) areas. The study clearly shows the VIIRS scene temperature bias during WUCD, as well as the bias removal after reprocessing the M15 and M16 with the improved calibration bias correction algorithm. The methodology can be applied to monitor and validate the imager with advanced infrared (IR) sounder onboard the same platform, such as CrIS for VIIRS (SNPP, JPSS), IASI for AVHRR (Metop), and GIIRS for AGRI (FengYun-4).

We investigate the use of 200K scenes as a valuable “stress test” for the evaluation of the calibration of AIRS and CrIS. Under these conditions both instruments show artifacts much larger than the nominal stated radiometric accuracy of about 0.1-0.2 K. Except for the AIRS shortwave trend, both instruments clearly perform well at the 1 K level even for these extremely low scene temperatures. Unfortunately, changes in extremes, in this case cold extremes, are of great interest to the evaluation of climate change effects, such as changes in the height of the tropopause or the frequency of severe storms. The evaluation of the AIRS performance at extremely low scene temperatures has been key to identifying the need for updating the polarization coefficients in the L1B software Version 7. These changes are expected to eliminate a large fraction of the observed AIRS artifacts. The CrIS instrument teams is also working on refining the calibration.

AIRS and CrIS are in very similar 1:30 PM ascending node orbits, with 12 km diameter footprints at nadir. Data from both instruments have have been available for the past 5 years. The level to which AIRS and CrIS observations agree for large area averages is a metric of how well data from different, but nominally equivalent, instruments can be concatenated to create the long time series necessary to reliably characterize climate change. We limit our analysis to 900 cm-1 atmospheric window channels. For random nadir sampled tropical zone data AIRS and CrIS agree within 100 mK, if the nine CrIS detector elements are averaged. Under tropical mean condition the CrIS elements disagree from each other by 0.5K. Under extreme condition the measurements of the nine CrIS elements are between 2K colder to 3 K warmer than AIRS. It is at present unclear why the nine CRIS detector elements disagree with each other by much more than their mean disagrees with the equivalent AIRS result. The observed effect may be decreased or at least more aggressive quality flagged in a future release of the CrIS calibrated radiances. If AIRS and CrIS were not in the same orbit at the same time, one might interpret the observed differences as evidence of a “climate change”.

Since the launch of the second Metop platform in September 2012, two IASI (Infrared Atmospheric Sounding Interferometers) instruments are flying on the same orbit, overflying the same area with 50 minutes delay. This provides a unique opportunity to perform multiple inter-comparisons and cross-monitoring. To do so, different methodologies have been implemented to provide complementary results giving qualitative and quantitative information on the instruments in terms of radiometric and spectral inter-calibration. This includes in particular comparisons between IASI and other infrared instruments. In this paper we will present an overview of the comparison that have been performed between IASI and the High-resolution Infrared Sounder (HIRS) flying on the same platform as well as comparisons with the Cross-track Infrared Sounder (CrIS) flying on Suomi-NPP. This monitoring which, besides giving confidence on the intercalibration of both IASI, provides a way to detect the slightest differences between IASI and other infrared multispectral instruments.

The accurate on-orbit radiometric calibration of optical sensors has become a challenge for space agencies who gather their effort through international working groups such as CEOS/WGCV or GSICS with the objective to insure the consistency of space measurements and to reach an absolute accuracy compatible with more and more demanding scientific needs. Different targets are traditionally used for calibration depending on the sensor or spacecraft specificities: from on-board calibration systems to ground targets, they all take advantage of our capacity to characterize and model them. But achieving the in-flight stability of a diffuser panel is always a challenge while the calibration over ground targets is often limited by their BDRF characterization and the atmosphere variability. Thanks to their agility, some satellites have the capability to view extra-terrestrial targets such as the moon or stars. The moon is widely used for calibration and its albedo is known through ROLO (RObotic Lunar Observatory) USGS model but with a poor absolute accuracy limiting its use to sensor drift monitoring or cross-calibration. Although the spectral irradiance of some stars is known with a very high accuracy, it was not really shown that they could provide an absolute reference for remote sensors calibration. This paper shows that high resolution optical sensors can be calibrated with a high absolute accuracy using stars. The agile-body PLEIADES 1A satellite is used for this demonstration. The star based calibration principle is described and the results are provided for different stars, each one being acquired several times. These results are compared to the official calibration provided by ground targets and the main error contributors are discussed.

The United States Geological Survey (USGS) has developed an empirical model, known as the Robotic Lunar Observatory (ROLO) Model, that predicts the reflectance of the Moon for any Sun-sensor-Moon configuration over the spectral range from 350 nm to 2500 nm. The lunar irradiance can be predicted from the modeled lunar reflectance using a spectrum of the incident solar irradiance. While extremely successful as a relative exo-atmospheric calibration target, the ROLO Model is not SI-traceable and has estimated uncertainties too large for the Moon to be used as an absolute celestial calibration target. In this work, two recent absolute, low uncertainty, SI-traceable top-of-the-atmosphere (TOA) lunar irradiances, measured over the spectral range from 380 nm to 1040 nm, at lunar phase angles of 6.6° and 16.9° , are used as tie-points to the output of the ROLO Model. Combined with empirically derived phase and libration corrections to the output of the ROLO Model and uncertainty estimates in those corrections, the measurements enable development of a corrected TOA lunar irradiance model and its uncertainty budget for phase angles between ±80° and libration angles from 7° to 51° . The uncertainties in the empirically corrected output from the ROLO model are approximately 1 % from 440 nm to 865 nm and increase to almost 3 % at 412 nm. The dominant components in the uncertainty budget are the uncertainty in the absolute TOA lunar irradiance and the uncertainty in the fit to the phase correction from the output of the ROLO model.

The accurate on orbit radiometric calibration of optical sensors has become a challenge for space agencies which have developed different technics involving on-board calibration systems, ground targets or extra-terrestrial targets. The combination of different approaches and targets is recommended whenever possible and necessary to reach or demonstrate a high accuracy. Among these calibration targets, the moon is widely used through the well-known ROLO (RObotic Lunar Observatory) model developed by USGS. A great and worldwide recognized work was done to characterize the moon albedo which is very stable. However the more and more demanding needs for calibration accuracy have reached the limitations of the model. This paper deals with two mains limitations: the residual error when modelling the phase angle dependency and the absolute accuracy of the model which is no more acceptable for the on orbit calibration of radiometers. Thanks to PLEIADES high resolution satellites agility, a significant data base of moon and stars images was acquired, allowing to show the limitations of ROLO model and to characterize the errors. The phase angle residual dependency is modelled using PLEIADES 1B images acquired for different quasi-complete moon cycles with a phase angle varying by less than 1°. The absolute albedo residual error is modelled using PLEIADES 1A images taken over stars and the moon. The accurate knowledge of the stars spectral irradiance is transferred to the moon spectral albedo using the satellite as a transfer radiometer. This paper describes the data set used, the ROLO model residual errors and their modelling, the quality of the proposed correction and show some calibration results using this improved model.

In-orbit verification of the co-registration of channels in a scanning microwave or infrared radiometer can in principle be done during normal in-orbit operation, by using the regular events of lunar intrusion in the instrument cold space calibration view. A technique of data analysis based on best fit of data across lunar intrusions has been used to check the mutual alignment of the spectral channels of the MHS instrument. MHS (Microwave Humidity Sounder) is a cross-track scanning radiometer in the millimetre-wave range flying on EUMETSAT and NOAA polar satellites, used operationally for the retrieval of atmospheric parameters in numerical weather prediction and nowcasting. This technique does not require any special operation or manoeuvre and only relies on analysis of data from the nominal scanning operation. The co-alignment of sounding channels and window channels can be evaluated by this technique, which would not be possible by using earth landmarks, due to the absorption effect of the atmosphere. The analysis reported in this paper shows an achievable accuracy below 0.5 mrad against a beam width at 3dB and spatial sampling interval of about 20 mrad. In-orbit results for the MHS instrument on Metop-B are also compared with the pre-launch instrument characterisation, showing a good correlation.

Overhauser magnetometer, a kind of static-magnetic measurement system based on the Overhauser effect, has been widely used in archaeological exploration, mineral resources exploration, oil and gas basin structure detection, prediction of engineering exploration environment, earthquakes and volcanic eruotions, object magnetic measurement and underground buried booty exploration. Overhauser magnetometer plays an important role in the application of magnetic field measurement for its characteristics of small size, low power consumption and high sensitivity. This paper researches the design and the application of the analog circuit of JOM-3 Overhauser magnetometer. First, the Larmor signal output by the probe is very weak. In order to obtain the signal with high signal to noise rstio(SNR), the design of pre-amplifier circuit is the key to improve the quality of the system signal. Second, in this paper, the effectual step which could improve the frequency characters of bandpass filter amplifier circuit were put forward, and theoretical analysis was made for it. Third, the shaping circuit shapes the amplified sine signal into a square wave signal which is suitable for detecting the rising edge. Fourth, this design elaborated the optimized choice of tuning circuit, so the measurement range of the magnetic field can be covered. Last, integrated analog circuit testing system was formed to detect waveform of each module. By calculating the standard deviation, the sensitivity of the improved Overhauser magnetometer is 0.047nT for Earth’s magnetic field observation. Experimental results show that the new magnetometer is sensitive to earth field measurement.

The inter-sensor radiometric comparison of the 2257 nm channel (M11) of SNPP VIIRS and the 2130 nm channel (B7) of Aqua MODIS curiously demonstrates a wildly varying time series, in stark contrast to the very stable results of other band pairs. A link is found between the few statistically robust outcomes in the time series and the land-based snowy scenes, specifically of Antarctica. With a refined procedure including a selection of land-based snowy scenes, we are able to generate a viable comparison time series of radiance of Aqua MODIS B7 over that of SNPP VIIRS M11. The refined time series shows multi-year stability and hovers around 0.39. The connection between the observed behaviors and their non-overlapping relative spectral responses (RSRs) is discussed.

MODIS onboard the Terra and Aqua satellites have operated since 1999 and 2002, respectively. The inter-comparison between their thermal emissive bands is a useful tool in assessing their calibration consistency and enhancing their product quality. Terra and Aqua MODIS has the same spectral bands and calibration algorithm. The comparison between them will be beneficial for instrument calibration. However, the comparison is hindered by the time difference of their measurements, since Terra is in the morning orbit and Aqua is in the afternoon orbit. GOES-16 was launched on November 19, 2016 and Himawari-8 was launched on October 7, 2014. The Advanced Baseline Imager (ABI) onboard GOES-16 and the Advanced Himawari Imager (AHI) onboard Himawari-8 are in the same class and have almost identical thermal spectral bands. Their comparison will be very useful for sensor calibration assessment. However, the comparison is challenged by the fact that they image different regions of the Earth. The sensors on GEO satellite and the sensors on LEO satellite may have matching bands with close spectral coverage. This work focuses on bridging the thermal band comparison between LEO-LEO sensors and between GEO-GEO sensors. The double difference method is applied to assess the BT measurements between the two MODIS instruments using the GOES imager as a bridge. The comparison between ABI and AHI can also be performed with bridging by either MODIS or VIIRS measurements. GOES-16 and Himawari-8 are both positioned over tropical ocean regions. Thus, the comparison with simultaneous nadir overpass can provide assessments for brightness temperature (BT) measurements over the ocean surface type. The comparison can also be extended to simultaneous off-nadir measurement over other types of targets that cover different BT range.

There are two nearly identical MODIS instruments currently operating on-board the NASA EOS Terra and Aqua spacecraft. Each MODIS is equipped with several on-board calibrators (OBCs) including a Spectro-Radiometric Calibration Assembly (SRCA). The SRCA is a multi-configuration calibrator that aids in determining the performance parameters of MODIS detectors on-orbit. Depending on its configuration, scheduled operations of the SRCA provide measurements to assess the on-orbit radiometric, spatial, and spectral performance. The SRCA was designed to utilize various combinations of three 10 Watt lamps and one 1 Watt lamp and included a spare of each type. On-orbit lamp degradation and failures reduced the available number of 10 Watt lamps from four to two for each mission by 2006. Over the past year, each instrument experienced an issue on-orbit. The nadir door of Terra MODIS closed as the instrument was autonomously commanded into safe-mode after a spacecraft commanding issue. The instrument and spacecraft operations were successfully recovered shortly after the event. For Aqua, a failure occurred for one of the two remaining 10 Watt lamps. We investigate each issue as it relates to the SRCA’s operation and its ability to properly characterize MODIS detector performance. For Terra MODIS, we present changes in MODIS spectral and spatial performance due to changes in the instrument environment. In the case of Aqua MODIS, losing a lamp reduces the output potential of the SRCA. We present the results from this impact and the adjustments made to calibration activities to maximize the effectiveness of the remaining lamps.

The modulation transfer function, or MTF, is a common measure of image fidelity, which has been historically characterized on-orbit using high contrast images of the lunar limb obtained by remote sensing instruments onboard both low-orbit and geostationary satellites. Himawari-8, launched in 2014, is a Japanese geostationary satellite that carries the Advanced Himawari Imager (AHI), a near-identical copy of the Advanced Baseline Imager (ABI) instrument onboard the GOES-16 satellite. In this paper, we apply a variation of the slantededge method for deriving the MTF from lunar images, first verified by us on simulated test images, to the Himawari-8/AHI L1A and L1B data. The MTF is derived along the North/South and East/West directions separately. The AHI L1A images used in the characterization of the MTF are obtained from lunar observations routinely acquired for validating the radiometric calibration. The L1B data, which is spatially re-sampled, come from serendipitous lunar observations where the Moon appears close to the Earth’s disk. We developed and implemented an algorithm to identify such occurrences using the SPICE/Icy package to predict the times where the Moon is visible in the L1B imagery and demonstrate their use for MTF derivation.

The VIIRS Day-Night-Band (DNB) is a panchromatic band with three gain stages used for delivering imagery under conditions ranging from daylight to low light nighttime scenes. Early in the S-NPP mission a gray haze was observed in some nighttime DNB imagery with the cause determined to be stray light contamination. This effect was characterized along with a proposed correction algorithm. The correction algorithm was subsequently included in operational data processing and re-processing. However, in order to process real-time data, prediction of the stray light correction is necessary. In this paper we present a new method to predict the DNB stray light correction Look-Up-Tables (LUTs). Since measurements suitable for characterizing the stray light contamination are sparse (about once a month during new-Moon), and because some of the measurements might not be accurate due to the presences of unaccounted light sources, such as algae glow and lightening, we have applied additional constraints to the model by assuming that certain patterns of the stray light are repeatable. Comparisons of the LUT parameters produced by the prediction algorithm with those from the measurements will be presented along with the impact on the derived Earth View products.

The MODIS instruments aboard the Terra and Aqua spacecraft have 20 reflective solar bands (RSB) with wavelengths spanning 412 nm to 2130 nm. The primary on-board calibration source for the RSB is a sunlit solar diffuser (SD), with its degradation tracked by a SD stability monitor (SDSM). The SDSM measurements show that the decrease in SD reflectance over time has a strong wavelength dependence, with longer wavelengths showing less degradation. The SDSM has 9 detectors to track the SD degradation at wavelengths from 412 nm to 936 nm, but is not designed to track the degradation at short-wave infrared (SWIR) wavelengths. In recent years, the SDSM has measured non-negligible degradation in the SD reflectance at 936 nm for both Terra (>;2%) and Aqua (>0.5%) MODIS. In addition, comparison of SD calibration results to earth view targets suggests that smaller but non-negligible SD degradation also exists at the SWIR band wavelengths. In this paper, we review the current status of the MODIS SD degradation as measured by the SDSM. We present efforts to extend the SD degradation measurements to the SWIR band wavelengths (1240 nm to 2130 nm) by fitting a wavelength-dependent model to the SDSM results from the visible and NIR wavelength detectors. The predicted degradation results are used to correct the MODIS SWIR band degradation, and comparisons are made with trends from pseudo-invariant earth targets. Results are presented for both Terra and Aqua MODIS.

Uyuni desert (-20.8° to -19.6° in latitude, -68.2° to -66.8° in longitude) covered by a few meters of salt can be a good target for Earth observation satellite with its flatness, brightness, and high altitude. We can validate the accuracy of GOES-16 Advanced Baseline Imager (ABI) visible and near-IR (VNIR) channels using the Uyuni desert as a reference. A selection and reflectance monitoring of uniform scenes over the Uyuni desert using a number of space-borne observational datasets is a main objective of this study. It is critical to identify the geospatially, temporally, and spectrally uniform area with at least 3 km x 3 km in size for the ABI Band 2 and 7 km x 7 km for the ABI Band 1, 3, 5, and 6. For radiometric and temporal stability, GOES-13 Imager visible (0.65 μm) data obtained near the satellite noon time is used. In terms of spatial stability, Visible Infrared Imaging Radiometer Suite (VIIRS) data onboard Suomi-National Polar-orbiting Partnership spacecraft (SNPP) is compared to find the uniform scenes with low covariance of reflectance over the radiometric and temporal stable areas. We selected two candidate targets over the Uyuni desert and conducted monitoring of the reflectance trending for the two targets from both the ABI and VIIRS data.

Interaction between the tropical ocean and atmosphere produces interannual climate variability dominated by the El Ni˜no Southern Oscillation (ENSO). We perform a Fourier analysis of the El Ni˜no events, which are characterized by positive sea-surface temperature (SST) anomalies. We consider an elementary nonlinear model for the ENSO phenomenon: the time rate of change of the SST depends on the existence of a strong positive feedback in the coupled ocean-atmosphere system, and on a nonlinear mechanism that limits the growth of unstable perturbations. A key element in this model is the inclusion of the effects of equatorially trapped oceanic waves propagating in a closed basin through a time delayed term. Numerical solution reveals solutions that are self-sustained oscillations. The model is extended by including external influences such as annual forcing, global warming, and stochastic effects. We investigate the range of the parameters that will cause drastic qualitative changes in the climate system, i.e. bifurcation.

Fourier transform infrared spectroscopy is an important technique in studying molecular energy levels, analyzing material compositions, and environmental pollutants detection. A novel rotational motion Fourier transform infrared spectrometer with high stability and ultra-rapid scanning characteristics is proposed in this paper. The basic principle, the optical path difference (OPD) calculations, and some tolerance analysis are elaborated. The OPD of this spectrometer is obtained by the continuously rotational motion of a pair of parallel mirrors instead of the translational motion in traditional Michelson interferometer. Because of the rotational motion, it avoids the tilt problems occurred in the translational motion Michelson interferometer. There is a cosine function relationship between the OPD and the rotating angle of the parallel mirrors. An optical model is setup in non-sequential mode of the ZEMAX software, and the interferogram of a monochromatic light is simulated using ray tracing method. The simulated interferogram is consistent with the theoretically calculated interferogram. As the rotating mirrors are the only moving elements in this spectrometer, the parallelism of the rotating mirrors and the vibration during the scan are analyzed. The vibration of the parallel mirrors is the main error during the rotation. This high stability and ultra-rapid scanning Fourier transform infrared spectrometer is a suitable candidate for airborne and space-borne remote sensing spectrometer.

We have examined, in earlier work, the relationship between naturally induced chlorophyll-a fluorescence and the underwater polarized oceanic light field. This shows the un-polarized fluorescence causes a reduction in the degree of polarization over the fluorescence spectral range. Theory shows that the peak of the reduction in polarization occurs at or near the fluorescence peak. Furthermore, it also shows that the magnitude of this reduction in degree of polarization can be related to both the magnitude of the fluorescence as well as the intensity of the underwater light field over the fluorescence spectral range. To examine this relationship in detail, a vector radiative transfer code (VRTE) for the coupled atmosphere-ocean system was employed for a variety of oligotrophic and eutrophic water conditions. The VRTE used measured inherent optical properties (IOPs) for these water conditions as inputs to simulate the complete elastic and inelastic components of the underwater light field, as well as the degree of linear polarization (DoLP) associated with it. These theoretical predictions were then compared with the results of DoLP measurements carried out using by our multiangular hyperspectral polarimeter. A comparison of the measured reduction in degree polarization of the underwater light field over the fluorescence spectral range, and the magnitude of the fluorescence causing it, confirmed the validity of our theoretical relationship, and the feasibility of determining the natural fluorescence existing in an underwater light field from polarization measurements.