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. Four CERES instruments are supporting the EOS missions; two aboard the Terra spacecraft, launched in 1999 and two aboard the Aqua spacecraft, launched in 2002. A fifth instrument, Flight Model 5 (FM5), launched in October 2011 aboard the S-NPP satellite, began taking radiance measurements on January 27th, 2012. The CERES FM5 instrument uses three scanning thermistor bolometers to make broadband radiance measurements in the shortwave (0.3 – 5.0 micrometers), total (0.3 - <100 micrometers) and water vapor window (8 – 12 micrometer) regions. An internal calibration module (ICM) used for in-flight calibration is built into the CERES instrument package consisting of an anodized aluminum blackbody source for calibrating the total and window sensors, and a shortwave internal calibration source (SWICS) for the shortwave sensor. The ICM sources, along with a solar diffusor called the Mirror Attenuator Mosaic (MAM), are used to define shifts or drifts in the sensor response over the life of the mission. In addition, validation studies are conducted to assess the pointing accuracy of the instrument and understand any spectral changes that may occur with the sensors allowing for corrections to be made to the radiance calculations in later CERES data products. This paper summarizes the on-orbit behavior of the CERES FM5 instrument by outlining trends in the internal calibration data and discussing the various validation studies used to assess the performance and stability of the instrument.

The Visible Infrared Imaging Radiometer Suite (VIIRS) aboard the Suomi National Polar-orbiting Partnership (SNPP) satellite carries out radiometric calibration of its reflective solar bands primarily through observing a sunlit onboard solar diffuser (SD). The SD bidirectional reflectance distribution function (BRDF) degrades over time. The degradation factor is determined by an onboard solar diffuser stability monitor (SDSM) which observes the Sun through a pinhole screen and the sunlit SD. The transmittance of the SDSM pinhole screen over a range of solar angles was determined prelaunch and used initially to determine the BRDF degradation factor. The degradation factor versus time curves were found to have a number of very large unphysical undulations likely due to the inaccuracies in the prelaunch determined SDSM screen transmittance. To validate and if necessary to refine both the SD and the SDSM screen transmittances, satellite yaw maneuvers were carried out. With the yaw maneuver data determined SDSM screen transmittance, the computed BRDF degradation factor curves still have large unphysical ripples, indicating that the projected solar horizontal angular step size in the yaw maneuver data is too large to resolve the transmittance at a fine angular scale. We develop a methodology to use both the yaw maneuver and regular on-orbit data to determine the SDSM screen transmittance at a fine angular scale with a relative error standard deviation from 0.00029 (672 nm; detector 5) to 0.00074 (926 nm; detector 8). With the newly determined SDSM screen transmittance, the computed BRDF degradation factor behaves much more smoothly over time.

Lunar observations by the Suomi-NPP instrument VIIRS help improve our understanding of the radiometric calibration of the reflected solar bands (RSB). The spacecraft performs a scheduled roll maneuver approximately nine times per year to acquire lunar data at nearly constant phase angles. The instrument also captures lunar radiometric data at other times when the instrument Space View port serendipitously points at the Moon. In this paper, we present results only from the scheduled Moon observations, comparing the observed lunar irradiance to ROLO model results to provide calibration coefficients for each band, mirror side, and detector. These results can be evaluated directly to the primary RSB calibration method derived from the Solar Diffuser. This paper also discusses recent improvements to our methodology for measuring the lunar irradiance, including a new method for determining the lunar position within the field of view, an all-detector calibration methodology, and an assessment of the uncertainties in our lunar observations. This paper includes lunar observation data through June 2014.

The Rayleigh scattering approach to absolute radiometric calibration of satellite optical sensors is investigated for SNPP VIIRS. The vicarious calibration coefficients are obtained by comparing measured and predicted top-ofatmosphere (TOA) reflectance sampled under “favorable” scene conditions, i.e., oceanic areas with stable water optical properties, where situations of clear sky, low wind speed, and low aerosol content are frequent. In such situations, and under suitable geometry, the dominant contribution to the satellite signal in the visible is due to molecular (Rayleigh) scattering, which can be computed accurately. A sensitivity study performed for suitable calibration sites indicates that, using thresholds of 7 m/s for wind speed, 0.1 for aerosol optical thickness, 0.0005 for Sun glint reflectance, and 60° for Sun and view zenith angles, the error on the TOA reflectance is 2.3% at 410.5 nm (M1), increasing to 4.5% at 671.4 nm (M5). The error budget is dominated by the effect of uncertainty on aerosol optical thickness at the longer wavelengths and on marine reflectance at the shorter wavelengths. Two methods are developed to compute the VIIRS reflectance. The first method (Method 1) consists in using for the region of interest environmental conditions obtained from ancillary data or climatology. The second method (Method 2) addresses the uncertainty in aerosol model and optical thickness by accounting for the aerosol content of the scene. Application of Method 1 to VIIRS data yields calibration coefficients that are site and air mass dependent, which is not satisfactory. This results from using climatology data to specify aerosol parameters. Method 2, which utilizes the measured VIIRS reflectance in the near infrared to estimate the aerosol reflectance, reduces substantially the site and angular geometry dependence of the calibration coefficients. Accuracy can be improved by better specifying the marine reflectance, estimating the aerosol model, and further stratifying the calibration data. The large number of realizations allows for absolute calibration of individual detectors, studies of angular dependence, linearity, and polarization sensitivity, which is not possible using vicarious techniques based on (too few) in situ measurements.

The Day-Night Band (DNB) on Suomi-NPP VIIRS is a visible/near-Infrared panchromatic band capable of observing the earth during both daytime and nighttime. The VIIRS DNB is the first in its class to have on-orbit radiometric calibration using on-board calibrators. This paper describe the DNB calibration methodology used by the NASA VIIRS Characterization Support Team (VCST), and the process to provide consistent calibration Look-Up-Tables (LUTs). The radiometric calibration processes include (1) using the Solar Diffuser observation of the Sun to determine the gain of the DNB’s low gain stage; (2) using the Solar Diffuser signals outside of direct Sun illumination to compute the gain ratios between DNB’s low-to-mid and mid-to-high gain stages; and (3) using the nighttime calibrator observations to track the dark offset drift. Time dependent modulated Relative Spectral Responses (RSRs) are used to correct the optical throughput change due to mirror darkening. The pitch maneuver’s deep space view is used to compute the airglow free HGS offset. DNB stray light is corrected based on a correction LUT estimated from dark surface during each month’s new moon.

The Suomi-NPP VIIRS Day-Night Band (DNB) offers quantitative measurements of visible and near-infrared light over a dynamic range from full daylight to the dimmest nighttime scenes. This range presents a challenge to radiometric calibration, but the instrument has exceeded all of its absolute radiometric requirements. Nevertheless, striping and banding are still visible, day or night, but especially in low-light scenes. The causes may be cross talk, stray light or hysteresis in the data used for calibration. These issues combine to reduce the utility of these unique observations for gaining new insight on the nocturnal environment. This paper presents methods for improving gain and offset uniformity for both day and night scenes while maintaining absolute radiometric accuracy. We evaluate removal of fixed-pattern non-uniformity in dark scenes on a per orbit basis using three different techniques: i) tracking the darkest 25th percentile calibration sector signal; ii) taking the mean of filtered dark Earth-view scenes to determine offset; iii) minimizing correlated error for dark scenes within an aggregation zone. For gain uniformity we discuss some problems with the current calibration methods, and demonstrate a technique to minimize the correlated error between detectors and aggregation zones using the moment matching technique for moonlit scenes. A similar technique can be used for daytime and twilight scenes. An alternative cross-calibration technique between gain stages uses indirect illumination of solar diffuser view. The use of the space view and blackbody view for cross-calibration is also discussed. Histogram equalization is discussed for minimizing striping and banding. In all cases, data with stray light is filtered out to prevent contamination of the destriping process.

Electronic and optical crosstalk is one of the major challenges facing space-based Earth observing sensors, the effects of which could pose serious risks to the successful retrieval of geophysical information. There was an extensive effort during the SNPP VIIRS design and testing phase to characterize the on-orbit VisNIR crosstalk and its impact on environmental products. This paper describes an approach to assess the level of optical and electronic crosstalk on the measured radiance, and thereafter the retrieved geophysical products. During SNPP VIIRS pre-launch testing, a set of electronic and optical cross-talk influence coefficients was derived from measurements, which represent the amount of signal contamination received by each detector when other detectors on the same focal plane were illuminated. These coefficients were used to assess the potential crosstalk and its uncertainty on typical SNPP VIIRS land, atmosphere and ocean scenes. The simulation results show SNPP VIIRS crosstalk contamination is very small, less than 0.3 % for the stressing scenes, except for bands M7 and I2 over the dark ocean regions. These results are encouraging and constitute further evidence that SNPP VIIRS produces high quality imagery. The simulation approach presented in this paper could also be used for early crosstalk impact assessments for future VIIRS instruments.

The Suomi-NPP Visible Infrared Imager Radiometer Suite (VIIRS) radiance is mapped to make image products using the ground-track Mercator (GTM) algorithm developed at Raytheon. This algorithm defines a process for transforming gridded map (x/y) coordinates of the image into Earth coordinates (longitude/latitude). The y-axis reference is the satellite ground track, which is mapped with an even scale. Great circles placed orthogonally with respect to the ground track define the x-axis. In its current state the algorithm is only defined for the Map-to-Earth (MtE) transformation, but the Earth-to-Map (EtM) transformation has no mathematical algorithm, and instead must use a slow search algorithm for every point. Because of this, the GTM is not a true map projection. This paper remedies this by describing an EtM transformation algorithm using a Ground Track Oblique Cassini (GTOC) projection. This is in somewhat similar to the Space Oblique Mercator (SOM) Projection developed for Landsat. However, Landsat has a very narrow swath, and the GTOC projection better preserves scale across a wider swath, making it more suited for sensors such as VIIRS. Also, unlike the SOM, it keeps the ground-track centered, which is a more efficient use of screen area when it is viewed. This paper describes details of the algorithm, including adjustments necessary for an elliptical orbit and an ellipsoidal Earth. It evaluates Map parameters including conformality and scale preservation, comparing this with other projections, including the SOM. It also evaluates improvements in efficiency relative to a search algorithm.

This paper describes observations of radiances and radiance trends at DomeC in Antarctica made by three sensors—the Infrared Atmospheric Sounding Interferometer (IASI), the Cross-track Infrared Sounder (CrIS), and the Atmospheric Infrared Sounder (AIRS). It includes comparisons with independently measured surface temperatures. AIRS and IASI have been in simultaneous routine operations since May 2007. All three instruments have been producing operational data simultaneously since April 2012. DomeC is on a high plateau and provides a source of nearly uniform dry scenes with a temperature range from about 190 K to about 250 K. Located on this plateau is an operational automated weather station that provides ground truth, including temperature measurements two meters above the surface every ten minutes. Calibration of infrared radiometers at cold scene temperatures is very difficult. But high accuracy even at cold temperatures is critical for establishing a climate-quality data record. Since CrIS is presently planned to serve as a follow-on to AIRS, it is important to understand any differences in their observed radiances. We will compare AIRS, IASI, and CrIS brightness temperatures in the window channel at 900 cm^-1.

We introduce and illustrate applications of the AIRS Level-1C (L1C) data product. While each spectrum in the Level- 1B (L1B) calibrated radiances is represented by 2378 channels, each spectrum in the L1C product is represented by 2645 channels, with monotonically increasing frequency. Typically 2000 of the 2378 L1B channels are copied unchanged into the 2645 channel array used in L1C. The dead or noisy channels in the L1B and new channels in the spectral gaps of L1B are filled using a Principal Component technique. We illustrate two applications of AIRS L1C: 1) to integrate over the band of broadband instruments such as MODIS and 2) resampling to emulate other hyperspectral instruments such as CrIS. The L1C data product will greatly facilitate the use of AIRS data for cross-calibration with other instruments.

The validation of the radiometric calibration of virtually all infrared radiometers has previously been carried out under carefully selected, generally spatially uniform conditions, with the assumption that the radiometric accuracy of the data may be dependent on scene brightness temperature, but is independent of other scene unique conditions, such as scene spatial uniformity. The availability of AIRS and CrIS observations from polar orbits with the identical ascending node presents an opportunity to evaluate the validity of this assumption. For each day between May 2012 and January 2014 we collected 22,000 Random Nadir Spectra (RNS). We then analyzed the time series of the daily differences between AIRS and CrIS Probability Density Function in the 900 cm^-1 atmospheric window channel. Under polar conditions the PDF differences between AIRS and CrIS are typically less than 50 mK for the 10%tile, the mean and the 90%tiles values of the PDF. Under area representative global conditions day and night CrIS is about 0.2K colder than AIRS at the 10%tile and mean values. These differences are well within the limits of the instrument requirements specification. However, the difference between AIRS and CrIS have a complicated zonal distribution, particular for the tropical zone. For day tropical land CrIS is 0.3 K warmer in the mean, 1K warmer in the 10%tile value (cold tails of the PDF) than AIRS. The reasons for these differences are still under investigation. A number of modifications to the CrIS radiometric calibration algorithms have been proposed.

The S-NPP Visible Infrared Imaging Radiometer Suite (VIIRS) instrument is built with strong heritage from EOS MODIS, and has very similar thermal emissive bands (TEB) calibration algorithm and on-board calibrating source - a V-grooved blackbody. The calibration of the two instruments can be assessed by comparing the brightness temperatures retrieved from VIIRS and Aqua MODIS simultaneous nadir observations (SNO) from their spectrally matched TEB. However, even though the VIIRS and MODIS bands are similar there are still relative spectral response (RSR) differences and thus some differences in the retrieved brightness temperatures are expected. The differences depend on both the type and the temperature of the observed scene, and contribute to the bias and the scatter of the comparison. In this paper we use S-NPP Cross-track Infrared Sounder (CrIS) data taken simultaneously with the VIIRS data to derive a correction for the slightly different spectral coverage of VIIRS and MODIS TEB bands. An attempt to correct for RSR differences is also made using MODTRAN models, computed with physical parameters appropriate for each scene, and compared to the value derived from actual CrIS spectra. After applying the CrIS-based correction for RSR differences we see an excellent agreement between the VIIRS and Aqua MODIS measurements in the studied band pairs M13-B23, M15-B31, and M16- B32. The agreement is better than the VIIRS uncertainty at cold scenes, and improves with increasing scene temperature up to about 290K.

Long-term, remote-sensing-based climate data records (CDRs) are highly dependent on having consistent, wellcalibrated satellite instrument measurements of the Earth’s radiant energy. Therefore, by making historical satellite calibrations consistent with those of today’s imagers, the Earth-observing community can benefit from a CDR that spans a minimum of 30 years. Most operational meteorological satellites rely on an onboard blackbody and space looks to provide on-orbit IR calibration, but neither target is traceable to absolute standards. The IR channels can also be affected by ice on the detector window, angle dependency of the scan mirror emissivity, stray-light, and detector-to-detector striping. Being able to quantify and correct such degradations would mean IR data from any satellite imager could contribute to a CDR. Recent efforts have focused on utilizing well-calibrated modern hyper-spectral sensors to intercalibrate concurrent operational IR imagers to a single reference. In order to consistently calibrate both historical and current IR imagers to the same reference, however, another strategy is needed. Large, well-characterized tropical-domain Earth targets have the potential of providing an Earth-view reference accuracy of within 0.5 K. To that effort, NASA Langley is developing an IR tropical mean calibration model in order to calibrate historical Advanced Very High Resolution Radiometer (AVHRR) instruments. Using Meteosat-9 (Met-9) as a reference, empirical models are built based on spatially/temporally binned Met-9 and AVHRR tropical IR brightness temperatures. By demonstrating the stability of the Met-9 tropical models, NOAA-18 AVHRR can be calibrated to Met-9 by matching the AVHRR monthly histogram averages with the Met-9 model. This method is validated with ray-matched AVHRR and Met-9 bias difference time series. Establishing the validity of this empirical model will allow for the calibration of historical AVHRR sensors to within 0.5 K, and thereby establish a climate-quality IR data record.

Radiometric performance of satellite instruments needs to be regularly monitored to determine if there is any drift in the instrument response over time despite the calibration with the best effort. If a drift occurs, it needs to be characterized in order to keep the radiometric accuracy and stability well within the specification. Instrument gain change over time can be validated independently using many techniques such as using stable earth targets (desert, ocean, snow sites etc), inter-comparison with other well calibrated radiometers (using SNO, SNO-x), deep convective clouds (DCC), lunar observations or other methods. This study focus on using vicarious calibration sites for the assessment of radiometric performance of Suomi National Polar-Orbiting Partnership (S-NPP) Visible Infrared Imaging Radiometer Suite (VIIRS) reflective solar bands. The calibration stability is primarily analyzed by developing the top-of-atmosphere (TOA) reflectance time series over these sites. In addition, the radiometric bias relative to AQUA MODIS is estimated over these calibration sites and analyzed. The radiometric bias is quantified in terms of observed and spectral bias. The spectral characterization and bias analysis will be performed using hyperspectral measurements and radiative transfer models such as MODTRAN.

The Thematic Mapper (TM) onboard the Landsat 5 (L5) has provided an unprecedented amount of earth observations for more than 25 years since its launch on March 1, 1984. The MODIS sensor onboard the Aqua satellite is a part of the afternoon constellation of spacecraft and has been successfully providing near-continuous observations of the earth’s surface and atmosphere since July 2002. A synergistic use of TM and MODIS reflective solar bands (RSB) measurements is immensely beneficial to the broad user community for different land cover change and global climate studies. A consistent radiometric calibration between the sensors is a prerequisite for creating high quality science products. Various pseudo-invariant calibration sites (PICS) identified by CEOS have been widely used to monitor the on-orbit calibration consistency for a number of sensors. Near-simultaneous observations of the Saharan PICS by L5 TM and Aqua MODIS are used in this study. The top-of-atmosphere (TOA) reflectance from the spectrally matching RSB are corrected for test site Bi-directional Reflectance Distribution Function (BRDF), relative spectral response (RSR) mismatch, and impacts for atmospheric water-vapor, and used to estimate the long-term calibration differences between the two sensors. The Operational Land Imager (OLI) onboard the Landsat 8 (L8) launched in February, 2013, is a follow-on mission to maintain the continuity of Landsat acquisitions. A similar cross-calibration methodology was extended to compare the spectrally matching bands of Aqua MODIS with OLI. A long-term drift is observed in bands 1 (3.7%) and 3 (1.86%) of L5 TM, which is expected to be mitigated in the next calibration coefficient update. With the exception of the SWIR-2 band (L5 TM band 7), the agreement with Aqua MODIS is seen to be within 4%. The L8 OLI and Aqua MODIS agreement is seen within 4% across all wavelengths.

The Terra satellite, flagship of NASA’s long-term Earth Observing System (EOS) Program, continues to provide useful earth science observations well past its 5-year design lifetime. This paper describes the evolution of Terra operations, including challenges and successes and the steps taken to preserve science requirements and prolong spacecraft life. Working cooperatively with the Terra science and instrument teams, including NASA’s international partners, the mission operations team has successfully kept the Terra operating continuously, resolving challenges and adjusting operations as needed. Terra retains all of its observing capabilities (except Short Wave Infrared) despite its age. The paper also describes concepts for future operations. This paper will review the Terra spacecraft mission successes and unique spacecraft component designs that provided significant benefits extending mission life and science. In addition, it discusses special activities as well as anomalies and corresponding recovery efforts. Lastly, it discusses future plans for continued operations.

The Multi-angle Imaging SpectroRadiometer (MISR) has successfully operated on the EOS/ Terra spacecraft since 1999. It consists of nine cameras pointing from nadir to 70.5° view angle with four spectral channels per camera. Specifications call for a radiometric uncertainty of 3% absolute and 1% relative to the other cameras. To accomplish this, MISR utilizes an on-board calibrator (OBC) to measure camera response changes. Once every two months the two Spectralon panels are deployed to direct solar-light into the cameras. Six photodiode sets measure the illumination level that are compared to MISR raw digital numbers, thus determining the radiometric gain coefficients used in Level 1 data processing. Although panel stability is not required, there has been little detectable change in panel reflectance, attributed to careful preflight handling techniques. The cameras themselves have degraded in radiometric response by 10% since launch, but calibration updates using the detector-based scheme has compensated for these drifts and allowed the radiance products to meet accuracy requirements. Validation using Sahara desert observations show that there has been a drift of ~1% in the reported nadir-view radiance over a decade, common to all spectral bands.

Since launch in December 1999, Terra MODIS has successfully operated for nearly 15 years, making continuous observations. Data products derived from MODIS observations have significantly contributed to a wide range of studies of key geophysical parameters of the earth’s eco-system of land, ocean, and atmosphere, and their changes over time. The quality of MODIS data products relies on the dedicated effort to monitor and sustain instrument health and operation, to calibrate and update sensor parameters and properties, and to improve calibration algorithms. MODIS observations are made in 36 spectral bands, covering wavelengths from visible to long-wave infrared. The reflective solar bands (1-19 and 26) are primarily calibrated by a solar diffuser (SD) panel and regularly scheduled lunar observations. The thermal emissive bands (20-25 and 27- 36) calibration is referenced to an on-board blackbody (BB) source. On-orbit changes in the sensor spectral and spatial characteristics are monitored by a spectroradiometric calibration assembly (SRCA). This paper provides an overview of Terra MODIS on-orbit operation and calibration activities and implementation strategies. It presents and summarizes sensor on-orbit performance using nearly 15 years of data from its telemetry, on-board calibrators, and lunar observations. Also discussed in this paper are changes in sensor characteristics, corrections applied to maintain MODIS level 1B (L1B) data quality, and efforts for future improvements.

Satellite observations of tropospheric carbon monoxide (CO) are employed in diverse applications including air quality studies, chemical weather forecasting and the characterization of CO emissions through inverse modeling. The TERRA / MOPITT ('Measurements of Pollution in the Troposphere') instrument incorporates a set of gas correlation radiometers to observe CO simultaneously in both a thermal-infrared (TIR) band near 4.7 µm and a near-infrared (NIR) band near 2.3 μm. This multispectral capability is unique to MOPITT. The MOPITT retrieval algorithm for vertical profiles of CO has been refined almost continuously since TERRA was launched at the end of 1999. Retrieval algorithm enhancements are the result of ongoing analyses of instrument performance, improved radiative transfer modeling, and systematic comparisons with correlative data, including in-situ profiles measured from aircraft and products from other satellite instruments. In the following, we describe the methods used to routinely evaluate MOPITT CO profiles. As the satellite instrument with the longest record for CO, methods for assessing the long-term stability are becoming increasingly important.

The Clouds and Earth’s Radiant Energy System (CERES) instruments onboard the Terra and Aqua spacecraft are part of the NASA Earth Observing System (EOS) constellation to make long-term observations of the earth. CERES measures the earth-reflected shortwave energy as well as the earth-emitted thermal energy, which are two components of the earth’s radiation energy budget. These measurements are made by five instruments- Flight Models (FM) 1 and 2 onboard Terra, FMs 3 and 4 onboard Aqua and FM5 onboard Suomi NPP. Each instrument comprises three sensors that measure the radiances in different wavelength bands- a shortwave sensor that measures in the 0.3 to 5 micron band, a total sensor that measures all the incident energy (0.3-200 microns) and a window sensor that measures the water-vapor window region of 8 to 12 microns. The stability of the sensors is monitored through on-orbit calibration and validation activities. On-orbit calibration is carried out using the Internal Calibration Module (ICM) that consists of a tungsten lamp, blackbodies, and a solar diffuser known as the Mirror Attenuator Mosaic (MAM). The ICM calibration provides information about the stability of the sensors’ broadband radiometric gains on-orbit. Several validation studies are conducted in order to monitor the behavior of the instruments in various spectral bands. The CERES Edition-4 data products for FM1-FM4 incorporate the latest corrections to the sensor responses using the calibration techniques. In this paper, we present the on-orbit performance stability as well as some validation studies used in deriving the CERES Edition-4 data products from all four instruments.

Fourteen and half years of vicarious calibration and cross calibration for Terra/ASTER/VNIR (Visible and Near Infrared Radiometer, one of three ASTER mission instruments onboard Terra satellite) are summarized together with an error budget analysis. As the results, it is found that Onboard Calibration (OBC) data derived Radiometric Calibration Coefficient (RCC) is situated within a range of uncertainty of vicarious calibration except the period after approximately 4000 days after launch. In other word, uncertainty of OBC RCC is overlapped with uncertainty of vicarious calibration for about 4000 days since launch. Meanwhile, cross calibration with MODIS, MISR and ETM+ supports vicarious calibration of VNIR. In other word, Cross RCC shows much consistent trend to Vicarious RCC than OBC RCC.

The ASTER instrument onboard the NASA’s Terra satellite launched in December 1999 has three subsystems divided by the spectral regions. ASTER thermal infrared (TIR) subsystem has five TIR bands with a spatial resolution of 90 m. Since March 2000 after the initial checkout period, many vicarious calibration (VC) experiments have been conducted for ASTER/TIR in lakes such as Lake Tahoe (NV/CA), Salton Sea (CA), and Lake Kasumigaura (Japan), and in dry lakes such as Railroad Valley (NV), Alkali Lake (NV), and Coyote Lake (CA). In the present paper, 307 VC matchup data obtained by three organizations were analyzed. Overall results show that a typical difference between the at-sensor radiance acquired by onboard calibration (OBC) and that predicted by VC is about 0.5 to 1 K in the water sites and about 1 to 2 K in the land sites. The results of the responsivity analysis indicate that VC is well tracking the responsivity changes measured by OBC, though the recent discrepancy at band 10 should be investigated with more VC results. The results of the offset analysis indicate that the short term calibration (STC) which is performed at a blackbody temperature of 270 K before every Earth observation has worked normally. It is therefore concluded that the ASTER/TIR instrument has been keeping the designed accuracy (1 K for the temperature range of 270 to 340 K) since the launch.

The MODerate-resolution Imaging Spectroradiometer (MODIS) on NASA’s Earth Observing System Terra satellite, launched into orbit on 18 December 1999, will have a “first light” 15th anniversary on 24 February 2015. For nearly 15 years the MODIS instrument has provided radiances in all spectral bands. Though some detectors have fallen below SNR thresholds, the vast majority of spectral bands continue to provide high quality L1B measurements for use in L2 science algorithms supporting global climate research. Radiometric accuracy of the Terra MODIS thermal emissive bands (TEBs) in the C6 L1B product has been assessed using various approaches over the nearly 15 year Terra MODIS data record, including comparisons with instruments on the ground, in aircraft under-flights, and on other satellites. All of these approaches contribute to the understanding of the Terra MODIS radiometric L1B performance. Early in the lifetime of Terra, ground-based measurements and NASA ER-2 aircraft under-flights revealed that TEBs in the infrared window (“window” bands) are well calibrated and performing within accuracy specifications. The ER-2 under-flights also suggested that many atmospheric bands may be performing outside of specification, especially LWIR CO2 sensitive bands that are subject to optical crosstalk, although analysis uncertainties are larger for atmospheric bands. Beginning in 2007, MetOp-A IASI observations were used to evaluate Terra MODIS TEB performance through Simultaneous Nadir Overpass (SNO) comparisons. These inter-satellite comparisons largely affirm the early aircraft and ground-based evaluations, showing that all Terra MODIS window bands have small biases, minimal trending, and minor detector and mirror side striping over the 2007-2013 timeframe. Most atmospheric bands are performing satisfactorily near to specification; however, biases, striping and trending are large and significantly out of specification in the water vapor sensitive band 27 and ozone sensitive band 30 while the CO2 sensitive band 36 bias significantly exceeds specification. The investigation has found that an effective spectral shift significantly reduces biases and scene temperature dependence (but not trends) in most atmospheric bands, bringing them closer to, if not within, specification.

Remotely sensed ocean color products require highly accurate top-of-atmosphere (TOA) radiances, on the order of 0.5% or better. Due to incidents both prelaunch and on-orbit, meeting this requirement has been a consistent problem for the MODIS instrument on the Terra satellite, especially in the later part of the mission. The NASA Ocean Biology Processing Group (OBPG) has developed an approach to correct the TOA radiances of MODIS Terra using spatially and temporally averaged ocean color products from other ocean color sensors (such as the SeaWiFS instrument on Orbview-2 or the MODIS instrument on the Aqua satellite). The latest results suggest that for MODIS Terra, both linear polarization parameters of the Mueller matrix are temporally evolving. A change to the functional form of the scan angle dependence improved the quality of the derived coefficients. Additionally, this paper demonstrates that simultaneously retrieving polarization and gain parameters improves the gain retrieval (versus retrieving the gain parameter only).

Terra is the flagship of NASA’s Earth observing systems (EOS), carrying five sensors (ASTER, CERES, MISR, MODIS, and MOPITT), which have been providing high-quality global observations for nearly 15 years. MODIS has 20 reflective solar bands (RSB) and are calibrated using a solar diffuser (SD) with its degradation tracked by a solar diffuser stability monitor (SDSM). Scheduled lunar roll observations and vicarious data from pseudo-invariant sites are used to characterize the scanangle dependence of the MODIS RSB. The Multi-angle Imaging SpectroRadiometer (MISR) makes near simultaneous measurements with MODIS at nine view angles spreading out in the forward and backward directions along the flight path via four spectral bands (blue, green, red and near-infrared). MISR calibration efforts are based on a combination of preflight, onboard, and field vicarious measurements. This study compares coincident MODIS and MISR near-nadir reflectances over their entire mission, and examine the calibration stability and consistency of the two instruments. Reflectances from low to high signal levels are based on measurements obtained from ocean, desert and Antarctic snow surfaces. The absolute calibration differences between MODIS and MISR are examined after correction of their spectral response differences based on the SCIAMACHY measured hyperspectral data for the same sites.

The Advanced Spaceborne Thermal Emissive and Reflection Radiometer (ASTER) and Moderate Resolution Imaging Spectrometer (MODIS) are two of the five sensors onboard the Earth Observing System’s Terra satellite. These sensors share many similar spectral channels while having much different spatial and operational parameters. ASTER is a tasked sensor and sometimes referred to a zoom camera of the MODIS that collects a full-earth image every one to two days. It is important that these sensors have a consistent characterization and calibration for continued development and use of their data products. This work uses a variety of test sites to retrieve and validate intercalibration results. The refined calibration of Collection 6 of the Terra MODIS data set is leveraged to provide the up-to-date reference for trending and validation of ASTER. Special attention is given to spatially matching radiance measurements using prelaunch spatial response characterization of MODIS. Despite differences in spectral band properties and spatial scales, ASTER-MODIS is an ideal case for intercomparison since the sensors have nearly identical views and acquisitions times and therefore can be used as a baseline of intercalibration performance of other satellite sensor pairs.

The Terra spacecraft contains five Earth-observation instruments, three of which are multispectral imaging sensors that complement each other in spectral and spatial coverage. The Moderate Resolution Imaging Spectroradiometer (MODIS) has 36 channels ranging from 0.4–14.4 μm, with spatial resolutions of 250, 500, and 1000 m. The Multi-angle Imaging SpectroRadiometer (MISR) uses individual imaging sensors to view the earth at nine discreet angles. Each radiometer has four channels in the visible and near infrared (VNIR), and the nadir-viewing camera has a spatial resolution of 275 m. The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) was designed with fourteen bands ranging from 0.5–11.6 μm. It is the high-resolution sensor on Terra, with a spatial resolution of 15 m in the VNIR, and 30 m in the shortwave infrared (SWIR). This work describes the vicarious techniques used to perform the absolute radiometric calibration of MODIS, MISR, and ASTER in the solar-reflective region (0.4–2.5 μm). It includes the reflectance-based approach, which uses ground-based personnel to make in situ measurements during the time of overpass. It also includes more recent results that were obtained using the University of Arizona’s automated Radiometric Calibration Test Site (RadCaTS) at Railroad Valley, Nevada. In addition to the absolute radiometric calibration of Terra sensors, RadCaTS is used to perform the cross comparison of MODIS, MISR, and ASTER with Landsat 7 ETM+ and Landsat 8 OLI.

The Advanced Baseline Imager (ABI) is the next-generation imaging sensor for the National Oceanic and Atmospheric Administration’s (NOAA’s) operational meteorological satellites in geostationary orbit. One pathway for traceability to reference standards of the visible and near-infrared radiometric response for ABI is to a 1.65 m diameter integrating sphere source standard of spectral radiance. This source illuminates the full entrance pupil via the ABI Earth-view port, thus determining the absolute spectral radiance responsivity in the visible and shortwave infrared. The spectral radiance values of the large sphere are assigned by Exelis using a double monochromator and a 15.24 cm diameter integrating sphere source standard that is calibrated by NIST. As part of the ABI program, Exelis was required by NASA to have the spectral radiance values assigned by Exelis to the large sphere be validated by NIST. Here we report the results of that activity, which took place in April, 2013. During the week of April 8, Exelis calibrated the 1.65 m diameter sphere at all 24 levels that correspond to the ABI calibration protocol. During the week of April 15, the NIST validation exercise for five selected levels took place. NIST deployed a portable spectral radiance source, a filter radiometer restricted to the visible and near-infrared, and two spectroradiometers that covered from 350 nm to 2500 nm. The NIST sphere source served as the validation standard. The comparison results, which are reported at the ABI bands, agreed to within the combined uncertainties. We describe the methodology, results, and uncertainty estimates related to this effort.

In this work, development of a fiber-optically coupled, vacuum-compatible, flat plate radiometric source applicable to the characterization and calibration of remote sensing optical sensors in situ in a thermal vacuum chamber is described. The original flat plate radiometric source configuration’s performance was presented at the 2009 Berlin SPIE. Following the original effort, design upgrades were incorporated in order to improve radiometric throughput and uniformity. Results of thermal and radiometric performance, with incorporated upgrades, of a flat plate illumination source in a temperature-controlled vacuum chamber operating at liquid nitrogen temperature are presented. Applications, including use with monochromatic tunable laser sources for the end-to-end system-level testing of large aperture sensors, are briefly discussed.

The "Bi-Directional Scattering Function" BSDF of a diffuser depends on several parameters, such as surface properties, observational conditions and further. This paper describes experimental activities to achieve a better understanding about the interaction between diffuser properties and performance with regards to its scattering behavior. For this purpose a set of 24 diffusers with defined surface properties have been manufactured and systematically been investigated in a dedicated radiometric calibration measurement facility. The experimental data are compared with existing theoretical models.

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 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-1 VIIIRS in the 0.4 – 1,63 μm wavelength using PASCAL (Polarization And Scatter Characterization Analysis of Lambertian materials) with an uncertainty better than 0.8%. PASCAL makes absolute measurements of BRDF in an analogous fashion to the National Institute of Standards and Technology (NIST) Spectral Tri-function Automated Reflectance Reflectometer (STARR) facility. BRDF is calculated on the basis of the measured incident power, reflected power and geometric factors thus eliminating the need for a standard. The detector rotates about the sample in the plane defined by the source beam and the azimuth rotation of the sample. Unique additional features of this instrument include the ability to vary the sample elevation and roll / clock the sample about its normal thus allowing BRDF measurements in the as use geometry. A description of PASCAL, validation and the BRDF results of the Solar Diffuser are presented. Part dependent non-uniformity of Spectralon® was also observed.

The Operational Land Imager (OLI) on Landsat-8 has been collecting imagery on orbit for 17 months. The radiometric performance of the OLI is monitored using on-board systems (lamps and solar diffusers) as well as by reference to lunar and ground measurements and other satellite systems. Over this nearly 1½ years of operation the OLI has been extremely radiometrically stable in all of its 9 spectral bands. Only the shortest wavelength band, centered at 443 nm, which has degraded about 0.8%, has changed by more than the variability among the measurements (~0.2%). This consistency between the lamps, diffusers, moon, and ground measurements lends high confidence to these statements, which is unusual for a system so early in its lifetime. Comparisons to other satellite systems and ground measurements show that the OLI is calibrated to within requirements and generally better than 3% in both radiance and reflectance.

The Landsat 8 satellite was launched on February 11, 2013, to systematically collect multispectral images for detection and quantitative analysis of changes on the Earth’s surface. The collected data are stored at the U.S. Geological Survey (USGS) Earth Resources Observation and Science (EROS) Center and continue the longest archive of medium resolution Earth images. There are two imaging instruments onboard the satellite: the Operational Land Imager (OLI) and the Thermal InfraRed Sensor (TIRS). This paper summarizes radiometric performance of the OLI including the bias stability, the system noise, saturation and other artifacts observed in its data during the first 1.5 years on orbit. Detector noise levels remain low and Signal-To-Noise Ratio high, largely exceeding the requirements. Impulse noise and saturation are present in imagery, but have negligible effect on Landsat 8 products. Oversaturation happens occasionally, but the affected detectors quickly restore their nominal responsivity. Overall, the OLI performs very well on orbit and provides high quality products to the user community.

The Thermal Infrared Sensor (TIRS) has completed over one year in Earth orbit following its launch onboard Landsat 8 in February 2013. During that time, TIRS has undergone initial on-orbit checkout and commissioning and has transitioned to an operational Landsat payload obtaining 500+ Earth scenes a day. The instrument was radiometrically calibrated during pre-flight characterization testing. A relative adjustment was made to the calibration during the on-orbit checkout of the instrument based on data from the onboard calibration sources to account for instrument changes that occurred through launch. The accuracy of the relative and absolute radiometric calibration depends in part on the stability of the instrument response over time. To monitor stability, TIRS routinely views its onboard calibration sources, which include a variable temperature blackbody and a port that allows the instrument to view deep space. The onboard calibration is validated by in situ measurements of large water bodies by instrumented buoys. In addition, the spacecraft is periodically slewed to image the moon across the field of view of TIRS. The moon provides a high contrast source which allows for studies of stray light and ghosting to be performed. These on-orbit methods provide the means to characterize the TIRS instrument performance post-launch. Analyses of these datasets over the first year on orbit indicate that while, internally, the instrument itself is far exceeding the noise and stability requirements, both bands were mis-calibrated by at least 2K (@300K) and had higher than expected variability in the in situ validation data. This is likely due to stray light which is also causing banding in Earth scenes. An initial bias correction was made on February 2014 and various approaches are being explored to correct the ghosting issues associated with the stray light.

The Operational Land Imager (OLI) aboard the LDCM satellite was rigorously radiometrically characterized prior to launch to assure absolute calibration that is NIST traceable. On orbit additional dedicated calibration collects are being made to continue monitoring and characterizing the OLI radiometric performance. In this paper we report on the OLI on-orbit uniformity performance, which is a natural extension of the absolute radiometric accuracy. Such performance characteristic in remote sensing instruments is assuring that the radiometric accuracy in low contrast images is preserved while avoiding non-uniformity artifacts in the produced radiometric product. The LDCM project science team working with the instrument teams developed a performance metric to monitor the uniformity performance. We will describe the uniformity performance metric and discuss associated error sources in obtaining the radiometric calibration parameters that impact the uniformity correction. We will compare the uniformity performance between solar diffuser observation and earth data.

Landsat 8 was launched on 11 February 2013 as the newest platform in the Landsat program. It contains two Earthobserving instruments, one of which is the Operational Land Imager (OLI). OLI includes an onboard radiometric calibration system that is used to monitor changes in its responsivity throughout the mission lifetime, and it consists of Spectralon solar diffuser panels as well as tungsten lamp assemblies. External techniques are used to monitor both OLI and its calibration system, and they include lunar views, side slither maneuvers of the satellite, and ground-based vicarious calibration. This work presents the absolute radiometric calibration results for Landsat 8 OLI that were obtained using two ground-based measurement techniques. The first is the reflectance-based approach, where measurements of atmospheric and surface properties are made during a Landsat 8 overpass, and it requires personnel to be on site during the time of measurement. The second uses the Radiometric Calibration Test Site (RadCaTS), which was developed by the Remote Sensing Group in the College of Optical Sciences at the University of Arizona so that radiometric calibration data can be collected without the requirement of on-site personnel. It allows more data to be collected annually, which increases the temporal sampling of trending results.

The Thermal Infrared Sensor (TIRS) on board Landsat 8 has exhibited a number of anomalous characteristics that have made it difficult to calibrate. These anomalies include differences in the radiometric appearance across the blackbody pre- and post-launch, variations in the cross calibration ratios between detectors that overlap on adjacent arrays (resulting in banding) and bias errors in the absolute calibration that can change spatially/temporally. Several updates to the TIRS calibration procedures were made in the months after launch to attempt to mitigate the impact of these anomalies on flat fielding (cosmetic removal of banding and striping) and mean level bias correction. As a result, banding and striping variations have been reduced but not eliminated and residual bias errors in band 10 should be less than 2 degrees for most targets but can be significantly more in some cases and are often larger in band 11. These corrections have all been essentially ad hoc without understanding or properly accounting for the source of the anomalies, which were, at the time unknown. This paper addresses the procedures that have been undertaken to; better characterize the nature of these anomalies, attempt to identify the source(s) of the anomalies, quantify the phenomenon responsible for them, and develop correction procedures to more effectively remove the impacts on the radiometric products. Our current understanding points to all of the anomalies being the result of internal reflections of energy from outside the target detector’s field-of-view, and often outside the telescope field-of-view, onto the target detector. This paper discusses how various members of the Landsat calibration team discovered the clues that led to how; these “ghosts” were identified, they are now being characterized, and their impact can hopefully eventually be corrected. This includes use of lunar scans to generate initial maps of influence regions, use of long path overlap ratios to explore sources of change and use of variations in bias calculated from truth sites to quantify influences from the surround on absolute bias errors.

Shortly after Landsat-8 launched in February 2013, the U.S. Geological Survey (USGS) Earth Resources Observation and Science (EROS) Center began creating radiometrically and geometrically corrected products. In order to provide these products as soon as possible, the Landsat Product Generation System (LPGS) was developed based on instrument designs and testing prior to launch. While every effort was made to ensure the LPGS produces highly accurate products, some aspects of the sensors are difficult to characterize during testing on the ground. Examples of these characteristics include differences between individual detectors that make up the focal plane array, and the way detectors view radiometric targets in preflight testing versus the way they view the Earth on orbit, and the accuracy of the measurements made on the ground. Once in orbit, more accurate measurements of these sensor characteristics were made that improved processing parameters, resulting in improved quality of the final imagery. This paper reviews the changes that have occurred to the processing of Landsat-8 data products which include parameter changes as well as some modifications to the processing system itself. These changes include: improved linearization of the data, both to parameters and the algorithm used for linearizing the data; improved radiance and reflectance conversion coefficients; individual detector coefficients to improve uniformity; and geometric alignment coefficients to improve the geometric accuracy. These improvements lead to a reprocessing campaign that occurred in early in 2014 that replaced all prior data with improved products.

The Landsat program is a joint United States Geological Survey (USGS) and National Aeronautics and Space Administration (NASA) enterprise for Earth Observation (EO), that represents the world’s longest running system of satellites for moderate-resolution optical remote sensing. The European Space Agency (ESA) has acquired Landsat data over Europe through the ESA ground stations over the last 40 years, in co-operation with USGS and NASA. A new ESA Landsat Multi-Spectral Scanner (MSS), Thematic Mapper (TM) and Enhanced Thematic Mapper Plus (ETM+) processor has been developed. This enhanced processor aligns the historical Landsat products to the highest quality standards that can be achieved with the current knowledge of the instruments. The updated processor is mainly based on the USGS algorithm; however the ESA processor has some different features that are detailed in this paper. Using this upgraded processor, ESA is currently performing for the first time a bulk-processing of its entire Landsat series MSS/TM/ETM+ historical archive to make all products available to users. Current achievements include the processing and online distribution of approximately 290 000 new Landsat 5 TM high-quality products acquired at the Kiruna ground station between 1983 and 2011. The Landsat 5 TM bulk-processed products are made available for direct download after registration at: https://earth.esa.int/web/guest/pi-community/apply for-data/fast-registration. The remainder of the ESA’s Landsat data, dating back more than 40 years, will gradually become available for all users during the course of 2014. The ESA Landsat processor algorithm enhancement, together with the results of the ESA archive bulk-processing, and an overview on the data quality on a subset of the Landsat 5 TM data are herein presented.

EUMETSAT’s mandate comprises the support of operational meteorology and climate monitoring. These goals are pursued with mandatory programmes, in the geostationary and sun-synchronous polar orbits. In the frame of optional programmes further tasks like altimetry and oceanography are supported. In the frame of third party programmes, EUMETSAT provides data from other agencies’ satellites to the user community. This paper provides an overview over the current and future geostationary and polar systems, as well as on third party and Oceanography missions. This includes an overview on the Meteosat Third Generation and EPS Second Generation programmes and also the Oceanography missions related to Jason and Copernicus. Finally related services are addressed.

The Copernicus programme is a European initiative for the implementation of information services dealing with environment and security, based on observation data received from Earth Observation (EO) satellites and ground based information. Within this context, ESA is responsible in particular, for the implementation of the Copernicus Sentinel missions, feeding the Copernicus services with operational EO data. The Sentinel-2 optical high-resolution imaging mission will be devoted to the operational and systematic monitoring of land and coastal areas. To maximize the products suitability and readiness to downstream usage for the majority of applications, the Sentinel-2 Payload Data Ground Segment (PDGS) will systematically generate, archive and distribute Level-1C products, which will provide Top-of-Atmosphere (TOA) reflectance images, orthorectified using a global Digital Elevation Model (DEM) and projected on Universal Transverse Mercator (UTM) coordinate system. A Level-1B product will also be available for expert users, providing radiance images in sensor geometry together with an appended geometric model. Additionally, a complementary atmospheric correction and enhanced cloud screening algorithm is being prototyped. This processor will allow converting the Level-1C TOA reflectance image into Bottom-of-Atmosphere (BOA) reflectance. The processor will be provided as plug-in software of the Sentinel-2 Toolbox that will run on user side. During the operational phase, the Sentinel-2 Mission Performance Centre (MPC), as integrating part of the mission ground segment, will be in charge of ensuring that mission performances are met in terms of data quality through the calibration and validation activities.

CarbonSat is a proposed Earth observation mission, which was selected in 2010 as one of two candidates for becoming the European Space Agency’s (ESA) eighth Earth Explorer (EE8). It is currently undergoing parallel feasibility studies (phase A) performed by two industrial consortia. CarbonSat aims at a better understanding of the natural and anthropogenic sources and sinks of the two most important anthropogenic greenhouse gases CO₂ and CH₄, which will contribute to a better understanding of climate feedback and forcing mechanisms. To achieve these objectives the instrument will quantify and monitor the spatial distribution of carbon dioxide (CO₂) and methane (CH₄). It will deliver global data sets of dry air column-averaged mixing ratios of these gases with high precision (1 - 3 ppm for CO₂ and 6 - 12 ppb for CH₄) and accuracy (0.5 ppm for CO2 and 5 ppb for CH₄). The measurements will provide global coverage every 12 days above 40 degrees latitude at a spatial resolution of 2 x 3 km². The retrieval products are inferred from observations of Earth radiance and solar irradiance at high to medium spectral resolution (0.1-0.55 nm) in the Near Infrared (747-773 nm) and Short Wave Infrared (1590- 1675 nm and 1925-2095 nm) spectral regions. The combination of high spatial resolution and global coverage requires a swath width larger than 180 km for three spatially co-aligned push-broom imaging spectrometers. The targeted product accuracy translates into stringent radiometric, spectral and geometric requirements for the instrument. This paper presents the system requirements derived from the demanding mission objectives and reports preliminary results of the feasibility studies. It highlights the key components of the instrument, focusing on the optical conceptual design, and addresses the identified critical performance aspects.

Fibertek is under contract from NASA Goddard to build four space qualified laser transmitters for the ICESat-2 (Ice, Cloud, and Land Elevation Satellite) program, a second generation orbiting laser altimeter. Pertinent laser parameters driving the design included laser wall plug efficiency, laser reliability, a relatively narrow linewidth with wavelength tunability, high beam quality (M²<1.6), short pulsewidths (<1.5ns), and energy scalable from 250 μJ to 900μJ in predefined steps. The laser design employs fiber coupled 880nm diodes and end-pump Nd:YVO4 slabs as the gain medium in a master oscillator/power amplifier (MOPA) architecture with an LBO second harmonic generator (SHG). Following the SHG is a telescope that sets the final beam size and divergence requirements. The first laser built will be the Integration and Test Laser (ITL) used for qualification of the design. The ITL will set the baseline parameters for the flight laser builds. The ITL will also validate the design for the telescope and will be subjected to the full environmental testing required for a space hardened flight laser. Environmental testing includes vibration, thermal vacuum conditions, and electromagnetic interference (EMI). Our presentation will address the measured laser parameters from ITL as compared to the as designed laser.

The NASA ESTO-funded Geostationary Trace gas and Aerosol Sensor Optimization (GeoTASO) development project demonstrates a reconfigurable multi-order airborne spectrometer and tests the performance of spectra separation and filtering on the sensor spectral measurements and subsequent trace gas and aerosol retrievals. The activities support mission risk reduction for the UV-Visible air quality measurements from geostationary orbit for the TEMPO and GEMS missions1 . The project helps advance the retrieval algorithm readiness through retrieval performance tests using scene data taken with varying sensor parameters. We report initial results of the project.

The Geostationary Coastal and Air Pollution Events (GEO-CAPE) Airborne Simulator (GCAS) was designed and built at the NASA Goddard Space Flight Center (GSFC) as a technology demonstration instrument for the atmospheric science study group of GEO-CAPE and potential validation instrument for NASA’s Tropospheric Emissions: Monitoring Pollution (TEMPO) mission. GCAS was designed to make high altitude remote sensing observations of tropospheric and boundary layer pollutants, coastal and ocean water leaving radiances, and visible imagery for cloud and surface information. The instrument has participated in one flight campaign in Houston, TX as part of the Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) in September 2013. An overview of the instrument’s design, characterization, and preliminary slant column retrievals of nitrogen dioxide (NO₂) and ozone (O₃) during the DISCOVER-AQ campaign will be provided in this paper.

MODIS is currently onboard NASA’s EOS Terra and Aqua spacecraft launched on December 18, 1999 and May 4, 2002, respectively. MODIS reflective solar bands (RSB) are calibrated on-orbit using solar illumination reflected from its onboard solar diffuser (SD). The solar diffuser stability monitor (SDSM) is designed to track the on-orbit degradation of the SD via alternate observations of the Sun and SD. A wavelength-dependent degradation pattern is observed for both MODIS instruments with a faster degradation rate observed at shorter wavelengths. The UV exposure of the SD to sunlight and the scattered light (the sunlight reflected from top of the atmosphere) through the instrument nadir port contributes to its reflectance degradation. The scatter off the diffuser onto the scan mirror is in the forward direction, whereas the scatter off the diffuser onto the SDSM scan mirror is in the backward direction. Since the outgoing angles (viewed by MODIS detectors) are the same as the scheduled SD calibration, the gain derived from scattering light facilitates monitoring the dependence on SD degradation on incident angles. A methodology is formulated to track the MODIS SD degradation using scattered light through the nadir-port and comparing the result with the SD degradation as measured by the SDSM. In this study, multiple orbits from a given day of each month are processed to obtain a SD response to the nadir-port illumination. Results show that a reasonable agreement is observed between the SD degradation estimates derived from both view-angles.

MODIS Reflective Solar Bands (RSB) are calibrated on-orbit using its onboard calibrators, including a Solar Diffuser (SD), a Solar Diffuser Stability Monitor (SDSM), and a Spectroradiometric Calibration Assembly (SRCA). A Space View (SV) port is used to provide a background reference, and also facilitate near monthly lunar observations via a spacecraft roll. In every scan, the earth’s surface, SV and onboard calibrators are viewed via a two sided scan mirror, whose reflectance depends on the angles of the incidence (AOI) as well as the wavelength of the incident light. Response versus Scan angle (RVS) is defined as a dependence function of the scan mirror’s reflectance over AOI. An initial RVS for each RSB was measured prelaunch for both Terra and Aqua MODIS. Algorithms have been developed to track the on-orbit RVS variation using the measurements from the onboard calibrators, supplemented with the Earth View (EV) response from pseudo-invariant desert targets obtained at different AOI. The current approach, as implemented in Collection 6 (C6), uses EV responses from the Libyan desert sites to track the on-orbit RVS change. It strongly depends on the long-term temporal stability of the desert sites. As an effort to validate and, if necessary, to improve MODIS RSB RVS characterization for future applications, the MODIS Characterization Support Team (MCST) has developed and tested an alternative approach to monitor the on-orbit RVS change, using a response from a single desert site. The purpose of using data from one site is to avoid the impact of possible differences in the long-term temporal stability among multiple sites on the calculation of the on-orbit RVS. This paper updates recent progress in the formulation of the alternative RVS approach. Comprehensive comparisons were also performed with current C6 RVS results for both Terra and Aqua MODIS. Results demonstrate that this alternative method provides a supplemental means to track the on-orbit RVS for MODIS RSB.

Terra and Aqua MODIS have operated near-continuously for over 14 and 12 years, respectively, and are key instruments for NASA’s Earth Observing System. Observations from the 16 thermal emissive bands (TEB), covering wavelengths from 3.5 to 14.4 μm with a nadir spatial resolution of 1 km are used to regularly generate a variety of atmosphere, ocean and land science products. The TEB detectors are calibrated using scan-by-scan observations of an on-board blackbody (BB). The current response versus scan angle (RVS) of the scan mirror was derived using a spacecraft deep-space pitch maneuver for Terra MODIS and characterized during prelaunch for Aqua MODIS. Earth view (EV) data over the complete range of angles of incidence (AOI) can be used to evaluate the on-orbit performance of the TEB RVS over the mission lifetime. Three approaches for tracking the TEB RVS on-orbit using EV observations are formulated. The first approach uses the multiple daily observations of Dome C BT at different AOI and their trend relative to coincident measurements from a ground temperature sensor. The second approach uses brightness temperatures (BT) retrieved over the cloud-free ocean to derive the trends at 13 AOI over the mission lifetime. The third approach tracks the dn response (normalized to the BB AOI) across the full swath width for Antarctic granules with the Dome C site at nadir. The viability of the three approaches is assessed and the long-term stability of the TEB RVS for both MODIS instruments is determined.

The key on-board calibrators (OBCs) of MODIS include a solar diffuser (SD) for the reflective solar bands calibration and a blackbody (BB) for the thermal emissive bands calibration. MODIS also has a space view (SV) port through which the detectors can view the dark space to provide background signal and the Moon during lunar calibration. As a whiskbroom scanning spectroradiometer, the spectral bands of MODIS are spread on its focal plane assemblies (FPA) in the along-scan direction. The images of these bands are spatially co-registered by delaying the observations of individual band according to their location on the FPA to account for the along-scan motion needed to view the same target. While this co-registration works well for the “far field” Earth view (EV) target, significant band-to-band image misregistration in the along-scan direction has been observed when the detectors view “near field” targets, such as the OBCs. In this paper, this “near field” misregistration phenomenon is presented and analyzed, using the OBC images acquired when the electric sector rotation is applied. It is shown that the amount of the misregistration is proportional to the band location and the linear coefficient is inversely proportional to the distance between the object and the scan mirror. The root cause of the misregistration is provided. Also discussed in this paper is the calibration impact due to the “near field” misregistration for MODIS and sensors with MODIS-like scanning mechanism.

Modern Earth-orbiting Earth-observing remote sensing sensors often use onboard solar diffusers (SD) to calibrate their reflective solar bands (RSB), such as the Visible Infrared Imaging Radiometer Suite (VIIRS) aboard the Suomi National Polar-orbiting Partnership (SNPP) satellite. The SD’s optical scattering property is measured by a bidirectional reflectance distribution function (BRDF). Once on orbit, the BRDF is found to degrade over time and the degradation factor is determined by, in the case of the SNPP VIIRS, an onboard solar diffuser stability monitor (SDSM) which observes the SD at a fixed view angle (relative to the SD surface). The SNPP VIIRS RSB however, observes the SD at a different angle. It is conventionally assumed (for cases like VIIRS) that the angular dependence of the BRDF degradation factor is negligible and hence the degradation factor determined by the SDSM is used to calibrate the RSB. We examine the angular dependence of the SNPP VIIRS SD BRDF degradation factor. We find that the degradation factor is clearly angle dependent when the SD BRDF degrades enough (< 0.98), and the larger the degradation the stronger the dependency.

This paper has been withdrawn by the publisher because it was not presented at the conference.

The MODerate resolution Imaging Spectroradiometer (MODIS) has 20 reflective solar bands (RSB), which are calibrated using a solar diffuser (SD) and near-monthly scheduled lunar observations via a space view (SV) port. The sensor responses observed at two different angles of incidence (AOI) from the SD and lunar measurements are used to track the on-orbit RSB gain changes as well as the response versus scan-angle (RVS) changes. The MODIS RSB have experienced wavelength dependent degradation since launch with the larger degradation observed at the shorter wavelengths. In addition to the SD and lunar observations, the MODIS Characterization Support Team (MCST) regularly monitors the response trending at multiple AOI over selected desert sites. In Collection 6 (C6), a new algorithm using the EV measurements from pseudoinvariant desert sites was developed to better characterize the MODIS scan-angle dependence and it led to a significant improvement in the long-term calibration consistency of the MODIS Level 1B (L1B) products. This approach is formulated for all RSB, and its application was recently extended to Terra band 10, leading to a significant improvement in the ocean-color products. This paper discusses the current status and performance of the on-orbit RVS characterization as applied in C6. Also, the various challenges and future improvement strategies associated with trending the EV response for the high-gain ocean bands are discussed.

Spatial cross-talk has been discovered in the visible channel data of the Multi-functional Transport Satellite (MTSAT)-1R. The slight image blurring is attributed to an imperfection in the mirror surface caused either by flawed polishing or a dust contaminant. An image processing methodology is described that employs a two-dimensional deconvolution routine to recover the original undistorted MTSAT-1R data counts. The methodology assumes that the dispersed portion of the signal is small and distributed randomly around the optical axis, which allows the image blurring to be described by a point spread function (PSF) based on the Gaussian profile. The PSF is described by 4 parameters, which are solved using a maximum likelihood estimator using coincident collocated MTSAT-2 images as truth. A subpixel image matching technique is used to align the MTSAT-2 pixels into the MTSAT-1R projection and to correct for navigation errors and cloud displacement due to the time and viewing geometry differences between the two satellite observations. An optimal set of the PSF parameters is derived by an iterative routine based on the 4-dimensional Powell’s conjugate direction method that minimizes the difference between PSF-corrected MTSAT-1R and collocated MTSAT-2 images. This iterative approach is computationally intensive and was optimized analytically as well as by coding in assembly language incorporating parallel processing. The PSF parameters were found to be consistent over the 5-days of available daytime coincident MTSAT-1R and MTSAT-2 images, and can easily be applied to the MTSAT-1R imager pixel level counts to restore the original quality of the entire MTSAT-1R record.

In this paper, the principle of the Ka-band airborne double-antenna microwave radiometer (ADAMR) based on the autogain compensative and noise coupling techniques is reviewed firstly. The radiometer has been applied successfully to detect the atmospheric supercooled water content. Although the auto-gain compensative technique can compensate the gain fluctuation to keep the radiometer's stability by measuring the output variation of reference noise source, it also introduces measurement error caused by the physical temperature change of the reference noise source. For this reason, a temperature correction method for the output voltage of this radiometer is proposed. The corrected equations are derived by using the regression relationship between the measurement error and the physical temperature of the reference noise source. In order to demonstrate the feasibility of this method, the outdoor contrast experiment was carried out. For the 30° antenna channel, the RMSE of the two-point calibration method is 2.039K while the RMSE of the correction method is 0.718K. For the 90° antenna channel, the RMSE of the two-point calibration method is 2.113K while the RMSE of the correction method is 0.448K. The results prove that the correction method can effectively correct the output of the radiometers with the auto-gain compensative technique.

The paper presents the design procedure that makes possible identification of the optimal parameters of the proposed light sources. These precise uniform light sources have a form of several or multiple optically connected integrating spheres. Due to high photometric and metrological characteristics the proposed light sources can be considered as one of the best candidates for VIIR calibration in optical range 0.4 – 2.3 μm. The paper discusses the principal engineering aspects connected with the design of these light sources such as optimal selection of integrating sphere geometry, halogen lamps, materials and etc.

The Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission is designed to make SItraceable measurements and provide a long-term benchmarking data record for the detection, projection, and attribution of changes in the Earths climate system. The CLARREO mission will include instruments operating in the reflected solar (RS) wavelength region from 320 nm to 2300 nm and the thermal infrared wavelength region from 5 μm to 50 μm. A major objective of CLARREO is to improve the accuracy of SI-traceable absolute calibration in the infrared and reflected solar wavelengths. In this paper we describe a tool developed to assess the uncertainty of the top of the atmosphere (TOA) Earth reflectance, to be measured by the CLARREO reflected solar (RS) instrument. The tool provides an error estimate based on the preliminary prototype instrument design. The on-orbit calibration approach currently implemented in the tool uses a direct view of the Sun through an attenuator. Several attenuation approaches are considered and incorporated as options of viewing the Sun through: a pinhole; a perforated plate; a combination between a pinhole and reduced exposure time and/or a neutral density (ND) filter. Additional approaches can readily be implemented. The tool is realized in Excel and is intended to facilitate error budget assessments specifically of the CLARREO RS instrument. Towards deriving a realistic estimate we started compiling a database of values for the various uncertainty contributors using results from testing prototypes or from other missions utilizing similar design.

The Joint Polar Satellite System (JPSS) represents the latest generation of polar-orbiting satellites operated by the National Oceanic and Atmospheric Administration (NOAA). The first in the JPSS series of satellites, the Suomi National Polar-orbiting Partnership (NPP) spacecraft was launched in November 2011 to bridge the gap between the current Polar Operational Environmental Satellites (POES) and the future JPSS-1. The Ozone Mapping Profiler Suite (OMPS) is a suite of hyperspectral instruments onboard the Suomi NPP spacecraft designed to continue atmospheric ozone records through both atmospheric profiles and global distribution mapping. OMPS will also be included on the future JPSS payloads. In order to properly extend measurements from previous ozone instruments, including the Solar Backscatter Ultraviolet (SBUV) instrument on POES, proper OMPS calibration is necessary. In this study, the postlaunch performance of the OMPS Nadir Mapper (NM) and Nadir Profiler (NP) are evaluated through their Sensor Data Records (SDRs), which validates their end-to-end calibration. This is achieved through stability monitoring and intercomparison.

The Suomi-NPP VIIRS thermal emissive bands (TEB) are radiometrically calibrated on-orbit with reference to a blackbody (BB) operated at a nominal temperature of approximately 292.5 K. The quality of the calibration can be evaluated at other temperature ranges using independent thermal sources. The thermal properties of the lunar surface are extremely stable over time, making it a feasible target for the TEB calibration stability assessment for the space-borne sensors with regular lunar observations. VIIRS is scheduled to view the Moon on a nearly monthly basis at approximately the same phase angle since January 2012, before the cryo-cooler door was open and TEB started to collect data. In this paper, the brightness temperatures (BT) of the lunar surface retrieved using the calibration coefficients derived from the BB calibration are trended for VIIRS TEB to examine the calibration stability. The lunar surface temperature varies greatly with location and also oscillates seasonally with the solar illumination geometry. Radiance from many lunar locations saturates TEB detectors. Therefore, the trending must base on the regions of the Moon that do not saturate the detectors at any lunar observation event and thus their BT can be consistently retrieved. To achieve that, a temporally dynamic spatial mask is built for each detector to clip the locations of the Moon that may saturate the detector at any lunar event. Results show the radiometric calibration of all TEB detectors has been stable within 1 K range since being functional.

Radiometric stability of the lunar surface and its smooth reflectance spectrum makes the moon an attractive candidate for calibrating satellite-based hyper/multi-band visible and infrared imagers. Long-term performance monitoring of satellite instrument using Moon can reveal the degradation of instruments. In this paper, analysis of Hyperion lunar observations and comparison with lunar model are performed in support of Cal/Val activities for satellite photometric imager such as GOES-R Advanced Baseline Imager (ABI) instrument. Hyperion makes hyper-spectral observations of the moon regularly with moon phase mostly at 7 degree and it covers visible and shirt-wavelength infrared (SWIR) channels with 10 nm spectral resolution. Five Hyperion lunar observations are analyzed. Lunar reflectance is derived from Hyperion observation and the mean absolute lunar spectral reflectance difference between Hyperion derivation and lunar model is 4.0 ± 2.62%. Through reflectance comparison, over-compensation of two strong atmospheric water absorption bands in Hyperion calibration is identified. The radiometric variance and degradation of Hyperion are assessed. To support the calibration of GOES-R ABI, hyper-spectral data of Hyperion lunar observation is convoluted with ABI spectral response functions for reflective solar bands to synthesize predicted lunar images to be observed by ABI. Lunar irradiances are derived from these synthesized lunar images for ABI and compared with lunar model predictions to quantify spectral biases. Long-term lunar imaging window of opportunities for GOES-R ABI are also assessed. The ability of using lunar model and Hyperion observation to calibrate satellite VNIR/SWIR sensors and reduce the measurement uncertainties is essential to support post-launch Cal/Val activities of GOES-R ABI.

The design, construction and performance test results of photon counting detector technology demonstrator based on silicon avalanche photodiodes is reported. This photon counting device have been designed and optimized for extremely high stability of their detection delay with applications in fundamental metrology and optical time transfer in space. The sensor is operated in an active quenching and gating mode. The single shot timing resolution is better than 25 ps rms over entire active area. Its detection delay is stable within 1 ps over several days of operation. All components in demonstrator have radiation resistant equivalents.

Long-term top of atmosphere (TOA) reflectance, brightness temperature, and band ratio time series over well-established validation sites provide important information for post-launch calibration stability monitoring and analysis. In this study, we present an automated and highly extensible global validation site time series system for the Visible and Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi National Polar-orbiting Partnership (NPP) satellite. The system includes 30 globally distributed sites. Validation site database and quality control parameters for each site can be easily modified without software code modification. VIIRS sensor data records over each validation site are automatically identified from NPP product archives. Validation time series plots for all VIIRS Reflective Solar Bands and Thermal Emissive Bands are updated daily and available online. Bands I2/M7 and I3/M10 inter-channel consistency analysis using the validation time series developed in this study is also included.

The first MODerate-resolution Imaging Spectroradiometer (MODIS), also known as the Proto-Flight model (PFM), is on-board the Terra spacecraft and has completed 14 years of on orbit flight as of December 18, 2013. MODIS remotely senses the Earth in 36 spectral bands, with a wavelength range from 0.4 μm to 14.4 μm. The 36 bands can be subdivided into two groups based on their spectral responsivity as Reflective Solar Bands (RSBs) and Thermal Emissive Bands (TEBs). Band 27 centered at 6.77 μm is a TEB used to study the global water vapor distribution. It was found recently that this band has been severely affected by electronic crosstalk. The electronic crosstalk magnitude, its on-orbit change and calibration impact have been well characterized in our previous studies through the use of regularly scheduled lunar observations. Further, the crosstalk correction was implemented in Earth view (EV) images and quantified the improvements of the same. However, improvements remained desirable on several fronts. Firstly, the effectiveness of the correction needed to be analyzed spatially and radiometrically over a number of scenes. Also, the temporal aspect of the correction had to be investigated in a rigorous manner. In order to address these issues, a one-orbit analysis was performed on the Level 1A (L1A) scene granules over a ten year period from 2003 through 2012. Results have been quantified statistically and show a significant reduction of image striping, as well as removal of leaked signal features from the neighboring bands. Statistical analysis was performed by analyzing histograms of the one-orbit granules at a scene and detector level before and after correction. The comprehensive analysis and results reported in this paper will be very helpful to the scientific community in understanding the impacts of crosstalk correction on various scenes and could potentially be applied for future improvements of band 27 calibration and, therefore, its retrieval for the Level 2 (L2) geophysical parameters.