Proceedings Volume 8510

Earth Observing Systems XVII

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Proceedings Volume 8510

Earth Observing Systems XVII

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Volume Details

Date Published: 27 September 2012
Contents: 14 Sessions, 59 Papers, 0 Presentations
Conference: SPIE Optical Engineering + Applications 2012
Volume Number: 8510

Table of Contents

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Table of Contents

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  • Front Matter: Volume 8510
  • Earth Radiation Budget Missions and Instruments
  • New Missions and Instruments
  • Pre-Launch Calibration and Characterization
  • On-Orbit Calibration and Characterization
  • Instrument Cross-Comparison and Vicarious Calibration
  • Atmospheric Infrared Sounder
  • Remote Sensing Data Analysis
  • VIIRS I
  • VIIRS II
  • VIIRS III
  • VIIRS IV
  • VIIRS V
  • Poster Session
Front Matter: Volume 8510
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Front Matter: Volume 8510
This PDF file contains the front matter associated with SPIE Proceedings Volume 8510, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.
Earth Radiation Budget Missions and Instruments
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ScaRaB: first results of the scanner for radiative budget on board the Indo-French satellite Megha-Tropiques
Thierry L. Trémas, Nadia Karouche, Alain Rosak, et al.
ScaRaB (SCAnner for RAdiation Budget) is the name of three radiometers whose two first flight models have been launched in 1994 and 1997. The instruments were mounted on-board Russian satellites, METEOR and RESURS. On October 12th, a last model has been launched from the Indian site of Sriharikota. ScaRaB is a passenger of MEGHATROPIQUES, an Indo-French joint Satellite Mission for studying the water cycle and energy exchanges in the tropics. The orbit is circular inclined 20deg. ScaRaB is compatible with CERES mission. Two main spectral bands are measured by the radiometer: A short-wave (SW) channel (0.2 – 4 μm) dedicated to solar fluxes and a Total (Tot) channel (0.2 – 200 μm) for (total) fluxes combining the infrared earth radiance and the albedo. The earth long-wave (LW) radiance is isolated by subtracting the SW channel to the Total channel. Thus is defined a supplemental (virtual) channel.
On-orbit solar calibration methods using the Clouds and Earth's Radiant Energy System (CERES) in-flight calibration system
The Clouds and Earth's Radiant Energy System (CERES) scanning thermistor bolometers measure earth-reflected solar and earth-emitted longwaveradiances, at the top- of-the-atmosphere. The bolometers measure the earthradiances in the broadband shortwave solar (0.3-5.0 microns) and total (0.3-<100 microns) spectral bands as well as in the 8-<12 microns water vapor window spectral band over geographical footprints as small as 10 kilometers at nadir. December 1999, the second and third set of CERES bolometers was launchedon the Earth Observing Mission Terra Spacecraft. May 2003, the fourth and fifth set of bolometers was launched on the Earth Observing Mission Aqua Spacecraft. Recently, (October 2011) the sixth instrument was launched on the National Polar-orbiting Operational Environmental Satellite System Preparatory Project (Suomi NPP) Spacecraft. Ground vacuum calibrations define the initial count conversion coefficients that are used to convert the bolometer output voltages into filtered earth radiances. The mirror attenuator mosaic (MAM), a solar diffuser plate, was built into the CERES instrument package calibration system in order to define in-orbit shifts or drifts in the sensor responses. The shortwave and shortwave part of the total sensors are calibrated using the solar radiances reflected from the MAM's. Each MAM consists of baffle-solar diffuser plate systems, which guide incoming solar radiances into the instrument fields of view of the shortwave and total wave sensor units. The MAM diffuser reflecting type surface consists of an array of spherical aluminum mirror segments, which are separated by a Merck Black A absorbing surface, overcoated with SIOx (SIO2 for PFM). Thermistors are located in each MAM plate and the total channel baffle. The CERES MAM is designed to yield calibration precisions approaching .5 percent for the total and shortwave detectors. In this presentation, the MAM solar calibration contrasting procedures will be presented along with on-orbit measurements for the eleven years the CERES instruments have been on-orbit. A switch to an azimuth rotation raster scan of the Sun rather than a fixed azimuth rotating elevation scan will be discussed. Comparisons are also made between the Terra, Aqua, and Suomi NPP CERES instruments during their MAM solar calibrations and total solar irradiance experimental results to determine how precise the CERES solar calibration facilities are at tracking the sun's irradiance.
Performance stability of the Clouds and Earth's Radiant Energy System (CERES) instrument sensors on board the Aqua and Terra spacecraft
The Clouds and Earth’s Radiant Energy System (CERES) instruments measure the earth-reflected shortwave energy as well as the earth-emitted thermal energy, which are two components of the earth’s energy budget. These measurements are made through four instruments on two spacecraft as part of the Earth Observing System (EOS) mission - Flight Models 1 and 2 onboard the Terra spacecraft, and Flight Models 3 and 4 onboard the Aqua spacecraft. Each instrument comprises of three sensors that measure the radiances in different spectral regions- a shortwave channel that measures energy in the 0.3 to 5 micron wavelength band, a total channel that measures all the incident energy (0.3- <100 microns) and a window channel that measures the water-vapor window region of 8 to 12 microns. The required accuracy of the CERES sensors is achieved through pre-launch ground-based calibrations as well as on-orbit calibration activities. Onorbit calibration is carried out using the Internal Calibration Module (ICM) that consists of a quartz-halogen tungsten lamp, blackbodies, and a solar diffuser plate known as the Mirror Attenuator Mosaic (MAM). The ICM calibration provides information about the change in the CERES sensors’ broadband radiometric gains on-orbit from the pre-launch values. Several validation studies are conducted in order to monitor the behavior of the instruments in various spectral bands. The CERES Edition-3 data products incorporate the latest upgrades to the calibration techniques. In this paper, we present the on-orbit performance stability as well as some validation studies using the CERES Edition-3 data products from all four instruments.
Performance of the Clouds and the Earth's Radiant Energy System (CERES) Flight Model 5 (FM5) instrument on NPP mission
Clouds and the Earth’s Radiant Energy System (CERES) instrument was designed to provide accurate measurements for the long-term monitoring of Earth’s radiation energy budget. Flight Model 5, the sixth of the CERES instrument was launched aboard the NPP spacecraft on October 2011 and it has started the Earth-viewing measurements on January 26, 2012. The CERES instrument with the three scanning sensors measure radiances in 0.3 to 5.0 micron region with Shortwave sensor, 0.3 to <100 microns with Total sensor and 8 to 12 micron region with Window sensor. The pre-launch accuracy goal for the CERES instrument measurements is to have the emitted longwave radiances within 0.5% and the shortwave radiances within 1.0%. An accurate determination of the radiometric gains and spectral responsivity of CERES FM5 sensors was accomplished through rigorous calibrations using the primary sources. Post-launch evaluation of the sensor performance consists of sensor calibrations with the on-board sources and the solar diffuser called Mirror Attenuator Mosaic (MAM). The calibration results using onboard sources are also compared to pre-launch values which serve as a traceability standard to carry the ground determined sensor radiometric gains to orbit. Several validation studies utilising targets such as tropical ocean and deep convective clouds are performed as part of the Cal/Val protocol. The scan elevation offset in the sensor measurement will be determined from the spacecraft pitch manuveur activity viewing the deep space. This paper covers the early-orbit checkout activities and the overall performance of the CERES-FM5 instrument. The postlaunch calibration and the validation results from the instrument are presented.
A strategy to assess the pointing accuracy of the CERES (FM5) scanner
Nathaniel P. Smith, Z. Peter Szewczyk, Phillip C. Hess, et al.
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 already in service; two aboard the Terra spacecraft, launched in 1999; and two aboard the Aqua spacecraft, launched in 2002. A fifth instrument (FM5), launched in October 2011 aboard the NPP satellite, began taking radiance measurements in January 2012. A technique to validate the computed geolocation of CERES measurements is referred to as a coastline detection algorithm. This technique 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. Our goal is to process the first five months of CERES FM5 data for a preliminary assessment of the pointing accuracy of the FM5 scanner. The paper briefly restates the algorithm used in the study, describes collection of coastline data, and shows results of error in a pixel geolocation in the direction of a scan (XT) and also along the groundtrack of the satellite (AT).
New Missions and Instruments
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Early orbit operations performance of the Suomi NPP OMPS instrument
The Ozone Mapping Profiler Suite (OMPS) was launched aboard the Suomi National Polar-orbiting Partnership (Suomi NPP) spacecraft on October 28, 2011. OMPS is meant to continue NOAA/NASA's long-term ozone data record and bridge the gap to the Joint Polar Satellite System (JPSS) missions later this decade. We present results from the OMPS Nadir and Limb sensors' early orbit checkout (EOC) operations with comparisons to pre-launch thermal vacuum tests. Characterization measurements of detector performance show that offset, gain, and read noise trends remain within 0.2% of the pre-launch values with significant margin below sensor requirements. Nadir Total Column detector dark generation rate trends show a slow growth in both halves of the focal plane as compared to initial on-orbit measurements. Nadir solar calibration measurements remain within 2% of the initial in-flight observation and indicate no spatially dependent change to within 1%. Limb Profiler solar calibration trending indicate a potential goniometry correction error as high as 5%. Spectral registration changes based on solar observations are determined to be less than one pixel for the Nadir Total Column and Limb sensors but approximately one pixel for Nadir Profiler. Preliminary comparisons to Thullier reference solar spectral irradiances show wavelength dependent differences greater than 5%.
Next-generation pushbroom filter radiometers for remote sensing
Individual focal plane size, yield, and quality continue to improve, as does the technology required to combine these into large tiled formats. As a result, next-generation pushbroom imagers are replacing traditional scanning technologies in remote sensing applications. Pushbroom architecture has inherently better radiometric sensitivity and significantly reduced payload mass, power, and volume than previous generation scanning technologies. However, the architecture creates challenges achieving the required radiometric accuracy performance. Achieving good radiometric accuracy, including image spectral and spatial uniformity, requires creative optical design, high quality focal planes and filters, careful consideration of on-board calibration sources, and state-of-the-art ground test facilities. Ball Aerospace built the Landsat Data Continuity Mission (LDCM) next-generation Operational Landsat Imager (OLI) payload. Scheduled to launch in 2013, OLI provides imagery consistent with the historical Landsat spectral, spatial, radiometric, and geometric data record and completes the generational technology upgrade from the Enhanced Thematic Mapper (ETM+) whiskbroom technology to modern pushbroom technology afforded by advanced focal planes. We explain how Ball’s capabilities allowed producing the innovative next-generational OLI pushbroom filter radiometer that meets challenging radiometric accuracy or calibration requirements. OLI will improve the multi-decadal land surface observation dataset dating back to the 1972 launch of ERTS-1 or Landsat 1.
Out of band scatter measurements from OLI optical bandpass filters
P. D. Fuqua, C. J. Panetta, J. D. Barrie, et al.
Multi-spectral Earth imaging sensors commonly use edge-bonded filter arrays (also known as “butcher blocks”) for spectral selection. These arrays are built from small filter “sticks” that are diced from coated wafers and then bonded together and placed in very close proximity to the detector array. Some filter designs are susceptible to excessive high angle scatter if the filters are constructed under less than ideal deposition conditions. This scatter can lead to optical crosstalk, which degrades system performance. Insufficient specifications and sub-optimum manufacturing practices lead to a phenomenon called angle resolved scatter (ARS), where light that should have been rejected by the filter is scattered into a very high-angle leak path, leading to optical crosstalk. The Landsat Data Continuity Mission’s (LDCM’s) operational land imager (OLI) instrument uses proximal filter arrays for spectral selection, so it is important to quantify the amount of transmitted, scattered light in wavelength ranges outside the pass band. This paper describes the scatter measurement techniques and Bi-Directional Transmission Distribution Function (BTDF) results for 3 OLI filters.
Dark and background response stability for the Landsat 8 Thermal Infrared Sensor
Kelly Vanderwerff, Matthew Montanaro
The Thermal Infrared Sensor (TIRS) is a pushbroom sensor that will be a part of the Landsat Data Continuity Mission (LDCM), which is a joint mission between NASA and the USGS. The TIRS instrument will continue to collect the thermal infrared data that are currently being collected by the Thematic Mapper and the Enhanced Thematic Mapper Plus on Landsats 5 and 7, respectively. One of the key requirements of the new sensor is that the dark and background response be stable to ensure proper data continuity from the legacy Landsat instruments. Pre launch testing of the instrument has recently been completed at the NASA Goddard Space Flight Center (GSFC), which included calibration collects that mimic those that will be performed on orbit. These collects include images of a cold plate meant to simulate the deep space calibration source as viewed by the instrument in flight. The data from these collects give insight into the stability of the instrument’s dark and background response, as well as factors that may cause these responses to vary. This paper quantifies the measured background and dark response of TIRS as well as its stability.
Instrumentation and first results of the reflected solar demonstration system for the Climate Absolute Radiance and Refractivity Observatory
The Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission key goals include enabling observation of high accuracy long-term climate change trends, use of these observations to test and improve climate forecasts, and calibration of operational and research sensors. The spaceborne instrument suites include a reflected solar (RS) spectroradiometer, emitted infrared spectroradiometer, and radio occultation receivers. The requirement for the RS instrument is that derived reflectance must be traceable to SI standards with an absolute uncertainty of <0.3% and the error budget that achieves this requirement is described in previous work. This work describes the Solar/Lunar Absolute Reflectance Imaging Spectroradiometer (SOLARIS), a calibration demonstration system for RS instrument, and presents initial calibration and characterization methods and results. SOLARIS is an Offner spectrometer with two separate focal planes each with its own entrance aperture and grating covering spectral ranges of 320-640, 600-2300 nm over a full field-of-view of 10 degrees with 0.27 milliradian sampling. Results from laboratory measurements including use of integrating spheres, transfer radiometers and spectral standards combined with field-based solar and lunar acquisitions are presented.
Multislit optimized spectrometer for ocean color remote sensing
Tim Valle, Chuck Hardesty, Curtiss O. Davis, et al.
The National Research Council’s recommended NASA Geostationary Coastal and Air Pollution Events (GEO-CAPE) science mission’s purpose is to identify “human versus natural sources of aerosols and ozone precursors, track air pollution transport, and study the dynamics of coastal ecosystems, river plumes and tidal fronts.” To achieve these goals two imaging spectrometers are planned, one optimized for atmospheric science and the other for ocean science. The NASA Earth Science Technology Office (ESTO) awarded the Multislit Optimized Spectrometer (MOS) Instrument Incubator Program (IIP) to advance a unique dispersive spectrometer concept in support of the GEO-CAPE ocean science mission. MOS is a spatial multiplexing imaging spectrometer that simultaneously generates hyperspectral data cubes from multiple ground locations enabling a smaller sensor with faster revisit times compared to traditional concepts. This paper outlines the science, motivation, requirements, goals, and status of the MOS program.
Pre-Launch Calibration and Characterization
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The distance dependences and spatial uniformities of spectral irradiance standard lamps
Howard W. Yoon, Gary D. Graham, Robert D. Saunders, et al.
We describe the characterization of a group of NIST spectral irradiance lamps at longer distances and larger angles than are typically issued by NIST. The spectral irradiances from the FEL lamps were measured from 50 cm to 150 cm at 8 different distances using a cosine-corrected filter radiometer to determine if the lamps adhere to the inverse square law. Using the filter radiometer, the spatial uniformities of the FEL lamps were also mapped over a 20 cm square area at 135 cm, 143 cm and 151 cm. In the NIST gonio-spectroradiometer facility, selected lamps were also mapped for the angular dependences of the spectral irradiances at a distance of 123 cm using a spectrograph which measures from 300 nm to 1100 nm for comparisons to the filter radiometer measurements. Using these measurements, an uncertainty budget for the distance and the angular uniformity correction of the FEL lamps was developed.
Validation of the dissemination of spectral irradiance values using FEL lamps
B. Carol Johnson, Gary D. Graham, Robert D. Saunders, et al.
Scales of spectral irradiance are disseminated by NIST using assignment of values to FEL lamp standards for defined conditions. These lamp standards can be used for absolute calibrations of irradiance radiometers, or more typically, be used in conjunction with a diffuse reflectance standard to establish a scale of spectral radiance and for subsequent absolute calibrations of radiance radiometers. The NIST FEL standards are valuable artifacts requiring special care. Many users optimize resources by in-house transfer of their primary standard to working standards. There are a number of sources of uncertainty in utilizing FEL lamps, e.g., lamp current, alignment, distance setting, instrument aperture size, drift, scattered light, and interpolation in the wavelength grid for the specified irradiance values. In this work, we validated the transfer activity by ITT of their primary, NIST-traceable FEL lamp standards. A portable irradiance bench that had kinematic mounts for an FEL lamp, on-axis baffle, and three different irradiance radiometers was built, tested, and deployed to ITT in Rochester, NY. We report the results of this comparison activity. An uncertainty budget was developed and it was found that the results agreed well within the combined uncertainties of 1.5% to 1.6% (k = 2).
Preferred mirror coatings for UV, visible, and IR space optical instruments
James B. Heaney, Lonny R. Kauder, Scott C. Freese, et al.
This paper will review the suitability of the common four types of reflecting surfaces – Ag, Al, Au and Be - for use aboard satellite borne remote sensing and astrophysical observatories, from the uv to far-ir spectral bands. The choice of appropriate protecting and reflectance enhancing overcoats for these reflecting metals will be discussed. Laboratory test data and optical diagnostic techniques used to verify durability of the selected coatings in a terrestrial storage environment and their sensitivity to a space radiation and cold temperature environment will be presented. For some of the selected coatings, a connection will be made between pre-launch laboratory quality checks and post-launch performance on orbit.
New approach to spectral features modeling
The origin of spectral features, speckle effects, is explained, followed by a discussion on many aspects of spectral features generation. The next part gives an overview of means to limit the amplitude of the spectral features. This paper gives a discussion of all means to reduce the spectral features amplitude (SFA), i.e. inner pixel averaging, coherence effects, and angular averaging, and to a lesser extend coherence effects and polarization. A new approach to model spectral features is presented, that is based on the averaging mechanisms, in a similar way as is used for speckle patterns. Formulae for all averaging methods are given and the use is discussed. The paper starts off with a short description on Spectral Features as observed in earth observation spectrometers, followed by speckle effects and averaging mechanisms. Next the origin of the averaging mechanisms in a spectrometer are given and a method to calculate them.
On-Orbit Calibration and Characterization
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On-orbit Performance of MODIS Solar Diffuser Stability Monitor
MODIS reflective solar bands (RSB) calibration is provided by an on-board solar diffuser (SD). On-orbit changes in the SD bi-directional reflectance factor (BRF) are tracked by a solar diffuser stability monitor (SDSM). The SDSM consists of a solar integration sphere (SIS) with nine detectors covering wavelengths from 0.41 to 0.94 μm. It functions as a ratioing radiometer, making alternate observations of the sunlight through a fixed attenuation screen and the sunlight diffusely reflected from the SD during each scheduled SD/SDSM calibration event. Since launch, Terra and Aqua MODIS SD/SDSM systems have been operated regularly to support the RSB on-orbit calibration. This paper provides an overview of MODIS SDSM design functions, its operation and calibration strategies, and on-orbit performance. Changes in SDSM detector responses over time and their potential impact on tracking SD on-orbit degradation are examined. Also presented in this paper are lessons learned from MODIS SD/SDSM calibration system and improvements made to the VIIRS SD/SDSM system, including preliminary comparisons of MODIS and VIIRS SDSM on-orbit performance.
Recent progress of MODIS solar diffuser on-orbit degradation characterization
H. Chen, Z. Wang, J. Sun, et al.
An on-board Solar Diffuser (SD) is used for the MODIS reflective solar bands (RSB) calibration. Its on-orbit bidirectional reflectance factor (BRF) degradation is tracked using an on-board Solar Diffuser Stability Monitor (SDSM). The SDSM is a ratioing radiometer with nine detectors, covering wavelengths from 412 nm to 936 nm. During each scheduled SD calibration event, the SDSM makes alternate observations of the Sun and the sunlight reflected by the SD. To best match the SDSM detector signals from its Sun view and SD view, a fix attenuation screen is placed in its Sun view path. This paper provides a brief description of MODIS RSB on-orbit calibration and the use of its on-board SD and SDSM subsystem, including different approaches developed and used to track MODIS SD on-orbit degradation. It reports recent progress made to better characterize MODIS SD on-orbit degradation and to support MODIS Level 1B (L1B) calibration look-up table (LUT) updates for the upcoming collection 6 (C6) reprocessing. Results of both Terra and Aqua SD on-orbit degradation derived from newly improved SDSM Sun view screen vignetting function and response fitting strategy, and their impact on RSB calibration uncertainties are also presented.
On-orbit performance of the MODIS reflective solar bands time-dependent response versus scan angle algorithm
Time-dependent Response versus Scan angle (RVS) is vital for MODIS Reflective Solar Bands (RSB) on-orbit calibration. Time-dependent RVS Look-Up Tables (LUT) have been applied to MODIS Level 1B (L1B) since Collection 4. Various approaches have been developed to derive the time-dependent RVS LUT for MODIS RSB. The Collection 4 time-dependent RVS was developed based on the response from the on-board calibrators. In Collection 5, the RVS is derived using the on-board calibrators with additional input of mirror side differences from invariant ocean targets. The Collection 5 methodology is carried over in Collection 6 for most RSB with the exception of Terra MODIS bands 1-4, and 8-9 and Aqua MODIS bands 8-9, where response trending from pseudo-invariant desert targets is used in addition to the measurements from the on-board calibrators. For these bands, the SD/SDSM calibration may not provide accurate gains and/or the linear approximation for the AOI dependence may not be adequate. As a result, earth scene response trending is used in Collection 6 for the derivation of the RVS for the aforementioned bands. In this report, we review all the methodologies used to derive the on-orbit RVS and the performance of the derived timedependent RVS.
Monitoring and assessment of the temperature fluctuation of Aqua MODIS cold focal plane assembly
The MODIS instruments on-board the Terra and Aqua spacecrafts have 16 thermal emissive bands (TEB), located on two cold focal plane assemblies (CFPA). The CFPAs are cryogenically cooled by a passive radiative cooler, with their temperatures further controlled at a nominal value of 83K. For Aqua MODIS, the cooler margin has gradually decreased since launch, which deteriorates the CFPA temperature stability. Since 2006, Aqua CFPA temperature fluctuates with the instrument temperature in both seasonal and orbital oscillation patterns. The magnitude of the fluctuation steadily increases on yearly basis. The gains of TEB detectors change with the CFPA temperature in a nearly linear way, as is demonstrated by both pre-launch calibration and on-orbit monitoring. As of mid 2012, the magnitude of the CFPA temperature fluctuation reaches 0.65K, causing band-dependent detector gain fluctuation of up to 6%. In this paper, the CFPA temperature and its related telemetries are monitored over both a short-term and long-term basis. The impact of the fluctuation to TEB radiometric calibration is assessed, too. Because the calibration is normally performed on a scanby- scan basis based on the observation of an onboard blackbody (BB), the detector gain change can be retrieved in nearly real time. Therefore, the impact is insignificant in general. However, for bands 33, 35 and 36, their detectors saturate when observing BB at BB temperature above certain saturation limits during quarterly held BB warmupcooldown (WUCD) 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.
On-board calibration radiance error correction for MetOp/AVHRR IR channel
The increasing need for accuracy in Advanced Very High Resolution Radiometer (AVHRR) radiance products requires a precise calibration of the instrument response. One concern is the error in the on-board calibration radiance, which combines the on-board black body (BB) imperfection effect and the temperature measurement error. The BB imperfection effect includes the radiance reduction due to the non-perfect BB (emissivity less than 1) and the reflection of the instrument and Earth scene environment through the BB. In addition, discriminating the temperature measurement error and BB imperfection is difficult due to insufficient on-board measurement information. In this work, an effective emissivity is used to analyze the on-board BB calibration radiance. The error in the effective emissivity is evaluated using an intercomparison approach, from the difference in radiance retrieved by AVHHR IR channels and the spectral radiance measured by the Infrared Atmospheric Sounding Interferometer (IASI) on the same satellite, MetOp-A. Two AVHRR IR channels (channels 4 and 5) are covered by the IASI spectrum and homogenous Earth scenes with brightness temperatures close to the on-board BB temperature are selected to evaluate the calibration radiance error. It is found that this error is 0.30% for channel 4 and 0.33% for channel 5. The correction of the calibration radiance provides the possibility to correct the errors due to other effects, such as the offset and nonlinearity in instrument response. The Earth scene brightness temperature dependent bias will be discussed and the source of the error will be discussed.
Recent advances in calibration of the GOES Imager visible channel at NOAA
Charles Dean, I-Lok Chang, Zhenping Li, et al.
To track the degradation of the Imager visible channel on board NOAA’s Geostationary Operation Environmental Satellite (GOES), a research program has been developed using the stellar observations obtained for the purpose of instrument navigation. For monitoring the responsivity of the visible channel, we use observations of approximately fifty stars for each Imager. The degradation of the responsivity is estimated from a single time series based on 30-day averages of the normalized signals from all the stars. Referencing the 30-day averages to the first averaged period of operation, we are able to compute a relative calibration coefficient relative to the first period. Coupling this calibration coefficient with a GOES-MODIS intercalibration technique allows a direct comparison of the star-based relative GOES calibration to a MODIS-based absolute GOES calibration, thus translating the relative star-based calibration to an absolute star-based calibration. We conclude with a discussion of the accuracy of the intercalibrated GOES Imager visible channel radiance measurements.
Instrument Cross-Comparison and Vicarious Calibration
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Cross-calibration of imaging sensors using model-based, SI-traceable predictions of AT-sensor radiance
Many inter-consistency efforts force empirical agreement between sensors viewing a source nearly coincident in time and geometry that ensures consistency between sensors rather than obtain an SI-traceable calibration with documented error budgets. The method described here provides inter-consistency via absolute radiometric calibration with defensible error budget avoiding systematic errors through prediction of at-sensor radiance for a site viewed by multiple sensors but not necessarily viewed at coincident times. The method predicts spectral radiance over a given surface site for arbitrary view and illumination angles and for any date dominated by clear-sky conditions. The foundation is a model-based, SItraceable prediction of at-sensor radiance over selected sites based on physical understanding of the surface and atmosphere. The calibration of the ground site will include spatial, spectral, and sun-view geometric effects based on satellite and ground-based data. The result is an interconsistency of hyperspectral and multispectral sensors spanning spatial resolutions from meters to kilometers all relative to the surface site rather than a single sensor. The sourcecentric philosophy of calibrating the site inherently accounts for footprint size mismatch, spectral band mismatch, and temporal and spatial sampling effects. The method for characterizing the test site allows its use for SI-traceable calibration of any sensor that can view the calibrated test site. Interconsistency is obtained through the traceability and error budget rather than coincident views. Such an approach to inter-consistency provides better understanding of biases between sensors as well producing more accurate results with documented SI-traceability that reduces the need for overlapping data sets.
A comparative study of stripe noise on MODIS and VIIRS thermal emissive bands
Marouan Bouali, Alexander Ignatov
Following successful launch of NPP satellite in October 2011, the VIIRS instrument started delivering high quality radiances from which improved Sea Surface Temperature (SST) products are generated. The design of VIIRS instrument is similar to the MODIS sensor, which includes a double sided mirror re ecting the Earth's radiance to 10 individual detectors. Despite pre-launch characterization and the use of on-board calibration systems, persistent discrepancies between detectors radiometric responses often lead to striping in the level 1 imagery, which is then propagated into level 2 derived geophysical products. The determination of calibration- based uncertainties in level 1 radiances is necessary to further improve the quality of ocean products. This paper characterizes radiometric errors between the multiple detectors and mirror-sides in MODIS and VIIRS thermal emissive bands. A unidirectional variational model is applied on several scenes corresponding to clear-sky top-of- atmosphere ocean radiances to extract the scan line noise due to potential detector-to-detector, mirror-side and random stripes. Data from Terra and Aqua MODIS and NPP VIIRS sensors is used to evaluate and compare the degree of stripe noise in emissive bands used to generate SST products.
NPP VIIRS and Aqua MODIS RSB comparison using observations from simultaneous nadir overpasses (SNO)
Suomi NPP (National Polar-orbiting Partnership) satellite (http://npp.gsfc.nasa.gov/viirs.html) began to daily collect global data following its successful launch on October 28, 2011. The Visible Infrared Imaging Radiometer Suite (VIIRS) is a key NPP sensor. Similar to the design of the OLS, SeaWiFS and MODIS instruments, VIIRS has on-board calibration components including a solar diffuser (SD) and a solar diffuser stability monitor (SDSM) for the reflective solar bands (RSB), a V-groove blackbody for the thermal emissive bands (TEB), and a space view (SV) port for background subtraction. Immediately after the VIIRS nadir door’s opening on November 21, 2011, anomalously large degradation in the SD response was identified in the near-IR wavelength region, which was unexpected as decreases in the SD reflectance usually occur gradually in the blue (~0.4 μm) wavelength region based on past experience. In this study, we use a well-calibrated Aqua MODIS as reference to track and evaluate VIIRS RSB stability and performance. Reflectances observed by both sensors from simultaneous nadir overpasses (SNO) are used to determine VIIRS to MODIS reflectance ratios for their spectral matching bands. Results of this study provide an immediate post-launch assessment, independent validation of the anomalous degradation observed in SD measurements at near-IR wavelengths and initial analysis of calibration stability and consistency.
Using SCIAMACHY to improve corrections for spectral band differences when transferring calibration between visible sensors
Benjamin Scarino, David R. Doelling, Daniel L. Morstad, et al.
The advent of well-calibrated and well-characterized visible sensors, such as the MODerate resolution Imaging Spectroradiometer (MODIS), has allowed the opportunity to cross-calibrate other contemporary, un-calibrated visible sensors. Most of the operational geostationary-Earth-orbit satellite (GEOsat) visible sensors do not have a direct means of on-orbit calibration, and the cross-calibration of MODIS with GEOsats is plagued by the differences in the sensor spectral response functions (SRFs). Spectral band adjustment factors (SBAFs) are needed to correct for the solar flux and inter-band gaseous absorption discrepancies that are caused by SRF differences, which are sometimes significant. In addressing this problem, this manuscript describes a spectral band correction technique that employs Envisat SCanning Imaging Absorption spectroMeter for Atmospheric CartograpHY (SCIAMACHY) hyper-spectral radiances to derive pseudo-radiance, or equivalent-radiance, values for the MODIS and GEOsat sensors over the calibration targets, which include a desert, deep convective clouds, and a MODIS-with-GEOsat ray-matching ocean domain. The regressions from these equivalent-radiance comparisons constitute the necessary adjustment factor. The regressions of MODIS and GEOsat pseudo-radiance values are well-behaved, with small standard error and offsets, for spectral bands that are similar. When comparing narrowband to broadband, however, the correction difference between deep convective and maritime stratus clouds can be as large as 6%. New scene-selection criteria are investigated to derive spectral band adjustment factors that are dependent on the calibration-target domains, which reduces this uncertainty. Application of these SBAFs, which are validated for accuracy using ray-matched SCIAMACHY and GEOstat radiances, is shown to bring independently derived absolute calibrations to within 1% agreement, or better, with one-another. These spectral band adjustment factors are critical for obtaining accurate and consistent absolute calibration among multiple independent and scene-dependent inter-calibration techniques given that the variation of the SBAFs as a function of scene type can be close to 8% for a narrowband-to-broadband correction.
Refined algorithms for star-based monitoring of GOES Imager visible-channel responsivities
I-Lok Chang, Charles Dean, Zhenping Li, et al.
Monitoring the responsivities of the visible channels of the Imagers on GOES satellites is a continuing effort at the National Environmental Satellite, Data and Information Service of NOAA. At this point, a large part of the initial processing of the star data depends on the operationalGOES Sensor Processing System(SPS) and GOES Orbit and AttitudeTracking System (OATS) for detecting the presence of stars and computing the amplitudes of the star signals. However, the algorithms of the SPS and the OATS are not optimized for calculating the amplitudes of the star signals, as they had been developed to determine pixel location and observation time of a star, not amplitude. Motivated by our wish to be independent of the SPS and the OATS for data processing and to improve the accuracy of the computed star signals, we have developed our own methods for such computations. We describe the principal algorithms and discuss their implementation. Next we show our monitoring statistics derived from star observations by the Imagers aboard GOES-8, -10, -11, -12 and -13. We give a brief introduction to a new class of time series that have improved the stability and reliability of our degradation estimates.
Atmospheric Infrared Sounder
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Relative trends of AIRS and IASI radiometric calibrations
This study examines relative trends in the radiometric calibrations of AIRS and IASI. The stability of the AIRS calibration in window channels over tropical oceans has been shown to be 5 mK/yr or better using 9 years of data. IASI data have been available for five years, and during IASI’s time in operation there have been significant El Niño and La Niña events. Those events introduce uncertainty into trend determinations that are more significant for IASI because of its shorter time in operation. When IASI and AIRS are directly compared in a double difference, the El Niño / La Niña effects cancel, allowing for an improved measurement of any instrumental trends in IASI over what can be done using IASI data alone. We find no significant relative trend between the two instruments. We do, however, find some data incompleteness effects for IASI that could introduce spurious trends over certain areas if ignored.
Validation of the radiometric stability of the Atmospheric Infrared Sounder
It has been widely accepted that an infrared sounder in low polar orbit is capable of producing climate quality data, if the spectral brightness temperatures have instrumental trends of less than 10 mK/yr. Achieving measurement stability at this level is not only very demanding of the design of the instrument, it is also pushes the state of art of measuring on orbit what stability is actually achieved. We discuss this using Atmospheric Infrared Sounder (AIRS) L1B data collected between 2002 and 2011. We compare the L1B brightness temperature observed in cloud filtered night tropical ocean spectra (obs) to the brightness temperature calculated based on the known surface emissivity, temperature and water vapor profiles from the ECMWF ReAnalysis (ERA) and the growth rates of CO2 , N2O and Ozone. The trend in (obscalc) is a powerful tool for the evaluation of the stability of the 2378 AIRS channels. We divided the channels into seven classes: All channels which sound in the stratosphere (at pressure levels below 150 hPa), 14 um CO2 sounding, 4 um CO2 P-branch sounding, 4um CO2 R-branch sounding, water vapor sounding, shortwave surface sounding and longwave surface sounding. The peak in the weighting function at 1050 hPa separates sounding and surface channels. The boundary between shortwave and longwave is 5 μm. Except for the stratosphere sounding channels, the remaining six groups have (obs-calc) trends of less than 20 mK/yr. The longwave surface channels have trends of 2 mK/yr, significantly less than the 8 mK/yr trend seem in the shortwave window channels. Based on the design of the instrument, trends within a group of channels should be the same. While the longwave and shortwave trends are less than the canonical 10 mK/yr, the larger trend in the shortwave channels could be an artifact of using the pre-launch determined calibration coefficients. This is currently under evaluation. The trend in (obs-calc) for the non-surface sounding channels, in particular for stratosphere sounding and upper tropospheric water channels, is dominated by artifacts created in calc, most likely due to changes in the ERA Ozone and water vapor. Based on this argument the best estimate of the trend for the channels within a channel group is given by the surface sensitive channels within the group. Based on this consideration we estimated the trend of all AIRS longwave channels as 2 mK/yr, while the shortwave channels have a trend of 8 mK/yr.
Significant advances in the AIRS Science Team Version-6 retrieval algorithm
Joel Susskind, John Blaisdell, Lena Iredell
The Goddard DISC generated products derived from AIRS/AMSU-A observations, starting from September 2002 when the AIRS instrument became stable, using the AIRS Science Team Version-5 retrieval algorithm. The AIRS Science Team Version-6 retrieval algorithm became operational at the Goddard DISC in late 2012. This paper describes some of the significant improvements in retrieval methodology contained in the Version-6 retrieval algorithm, compared to that used in Version-5. In particular, the Science Team made major changes with regard to the algorithms used to 1) derive surface skin temperature and surface spectral emissivity; 2) generate the initial state used to start the cloud clearing and retrieval procedures; and 3) determine Quality Control. This paper describes these advances found in the AIRS Version- 6 retrieval algorithm and demonstrates the improvements of some AIRS Version-6 products compared to those obtained using Version-5.
Level-1C product from AIRS: principal component filtering
Evan M. Manning, Yibo Jiang, Hartmut H. Aumann, et al.
The Atmospheric Infrared Sounder (AIRS), launched on the EOS Aqua spacecraft on May 4, 2002, is a grating spectrometer with 2378 channels in the range 3.7 to 15.4 microns. In a grating spectrometer each individual radiance measurement is largely independent of all others. Most measurements are extremely accurate and have very low noise levels. However, some channels exhibit high noise levels or other anomalous behavior, complicating applications needing radiances throughout a band, such as cross-calibration with other instruments and regression retrieval algorithms. The AIRS Level-1C product is similar to Level-1B but with instrument artifacts removed. This paper focuses on the “cleaning” portion of Level-1C, which identifies bad radiance values within spectra and produces substitute radiances using redundant information from other channels. The substitution is done in two passes, first with a simple combination of values from neighboring channels, then with principal components. After results of the substitution are shown, differences between principal component reconstructed values and observed radiances are used to investigate detailed noise characteristics and spatial misalignment in other channels.
Remote Sensing Data Analysis
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Monitoring sea ice based on NOAA/AVHRR data
Junyi Shi, Jianmao Guo, Tengfei Zheng, et al.
Every year there are ice disasters in the Bohai Sea, which bring serious effect on the human’s life and production. So how to monitor the ice disaster becomes an important issue. The remote sensing technology has a good advantage of monitoring ice disaster over others. In this paper, NOAA/AVHRR data is used to retrieval each parameter of sea surface. Firstly, according to the worked brightness temperature difference can separate sea from land. Then taking advantage of the difference of the albedo of visible light and near infrared band to get rid of clouds and seawater, however, due to the thin ice albedo there exists some errors, thus we can use the multi channel split window method (MCSST) further extraction of sea ice in accordance with sea surface temperature, then we can get the sea ice area on the basis of number of pixels and satellite spatial resolution. Secondly, after getting the region of sea ice, sea ice thickness can be obtained through the empirical formula between ice thickness and near infrared band albedo. Lastly, after solving the extraction of the ice information within mixed pixels, ice concentration also can be calculated.
VIIRS I
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Radiometric calibration of a 100 cm sphere integrating source for VIIRS solar diffuser stability monitor bands
Eugene D. Kim, Vijay Murgai, Reinhard W. Menzel
The Visible Infrared Imaging Radiometer Suite (VIIRS) sensor on the Joint Polar-orbiting Satellite System (JPSS) mission has a solar diffuser as a reflective band calibrator. Due to UV solarization of the solar diffuser, the Solar Diffuser Stability Monitor (SDSM) is on-board to track the reflectance change of the solar diffuser in visible to near IR wavelengths. A 100 cm Sphere Integrating Source (SIS) has been used to configure and test the SDSM on the ground since MODerate resolution Imaging Spectroradiometer (MODIS) programs. Recent upgrades of the radiance transfer and BRDF measurement instruments in Raytheon have enabled more spectral data and faster measurement time with comparable uncertainty to the previous methods. The SIS has a Radiance Monitor, which has been mainly used as a SIS real-time health checker. It has been observed that the Radiance Monitor response is sufficiently linear and stable thus the Radiance Monitor can be used as a calibrator for ground tests. This paper describes the upgraded SIS calibration instruments, and the changes in the calibration philosophy of the SIS for the SDSM bands.
Preliminary assessment of Suomi-NPP VIIRS on-orbit radiometric performance
Hassan Oudrari, Jeff McIntire, David Moyer, et al.
The Visible-Infrared Imaging Radiometer Suite (VIIRS) is a key instrument on-board the Suomi National Polarorbiting Partnership (NPP) spacecraft that was launched on October 28th 2011. VIIRS was designed to provide moderate and imaging resolution of the planet Earth twice daily. It is a wide-swath (3,040 km) cross-track scanning radiometer with spatial resolutions of 375 m and 750 m at nadir for imaging and moderate bands, respectively. It has 22 spectral bands covering the spectrum between 0.4 μm and 12.5 μm, including 14 reflective solar bands (RSB), 7 thermal emissive bands (TEB), and 1 day-night band (DNB). VIIRS observations are used to generate 22 environmental data record (EDRs). This paper will briefly describe NPP VIIRS calibration strategies performed by the independent government team, for the initial on-orbit Intensive Calibration and Validation (ICV) activities. In addition, this paper will provide an early assessment of the sensor on-orbit radiometric performance, such as the sensor signal to noise ratios (SNRs), dual gain transition verification, dynamic range and linearity, reflective bands calibration based on the solar diffuser (SD) and solar diffuser stability monitor (SDSM), emissive bands calibration based on the on-board blackbody calibration (OBC), and cross-comparison with MODIS. A comprehensive set of performance metrics generated during the pre-launch testing program will be compared to VIIRS early on-orbit performance, and a plan for future cal/val activities and performance enhancements will be presented.
VIIRS day-night band gain and offset determination and performance
J. Geis, C. Florio, D. Moyer, et al.
On October 28th, 2011, the Visible-Infrared Imaging Radiometer Suite (VIIRS) was launched on-board the Suomi National Polar-orbiting Partnership (NPP) spacecraft. The instrument has 22 spectral bands: 14 reflective solar bands (RSB), 7 thermal emissive bands (TEB), and a Day Night Band (DNB). The DNB is a panchromatic, solar reflective band that provides visible through near infrared (IR) imagery of earth scenes with radiances spanning 7 orders of magnitude. In order to function over this large dynamic range, the DNB employs a focal plane array (FPA) consisting of three gain stages: the low gain stage (LGS), the medium gain stage (MGS), and the high gain stage (HGS). The final product generated from a DNB raw data record (RDR) is a radiance sensor data record (SDR). Generation of the SDR requires accurate knowledge of the dark offsets and gain coefficients for each DNB stage. These are measured on-orbit and stored in lookup tables (LUT) that are used during ground processing. This paper will discuss the details of the offset and gain measurement, data analysis methodologies, the operational LUT update process, and results to date including a first look at trending of these parameters over the early life of the instrument.
NPP VIIRS early on-orbit geometric performance
Robert E. Wolfe, Guoqing Lin, Masahiro Nishihama, et al.
The NASA/NOAA Visible Infrared Imager Radiometer Suite (VIIRS) instrument on‐board the Suomi National Polar‐orbiting Partnership satellite was launched in October 2011. Assessment of VIIRS’ geometric performance includes measurements of the sensor’s spatial response, band‐to‐band co‐registration (BBR), and geolocation accuracy and precision. The instrument sensor (detector) spatial response is estimated by line spread functions (LSFs) in the scan and track directions. The LSFs are parameterized by dynamic field of view in the scan direction and instantaneous FOV in the track direction, modulation transfer function for the 16 moderate resolution bands (M‐bands), and horizontal spatial resolution for the five imagery bands (I‐bands). VIIRS BBR for the M and I bands is defined as the overlapped fractional area of angular pixel sizes from the corresponding detectors in a band pair, including nested I‐bands into M‐bands, and measured on-orbit using lunar and earth data. VIIRS geolocation accuracy and precision are affected by instrument parameters, ancillary data (i.e., ephemeris and attitude), and thermally induced pointing variations with respect to orbital position. These are being tracked by a ground control point matching program and corrected in geolocation parameter lookup tables in the ground data processing software. This on-orbit geometric performance assessment is an important aspect of the VIIRS sensor data record calibration and validation process. In this paper, we will discuss VIIRS’ geometric performance based on the first seven‐month of VIIRS' on-orbit earth and lunar data, and compare these results with the at‐launch performance based on ground test data and numerical modeling results. Overall, VIIRS’ on-orbit geometric performance is very good and matches the prelaunch performance, and is thus expected to meet the needs of both the long-term monitoring and operational communities.
Suomi NPP VIIRS SDR postlaunch calibration/validation: an overview of progress, challenges, and the way forward
The JPSS preceded by NPP is our nation's future generation polar-orbiting operational environmental satellite system. The successful launch of NPP with the key instrument Visible/Infrared Imager Radiometer Suite (VIIRS) ushers in a new era of operational Earth observing capabilities in the afternoon orbit. Since Launch, the VIIRS Sensor Data Record (SDR) postlaunch calibration/validation has been progressing well as planned. This paper provides an overview of the VIIRS calibration performance postlaunch, the overall calibration/validation strategies both onboard and vicarious, and the team effort ensuring the high quality of VIIRS SDRs, as well as the challenges and way forward.
VIIRS II
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Characterization and performance of the Suomi-NPP/VIIRS solar diffuser stability monitor
Jon P. Fulbright, Ning Lei, Kwofu Chiang, et al.
We describe the on-orbit characterization and performance of the Solar Diffuser Stability Monitor (SDSM) on-board Suomi-NPP/VIIRS. This description includes the observing procedure of each SDSM event, the algorithms used to generate the Solar Diffuser degradation corrective factors, and the results for the mission to date. We will also compare the performance of the VIIRS SDSM and SD to the similar components operating on the MODIS instrument on the EOS Terra and Aqua satellites.
VIIRS solar diffuser bidirectional reflectance distribution function (BRDF) degradation factor operational trending and update
E. Haas, D. Moyer, F. De Luccia, et al.
The Visible-Infrared Imaging Radiometer Suite (VIIRS) was launched onboard the Suomi National Polar-orbiting Partnership (NPP) spacecraft on October 28, 2011. Among the bands on VIIRS are 14 reflective solar bands (RSBs). The RSBs are calibrated using the sun as a source, after attenuation and reflection of sunlight from a Solar Diffuser (SD). The reflectance of the SD is known to degrade over time, particularly at the blue end of the visible spectrum. VIIRS incorporates a separate instrument, a Solar Diffuser Stability Monitor (SDSM), in order to measure and trend the SD Bidirectional Reflectance Distribution Function BRDF changes over time. Inadequate knowledge of the SDSM screen transmission as a function of solar geometry and SDSM detector dependent modulation effects require a unique processing methodology to eliminate unphysical artifacts from the SD BRDF trending. The unique methodology is used to generate periodic updates to operational Look-up Tables (LUTs) used by the Sensor Data Record (SDR) operational code to maintain the calibration of the RSBs. This paper will discuss on-orbit SD BRDF behavior along with the processing methodology used to generate RSB LUT updates incorporating the trended SD BRDF behavior.
Characterization of Suomi-NPP VIIRS reflective solar bands dual gain anomaly
Shihyan Lee, Jeff McIntire, Hassan Oudrari
The Visible/Infrared Imager Radiometer Suite (VIIRS) contains six dual gain bands in the reflective solar spectrum. The dual gain bands are designed to switch gain mode at pre-defined thresholds to achieve high resolution at low radiances while maintaining the required dynamic range for science. During pre-launch testing, an anomaly in the electronic response before transitioning from high to low gain was discovered and was characterized. This anomaly has been confirmed using MODIS data collected during Simultaneous Nadir Overpasses (SNOs). The analysis of the Earth scene data shows that this dual gain anomaly can be characterized using sensor earth-view observations. To help understand this dual gain artifact, the anomaly region and electronic offsets were tracked during the first 8 months of VIIRS operation. The temporal analysis shows the anomaly region can drift ~20 DN and is impacted by a detector’s DC Restore. The estimated anomaly flagging regions cover ~2.5 % of the high gain dynamic range and are consistent with prelaunch analysis and the on-orbit flagging LookUp Table. The prelaunch results had a smaller anomaly range, likely due to more stable electronics over a shorter data collection time. Finally, this study suggests future calibration efforts to focus on the anomaly’s impact on science products and a possible correction method to reduce uncertainties.
Initial on-orbit radiometric calibration of the Suomi NPP VIIRS reflective solar bands
Ning Lei, Zhipeng Wang, Jon Fulbright, et al.
The on-orbit radiometric response calibration of the VISible/Near InfraRed (VISNIR) and the Short-Wave InfraRed (SWIR) bands of the Visible/Infrared Imager/Radiometer Suite (VIIRS) aboard the Suomi National Polar-orbiting Partnership (NPP) satellite is carried out through a Solar Diffuser (SD). The transmittance of the SD screen and the SD’s Bidirectional Reflectance Distribution Function (BRDF) are measured before launch and tabulated, allowing the VIIRS sensor aperture spectral radiance to be accurately determined. The radiometric response of a detector is described by a quadratic polynomial of the detector’s digital number (dn). The coefficients were determined before launch. Once on orbit, the coefficients are assumed to change by a common factor: the F-factor. The radiance scattered from the SD allows the determination of the F-factor. In this Proceeding, we describe the methodology and the associated algorithms in the determination of the F-factors and discuss the results.
Operational calibration of VIIRS reflective solar band sensor data records
Jason C. Cardema, Kameron W. Rausch, Ning Lei, et al.
The Visible-Infrared Imaging Radiometer Suite (VIIRS) is an instrument on-board the Suomi National Polar-orbiting Partnership (NPP) spacecraft, which launched on October 28, 2011. VIIRS performs measurements in 14 reflective solar bands (RSBs) spanning wavelengths from 412 nm to 2.25 um, which are calibrated by using solar radiance reflected from a Solar Diffuser (SD). The SD reflectance degrades over time, and a Solar Diffuser Stability Monitor (SDSM) is used to track the changes. The ratio between the calculated solar radiance reflected from the SD and the VIIRS measurement of this radiance using the pre-launch calibration coefficients is known as the “F factor.” The F factor is applied in the ground processing as a scale correction to the pre-launch calibration coefficients used to generate the calibrated radiances and reflectances comprising the Sensor Data Records (SDRs). The F factor is trended over time to track instrument response degradation. The equation for calculating expected solar radiance, and the coefficients used to convert the raw digital numbers measured by the detectors into radiance and reflectance values, are based on parameters stored in various Look-Up Tables (LUTs). This paper will discuss on-orbit RSB calibration for VIIRS, along with a description of the processing methodology, which includes operational LUT updates based on off-line calculations of F factor trending behavior.
VIIRS III
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Discovery and characterization of on-orbit degradation of the Visible Infrared Imaging Radiometer Suite (VIIRS) Rotating Telescope Assembly (RTA)
F. De Luccia, D. Moyer, E. Johnson, et al.
The Suomi National Polar-orbiting Partnership (NPP) satellite was launched on Oct. 28, 2011, and began the commissioning phase of several of its instruments shortly thereafter. One of these instruments, VIIRS, was found to exhibit a gradual but persistent decrease in the optical throughput of several bands, with the near-infrared bands being more affected than those in the visible. The rate of degradation quickly increased upon opening of the nadir door that permits the VIIRS telescope to view the earth. Simultaneously, a second instrument on NPP, the Solar Diffuser Stability Monitor (SDSM), was experiencing a similar decrease in response, leading the investigation team to suspect that the cause must be the result of some common contamination process. This paper will discuss a series of experiments that were performed to demonstrate that the VIIRS and SDSM response changes were due to separate causes, and which enabled the team to conclude that the VIIRS sensor degradation was the result of ultraviolet light exposure of the rotating telescope assembly. The root cause investigation of the telescope degradation will be addressed in a separate paper.
Root cause determination of on-orbit degradation of the VIIRS rotating telescope assembly
J. D. Barrie, P. D. Fuqua, M. J. Meshishnek, et al.
The Visible Infrared Imaging Radiometer Suite (VIIRS) is a sensor onboard the recently launched Suomi NPP spacecraft. Shortly after launch, VIIRS was found to exhibit a pronounced decrease in the optical throughput of several bands, with the near-infrared bands being more affected than those in the visible. The anomaly investigation team performed several experiments that concluded the primary source of degradation was throughput loss in the VIIRS rotating telescope assembly, likely caused by ultraviolet light illumination. This paper will discuss the laboratory investigation that determined the root cause of the telescope degradation to be UV photo-darkening of a tungsten oxide contaminant film that had been inadvertently deposited during the mirror manufacturing process. We will present data from experiments conducted on witness mirrors manufactured along with the telescope, as well as other mirrors of the same type that were not contaminated.
VIIRS on-orbit optical anomaly: investigation, analysis, root cause determination and lessons learned
Glenn Iona, James Butler, Bruce Guenther, et al.
A gradual, but persistent, decrease in the optical throughput was detected during the early commissioning phase for the Suomi National Polar-Orbiting Partnership (SNPP) Visible Infrared Imager Radiometer Suite (VIIRS) Near Infrared (NIR) bands. Its initial rate and unknown cause were coincidently coupled with a decrease in sensitivity in the same spectral wavelength of the Solar Diffuser Stability Monitor (SDSM) raising concerns about contamination or the possibility of a system-level satellite problem. An anomaly team was formed to investigate and provide recommendations before commissioning could resume. With few hard facts in hand, there was much speculation about possible causes and consequences of the degradation. Two different causes were determined as will be explained in this paper. This paper will describe the build and test history of VIIRS, why there were no indicators, even with hindsight, of an on-orbit problem, the appearance of the on-orbit anomaly, the initial work attempting to understand and determine the cause, the discovery of the root cause and what Test-As-You-Fly (TAYF) activities, can be done in the future to greatly reduce the likelihood of similar optical anomalies. These TAYF activities are captured in the “lessons learned” section of this paper.
VIIRS IV
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VIIRS thermal emissive bands calibration algorithm and on-orbit performance
D. Moyer, J. McIntire, F. De Luccia, et al.
The Visible-Infrared Imaging Radiometer Suite (VIIRS) was launched October 28, 2011 on-board the Suomi National Polar-orbiting Partnership (NPP) spacecraft as a primary sensor. It has 22 bands: 14 reflective solar bands (RSBs), 7 thermal emissive bands (TEBs) and a Day Night Band (DNB). VIIRS TEB on-orbit calibration uses a quadratic algorithm with its calibration coefficients derived from pre-launch measurements and an on-board calibration blackbody (OBC BB) to provide scan-to-scan gain drift compensation. This paper will discuss the calibration methodology, OBC BB performance and stability, detector signal-to-noise and radiometric performance.
NPP VIIRS emissive band radiance calibration
Quanhua Liu, Changyong Cao, Fuzhong Weng
VIIRS thermal emissive bands (TEB) calibration data (blackbody and space counts) have been analyzed. The analysis results indicate that the Visible Infrared Imaging Radiometer Suite (VIIRS) TEB is stable and exceeds the specification. VIIRS Blackbody temperature is stable, too. The 6 platinum resistance thermometers (PRT) are also stable, except for the 3rd and 6th PRT have a periodic variation of 50 mK. Using the calibration data during the Blackbody temperature cool down and warm up, we found that noise equivalent deviation of temperatures (NEdT) varies with the Blackbody temperature. We developed a model that can predict the scene temperature dependent NEdT for the VIIRS M15 band. Comparisons between the VIIRS and other sensors such as AVHRR, MODIS and CrIS demonstrated that VIIRS TEB agrees generally with those sensors.
VIIRS emissive band radiometric performance trending
Eric Johnson, Courtney Ranshaw
The Visible/Infrared Imaging Radiometer Suite (VIIRS) is a key sensor on the Suomi National Polar-orbiting Partnership (NPP) satellite launched on October 28, 2011 into a polar orbit of 824 km nominal altitude. VIIRS collects radiometric and imagery data of the Earth’s atmosphere, oceans, and land surfaces in 22 spectral bands spanning the visible and infrared spectrum from 0.4 to 12.5 μm. This paper summarizes the radiometric performance measured in the 7 VIIRS thermal emissive bands (3.7 to 12.5 μm), covering both pre-launch thermal-vacuum testing and early on-orbit characterizations. Radiometric characteristics trended include radiometric response and radiometric sensitivity (SNR/NEdT).
VIIRS V
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VIIRS on-orbit calibration for ocean color data processing
Robert E. Eplee Jr., Kevn R. Turpie, Gwyn F. Fireman, et al.
The NASA VIIRS Ocean Science Team (VOST) has the task of evaluating Suomi NPP VIIRS ocean color data for the continuity of the NASA ocean color climate data records. The generation of science quality ocean color data products requires an instrument calibration that is stable over time. Since the VIIRS NIR Degradation Anomaly directly impacts the bands used for atmospheric correction of the ocean color data (Bands M6 and M7), the VOST has adapted the VIIRS on-orbit calibration approach to meet the ocean science requirements. The solar diffuser calibration time series and the solar diffuser stability monitor time series have been used to derive changes in the instrument response and diffuser reflectance over time for bands M1–M11. The lunar calibration observations have been used, in cooperation with the USGS ROLO Program, to derive changes in the instrument response over time for these same bands. In addition, the solar diffuser data have been used to develop detector-dependent striping and mirror side-dependent banding corrections for the ocean color data. An ocean surface reflectance model has been used to perform a preliminary vicarious calibration of the VIIRS ocean color data products. These on-orbit calibration techniques have allowed the VOST to produce an optimum timedependent radiometric calibration that is currently being used by the NASA Ocean PEATE for its VIIRS ocean color data quality evaluations. This paper provides an assessment of the current VIIRS radiometric calibration for the ocean color data products and discusses the path forward for improving the quality of the calibration.
Suomi NPP VIIRS ocean color data product early mission assessment
Kevin R. Turpie, Wayne D. Robinson, Bryan A. Franz, et al.
Following the launch of the Visible Infrared Imaging Radiometer Suite (VIIRS) aboard the Suomi National Polarorbiting Partnership (NPP) spacecraft, the NASA NPP VIIRS Ocean Science Team (VOST) began an evaluation of ocean color data products to determine whether they could continue the existing NASA ocean color climate data record (CDR). The VOST developed an independent evaluation product based on NASA algorithms with a reprocessing capability. Here we present a preliminary assessment of both the operational ocean color data products and the NASA evaluation data products regarding their applicability to NASA science objectives.
NPP VIIRS on-orbit calibration and characterization using the moon
The Visible Infrared Imager Radiometer Suite (VIIRS) is one of five instruments on-board the Suomi National Polarorbiting Partnership (NPP) satellite that launched from Vandenberg Air Force Base, Calif., on Oct. 28, 2011. VIIRS has been scheduled to view the Moon approximately monthly with a spacecraft roll maneuver after its NADIR door open on November 21, 2012. To reduce the uncertainty of the radiometric calibration due to the view geometry, the lunar phase angles of the scheduled lunar observations were confined in the range from -56° to -55° in the first three scheduled lunar observations and then changed to the range from -51.5° to -50.5°, where the negative sign for the phase angles indicates that the VIIRS views a waxing moon. Unlike the MODIS lunar observations, most scheduled VIIRS lunar views occur on the day side of the Earth. For the safety of the instrument, the roll angles of the scheduled VIIRS lunar observations are required to be within [-14°, 0°] and the aforementioned change of the phase angle range was aimed to further minimize the roll angle required for each lunar observation while keeping the number of months in which the moon can be viewed by the VIIRS instrument each year unchanged. The lunar observations can be used to identify if there is crosstalk in VIIRS bands and to track on-orbit changes in VIIRS Reflective Solar Bands (RSB) detector gains. In this paper, we report our results using the lunar observations to examine the on-orbit crosstalk effects among NPP VIIRS bands, to track the VIIRS RSB gain changes in first few months on-orbit, and to compare the gain changes derived from lunar and SD/SDSM calibration.
An overview of Suomi NPP VIIRS calibration maneuvers
The first Visible Infrared Imager Radiometer Suite (VIIRS) instrument was successfully launched on-board the Suomi National Polar-orbiting Partnership (SNPP) spacecraft on October 28, 2011. Suomi NPP VIIRS observations are made in 22 spectral bands, from the visible (VIS) to the long-wave infrared (LWIR), and are used to produce 22 Environmental Data Records (EDRs) with a broad range of scientific applications. The quality of these VIIRS EDRs strongly depends on the quality of its calibrated and geo-located Sensor Date Records (SDRs). Built with a strong heritage to the NASA’s EOS MODerate resolution Imaging Spectroradiometer (MODIS) instrument, the VIIRS is calibrated on-orbit using a similar set of on-board calibrators (OBC), including a solar diffuser (SD) and solar diffuser stability monitor (SDSM) system for the reflective solar bands (RSB) and a blackbody (BB) for the thermal emissive bands (TEB). Onorbit maneuvers of the SNPP spacecraft provide additional calibration and characterization data from the VIIRS instrument which cannot be obtained pre-launch and are required to produce the highest quality SDRs. These include multiorbit yaw maneuvers for the characterization of SD and SDSM screen transmission, quasi-monthly roll maneuvers to acquire lunar observations to track sensor degradation in the visible through shortwave infrared, and a driven pitch-over maneuver to acquire multiple scans of deep space to determine TEB response versus scan angle (RVS). This paper provides an overview of these three SNPP calibration maneuvers. Discussions are focused on their potential calibration and science benefits, pre-launch planning activities, and on-orbit scheduling and implementation strategies. Results from calibration maneuvers performed during the Intensive Calibration and Validation (ICV) period for the VIIRS sensor are illustrated. Also presented in this paper are lessons learned regarding the implementation of calibration spacecraft maneuvers on follow-on missions.
Analysis of Suomi–NPP VIIRS vignetting functions based on yaw maneuver data
Jeff McIntire, Boryana Efremova, David Moyer, et al.
The Suomi – NPP Visible Infrared Imager Radiometer Suite (VIIRS) reflective bands are calibrated on-orbit via reference to regular solar observations through a solar attenuation screen (SAS) and diffusely reflected off a Spectralon ® panel. The degradation of the Spectralon panel BRDF due to UV exposure is tracked via a ratioing radiometer (SDSM) which compares near simultaneous observations of the panel with direct observations of the sun (through a separate attenuation screen). On-orbit, the vignetting functions of both attenuation screens are most easily measured when the satellite performs a series of yaw maneuvers over a short period of time (thereby covering the yearly angular variation of solar observations in a couple of days). Because the SAS is fixed, only the product of the screen transmission and the panel BRDF was measured. Moreover, this product was measured by both VIIRS detectors as well as the SDSM detectors (albeit at different reflectance angles off the Spectralon panel). The SDSM screen is also fixed; in this case, the screen transmission was measured directly. Corrections for instrument drift and degradation, solar geometry, and spectral effects were taken into consideration. The resulting vignetting functions were then compared to the pre-launch measurements as well as models based on screen geometry.
VIIRS VisNIR/SMWIR end of life sensitivity predictions
Vijay Murgai, Neil Nelson, Eric Johnson, et al.
The Visible/Infrared Imaging Radiometer Suite (VIIRS) is a key sensor on the Suomi National Polar-orbiting Partnership (NPP) satellite launched on October 28, 2011 into a polar orbit of 824 km nominal altitude. VIIRS collects radiometric and imagery data of the Earth’s atmosphere, oceans, and land surfaces in 22 spectral bands spanning the visible and infrared spectrum from 0.4 to 12.5 μm. The radiometric response for VIIRS spectral bands in the 600 – 2300 nm wavelength range (I1, M5, M6, M7 / I2, M8, M9, M10 / I3, M11), which started with significant signal to noise ratio margin at beginning of life, has shown some degradation on orbit. This degradation has been correlated with UV exposure of the VIIRS optics. UV exposure of witness samples from the Rotating Telescope Assembly (RTA) mirrors by Aerospace Corporation showed reflectance loss with the same spectral signature as the response degradation observed for VIIRS. The investigation and root cause determination for the VIIRS response degradation are discussed in separate papers. A model of VIIRS throughput degradation has been developed from witness sample UV exposure test results made by Aerospace. A direct relationship is assumed between UV dose (fluence) and the reflectance degradation of the RTA mirrors. The UV dose on orbit for the primary mirror is proportional to the incident earthshine and its solid angle of view. For subsequent mirrors the UV dose is weighted by solid angle and preceding mirror UV reflectance. UV dose is converted to reflectance change based on witness sample exposure measurements. The change in VIIRS throughput is calculated by multiplying the reflectance of the four RTA mirrors and agrees with the on-orbit measured response changes as a function of UV exposure time. Model predictions of the radiometric sensitivity for the affected VIIRS bands show positive margin at end of life for all affected bands.
Poster Session
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Analog and digital saturation in the MODIS reflective solar bands
The MODIS instrument on the Terra and Aqua spacecrafts is a 12 bit sensor with an analog-to-digital (A/D) range of 0 to 4095 DN. Each sensor system is limited by a range at the low and high ends of the dynamic scale. At the low end, quantization noise is the limiting factor whereas at the high end the maximum value is limited by the capability of the amplifier, 4095 in the case of MODIS. However, in both Terra and Aqua MODIS certain detectors in the Reflective Solar Bands (RSB) tend to pre-saturate at a value lower than 4095. This paper serves as a comprehensive report on the algorithms developed to characterize the pre-saturation limit in the RSB. The paper also provides the digital and pre-saturation (analog saturation) limits for the RSB that are currently being used in the Level 1B (L1B) products. The digital and analog saturation limits are well characterized using the Level 1A (L1A) raw Earth-View (EV) data and through the on-board Electronic Calibration (E-CAL). Also, in this paper an analysis is done to study the sensors dynamic range due to the long term changes in the instrument response. In summary, the algorithms and results reported in this paper are important as the radiometric accuracy / uncertainty for instruments such as MODIS, VIIRS (NPP) tends to be coupled to pre-saturation.
Evolving high fidelity climate sensor simulators to preserve climate data record continuity
Kelly K. Teague, G. Louis Smith, Kory Priestley
Six CERES scanning radiometers have flown to date. The Proto-­‐Flight Model flew aboard the Tropical Rainfall Measuring Mission spacecraft in November 1997. Two CERES instruments, Flight Models (FM) 1 and 2, are aboard the Terra spacecraft, which was launched in December 1999. Two more CERES instruments, FM-­‐3 and FM-­‐4, are on the Aqua spacecraft, which was placed in orbit in May 2002. These instruments continue to operate after providing over a decade of Earth Radiation Budget data. FM-­‐5 is onboard the NPP spacecraft and launched in October 2011. FM-­‐6 is being built for use on the JPPS spacecraft. A successor to these CERES instruments is presently in the definition stage. This paper describes the role of instrument simulators in the life cycle of the CERES instruments and how the simulators may be modified to better represent the instrument and its operations. NASA LaRC originally built the CERES instrument simulators. They were created to test CERES flight loads and view the resulting instrument response. The simulator’s interface to the instrument processor and spacecraft bus enables the verification of all software modifications, which are uploaded to orbiting instruments. The simulators were recently redesigned to provide additional functionality, however not all instrument operations are completely replicated. The existing simulator software provides the necessary stubs to incorporate modifications and improvements. One possible upgrade is a simulation to imitate the CERES detector assembly. Another useful enhancement is fault injection into select instrument systems, to simulate operational failures and resolve anomaly situations. Many features could be added to the simulator, all of which can ultimately improve instrument performance.
Assessment of the NPP VIIRS RVS for the thermal emissive bands using the first pitch maneuver observations
The Visible Infrared Imaging Radiometer Suite (VIIRS) is a key sensor carried on Suomi NPP (National Polar-orbiting Partnership) satellite (http://npp.gsfc.nasa.gov/viirs.html) (launched in October 2011). VIIRS sensor design draws on heritage instruments including AVHRR, OLS, SeaWiFS and MODIS. It has on-board calibration components including a solar diffuser (SD) and a solar diffuser stability monitor (SDSM) for the reflective solar bands (RSB), a V-groove blackbody for the thermal emissive bands (TEB), and a space view (SV) port for background subtraction. These on-board calibrators are located at fixed scan angles. The VIIRS response versus scan angle (RVS) was characterized prelaunch in lab ambient conditions and is currently used to characterize the on-orbit response for all scan angles relative to the calibrator scan angle (SD for RSB and blackbody for TEB). Since the RVS is vitally important to the quality of calibrated radiance products, several independent studies were performed to analyze the prelaunch RVS measurement data. A spacecraft level pitch maneuver was scheduled during the first three months of intensive Cal/Val. The NPP pitch maneuver provided a rare opportunity for VIIRS to make observations of deep space over the entire range of scan angles, which can be used to characterize the TEB RVS. This study will provide our analysis of the pitch maneuver data and assessment of the derived TEB RVS. A comparison between the RVS determined by the pitch maneuver observations and prelaunch lab tests will be conducted for each band, detector, and half angle mirror (HAM) side.
Suomi NPP VIIRS spectral characterization: understanding multiple RSR releases
Chris Moeller, Jeff McIntire, Tom Schwarting, et al.
The Suomi National Polar-orbiting Partnership (S-NPP) satellite was successfully launched on October 28, 2011, beginning the on-orbit era of the Visible Infrared Imager Radiometer Suite (VIIRS). In support of atlaunch readiness, VIIRS underwent a rigorous pre-launch test program to characterize its spatial, radiometric, and spectral performance. Spectral measurements, the subject of this paper, were collected during instrument level testing at Raytheon Corp. (summer 2009), and then again in a special spectral test for VisNIR bands during spacecraft level testing at Ball Aerospace and Technologies Corp. (spring 2010). These spectral performance measurements were analyzed by industry (Northrop Grumman, NG) and by the Relative Spectral Response (RSR) subgroup of the Government team, (NASA, Aerospace Corp., MIT/Lincoln Lab, Univ. Wisconsin) leading to releases of the S-NPP VIIRS RSR characterization by both NG and the Government team. The NG RSR analysis was planned to populate the Look-Up-Tables (LUTs) that support the various VIIRS operational products, while the Government team analysis was initially intended as a verification of the NG RSR product as well as an early release RSR characterization for the science community’s pre-launch application. While the Government team deemed the NG December 2010 RSR release as acceptable for the “at-launch” RSR characterization during the pre-launch phase, the Government team has now (post-launch checkout phase) recommended for using the NG October 2011 RSR release as an update for the LUTs used in VIIRS SDR and EDR operational processing. Meanwhile the Government team RSR releases remain available to the community for their investigative interests, and may evolve if new understanding of VIIRS spectral performance is revealed in the S-NPP post-launch era.
On-orbit characterization of the GOES Imager channel-to-channel co-registration
Michael G. Grotenhuis, Xiangqian Wu, Fangfang Yu, et al.
The channel-to-channel co-registration of a satellite imaging system is an important performance metric that has a direct impact upon the reliability of the imager’s quantitatively-derived products. In this work, standard full-disk image data is used to measure the on-orbit channel-to-channel co-registration of the infrared channels of several GOES Imagers at a sub-pixel level. This is accomplished with two separate methods, one of which furthers preliminary research by Wu et. al.1 using GOES-8 and 9 spatial-spectral brightness temperature gradients, the other of which uses a statistical approach. The diurnal, seasonal, and long-term co-registration behavior is analyzed.