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NASA NTRS2022

Look-up Table Approach for Uncertainty Determination for Operational Vicarious Calibration of Earth Imaging Sensors

Understanding the uncertainty of a vicarious calibration is essential for any application to Earth imaging sensors. The Radiometric Calibration Network provides SI-traceable spectral top-of-atmosphere (TOA) reflectance from a network of ground sites and uses a look-up table (LUT) approach for uncertainty determination. The uncertainty LUT was derived using Monte Carlo techniques applied to the relevant solar geometry, surface, and atmospheric variables. While surface reflectance is typically the dominant uncertainty source, atmospheric contributions do play an important role, depending upon the exact scenario and conditions. This approach allows knowledge of TOA reflectance uncertainty to within 0.5%.

Brian N. Wenny↗

NASA NTRS1998

Bidirectional Reflectance Factors used in Lidar Calibration

Many atmospheric remote sensing applications of infrared lidar systems require that the backscatter signal be radiometrically calibrated. These systems are usually monostatic, consequently the reflected radiance from hard targets used in calibration will include the diffuse and the retroreflectance characteristics of the material. Radiometers which are part of orbiting sensors frequently contain onboard calibration subsystems. The onboard calibrator often utilizes onboard reflectance panels which are deployed at particular orbital locations to use the reflected sun light to calibrate the radiometers. To meet the need for correlative calibration of these remote sensing techniques a physically derived model could be used to extend the angular range and to improve the angular resolution of the measured reflectance properties of the calibration materials. A modified version of the B. Hake and E. Wells model has been adapted and will be described.

Haner, David A.↗

NASA NTRS2012

Radio Frequency Plasma Discharge Lamps for Use as Stable Calibration Light Sources

Stable high radiance in visible and near-ultraviolet wavelengths is desirable for radiometric calibration sources. In this work, newly available electrodeless radio-frequency (RF) driven plasma light sources were combined with research grade, low-noise power supplies and coupled to an integrating sphere to produce a uniform radiance source. The stock light sources consist of a 28 VDC power supply, RF driver, and a resonant RF cavity. The RF cavity includes a small bulb with a fill gas that is ionized by the electric field and emits light. This assembly is known as the emitter. The RF driver supplies a source of RF energy to the emitter. In commercial form, embedded electronics within the RF driver perform a continual optimization routine to maximize energy transfer to the emitter. This optimization routine continually varies the light output sinusoidally by approximately 2% over a several-second period. Modifying to eliminate this optimization eliminates the sinusoidal variation but allows the output to slowly drift over time. This drift can be minimized by allowing sufficient warm-up time to achieve thermal equilibrium. It was also found that supplying the RF driver with a low-noise source of DC electrical power improves the stability of the lamp output. Finally, coupling the light into an integrating sphere reduces the effect of spatial fluctuations, and decreases noise at the output port of the sphere.

McAndrew, Brendan↗

NASA NTRS2017

MODIS Aqua Optical Throughput Degradation Impact on Relative Spectral Response and Calibration on Ocean Color Products

Since Moderate Resolution Imaging Spectroradiometer Aqua's launch in 2002, the radiometric system gains of the reflective solar bands have been degrading, indicating changes in the systems optical throughput. To estimate the optical throughput degradation, the electronic gain changes were estimated and removed from the measured system gain. The derived optical throughput degradation shows a rate that is much faster in the shorter wavelengths than the longer wavelengths. The wavelength-dependent optical throughput degradation modulated the relative spectral response (RSR) of the bands. In addition, the optical degradation is also scan angle-dependent due to large changes in response versus the scan angle over time. We estimated the modulated RSR as a function of time and scan angles and its impacts on sensor radiometric calibration for the ocean science. Our results show that the calibration bias could be up to 1.8 % for band 8 (412 nm) due to its larger out-of-band response. For the other ocean bands, the calibration biases are much smaller with magnitudes at least one order smaller.

Lee, Shihyan↗

NASA NTRSDate not supplied

Comparison of Detector Based and Source Based Absolute Radiance Standards

A detailed comparison of two separate radiometric calibration standards was conducted with analysis of error sources for each. One is a detector based standard, with radiance traceable to fundamental units using the electrical substitution method. The other is based on a calibrated field emission lamp (FEL) generating blackbody radiation. This study was motivated by the discontinuance of the FEL lamps by the manufacturer and a desire to calibrate sensors using non-blackbody spectral profiles. Three spectrometers were calibrated simultaneously by both methods to separate spectrometer artifacts from differences in the radiometric standards and error in the irradiance to radiance conversion procedure needed for the FEL. Conducting this study now is important to provide continuity between the extensive prior FEL based calibration database with a replacement method while calibrated FEL lamps are still available. This also begins a longer term repeatability study of the spectrometers used in this work for evaluation as calibrated transfer standards, usable with both monochromatic and broad spectrum radiance sources. Eliminating the tie to the FEL blackbody spectrum with a detector based standard allows for flexibility in the illumination source. In particular, for Earth science sensors intended for use with sunlit scenes, augmenting traditional tungsten halogen lighting with blue and ultraviolet light emitting diodes allows for a better match to the solar spectrum during laboratory testing.

radiometry↗

NASA NTRSDate not supplied

Comparison of Detector Based and Source Based Absolute Radiance Standards

radiometry↗

NASA NTRS2019

MODIS Aqua Reflective Solar Bands Calibration for NASA's R2018 Ocean Color Products

Remote sensing ocean color products have stringent requirements on radiometric calibration stability. To address a calibration deficiency in MODIS Aqua in recent years, the NASA Ocean Biological Processing Group (OBPG) developed a new calibration for the reflective solar bands. Prior to the reprocessing of NASA's ocean color products for 2018 (R2018), the OBPG MODIS products had been based on calibration provided by the MODIS Calibration Support Team (MCST). Several modifications were made to the MCST calibration approach to improve the calibration accuracy for ocean color products. These include: 1) apply 936nm detector normalization to solar diffuser stability monitor (SDSM) data to reduce coherent noise; 2) modeling solar diffuser (SD) degradation wavelength dependency to determine SD degradation in near-infrared and shortwave infrared wavelength; 3) detector gains are computed using SD screen-closed data to better match ocean radiance levels in all bands; 4) a simple atmospheric correction is performed to reduce bidirectional reflectance distribution function (BRDF) effects in desert trends; 5) modulated relative spectral response (RSR) impact on ocean data is estimated and used to adjust the calibration coefficients. 6) smoothing is used to characterize the temporal change in calibration, and response versus scan angle (RVS) changes are characterized using 2nd order polynomials to improve spatial/temporal calibration stability. Relative to the previous R2014 ocean color products, the R2018 calibration removed the suspect late-mission global trends in blue-band water-leaving reflectance, and some anomalously large short-term variability (spikes) in the temporal trend of chlorophyll concentration. This paper will describe the OBPG calibration with a focus on the differences between the MCST and OBPG approaches.

calibration↗

NASA NTRS1984

LANDSAT instruments characterization

Work performed for the LANDSAT instrument characterization task in the areas of absolute radiometry, coherent noise analysis, and between-date smoothing is reported. Absolute radiometric calibration for LANDSAT-5 TM under ambient conditions was performed. The TM Radiometric Algorithms and Performance Program (TRAPP) was modified to create optional midscan data files and to match the TM Image Processing System (TIPS) algorithm for pulse determination. Several data reduction programs were developed, including a linear regression and its plotted result. A fast Fourier transformation study was conducted on the resequenced TM data. Subscenes of homogeneous water within scenes over Pensacola, Florida were used for testing the FFT on the resequenced data. Finally, a gain and pulse height stability study of LANDSAT 5 TM spectral bands was performed.

Lee, Y.↗

NASA NTRS1989

Radar scattering from desert terrains, Pisgah/Lavic Region, California: Implications for Magellan

A major component of the 1988 Mojave Field Experiment involved the simultaneous acquisition of quad-polarization multifrequency airborne Synthetic Aperture Radar (SAR) imaging radar data and ground measurements thought to be relevant to the radar scattering behavior of a variety of desert surfaces. In preparation for the Magellan mission to Venus, the experiment was designed to explore the ability of SAR to distinguish types of geological surfaces, and the effects of varying incidence angles on the appearance of such surfaces. The airborne SAR system acquired images at approx. 10 m resolution, at 3 incidence angles (30, 40, 50 degs) and at 3 wavelengths (P:68 cm, L:24 cm, C:5.6 cm). The polarimetric capabilities of the instrument allow the simulation of any combination of transmit and receive polarizations during data reduction. Calibrated trihedral corner reflectors were deployed within each scene to permit absolute radiometric calibration of the image data. Initial analyses of this comprehensive radar data set is reported, with emphasis on implications for interpretation of Magellan data.

Plaut, J. J.↗

NASA NTRS1993

Normalization and calibration of geostationary satellite radiances for the International Satellite Cloud Climatology Project

Procedures are described for normalizing the radiometric calibration of image radiances obtained from geostationary weather satellites that contributed data to the International Satellite Cloud Climatology Project. The key step is comparison of coincident and collocated measurements made by each satellite and the concurrent AVHRR on the 'afternoon' NOAA polar-orbiting weather satellite at the same viewing geometry. The results of this comparison allow transfer of the AVHRR absolute calibration, which has been established over the whole series, to the radiometers on the geostationary satellites. Results are given for Meteosat-2, 3, and 4, for GOES-5, 6, and 7, for GMS-2, 3, and 4 and for Insat-1B. The relative stability of the calibrations of these radiance data is estimated to be within +/- 3 percent; the uncertainty of the absolute calibrations is estimated to be less than 10 percent. The remaining uncertainties are at least two times smaller than for the original radiance data.

Desormeaux, Yves↗

NASA NTRS2000

Pre-Launch Algorithm and Data Format for the Level 1 Calibration Products for the EOS AM-1 Moderate Resolution Imaging Spectroradiometer (MODIS)

The Moderate Resolution Imaging Spectroradiometer (MODIS) radiometric calibration product is described for the thermal emissive and the reflective solar bands. Specific sensor design characteristics are identified to assist in understanding how the calibration algorithm software product is designed. The reflected solar band software products of radiance and reflectance factor both are described. The product file format is summarized and the MODIS Characterization Support Team (MCST) Homepage location for the current file format is provided.

Guenther, Bruce W.↗

NASA NTRS2012

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 interconsistency 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, SI-traceable 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 sunview 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 source-centric 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.

Thome, Kurtis↗

NASA NTRS2018

Effects of Time-Varying Relative Spectral Response on the Calibration of MODIS Reflective Solar Bands

Calibration of the on-orbit gain changes of the narrow bandwidth reflective solar bands (RSB) of Terra and Aqua MODIS is usually based on the band center wavelength. The relative spectral response (RSR) of each band is assumed to be constant on orbit and the time dependence of an overall gain factor is calculated. Any on-orbit changes to the RSR of the MODIS bands will introduce some error into the calibration and may also have an impact on the Earth scene radiance retrieval. We consider two different ways to track how the RSR of the MODIS RSB may be changing on orbit, and the effect that these changes will have on the calibration. First, we examine in-band RSR measurements from the spectro-radiometric calibration assembly (SRCA) carried on-board both MODIS instruments. Second, we study the broadband degradation of the MODIS scan mirror and how it may be changing the effective out-of-band response of the RSB. We find that RSR changes have a small effect on the radiance calibrated using the on-board solar diffuser, generally less than 0.5% in all cases at any time in the missions, with bands 1, 8, and 9 impacted the most.

Twedt, Kevin A.↗

NASA NTRSDate not supplied

Short Time Scale Stability Monitoring of GOES-16 Visible Channels by Utilizing Daily Inter-Calibration Events with both VIIRS and MODIS Sensors

The CERES project relies on MODIS, VIIRS and geostationary (GEO) imager retrieved cloud properties to compute surface fluxes and convert CERES and GEO radiances into TOA fluxes. The CERES TOA and surface fluxes need to be of climate quality and any anomaly or discontinuity in the calibration of the MODIS, VIIRS, GEO radiances need to be mitigated or avoided. Due to the nature of the CERES instrument calibration, there is a lag time of 3 months before the processing of the CERES product. This allows the CERES team to investigate any unforeseen problems in the input datasets or GEO calibration discontinuities or anomalies before processing. The CERES geostationary imager calibration team is developing a daily monitoring system of GEO, MODIS and VIIRS visible channel radiances in order to detect any day to day discontinuities as part of the CERES/GEO coincident ray-matching calibration efforts. a GEO discontinuity can be detected using two MODIS and 2 VIIRS sensors simultaneously, thus increasing the sampling greatly over a single GEO/LEO radiance pairs. This method is being automated and has already detected three erroneous radiometric calibration events, which were verified with the GOES-16 event log page. One advantage of daily monitoring is that the time period needed to verify calibration drifts is reduced and the confidence to detect even smaller magnitudes of the calibration drift is increased over monthly monitoring. By utilizing Terra and Aqua MODIS and NPP and NOAA20 VIIRS imagers to inter-calibrate GOES-16, the GOES-16 calibration can be referenced to anyone of these imagers. If the CERES project transitions between the Aqua-MODIS imager to the NOAA20 VIIRS imager, the NOAA-20 VIIRS imager can be radiometrically scale to Aqua-MODIS calibration, thus avoiding a GOES-16 calibration discontinuity.

David Robert Doelling↗

NASA NTRS1991

Solar-diffuser panel and ratioing radiometer approach to satellite sensor on-board calibration

The use of a solar-diffuser panel is a desirable approach to the on-board absolute radiometric calibration of satellite multispectral sensors used for earth observation in the solar reflective spectral range. It provides a full aperture, full field, end-to-end calibration near the top of the sensor's dynamic range and across its entire spectral response range. A serious drawback is that the panel's reflectance, and the response of any simple detector used to monitor its reflectance may change with time. This paper briefly reviews some preflight and on-board methods for absolute calibration and introduces the ratioing-radiometer concept in which the radiance of the panel is ratioed with respect to the solar irradiance at the time the multispectral sensor is viewing the panel in its calibration mode.

Slater, Philip N.↗

NASA NTRS1991

Reflectance stability analysis of Spectralon diffuse calibration panels

The Multi-angle Imaging SpectroRadiometer (MISR) plans to use deployable diffuse reflectance panels to provide periodic radiometric calibrations of its nine cameras while in-flight. Near-Lambertian reflectance characteristics are desirable to facilitate flat-field camera intercomparisons. Also required is panel spatial and spectral uniformity, and stability with time. Spectralon, a commercially available polytetrafluoroethylene (PTFE) compound, has been baselined in the MISR design. To assess the suitability of this material, a series of degradation tests were planned and implemented. These included UV vacuum exposure and proton bombardment tests which simulated the exposure levels to be encountered during the mission life. Proton levels are now considered too low to be of concern, but UV vacuum tests demonstrate sensitivity to material contamination. Material investigations have concluded that hydrocarbons are present in the bulk of the material, and that plastic packaging materials can introduce additional surface-layer contamination. It is found however, that these unwanted elements can be eliminated through vacuum pumping at elevated temperatures. Exposure to a UV source, while in vacuum, is again planned for a set of targets which have been vacuum baked. This will assess the stability of the pure PTFE form.

Bruegge, Carol J.↗

NASA NTRS2000

On-Orbit Calibration of ADEOS OCTS with an AVIRIS Underflight

The Ocean Color Temperature Scanner (OCTS) onboard the Advanced Earth Observation Satellite (ADEOS) was launched on August 17, 1996. Calibration of OCTS is required for use of the on-orbit measured data for retrieval of physical properties of the ocean. In the solar reflected portion of the electromagnetic spectrum, OCTS measures images with nominally 700-m spatial resolution through eight multispectral bands. The objective of this research was to establish the absolute radiometric calibration of OCTS on orbit through an underflight by the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS). AVIRIS is a NASA earth-observing imaging spectrometer designed, built and operated by the Jet Propulsion Laboratory (JPL). AVIRIS acquires data from 20-km altitude on a NASA ER-2 aircraft, above most of the Earth's atmosphere. AVIRIS measures the solar reflected spectrum from 370 nm to 2500 nm through 224 contiguous spectral channels. The full width at half maximum (FWHM) of the spectral channels is nominally 10-nm. AVIRIS spectra are acquired as images of 11 km by up to 800 km extent with 20-m spatial resolution. The high spectral resolution of AVIRIS data allows direct convolution to the spectral response functions of the eight multispectral bands of OCTS. The high spatial resolution of AVIRIS data allows for spatial re-sampling of the data to match the ADEOS sensors spatial resolution. In addition, the AVIRIS high spatial resolution allows assessment of the scaling effects due to environmental factors of thin cirrus clouds, sub-pixel cloud cover, white caps, ocean foam, sun-glint, and bright-target adjacency. The platform navigation information recorded by AVIRIS allows calculation of the position and observation geometry of each spectrum for matching to the OCTS measurement. AVIRIS is rigorously characterized and calibrated in the laboratory prior to and following the flight season. The stability and repeatability of AVIRIS calibration have been validated through an extensive series of inflight calibration experiments. In the OCTS portion of the spectrum, using pre-and post-flight runway calibrations of AVIRIS coupled with the on-board calibrator an absolute calibration accuracy of better than 3% spectral, 2% radiometric and 5% spatial has been achieved. An analogous satellite underflight calibration experiment was performed with AVIRIS and the Optical Sensor (OPS) onboard the Japanese Earth Resources Satellite (JERS).

Green, Robert O.↗

NASA NTRS1998

On-Orbit Calibration of ADEOS OCTS with an AVIRIS Underflight

The Ocean Color Temperature Scanner (OCTS) onboard the Advanced Earth Observation Satellite (ADEOS) was launched on August 17, 1996. Calibration of OCTS is required for use of the on-orbit measured data for retrieval of physical properties of the ocean. In the solar reflected portion of the electromagnetic spectrum, OCTS measures images with nominally 700-m spatial resolution through eight multispectral bands. The objective of this research was to establish the absolute radiometric calibration of OCTS on orbit through an underflight by the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS). AVIRIS is a NASA Earth-observing imaging spectrometer designed, built and operated by the Jet Propulsion Laboratory (JPL). AVIRIS acquires data from 20-km altitude on a NASA ER-2 aircraft, above most of the Earth's atmosphere. AVIRIS measures the solar reflected spectrum from 370 nm to 2500 nm through 224 contiguous spectral channels. The full width at half maximum (FWHM) of the spectral channels is nominally 10-nm. AVIRIS spectra are acquired as images of 11 km by up to 800 km extent with 20-m spatial resolution. The high spectral resolution of AVIRIS data allows direct convolution to the spectral response functions of the eight multispectral bands of OCTS. The high spatial resolution of AVIRIS data allows for spatial re-sampling of the data to match the ADEOS sensors spatial resolution. In addition, the AVIRIS high spatial resolution allows assessment of the scaling effects due to environmental factors of thin cirrus clouds, sub-pixel cloud cover, white caps, ocean foam, sun-glint, and bright-target adjacency. The platform navigation information recorded by AVIRIS allows calculation of the position and observation geometry of each spectrum for matching to the OCTS measurement. AVIRIS is rigorously characterized and calibrated in the laboratory prior to and following the flight season. The stability and repeatability of AVIRIS calibration have been validated through an extensive series of inflight calibration experiments. In the OCTS portion of the spectrum, using pre- and post-flight runway calibrations of AVIRIS coupled with the on-board calibrator an absolute calibration accuracy of better than 3% spectral, 2% radiometric, and 5% spatial, has been achieved. An analogous satellite underflight calibration experiment was performed with AVIRIS and the Optical Sensor (OPS) onboard the Japanese Earth Resources Satellite (JERS).

Green, Robert O.↗