In this work, we describe radiometric platforms able to produce realistic spectral distributions and spatial scenes for the development of application-specific metrics to quantify the performance of sensors and systems. Using these platforms, sensor and system performance may be quantified in terms of the accuracy of measurements of standardized sets of complex source distributions. The same platforms can also serve as a basis for algorithm testing and instrument comparison. The platforms consist of spectrally tunable light sources (STS's) coupled with spatially programmable projection systems. The resultant hyperspectral image projectors (HIP) can generate complex spectral distributions with high spectral fidelity; that is, scenes with realistic spectral content. Using the same fundamental technology, platforms can be developed for the ultraviolet, visible, and infrared regions. These radiometric platforms will facilitate advanced sensor characterization testing, enabling a pre-flight validation of the pre-flight calibration.

Samples from soil and leaf litter were obtained at a site located in the savanna biome of South Africa (Skukuza; 25.0°S, 31.5°E) and their bidirectional reflectance distribution functions (BRDF) were measured using the out-of-plane scatterometer located in the National Aeronautics and Space Administration's (NASA's) Goddard Space Flight Center (GSFC) Diffuser Calibration Facility (DCaF). BRDF was measured using P and S incident polarized light over a range of incident and scatter angles. A monochromator-based broadband light source was used in the ultraviolet (uv) and visible (vis) spectral ranges. The diffuse scattered light was collected using an uv-enhanced silicon photodiode detector with output fed to a computer-controlled lock-in amplifier. Typical measurement uncertainties of the reported laboratory BRDF measurements are found to be less than 1% (k=1). These laboratory results were compared with airborne measurements of BRDF from NASA's Cloud Absorption Radiometer (CAR) instrument over the same general site where the samples were obtained. This study presents preliminary results of the comparison between these laboratory and airborne BRDF measurements and identifies areas for future laboratory and airborne BRDF measurements. This paper presents initial results in a study to try to understand BRDF measurements from laboratory, airborne, and satellite measurements in an attempt to improve the consistency of remote sensing models.

As part of an effort to reduce uncertainties in the radiometric calibrations of integrating sphere sources and standard lamp irradiance sources, the Goddard Space Flight Center (GSFC) Radiometric Calibration Facility's (RCF) primary radiometer was characterized at the NIST facility for Spectral Irradiance and Radiance Calibrations with Uniform Sources (SIRCUS). Based on those measurements, a nominal slit scattering function was developed for the radiometer. This allowed calculations of band averaged spectral radiances and irradiances for the radiometer's measurements of sphere and standard lamp sources, respectively. From these calculations the effects of bandwidth and spectral stray light were isolated for measurements in the blue spectral region. These effects, which depend on the spectral distribution of the source being measured, can be as large as 8% for measurements at 400 nm. The characterization results and a correction algorithm for these effects are presented here.

In addition to radiometric, spatial, and spectral calibration requirements, MODIS design specifications include polarization sensitivity requirements of less than 2% for all Reflective Solar Bands (RSB) except for the band centered at 412nm. To the best of our knowledge, MODIS was the first imaging radiometer that went through comprehensive system level (end-to-end) polarization characterization. MODIS polarization sensitivity was measured pre-launch at a number of sensor view angles using a laboratory Polarization Source Assembly (PSA) that consists of a rotatable source, a polarizer (Ahrens prism design), and a collimator. This paper describes MODIS polarization characterization approaches used by MODIS Characterization Support Team (MCST) at NASA/GSFC and addresses issues and concerns in the measurements. Results (polarization factor and phase angle) using different analyzing methods are discussed. Also included in this paper is a polarization characterization comparison between Terra and Aqua MODIS. Our previous and recent analysis of MODIS RSB polarization sensitivity could provide useful information for future Earth-observing sensor design, development, and characterization.

MODIS's solar diffuser is one of the key calibration sources for its reflective bands. Geometric optical modeling shows that Earthshine illuminating the solar diffuser contaminates measurements of the direct solar irradiance. Before launch, a simple model was used that did not consider the non-diffuse component and the atmospheric transfer of the Earthshine contamination. Recently, a more detailed Earthshine model has been recently developed to better determine the magnitude and characteristics of Earthshine contamination. The model includes a geometric optical model of the instrument, a model of the Earth/Sun/instrument geometry during the calibration interval, an atmospheric model, and various bi-directional models of Earth surface types. Several types of vegetation and open-ocean with different wind speeds are modeled. Analysis was performed of the solar diffuser data with particular emphasis on the surface type at the Earth locations where specular reflections (glint) might occur, i.e., where the solar and view zenith angles are almost the same and the relative azimuth angle is near 180°. The new model compares well with detailed analysis of the solar diffuser data, both over open-ocean with glint, and over vegetation. Both the modeling and analysis show a spectral dependence in the non-diffuse radiation that increases with wavelength. The modeling and analysis give lower and upper bounds on the Earthshine contamination and suggest approaches for minimizing its impact on the MODIS calibration.

MODIS is a major instrument for NASA's EOS missions, currently operating aboard the EOS Terra and Aqua spacecraft launched in December 1999 and May 2002, respectively. It was designed to extend heritage sensor measurements and data records and to enable new research studies of the Earth's land, oceans, and atmosphere. MODIS has 36 spectral bands (0.41 - 14.4μm) located on four focal plane assemblies (FPA). It makes measurements at three nadir spatial resolutions: 0.25km, 0.5km, and 1km. Because of instrument design complexity and more stringent calibration requirements, extensive calibration and characterization activities were conducted pre-launch by the sensor vendor for both Terra and Aqua MODIS. For the 20 reflective solar bands (RSB) with wavelengths below 2.2μm, these activities include detector noise characterization, radiometric response at different instrument temperatures and at different scan angles, and relative spectral response. On-orbit RSB calibration is performed using a solar diffuser (SD) and a solar diffuser stability monitor (SDSM). In addition, regular lunar observations are made to track RSB radiometric stability. This paper provides a summary of Terra and Aqua MODIS RSB pre-launch and on-orbit calibration and characterization activities, methodologies, data analysis results, and lessons learned. It focuses on major issues that could impact MODIS RSB calibration and data product quality. Results presented in this paper include RSB detector noise characterization, response versus scan angle and instrument temperature, SD bi-directional reflectance factors characterization, and on orbit calibration stability. Similar discussions on MODIS thermal emissive bands (TEB) are presented in a separate paper in these proceedings (Xiong et. al).

The MODerate Resolution Imaging Spectroraiometer (MODIS) reflective solar bands (RSB) are calibrated on-orbit using solar illuminations reflected from its onboard solar diffuser (SD) plate. The specified calibration uncertainty requirements for MODIS RSB are ±2% in reflectance and ±5% in radiance at their typical top of atmosphere (TOA) radiances. The onboard SD bi-directional reflectance factor (BRF) was characterized pre-launch by the instrument vendor using reference samples traceable to NIST reflectance standard. The SD on-orbit degradation is monitored using a solar diffuser stability monitor (SDSM). One of contributors to the RSB calibration uncertainty is the earthshine (ES) illumination on the SD plate during SD calibration. This effect was estimated pre-launch by the instrument vendor to be of 0.5% for all RSB bands. Analyses of on-orbit observations show that some of the SD calibration data sets have indeed been contaminated due to extra ES illumination and the degree of ES impact on the SD calibration is spectrally dependent and varies with geo-location and atmospheric conditions (ground surface type and cloudiness). This paper illustrates the observed ES impacts on the MODIS RSB calibration quality and compare them with the effects derived from an ES model based on the viewing geometry of MODIS SD aperture door and likelihood atmospheric conditions. It also describes an approach developed to minimize the ES impact on MODIS RSB calibration.

The characterization of the polarization sensitivity of a remote sensing sensor can have a large impact on the data quality of the top-of-atmosphere radiances measured by optical sensors on earth-orbiting satellites. This paper describes an algorithm to improve the polarization characterization of certain elements of an imaging sensor (e.g. detectors, or mirror sides) relative to each other, as well as the application to an ocean color sensor. The key step in the analysis is the separation of the measured radiances into two groups: those that are increased by the polarization correction, and those that are decreased.

The Moderate Resolution Imaging Spectroradiometer (MODIS) is a major instrument for NASA's Earth Observing System (EOS), currently operating on-board the EOS Terra spacecraft, launched in December 1999, and Aqua spacecraft, launched in May 2002. MODIS is a whiskbroom scanning radiometer using a double-sided paddle wheel scan mirror. It makes measurements in 36 spectral bands with wavelengths from visible (VIS) to long-wave infrared (LWIR). Bands 20-25 and 27-36 are the thermal emissive bands (TEB) covering wavelengths from 3.5 to 14.4μm. During pre-launch thermal vacuum measurements, a laboratory blackbody calibration source (BCS) was used as the primary calibration source for the TEB. For on-orbit operation, an on-board blackbody (BB) source and a space view (SV) port are used together for the TEB calibration on a scan-by-scan basis. This paper provides an overview of Terra and Aqua MODIS pre-launch and on-orbit calibration and characterization activities, methodologies, data analysis results, and lessons learned for the thermal emissive bands. It focuses on major issues that could impact MODIS TEB calibration and data quality. Results presented in this paper include detector noise characterization, response versus scan angle (RVS), and response versus instrument and focal plane temperatures. Similar discussions for the MODIS reflective solar bands (RSB) are presented in a separate paper in these proceedings (Xiong et. al).

Five cases using NASA ER-2 aircraft based SHIS and MAS radiances have been used to assess the L1B radiometric performance of Terra and Aqua MODIS Collection 5 radiances for LWIR bands 31-36. The composite results of these cases show that the split window bands 31 (11 μm) and 32 (12 μm) have performed well within the 0.5% radiometric specification over their lifetime. This is in agreement with results from other ground based and satellite based comparisons that are discussed in the paper. However, the LWIR CO₂-sensitive bands 34-36 appear to be performing outside of their 1% accuracy specification, especially for Terra MODIS. This is also observed in global Aqua AIRS-MODIS comparisons. Possible causes for this behavior are under investigation, with the most likely contributors being spectral characterization error, OOB influences due to spectral filter leaks, or possibly scan mirror characterization. It seems that an optical leak from Terra MODIS band 31 into bands 32-36 is probably not a significant contributor to the large residuals of bands 34-36, owing to an effective radiometric correction. Calibration coefficient error is probably only a small contributor since, after adjustments in 2002, the on-orbit calibration now closely follows that of the pre-launch calibration.

With increasing efforts on data fusion and long-term climate data records (CDR) using observations made by multiple sensors on the same or different platforms, sensor cross-calibration has become increasingly important. It is known that the uncertainty of climate models or science data records depends not only on the calibration quality of individual sensors but also on their calibration consistency. This paper provides an overview of inter-comparison methodologies applied by the MODIS Characterization Support Team (MCST) at NASA/GSFC for the studies of Terra and Aqua MODIS on-orbit calibration consistency. Improved over heritage sensors, MODIS was built with a set of on-board calibrators (OBC) that include a blackbody (BB), a space view (SV) port, a solar diffuser (SD), and a solar diffuser stability monitor (SDSM). The BB is primarily used for the thermal emissive bands (TEB) calibration and the SD/SDSM system for the reflective solar bands (RSB) calibration. Detector responses to the SV provide measurements for the instrument background. Although instrument design requirements and calibration approaches are nearly identical for both Terra and Aqua MODIS and they all went through extensive and similar pre-launch calibration and characterization activities, their on-orbit calibration consistency still has to be carefully examined and validated as many science products are generated from observations made by both instruments. Methodologies discussed in this paper include inter-comparison studies using the Moon, a third sensor, and ground targets. Our results show that Terra and Aqua reflective solar bands and thermal emissive bands have been calibrated consistently to within their combined uncertainty requirements. For the 11mm and 12mm bands used for surface temperature measurements, the calibration differences between Terra and Aqua MODIS are less than ±0.15K at scene temperatures from 240-280K and less than ±0.50K at cold scene temperatures from 190 to 230K (before corrections). For most reflective solar bands, their reflectance calibration differences are typically less than ±2%.

The Landsat suite of satellites has collected the longest continuous archive of multispectral data of any land observing space program. From the Landsat program's inception in 1972 to the present, the Earth science user community has benefited from a historical record of remotely sensed data. However, little attention has been paid to ensuring that the data are calibrated and comparable from mission to mission. Launched in 1982 and 1984 respectively, the Landsat 4 (L4) and Landsat 5 (L5) Thematic Mappers (TM) are the backbone of an extensive archive of moderate resolution Earth imagery. To evaluate the "current" absolute accuracy of these two sensors, image pairs from the L5 TM and L4 TM sensors were compared. The approach involves comparing image statistics derived from large common areas observed eight days apart by the two sensors. The average percent differences in reflectance estimates obtained from the L4 TM agree with those from the L5 TM to within 15 percent. Additional work to characterize the absolute differences between the two sensors over the entire mission is in progress.

Oscillations in radiometric gains of the short wave infrared (SWIR) bands in Landsat-4 (L4) and Landsat-5 (L5) Thematic Mappers (TMs) are observed through an analysis of detector responses to the Internal Calibrator (IC) pulses. The oscillations are believed to be caused by an interference effect due to a contaminant film buildup on the window of the cryogenically cooled dewar that houses these detectors. This process of contamination, referred to as outgassing effects, has been well characterized using an optical thin-film model that relates detector responses to the accumulated film thickness and its growth rate. The current models for L4 TM are based on average detector responses to the second brightest IC lamp and have been derived from three data sets acquired during different times throughout the instrument's lifetime. Unlike in L5 TM outgassing characterization, it was found that the L4 TM responses to all three IC lamps can be used to provide accurate characterization and correction for outgassing effects. The analysis of single detector responses revealed an up to five percent difference in the estimated oscillating periods and also indicated a gradual variation of contaminant growth rate over the focal plane.

Landsat-5 Thematic Mapper (TM) has been imaging the Earth since March 1984 and Landsat-7 Enhanced Thematic Mapper Plus (ETM+) was added to the series of Landsat instruments in April 1999. The stability and calibration of the ETM+ has been monitored extensively since launch. Though not monitored for many years, TM now has a similar system in place to monitor stability and calibration. University teams have been evaluating the on-board calibration of the instruments through ground-based measurements since 1999. This paper considers the calibration efforts for the thermal band, Band 6, of both the Landsat-5 and Landsat-7 instruments. Initial calibration results for the Landsat-7 ETM+ thermal band found a bias error which was corrected through changes in the processing systems in late 2000. Recent results are suggesting a calibration error in gain, apparent with high temperature targets. For typical earth temperature targets, from about 5-20C, the gain error is small enough to be within the noise of the vicarious calibration process. However, for very high temperature targets (greater then 35C), Landsat-7 appears to be predicting several degrees too low. Questions remain on whether the change happened suddenly or is varying slowly, so the team will wait for another collection season before making any updates to the calibration. The calibration efforts for Landsat-5 TM considers only data collected since 1999, though there are efforts underway to extend the calibration history prior to the Landsat-7 launch. The latest data suggests that the Landsat-5 thermal band has a bias error of about 0.65K too low since 1999. Studies early in the life of Landsat-5 show that the instrument was calibrated within the error of the calibration process. It is impossible to tell, at this point, when or how the change in bias may have occurred. A correction will be calculated and implemented in the US processing system in 2006 for data acquired since April 1999.

The Landsat series of sensors have supplied the remote sensing community with a continuous data set dating to the early 1970s. An important aspect of retaining the continuity of these data is that a Landsat follow-on as well as current Landsat instruments must be understood radiometrically throughout their mission. The Advanced Land Imager (ALI), for example, was developed as a prototype for the next generation of Landsat Instruments, and as such there was a significant effort to understand its radiometric characteristics as well as how it compares with previous Landsat sensors. The Remote Sensing Group at the University of Arizona has been part of this effort since the late 2000 launch of ALI through the use of the reflectance-based method of vicarious calibration. The reflectance-based approach consists of ground-based measurements of atmospheric conditions and surface reflectance at the time of satellite overpass to predict the at-sensor radiance seen by the sensor under study. The work compares results from the reflectance-based approach obtained from well-characterized test sites such as Railroad Valley Playa in Nevada and Ivanpah Playa in California as applied to ALI, Landsat-5 TM, and Landsat-7 EMT+. The results from the comparison use a total of 14 ALI dates spanning in time from 2001 to late 2005 and show that ALI agrees with the current radiometric results from TM and ETM+ to within 5%.

Increasingly, data from multiple sensors are used to gain a more complete understanding of land surface processes at a variety of scales. Although higher-level products (e.g., vegetation cover, albedo, surface temperature) derived from different sensors can be validated independently, the degree to which these sensors and their products can be compared to one another is vastly improved if their relative spectroradiometric responses are known. Most often, sensors are directly calibrated to diffuse solar irradiation or vicariously to ground targets. However, space-based targets are not traceable to metrological standards, and vicarious calibrations are expensive and provide a poor sampling of a sensor's full dynamic range. Cross-calibration of two sensors can augment these methods if certain conditions can be met: (1) the spectral responses are similar, (2) the observations are reasonably concurrent (similar atmospheric & solar illumination conditions), (3) errors due to misregistrations of inhomogeneous surfaces can be minimized (including scale differences), and (4) the viewing geometry is similar (or, some reasonable knowledge of surface bi-directional reflectance distribution functions is available). This study explores the impacts of cross-calibrating sensors when such conditions are met to some degree but not perfectly. In order to constrain the range of conditions at some level, the analysis is limited to sensors where cross-calibration studies have been conducted (Enhanced Thematic Mapper Plus (ETM+) on Landsat- 7 (L7), Advance Land Imager (ALI) and Hyperion on Earth Observer-1 (EO-1)) and including systems having somewhat dissimilar geometry, spatial resolution & spectral response characteristics but are still part of the so-called "A.M. constellation" (Moderate Resolution Imaging Spectrometer (MODIS) aboard the Terra platform). Measures for spectral response differences and methods for cross calibrating such sensors are provided in this study. These instruments are cross calibrated using the Railroad Valley playa in Nevada. Best fit linear coefficients (slope and offset) are provided for ALI-to-MODIS and ETM+-to-MODIS cross calibrations, and root-mean-squared errors (RMSEs) and correlation coefficients are provided to quantify the uncertainty in these relationships. In theory, the linear fits and uncertainties can be used to compare radiance and reflectance products derived from each instrument.

The Atmospheric Infrared Sounder (AIRS) measures the infrared spectrum in 2378 channels between 3.7 and 15.4 microns with a very high spectral resolution of approximately 1200. AIRS footprints are approximately 1.1 by 0.6 degrees. Because AIRS is a grating spectrometer, each channel has a unique spatial response. Image rotation due to the scan mirror causes these spatial responses to rotate. In effect, each channel has 90 spatial responses, one for each scene footprint in the scan line. Although the spatial response for most channels is symmetric and nearly uniform, some channels have significantly asymmetric response. This paper reviews and describes the prelaunch measurements that characterized the spatial response functions. Next, it describes the conversion of the ground-based results into footprint-specific response functions valid in flight. Then we describe the postlaunch validation of the measurements, including centroid location, axes orientations, and a check on the full two-dimensional response functions. This latter check involves comparison of AIRS data with that of the Moderate Resolution Imaging Spectrometer (MODIS), which flies on the same platform as AIRS. An important result is that AIRS/MODIS brightness temperature comparisons are significantly improved (scatter reduced) when the AIRS spatial response is explicitly taken into account. Finally, a status report is given on attempts to fully verify the prelaunch measurements by deriving the AIRS spatial response from flight data alone.

In an effort to validate the accuracy and stability of AIRS data at low scene temperatures (200-250 K range), we evaluated brightness temperatures at 11 microns with Aqua MODIS band 31 and HIRS/3 channel 8 for Antarctic granules between September 2002 and May 2006. We found excellent agreement with MODIS (at the 0.2 K level) over the full temperature range in data from early in the Aqua mission. However, in more recent data, starting in April 2005, we found a scene temperature dependence in MODIS-AIRS brightness temperature differences, with a discrepancy of 1- 1.5 K at 200 K. The comparison between AIRS and HIRS/3 (channel 8) on NOAA 16 for the same time period yields excellent agreement. The cause and time dependence of the disagreement with MODIS is under evaluation, but the change was coincident with a change in the MODIS production software from collection 4 to 5. AIRS and MODIS (Flight Model 1) are onboard the EOS Aqua spacecraft, launched into a 1:30 PM polar orbit on May 4, 2002. AIRS has 2378 infrared channels with high spectral resolution (1200) covering the 3.7 to 15.4 micron wavelength range, with a nominal spatial resolution of 13.5 km. MODIS has 36 relatively broad spectral bands with spatial resolution of 1 km for the LWIR bands. HIRS/3 is onboard NOAA-16 (L), launched into a 2:00 PM polar orbit on Sep. 21, 2000.

Clouds and the Earth's Radiant Energy system (CERES) sensors provide accurate measurements for the long-term monitoring of the Earth's radiation budget components. The three scanning thermistor bolometer sensors on CERES measure broadband radiances in the shortwave (0.3 to 5.0 micrometer), total (0.3 to >100 micrometer) and in 8 - 12 micrometer water vapor window regions. Currently four of the CERES instruments (Flight Models 1 through 4 [FM1 - FM4]) are flying aboard EOS Terra and Aqua platforms with two instruments aboard each spacecraft. The sensor calibrations are performed with onboard blackbody sources and a tungsten lamp as well as a solar diffuser plate known as the Mirror Attenuator Mosaic (MAM). The calibration results collectively depict the ground to orbit shifts and the on-orbit drifts in the sensor reponses. Deep convective clouds and tropical ocean are used as validation targets to understand the sensors' stability on-orbit. With two CERES instruments on the same platform, comparison of measurements from similar sensors viewing the same geolocation are performed. The different calibration and validation studies performed on CERES bring to light the radiometric gain and spectral variation of the sensors from pre and post launch. This paper discusses briefly the contribution of each calibration and validation study in understanding CERES sensors' behavior. It also shows the results from these studies which enabled to correct the data products with a calibration stability of better than 0.2%.

It is estimated that in order to best detect real changes in the Earth's climate system, space based instrumentation measuring the Earth Radiation Budget (ERB) must remain calibrated with a stability of 0.3% per decade. Such stability is beyond the specified accuracy of existing ERB programs such as the Clouds and the Earth's Radiant Energy System (CERES, using three broadband radiometric scanning channels: the shortwave 0.3 - 5μm, total 0.3- > 100μm, and window 8 - 12μm). It has been shown that when in low earth orbit, optical response to blue/UV radiance can be reduced significantly due to UV hardened contaminants deposited on the surface of the optics. Since typical onboard calibration lamps do not emit sufficient energy in the blue/UV region, this darkening is not directly measurable using standard internal calibration techniques. This paper describes a study using a model of contaminant deposition and darkening, in conjunction with in-flight vicarious calibration techniques, to derive the spectral shape of darkening to which a broadband instrument is subjected. Ultimately the model uses the reflectivity of Deep Convective Clouds as a stability metric. The results of the model when applied to the CERES instruments on board the EOS Terra satellite are shown. Given comprehensive validation of the model, these results will allow the CERES spectral responses to be updated accordingly prior to any forthcoming data release in an attempt to reach the optimum stability target that the climate community requires.

The Japanese Advanced Meteorological Imager (JAMI) was developed by Raytheon and delivered to Space Systems/Loral as the Imager Subsystem for Japan's MTSAT-1R satellite. MTSAT-1R was launched from the Tanegashima Space Center on 2005 February 26 and became formally operational on 2005 June 28. This paper compares in-flight performance of JAMI with predictions made before launch. The performance areas discussed include radiometric sensitivity (NEDT and SNR) versus spectral channel, calibration accuracy versus spectral channel derived from comparisons of JAMI and AIRS measurements and image navigation and registration.

The Imagers carried by NOAA's Geostationary Operational Environmental Satellites observe the Earth and its atmosphere in four channels in the thermal infrared and one in the visible part of the spectrum. Because of angle-dependent anomalous absorption in the scan mirror's SiO_x coatings, the throughput of the Imagers in the infrared depends on the east-west angle of observation. If not accounted for, this effect would introduce artificial east-west gradients into the Imagers' observations of scene brightness temperature. Therefore, NOAA includes a model of the radiative processes at the scan mirror in its operational calibration. The input to the model includes a-priori values of the emissivity of the scan mirror vs east-west scan angle. The values NOAA uses operationally are estimated during post-launch testing from observations of frames of space that span the entire east-west extent of the Imagers' field of regard above and below the Earth's disk. However, we also have an alternative source of emissivity-vs-angle values - laboratory measurements made on witness samples of the scan mirrors at MIT Lincoln Laboratory. Are those emissivity values as effective as (or more effective than) the ones NOAA estimates in post-launch testing? To answer this question, we compared the results of in-orbit calibrations with the two sets of emissivity vs scan angle. Although the results depend slightly on channel and observation conditions, the values from the post-launch measurements in space are usually the better choice.

One of the top radiometric priorities of the high-spatial resolution, commercial remote sensing industry is to achieve a superior level of image quality in all imagery products. Errors in detector gain and offset correction during product generation create noticeable image artifacts such as banding and streaking that degrade the overall image quality. Banding and streaking can be minimized by relative radiometric calibration, however, this calibration is only a temporary solution as the gain and offset of each detector will drift over time. The work presented here examines the relative radiometric performance of the QuickBird panchromatic and multispectral bands and tracks the performance from January 2005 until the present. During radiometric operations, uniform scenes of desert, ocean, forest, and snow areas are identified in the DigitalGlobe ImageLibrary. Products for these uniform scenes are generated and detector statistics are calculated for each scene. The QuickBird focal plane contains detectors that are masked so that no light reaches them. The statistics for the masked detectors are analyzed to study image-to-image variability and determine changes in detector offsets over time. Next, the detector averages for all active detectors are radiometrically corrected, and banding and streaking metrics are applied. Banding and streaking are trended to monitor changes over time. Quality metrics are also established based on the banding and streaking results to determine when the detector's gains and offsets have drifted sufficiently to require recalibration. Relative radiometric performance of the uniform scenes is compared with and without recalibration.

The NASA Ocean Biology Processing Group's Calibration and Validation (Cal/Val) Team implemented daily solar calibrations of SeaWiFS to look for step-function changes in the instrument response and has used these calibrations to supplement the monthly lunar calibrations in monitoring the radiometric stability of SeaWiFS during its first year of on-orbit operations. The Team has undertaken an analysis of the mission-long solar calibration time series, with the lunar-derived radiometric corrections over time applied, to assess the long-term degradation of the solar diffuser reflectance over nine years on orbit. The SeaWiFS diffuser is an aluminum plate coated with YB71 paint. The bidirectional reflectance distribution function of the diffuser was not fully characterized before launch, so the Cal/Val Team has implemented a regression of the solar incidence angles and the drift in the node of the satellite's orbit against the diffuser time series to correct for solar incidence angle effects. An exponential function with a time constant of 200 days yields the best fit to the diffuser time series. The decrease in diffuser reflectance over the mission is wavelength-dependent, ranging from 9% in the blue (412 nm) to 5% in the red and near infrared (670-865 nm). The degradation of diffuser reflctance is similar to that observed for SeaWiFS radiometric response itself from lunar calibration time series for bands 1-5 (412-555 nm), though the magnitude of the change is four times larger for the diffuser. Evidently, the same optical degradation process has affected both the telescope optics and the solar diffuser in the blue and green. The Cal/Val Team has developed a methodology for computing the signal-to-noise ratio (SNR) for SeaWiFS on orbit from the diffuser time series. The on-orbit change in the SNR for each band over the nine-year mission is less than 7%. The on-orbit performance of the SeaWiFS solar diffuser should offer insight into the long-term on-orbit performance of solar diffusers on other instruments, such as MODIS, VIIRS, and ABI.

In-flight performance and calibration results of the Ozone Monitoring Instrument OMI, successfully launched on 15 July 2004 on the EOS-AURA satellite, are presented and discussed. The radiometric calibration in comparison to the high-resolution solar irradiance spectrum from the literature convolved with the measured spectral slit function is presented. A correction algorithm for spectral shifts originating from inhomogeneous ground scenes (e.g. clouds) is discussed. Radiometric features originating from the on-board reflection diffusers are discussed, as well as the accuracy of the calibration of the instrument's viewing properties. It is shown that the in-flight performance of both CCD detectors shows evidence of particle hits by trapped high-energetic protons, which results in increased dark currents and increase in the Random Telegraph Signal (RTS) behaviour.

The OMI instrument that flies on the EOS Aura mission was launched in July 2004. OMI is a UV-VIS imaging spectrometer that measures in the 270 - 500 nm wavelength range. OMI provides daily global coverage with high spatial resolution. Every orbit of 100 minutes OMI generates about 0.5 GB of Level 0 data and 1.2 GB of Level 1 data. About half of the Level 1 data consists of in-flight calibration measurements. These data rates make it necessary to automate the process of in-flight calibration. For that purpose two facilities have been developed at KNMI in the Netherlands: the OMI Dutch Processing System (ODPS) and the Trend Monitoring and In-flight Calibration Facility (TMCF). A description of these systems is provided with emphasis on the use for radiometric, spectral and detector calibration and characterization. With the advance of detector technology and the need for higher spatial resolution, data rates will become even higher for future missions. To make effective use of automated systems like the TMCF, it is of paramount importance to integrate the instrument operations concept, the information contained in the Level 1 (meta-)data products and the inflight calibration software and system databases. In this way a robust but also flexible end-to-end system can be developed that serves the needs of the calibration staff, the scientific data users and the processing staff. The way this has been implemented for OMI may serve as an example of a cost-effective and user friendly solution for future missions. The basic system requirements for in-flight calibration are discussed and examples are given how these requirements have been implemented for OMI. Special attention is paid to the aspect of supporting the Level 0 - 1 processing with timely and accurate calibration constants.

The National Oceanic and Atmospheric Administration's (NOAA) National Environmental Satellite, Data, and Information Service (NESDIS) is responsible for receiving and processing environmental satellite observations and disseminating the products to NOAA's user community. NOAA's NPOESS Data Exploitation (NDE) Project will link the civilian environmental satellite information users to NPOESS data. NDE enables essential system upgrades to prepare NESDIS for NPOESS and provide a continuing capability throughout the NPOESS life cycle. NDE will employ an enterprise project approach, developing functionality to be shared across NOAA systems to reduce costs, risks, and to minimize redundancy. NDE will use the latest proven methods, tools and techniques to establish key elements of NOAA's 21st Century satellite data management capability. NDE activities include plans to serve the user community through the delivery of tailored products, NOAA-Unique products, and training.

This paper considers an evolved technique for significantly enhanced enterprise-level data processing, reprocessing, archival, dissemination, and utilization. There is today a robust working paradigm established with the Advanced Weather Interactive Processing System (AWIPS)-NOAA/NWS's information integration and fusion capability. This process model extends vertically, and seamlessly, from environmental sensing through the direct delivery of societal benefit. NWS, via AWIPS, is the primary source of weather forecast and warning information in the nation. AWIPS is the tested and proven "the nerve center of operations" at all 122 NWS Weather Forecast Offices (WFOs) and 13 River Forecast Centers (RFCs). However, additional line organizations whose role in satisfying NOAA's five mission goals (ecosystems, climate, weather & water, commerce & transportation, and mission support) in multiple program areas might be facilitated through utilization of AWIPS-like functionalities, including the National Marine Fisheries Service (NMFS); National Environmental Satellite, Data, and Information Service (NESDIS); Office of Oceanic & Atmospheric Research (OAR); and the National Ocean Service (NOS). In addition to NOAA's mission goals, there are nine diverse, recommended, and important societal benefit areas in the US Integrated Earth Observation System (IEOS). This paper shows how the satisfaction of this suite of goals and benefit areas can be optimized by leveraging several key ingredients: (1) the evolution of AWIPS towards a net-centric system of services concept of operations; (2) infusion of technologies and concepts from pathfinder systems; (3) the development of new observing systems targeted at deliberate, and not just serendipitous, societal benefit; and (4) the diverse, nested local, regional, national, and international scales of the different benefits and goal areas, and their interoperability and interplay across the system of systems.

Based on the TRMM (Tropical Rainfall Measuring Missio) remote sensing data, the relationship between the daily precipitation and the SST (Sea Surface Temperature) in the low latitude ocean area were analyzed during the Asia monsoon season in this paper. By calculated the corresponding and lag correlation coefficient of the precipitation and the SST in the low latitude ocean area in different domain, the paper discussed the relationship between the daily precipitation and the SST in these areas during the onset, the middle and the terminative period of Asia monsoon season. The results shown that the relationship was differently in dissimilitude ocean area and period.

Alpine meadows in the Hengduan Mountains of northwestern Yunnan, P.R. China are incredibly diverse. The regional climate is warming at a relatively rapid rate. In this paper, analyses of historical climate station data show that mean annual temperature over the last two decades has increased at a rate of 0.6°C/10 yr. In addition, analyses of historical remote sensing data show that the vegetation distribution in this region has changed evidently. We present simulation results from a general circulation model (HadCM3) and a dynamic vegetation model (MC1) showing how changes in future climate may alter alpine ecosystem of the Baima Nature Reserve in northwestern Yunnan.

Production of reliable climate datasets from multiple observational measurements acquired by remote sensing satellite systems available now and in the future places stringent requirements on the stability of sensors and consistency among the instruments and platforms. Detecting trends in environmental parameters measured at solar reflectance wavelengths (0.3 to 2.5 microns) requires on-orbit instrument stability at a level of 1% over a decade. This benchmark can be attained using the Moon as a radiometric reference. The lunar calibration program at the U.S. Geological Survey has an operational model to predict the lunar spectral irradiance with precision ~1%, explicitly accounting for the effects of phase, lunar librations, and the lunar surface photometric function. A system for utilization of the Moon by on-orbit instruments has been established. With multiple lunar views taken by a spacecraft instrument, sensor response characterization with sub-percent precision over several years has been achieved. Meteorological satellites in geostationary orbit (GEO) capture the Moon in operational images; applying lunar calibration to GEO visible-channel image archives has the potential to develop a climate record extending decades into the past. The USGS model and system can provide reliable transfer of calibration among instruments that have viewed the Moon as a common source. This capability will be enhanced with improvements to the USGS model absolute scale. Lunar calibration may prove essential to the critical calibration needs to cover a potential gap in observational capabilities prior to deployment of NPP/NPOESS. A key requirement is that current and future instruments observe the Moon.

In this paper, we study the feasibility of a method for vicarious calibration of the GOES Imager visible channel using the Moon. The measured Moon irradiance from 26 unclipped moon imagers exhausted all the potential Moon appearances between July 1998 and December 2005, together with the seven scheduled Moon observation data obtained after November 2005, were compared with the USGS lunar model results to estimate the degradation rate of the GOES-10 Imager visible channel. A total of nine methods of determining the space count and identifying lunar pixels were employed in this study to measure the Moon irradiance. Our results show that the selected mean and the masking Moon appears the best method. Eight of the nine resulting degradation rates range from 4.5%/year to 5.0%/year during the nearly nine years of data, which are consistent with most other degradation rates obtained for GOES-10 based on different references. In particular, the degradation rate from the Moon-based calibration (4.5%/year) agrees very well with the MODIS-based calibration (4.4%/year) over the same period, confirming the capability of relative and absolute calibration based on the Moon. Finally, our estimate of lunar calibration precision as applied to GOES-10 is 3.5%.

The NASA Ocean Biology Processing Group's Calibration and Validation Team has used monthly lunar calibrations of SeaWiFS to establish and maintain the on-orbit radiometric stability of instrument at the 0.1% level over its 9-year mission. The Cal/Val Team has compared the SeaWiFS lunar observations with the USGS ROLO photometric model of the Moon to verify the long-term stability of the SeaWiFS radiometric calibration. This stability has allowed the Team to apply a system-level vicarious calibration of the sensor/atmospheric calibration algorithm that is independent of time, yielding a single gain per band. SeaWiFS bands 1-6 (412-670 nm) are calibrated against water-leaving radiances measured by the Marine Optical Buoy (MOBY) that have been propagated to the top of the atmosphere. Band 7 (765 nm) is calibrated relative to band 8 (865 nm) so that the atmospheric correction algorithm selects maritime aerosol models over open ocean scenes. The long-term radiometric stability of SeaWiFS allows the Cal/Val Team to directly compare the mean residuals of the lunar observations from the ROLO model with the vicarious gains. A linear fit of the vicarious gains vs - (mean ROLO residual) for bands 1-6 gives a slope of 1.084 with a correlation of 0.980. The predicted mean ROLO residual for band 7, computed from the observed mean residual for band 8 and the vicarious gain for band 7, agrees with the observed mean residual for band 7 to within 0.5%. The radiometric stability of SeaWiFS allows the comparison of the prelaunch calibration of SeaWiFS, the calibration of MOBY, and the calibration of the USGS ROLO model. Such a comparison is of interest to other Earth-observing instruments which use the Moon as a calibration reference, such as MODIS, VIIRS, and ABI.

The Remote Sensing Group at the University of Arizona has successfully used various vicarious calibration methods for the absolute radiometric calibration of over 13 separate sensors since 2000 including nearly 40 sets of ground-based data collected at large uniform test sites imaged by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). The results from this work have been used to examine the VNIR and SWIR bands showing differences that exceed 10% in some bands. The current work extends the reflectance-based approach to the backward-looking telescope of the VNIR system of ASTER that is used for development of digital elevation models. The off-nadir band, Band 3B is identical to the NIR band of ASTER Band 3 except with a view of 23.5 degrees relative to the nadir-looking telescope. The study of Band 3B is done relative to Band 3 using the playa sites in California and Nevada as well as reflectance-based calibration approaches. The calibration of the nadir and off-nadir views agreed to better than 0.7% for five dates spanning 2000-2002 in the summer months at Ivanpah Playa. Other dates and sites showed differences much larger than can be explained by radiative transfer modeling and atmospheric effects pointing to a possible surface directional effect.

The Remote Sensing Group at the University of Arizona has been using reflectance-based vicarious calibration of earth-observing satellites since the 1980s. Among the sensors characterized by the group are the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and the MODerate Resolution Imaging Spectroradiometer (MODIS) that are both on NASA's Terra platform. The spatial resolution of MODIS requires that the group use a large-sized site such as Railroad Valley Playa, Nevada as a test site. In addition, the large footprint size of MODIS forced a modification to the ground-sampling scheme for the surface reflectance retrieval. This work examines the impact of the new sampling scheme through coincident ASTER and MODIS imagery making use of the higher resolution spatial resolution of ASTER. ASTER and MODIS imagery were obtained for dates on which both sensors imaged the Railroad Valley test site and ground-based data were collected at the site. The results of the comparison between the sensors shows differences in the radiometric calibration that exceed the accuracy requirements of the sensors, but that the sampling strategy for large-footprint sensors produces reflectance-based results at the same 3% level of accuracy as that for small-footprint sensors.

The recent deployment of on-orbit active sensors operating at optical wavelengths requires new calibration methods to be investigated. In response to this, a ground-based active radiometer for measuring backscattered surface reflectance has been developed by the Remote Sensing Group at the University of Arizona. This instrument, known as the reflectometer, was designed to match the illumination and detection geometry of spaceborne lidar systems. The reflectometer uses a Nd:YAG laser operating at 1064 nm (with the capability of 532 nm), illuminates the target sample at normal incidence by use of a beam expander and fold mirror, then collects the reflected light at nadir through an aperture in the fold mirror. In order to reduce stray light, a 3 nm bandwidth filter centered on the laser wavelength is mounted in front of the silicon detector and a half cylinder shell encloses the optical system. Previous measurements at White Sands Missile Range, NM have produced results that are within 3% of coincident measurements using a field spectrometer.¹ The results of these measurements are presented, including further laboratory testing using tarpaulin witness samples and future improvements of the original system design. In addition, comparison of reflectometer measurements to MODIS derived reflectance as it relates to on-orbit lidar retroreflection will be discussed. The benefits of validating MODIS derived reflectance will become essential with the launch of CALIPSO and its incorporation into the A-train.

Micro systems technology allows building ever-smaller systems. This has lead to many activities all over the world that are focused on building micro- and nano satellites. Most of these satellites are seen as technology qualifiers, meaning that they are used to prove that the developed technology can be used on board of spacecraft and can survive the launch environment. At this moment in time there is so much technology available and under development that one can start to think about building mature satellites on a micro scale (mature in the sense that the satellite can perform a scientifically or socially significant function). For satellites with an optical payload, a minimum aperture and baffle size are required, thus setting a minimum size for the satellite. The overall size of the satellite can be reduced by building the satellite around the instrument instead of building an instrument that is put on top of a satellite bus.

The combined performance of the Atmospheric Infrared Sounder (AIRS) and the Moderate Resolution Imaging Spectroradiometer (MODIS) on the Earth Observing System (EOS) Aqua spacecraft is possible in a single instrument with today's technology. Combining the capability allows better accuracy and resolution of products produced by both instruments. This paper describes the top level requirements expected from such an instrument, the types of products anticipated, and discusses technology readiness.

TROPOMI (Tropospheric Ozone-Monitoring Instrument) is a five-channel UV-VIS-NIR-SWIR non-scanning nadir viewing imaging spectrometer that combines a wide swath (114°) with high spatial resolution (10 × 10 km² ). The instrument heritage consists of GOME on ERS-2, SCIAMACHY on Envisat and, especially, OMI on EOS-Aura. TROPOMI has even smaller ground pixels than OMI-Aura but still exceeds OMI's signal-to-noise performance. These improvements optimize the possibility to retrieve tropospheric trace gases. In addition, the SWIR capabilities of TROPOMI are far better than SCIAMACHY's both in terms of spatial resolution and signal to noise performance. TROPOMI is part of the TRAQ payload, a mission proposed in response to ESA's EOEP call. The TRAQ mission will fly in a non-sun synchronous drifting orbit at about 720 km altitude providing nearly global coverage. TROPOMI measures in the UV-visible wavelength region (270-490 nm), in a near-infrared channel (NIR) in the 710-775 nm range and has a shortwave infrared channel (SWIR) near 2.3 μm. The wide swath angle, in combination with the drifting orbit, allows measuring a location up to 5 times a day at 1.5-hour intervals. The spectral resolution is about 0.45 nm for UVVIS- NIR and 0.25 nm for SWIR. Radiometric calibration will be maintained via solar irradiance measurements using various diffusers. The instrument will carry on-board calibration sources like LEDs and a white light source. Innovative aspects include the use of improved detectors in order to improve the radiation hardness and the spatial sampling capabilities. Column densities of trace gases (NO₂, O₃, SO₂ and HCHO) will be derived using primarily the Differential Optical Absorption Spectroscopy (DOAS) method. The NIR channel serves to obtain information on clouds and the aerosol height distribution that is needed for tropospheric retrievals. A trade-off study will be conducted whether the SWIR channel, included to determine column densities of CO and CH₄, will be incorporated in TROPOMI or in the Fourier Transform Spectrometer SIFTI on TRAQ. The TROPI instrument is similar to the complete TROPOMI instrument (UV-VIS-NIR-SWIR) and is proposed for the CAMEO initiative, as described for the U.S. NRC Decadal Study on Earth Science and Applications from Space. CAMEO also uses a non-synchronous drifting orbit, but at a higher altitude (around 1500 km). The TROPI instrument design is a modification of the TROPOMI design to achieve identical coverage and ground pixel sizes from a higher altitude. In this paper capabilities of TROPOMI and TROPI are discussed with emphasis on the UV-VIS-NIR channels as the TROPOMI SWIR channel is described in a separate contribution [5].

The Geostationary Operational Environmental Satellite-R (GOES-R), scheduled for launch in 2014, will be the first in a series of next generation weather satellites. It will be 3-axis stabilized in geostationary orbit, and will have an Advanced Baseline Imager (ABI) that can make full-Earth disk images, covering most of the Western Hemisphere, in spectral bands ranging from 0.47-13.3 μm. We are now designing a Full-Disk Ratioing Radiometer (FDRR) to determine the ratio of the full-disk irradiance to the solar irradiance in spectral bands that match the four shortest wavelengths of the ABI's Visible and Near IR (VNIR) spectral bands. When hard-mounted to the nadir face of a GOES-R satellite, this FDRR can determine the full-disk albedo in each band, with the added benefit that the ABI's corresponding channels can be calibrated by comparison of these measurements to the Earth's irradiance measurements derived from simultaneous full disk images made by the ABI. The FDRR uses an integrating sphere with two baffled pinholes. One pinhole has a baffle that restricts its field-of-view (FOV) to a circle 20.1° in diameter, centered at nadir, viewing the Earth's full disk continuously throughout its daily cycle. This baffle has a shutter that allows it to be closed for dark current measurements during the day and to prevent solar intrusion at night. The second pinhole, with a much smaller diameter, has a baffle that restricts its FOV to about 1° in the East-West direction and +/-25° in the North/South direction, allowing the direct solar irradiance to enter the sphere for a brief interval once each night. A radiationhardened fiber optic light pipe couples the output of the sphere to filters and detectors in an electronics box. These filters and detectors have spectral bands matched to those in the ABI. This technique measures the ratio of the full-disk irradiance to the direct solar irradiance, determining the Earth's albedo independent of the detector's response, the transmission of the filters and the fibers, and the sphere's reflectivity.

MIBS is a spectrometer operating in the thermal infrared wavelength region, designed in frame of the phase A study for the ESA EarthCARE mission as part of the multispectral Imaging instrument MSI, which uses a 2D microbolometer array detector in stead of the more common MCT detectors. Utilization of a microbolometer and using an integrated calibration system, results in a sensor with a size and mass reduction of at least an order of magnitude when compared to currently flying instruments with similar spectral resolution. In order to demonstrate feasibility a breadboard has been designed, which will be build and aligned in 2006 and will be ready for testing the forth quarter of 2006.

The Atmospheric Dynamics/Aeolus mission is the 4^th Earth Explorer mission of the Earth Observation Explorer Programme of the European Space Agency (ESA). Its objective is to measure vertical tropospheric profiles of horizontal wind speed components. These global observations of wind profiles from space will improve the quality of weather forecasts and advance our understanding of atmospheric dynamics and climate processes. The 1.3-ton, 1.4-kW Aeolus spacecraft uses an incoherent Doppler Wind lidar (ALADIN) to measure wind speed. It uses a tripled-frequency Nd:YAG laser emitting ultraviolet pulses at a repetition rate of 100 Hz, during a measurement period of 7 sec repeated every 28 sec. The return signal is detected with a double interferometric receiver composed of a Fizeau interferometer to detect the Mie signal scattered by aerosols and a double-edge Fabry-Perot interferometer to detect the Rayleigh signal scattered by atmospheric molecules. A custom-made accumulation CCD is used to detect and integrate the return photons over several laser pulses. The spacecraft has recently passed the CDR level and launch is planned for 2008. An airborne version of the ALADIN instrument has been made with equipment developed during the pre-development phase of the mission. An interferometric receiver with a high-level of representativity to the space receiver and a laser transmitter breadboard have been refurbished and complemented with a telescope, a co-alignment mechanism and custom control and processing electronics to produce the first airborne, direct-detection Doppler Wind lidar worldwide. The lidar was functionally tested in flight in October 2005 and will be used in ground and airborne campaigns in 2006 and 2007 to prepare the exploitation of the Aeolus space mission.

Multiple light taps in a plastic optical fiber provides a possibility of chemical sensing along its entire length. Unlike some point-by-point measurement techniques like fluorescence endoscopy, the technique described here makes it possible to sense large areas simultaneously and should be useful as an environmental chemical sensor.

The FPICC (Fabry-Perot Interferometer for Column CO₂) is a new instrument developed under the Instrument Incubator Program that uses a novel technique for measuring the absorption of CO₂ sunlight reflected from the Earth. The optical setup consists of three channels. The first channel is built to measure carbon dioxide by using a solid Fabry-Perot etalon to restrict the measurement to light in CO₂ absorption bands. The second and third channels focus on the O₂ A band (759-771 nm) composed of about 300 absorption lines, which vary in strength and width according to pressure and temperature. We performed measurements using solid Fabry-Perot etalons with different FSR and different pre-filters. We demonstrated the instrument's significant capability to detect CO₂ and O₂ in laboratory, as well as in ground based and airborne experiments. The initial tests indicate that when the instrument is used with a sun tracker the sensitivity for CO₂ detection is 2.1 ppm in one second average, and the sensitivity to the oxygen column pressure changes is as low as 0.88 mbar. The reduced sensitivity for the airborne experiments arises because the atmospheric scattering processes make the path length more variable and uncertain. One solution to this problem is to use the glint reflection from water surfaces. For this purpose we design and perform a theoretical study to build a different version of the FPICC instrument to be used on a satellite orbiting the Earth and working in a glint mode. This Fabry-Perot based technique is applicable to other species as well. For example one could use the FPICC instrument for fractionations measurements of the stable carbon isotope (¹³C/¹²C). The instrument can be used to study the atmosphere of Mars, which consists primarily of CO₂. A theoretical study and design of a version of the instrument for Mars for CO₂ and CH₄ measurements will be presented. We report results on the recent calibration of the instrument, recent data from ground tests at Goddard, design versions, and theoretical models for the Earth and Mars instruments.

The Total Irradiance Monitor (TIM) is a total solar irradiance radiometer on NASA's SORCE mission launched in 2003 and on the NASA/Glory mission launching in 2008. The primary sensors in TIM must absorb energy with accurately calibrated efficiency across the entire solar spectrum. To achieve high efficiency and good thermal conduction, the four sensors in each instrument are hollow conical silver cavities with a cylindrical entrance extension and a diffuse black nickel phosphorous (NiP) interior that converts absorbed incident radiation to thermal energy. A stable resistive heater wire embedded in the cone along with thermistors mounted on the cavity exterior are used in a temperature-sensing servo loop to measure the spectrally-integrated incident solar radiation. Characterization of the absorptance properties of the cavities across the solar spectrum is a dominant driver of instrument accuracy, and a dedicated facility has been developed to acquire these calibrations with uncertainties of approximately 50 ppm (0.005%). This paper describes the absorptance calibration facility, presents the preliminary cavity reflectance results for the Glory mission's TIM instrument, and details the uncertainty budget for measuring these cavity reflectances.

Aperture area knowledge is a primary calibration in radiometric instruments. Corrections for edge effects, particularly diffraction and scatter, must also be taken into account for high accuracy measurements. The Total Irradiance Monitor (TIM) is a total solar irradiance radiometer on NASA's SORCE mission launched in 2003 and on the NASA/Glory mission launching in 2008. In order to measure irradiance, the TIM instrument measures the total optical power that passes through circular diamond-turned precision apertures. The geometric areas of the 8-mm diameter apertures are measured to approximately 25 parts per million (ppm) at the National Institute of Standards and Technology [1]. Due to scatter and diffraction, not all light that passes through the geometric area of an aperture will enter the radiometer cavity of the instrument, and corrections must be made for these edge effects. Diffraction effects are generally well understood and are calculated from the instrument geometry. Scatter, on the other hand, is dependent on the microscopic edge quality of each individual aperture, and so must be measured. This paper describes the measurement of aperture edge diffraction and scatter for the precision apertures on NASA's Glory/TIM instrument.

In this paper we will demonstrate our fiber Bragg grating (FBG) accelerometer system in seismic wave detection applications. Optical fiber sensors using fiber Bragg grating have a number of advantages such as immune to electromagnetic interference, lightweight, and low power consumption. Most important, the FBG sensor has high sensitivity to dynamic strain signals and the strain sensitivity can approach sub micro-strain. The basic principle of the FBG seismic sensing system is that it transforms the acceleration of ground motion into the strain signal of the FBG sensor through mechanical design, and after the optical demodulation generates the analog voltage output proportional to the strain changes. The customized FBG seismic sensor prototype is described, which includes the electro-optical design, mechanical design and the hardware and software interface of the sensor system. The laboratory evaluation of the system is performed systematically on a commercial vibration stage. Studies of the sensor properties show that the sensor has a high sensitivity (2500 mV/g at 90 Hz) to the acceleration signal, a large dynamic range (80 dB), the good linearity and stability after device integration and packaging.

MODerate resolution Imaging Spectro-radiometer (MODIS) has been operated on-board the Terra spacecraft since December 18, 1999 and Aqua MODIS since May 4, 2002. Both MODIS Relative Solar Bands (RSBs) and Thermal Emissive Bands (TEBs) are calibrated on-orbit by a set of on-board calibrations (OBCs) in radiometric, spatial and spectral modes, providing accurate measurements for scientific researches. The Spectro-Radiometric Calibration Assembly (SRCA) is one of the key OBCs which can be operated at all three calibration modes. When operating in spectral mode, the SRCA is utilized for MODIS On-Orbit Spectral Characterization (MOOSC), monitoring and measuring the center wavelength (CW) shift of each RSB throughout the entire mission. However, some uncertainties in the SRCA measurement may affect the precision of the results due to possible system degradation, mechanical/optical backlash, deformation, and optical performance change. In this study, the instrument background and the algorithm for calculating the CW shift of RSBs using the SRCA measurements are briefly introduced. We analyze or estimate the impact on the final CW value caused by the uncertainties on the Terra MODIS on-orbit spectral characterizations, including cavity temperature variation, limited number of sample points, noise of background, and the variation of β and θ_off. The results show that the influence is small and the maximum uncertainty is less than 1nm. The lessons we learned in this study provide helpful information and experiences for the sensors which have no on-orbit spectral characterization capability and the useful guidance for the next generation satellite remote sensors.

MODerate resolution Imaging Spectro-radiometer (MODIS), as part of NASA's Earth Observe System (EOS) mission, is widely utilized in diversified scientific research areas. Both Terra and Aqua MODIS observe the earth in sun-synchronous orbit at three nadir spatial resolutions. MODIS has thirty-six bands that are located in four Focal Plane Assembles (FPAs) by wavelength: Visible (VIS), Near-Infrared (NIR), Short-and Middle-wavelength IR (SMIR), and Long wavelength IR (LWIR). MODIS Band-to-Band Registration (BBR) was measured pre-launch at the instrument vendor. Mis-registration exists between bands and FPAs. The spatial characterization could change in storage, at launch, and years on-orbit. In this study, a special ground scene with unique features has been selected as our study area to calculate the spatial registration in both along-scan and along-track for bands 2 - 7 relative to band 1. The results from the earth scene targets have been compared with on-board calibrator, the Spectro-Radiometric Calibration Assembly (SRCA), with good agreement. The measured differences between the SRCA and our ground scene approach are less than 20m on average for VIS/NIR bands both along-scan and along-track. The differences for SMIR bands are 20m along-scan and 0.1 - 0.18 km for along track. The SMIR FPA crosstalk could be a contributor to the difference. For Aqua MODIS instruments, the spatial deviation is very small between the bands located on the same FPA or between VIS and NIR FPAs but is relatively large between warm (VIS and NIR) and cold (SMIR and LWIR) FPAs. The spatial deviation for MODIS/Terra can be ignorable but not for MODIS/Aqua. The results from this study show that the spatial deviation of Aqua MODIS may impact on the science data when multi-band data from both warm and cold FPAs is combined.