This PDF file contains the front matter associated with SPIE Proceedings Volume 6677, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

The SSULI (Special Sensor Ultraviolet Limb Imager) is a low-resolution hyperspectral far- and extreme-ultraviolet limb-scanning imager designed to monitor ionospheric and thermospheric airglow. SSULI has a spectral range from 80 to 170 nm, and a nominal resolution of 2.1 nm (at 147 nm). The instrument is scheduled to fly aboard all DMSP Block 5D3 weather satellites. The first SSULI instrument was launched in fall 2003, aboard DMSP F16, and has been collecting data since December 2003. The second SSULI flight aboard DMSP F17 began in fall 2006. On the ground, the SSULI instruments are calibrated using a monochromator to isolate single emission features of interest produced by a gas discharge lamp, whereas the flight spectra consists of numerous overlapping emissions. The determination of individual emission feature contribution against the entire airglow spectrum is determined using the multiple linear regression technique with basis functions defining each observable emission. The accuracy of the emission extraction depends primarily on the ability to model the characteristics of the instrument line-shape, encompassing both optical and electronic effects. In the course of developing the ground calibration algorithms, we are now able to produce line-shapes much more faithful to the observed calibration features, as well as model instrument characteristics such as scattered light and detector background components. This improved instrument characterization can then be passed to the operational orbital emission extraction software to increase the fidelity of retrieved altitude profiles for observed ultraviolet emissions. In addition, the techniques used with the ground calibration can monitor deviations in line-shape and instrument sensitivity as a function of observed count rate, and these modified line-shapes can also be passed to the ground analysis software. Validation of this method using SSULI 003 and 004 ground calibration data will be presented.

The presence of structures, as observed in real data from earth observing satellites, that are due to the on-board diffusers are discussed. These structures are shown to be caused by the speckles created by the diffusers in the entrance slit of the spectrometer. A dedicated set-up for the study of these spectral features will be presented together with results on different types of diffusers, i.e. surface diffusers and volume diffusers. Finally, methods to reduce the amplitude of the spectral features will be presented. These methods become more important since the use of infra red channels at high spectral resolutions is aimed for in future missions.

Onboard diffuse reflecting plaques are carried to orbit as radiometric reference standards for Earth-observing satellite instruments. For many instruments the reflectance properties of the plaque are characterized independently of the instrument, and the effects of scattering by the diffuser housing are determined through mathematical modeling. The pre-launch laboratory calibration of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) included a system-level calibration of the onboard diffuser using an external lamp and a reference plaque at the sensor's Earth-view port. The calibration of the onboard diffuser was made relative to the reference plaque using SeaWiFS as a transfer radiometer. Recent developments in laboratory light sources enable a significant improvement to the SeaWiFS calibration technique. These include sets of fiber-optically coupled tunable lasers that illuminate integrating spheres or the prime focus of a collimator, to produce uniform, high radiant flux Lambertian or collimated sources, respectively. In addition, newly developed, spectrally tunable supercontinuum-based light sources can provide sets of radiance spectra for the collimator to validate the laser-based diffuser calibration. An absolute calibration of the diffuser system in the laboratory also provides the first step in a two-part transfer-to-orbit experiment, in which the second step uses the illumination of the diffuser on orbit by the Sun. For hyperspectral instruments, the laboratory calibration must account for spectral artifacts in the diffuser material. For on-orbit measurements, the calibration must account for the effects of Earth-shine as a contaminating source of irradiance illuminating the diffuser.

Earth-observing satellite sensors are calibrated in the laboratory against blackbody and lamp-based uniform optical radiation standards. These sources and additional characterization tests fail to approximate the spatially, spectrally, and temporally complex scenes viewed on-orbit by these sensors. The lack of appropriate diagnostic tools limits the ability of researchers to fully characterize and understand the radiometric performance of sensors before deployment. The consequences of these limitations are that problems in a sensor's performance, e.g. optical crosstalk, scattered light, earth-shine, are often first observed on-orbit. Advanced radiometric characterization artifacts, able to produce realistic spectral distributions and spatial scenes in the laboratory, would enable more complete instrument characterization, with the resulting potential benefit of improved on-orbit performance.

An application-specific contracted integrating sphere source of uniform spectral radiance is described. The source is used for pre-launch test and calibration of imaging radiometers which will be used as satellite borne earth remote sensors. The calibration source is primarily intended to serve as a transfer standard of radiance. Design criteria for the uniform radiance source are presented. Included is a summary of the end-user specifications in regards to spectral radiance, radiance levels of attenuation, radiance stability, and aperture uniformity. Radiometric theory used to predict the source radiance for a specific spectral flux input is reviewed. Reasoning for the use of an integrating sphere platform for this application and characteristic features of the source are discussed. Calibration methods and instrumentation are described. The resultant data presented include the modeled data compared with the measured performance. Methods of data reduction and uncertainty are addressed where applicable.

Historically, the traceability of the laboratory calibration of Earth-observing satellite instruments to a primary radiometric reference scale (SI units) is the responsibility of each instrument builder. For the NASA Earth Observing System (EOS), a program has been developed using laboratory transfer radiometers, each with its own traceability to the primary radiance scale of a national metrology laboratory, to independently validate the radiances assigned to the laboratory sources of the instrument builders. The EOS Project Science Office also developed a validation program for the measurement of onboard diffuse reflecting plaques, which are also used as radiometric standards for Earth-observing satellite instruments. Summarized results of these validation campaigns, with an emphasis on the current state-of-the-art uncertainties in laboratory radiometric standards, will be presented. Future mission uncertainty requirements, and possible enhancements to the EOS validation program to ensure that those uncertainties can be met, will be presented.

A comparison of the area measurements of the limiting apertures used for total solar irradiance measurements in the Active Cavity Radiometer Irradiance Monitor II (ACRIM II) and Active Cavity Radiometer Irradiance Monitor III (ACRIM III) were conducted between the National Institute of Standards and Technology (NIST) and the Jet Propulsion Laboratory (JPL). The ACRIM apertures, due to their unique size and design, necessitated modifications to the NIST aperture measurement system. The changes and the validation procedures undertaken are described in this paper. This is part of an Earth Observing System (EOS)-sponsored international comparison of aperture area measurements of apertures that have institutional heritage with historical solar irradiance measurements.

The total solar irradiance (TSI) climate data record includes overlapping measurements from 10 spaceborne radiometers. The continuity of this climate data record is essential for detecting potential long-term solar fluctuations, as offsets between different instruments generally exceed the stated instrument uncertainties. The risk of loss of continuity in this nearly 30-year record drives the need for future instruments with <0.01% uncertainty on a absolute scale. No facility currently exists to calibrate a TSI instrument end-to-end for irradiance at solar power levels to these needed accuracy levels. The new TSI Radiometer Facility (TRF) is intended to provide such calibrations. Based on a cryogenic radiometer with a uniform input light source of solar irradiance power levels, the TRF allows direct comparisons between a TSI instrument and a reference cryogenic radiometer viewing the same light beam in a common vacuum system. We describe here the details of this facility designed to achieve 0.01% absolute accuracy.

The Visible/Infrared Imager/Radiometer Suite (VIIRS) collects visible/infrared imagery and radiometric data. The radiometric requirements are such that the instrument's polarization sensitivity must be very well understood. This paper presents the ZEMAX and FORTRAN polarization ray trace models of the instrument's visible light path. This will include the measured optical surface reflectance data, the band pass shapes and a comparison of the results of the two models.

The advent of large telescopes for remote sensing presents special challenges for optical testing, particularly for verifying focal plane array alignment. If testing in air, the large well-enclosed telescope cavity can create air stagnation or thermal gradient effects that can distort the optical wavefront unpredictably, resulting in noisy and inaccurate measurements. Testing in vacuum presents instrumentation challenges but eliminates the air effects and provides excellent data. This paper describes the experimental setups and compares through-focus test results for a large remote sensing telescope when tested in both air and in a vacuum.

Spectrometers that include extended-range linear InGaAs arrays make it possible to measure optical signals to 2500 nm. Available arrays, however, have more than 100 times the dark current as that of conventional arrays, which are limited to 1700 nm. This behavior leads to non-linearity in a short-wave infrared spectroradiometer used to monitor spectral radiance of an integrating sphere uniform source. A method of improving linearity in an extended-range InGaAs array is presented. The non-linearity is corrected using a multi-point calibration at a number of lamp power levels whereby the calibration factor for each wavelength point depends on the lamp power in the integrating sphere. An algorithm in the spectroradiometer software chooses the correct calibration factors and reports the system spectral radiance values accordingly. This method reduced error by more than a factor of two.

The Moon has been shown to be an extremely stable radiometric reference for calibration and long-term stability measurements of on-orbit sensors. The majority of previous work has been in the visible part of the spectrum, using ground-based lunar images. The SOLar-STellar Irradiance Comparison Experiment (SOLSTICE) on the SOlar Radiation and Climate Experiment (SORCE) can be used to extend the lunar spectral irradiance dataset to include the 115-300 nm range. SOLSTICE can directly measure both the solar and lunar spectra from orbit, using the same optics and detectors. An observing campaign to map out the dependence on phase angle began in mid 2006, and continues through the present. The geometry of SORCE's orbit is very favorable for lunar observations, and we have measurements of almost the entire 0-180 degree range of phases. In addition to Earth Observing Systems using the Moon for calibration, recent planetary missions have also made ultraviolet observations of the Moon during Earth flyby, and these SOLSTICE measurements can be useful in calibrating their absolute responsivity.

The NASA Ocean Biology Processing Group's Calibration and Validation (Cal/Val) Team has used SeaWiFS onorbit lunar and gain calibration data, in conjunction with mission-long trends of global ocean color data products, to diagnose and correct recently emergent residual drifts in the radiometric response of the instrument. An anomaly analysis of the time series of global mean normalized water-leaving radiances, the atmospheric correction parameter ∈, and chlorophyll show significant departures from the mission-long trends beginning in January 2006. The lunar time series trends for the near infrared (NIR) bands (765 nm and 865 nm) show significant periodic departures from mission-long trends beginning at the same time. ∈ is dependent on the ratio of these two bands; trends in this parameter would propagate through the atmospheric correction algorithm to the retrieved water-leaving radiances. An analysis of fit residuals from the lunar time series shows that the focal plane temperature dependencies of the radiometric response of the detectors for these two bands have changed over the 9+ year mission. The Cal/Val Team has used these residuals to compute a revised set of temperature corrections for data collected starting 1 January 2006. The lunar calibration data and a mission-long ocean color test data set have been reprocessed with the revised temperature corrections. The reprocessed data show that the trends in the NIR bands have been minimized and that the departures of the water-leaving radiances, ∈, and chlorophyll from the mission-long trends have been greatly reduced. The anomaly analysis of the water-leaving radiances in the 510 nm band still shows a residual drift of -2.9% over the mission. The anomaly analysis of the ∈ time series shows a residual drift of +2.8% over the mission. A corresponding drift is not observed in the lunar calibration time series for the NIR bands. The lunar calibration data are obtained at a different set of instrument gains than are the ocean data. An analysis of the mission-long time series of on-orbit gain calibration data shows that the gain ratios for the NIR bands change -0.76% (765 nm) and +0.56% (865 nm) over the mission, corresponding to a -1.3% drift in the band ratio. The lunar calibration time series for the NIR bands have been corrected for this gain drift, and the change in radiometric response over time has been recomputed for each band. The mission-long ocean color test data set has been reprocessed with these revised corrections for the NIR bands. The anomaly analysis of the reprocessed water-leaving radiances at 510 nm shows the drift to have been essentially eliminated, while the anomaly analysis of epsilon shows a reduced drift of +2.0%. These analyses show the sensitivity of ocean color data to small drifts in instrument calibration and demonstrate the use of time series of global mean geophysical parameters to monitor the long-term stability of the instrument calibration on orbit. The two updates to SeaWiFS radiometric calibration have been incorporated into the recent reprocessing of the SeaWiFS mission-long ocean data set.

The Landsat archive provides more than 35 years of uninterrupted multispectral remotely sensed data of Earth observations. Since 1972, Landsat missions have carried different types of sensors, from the Return Beam Vidicon (RBV) camera to the Enhanced Thematic Mapper Plus (ETM+). However, the Thematic Mapper (TM) sensors on Landsat 4 (L4) and Landsat 5 (L5), launched in 1982 and 1984 respectively, are the backbone of an extensive archive. Effective April 2, 2007, the radiometric calibration of L5 TM data processed and distributed by the U.S. Geological Survey (USGS) Center for Earth Resources Observation and Science (EROS) was updated to use an improved lifetime gain model, based on the instrument's detector response to pseudo-invariant desert site data and cross-calibration with the L7 ETM+. However, no modifications were ever made to the radiometric calibration procedure of the Landsat 4 (L4) TM data. The L4 TM radiometric calibration procedure has continued to use the Internal Calibrator (IC) based calibration algorithms and the post calibration dynamic ranges, as previously defined. To evaluate the "current" absolute accuracy of these two sensors, image pairs from the L5 TM and L4 TM sensors were compared. The number of coincident image pairs in the USGS EROS archive is limited, so the scene selection for the cross-calibration studies proved to be a challenge. Additionally, because of the lack of near-simultaneous images available over well-characterized and traditionally used calibration sites, alternate sites that have high reflectance, large dynamic range, high spatial uniformity, high sun elevation, and minimal cloud cover were investigated. The alternate sites were identified in Yuma, Iraq, Egypt, Libya, and Algeria. The cross-calibration approach involved comparing image statistics derived from large common areas observed eight days apart by the two sensors. This paper summarizes the average percent differences in reflectance estimates obtained between the two sensors. The work presented in this paper is a first step in understanding the current performance of L4 TM absolute calibration and potentially serves as a platform to revise and improve the radiometric calibration procedures implemented for the processing of L4 TM data.

The Thematic Mapper (TM) is a multi-spectral electro-optical sensor featured onboard both the Landsat 4 (L4) and Landsat 5 (L5) satellites. TM sensors have seven spectral bands with center wavelengths of approximately 0.49, 0.56, 0.66, 0.83, 1.65, 11.5 and 2.21 μm, respectively. The visible near-infrared (VNIR) bands are located on the primary focal plane (PFP), and two short-wave infrared (SWIR) bands and the thermal infrared (TIR) band are located on the cold focal plane (CFP). The CFP bands are maintained at cryogenic temperatures of about 91 K, to reduce thermal noise effects. Due to the cold temperature, an ice film accumulates on the CFP dewar window, which introduces oscillations in SWIR and an exponential decay in TIR band responses. This process is usually monitored and characterized by the detector responses to the internal calibrator (IC) lamps and the blackbody. The ice contamination on the dewar window is an effect of the sensor outgassing in a vacuum of the space environment. Outgassing models have been developed, which are based on the thin-film optical interference phenomenon. They provide the coefficients for correction for outgassing effects for the entire mission's lifetime. While the L4 TM ceased imaging in August 1993, the L5 TM continues to operate even after more than 23 years in orbit. The process of outgassing in L5 TM is still occurring, though at a much lower rate than during early years of mission. Although the L4 and L5 TM sensors are essentially identical, they exhibit slightly different responses to the outgassing effects. The work presented in the paper summarizes the results of modeling outgassing effects in each of the sensors and provides a detailed analysis of differences among the estimated modeling parameters. For both sensors, water ice was confirmed as a reasonable candidate for contaminant material, the contaminant growth rate was found to be gradually decreasing with the time since launch, and the indications exist that some film may remain after the CFP warm-up procedures, which are periodically initiated to remove accumulated contamination. The observed difference between the models could be contributed to differences in the operational history for the sensors, the content and amount of contaminant impurities, the sensor spectral filter responses, and the internal calibrator systems.

The CERES Flight Models 1 through 4 instruments were launched aboard NASA's Earth Observing System (EOS) Terra and Aqua Spacecraft into 705 Km sun-synchronous orbits with 10:30 a.m. and 1:30 p.m. equatorial crossing times. These instruments supplement measurements made by the CERES Proto Flight Model (PFM) instrument launched aboard NASA's Tropical Rainfall Measuring Mission (TRMM) spacecraft on November 27, 1997 into a 350 Km, 38-degree mid-inclined orbit. The archived CERES Science data products consist of geolocated and calibrated instantaneous filtered and unfiltered radiances through temporally and spatially averaged TOA, Surface, and Atmospheric fluxes. CERES filtered radiance measurements cover three spectral bands including shortwave (0.3 to 5 micron), total (0.3 to <100 micron) and an atmospheric window channel (8 to 12 micron). Earth Radiation Budget measurements made by the CERES represent a new era in radiation climate data. CERES climate data products realize a factor of 2 to 4 improvement in calibration accuracy and stability over the previous ERBE products. This improvement is derived from two sources: incorporation of lessons learned from the ERBE mission and the development of a rigorous and comprehensive radiometric validation protocol which consists of studies covering different spatial, spectral and temporal time scales on data collected both pre and post launch. This approach has resulted in unprecedented levels of accuracy for radiation budget data products with calibration stability of better than 0.2% and calibration traceability from ground to flight of 0.25%. The current work summarizes the status of the radiometric accuracy and stability of the CERES Edition2 Level 1 data products.

The Clouds and the Earth's Radiant Energy System (CERES) is the only project currently measuring the global Earth Radiation Budget (ERB) from space. Two CERES instruments are located on the EOS Terra platform and two more are placed on the EOS Aqua satellite. One more CERES unit provided 8 months of ERB data in 1998 from the TRMM platform. Each of the CERES devices uses three broadband radiometric scanning telescopes: the shortwave (SW 0.3 → 5μm), Total (0.3 → 100μm), and window (8 → 12μm) channels. Rigorous pre-launch ground calibration is performed on each CERES unit to achieve an accuracy goal of 1% for Short Wave (SW) and 0.5% for outgoing Long Wave (LW) radiance. Any ground to flight or in-flight changes in radiometer response is monitored using onboard calibration sources. For the total and window channels these take the form of concentric groove blackbodies, while the SW channels use stable tungsten lamps. Recent studies have shown that the SW response of space based broadband radiometers can change dramatically due to optical contamination. With these changes having most impact on optical response to blue-UV radiance, where tungsten lamps are largely devoid of output, such changes are hard to monitor accurately using existing on-board sources. This study details an attempt to use the vicarious stability metric of deep convective clouds (DCC), nighttime LW scenes and a newly developed SW optical darkening model to place all CERES instrument measurements on the same radiometric scale. The results show that scene dependant dispersion in nadir comparisons between instruments on the same satellite are significantly reduced. Also the suggestion is that the pre-flight contamination of the CERES instruments may require an increase in Terra and Aqua measured SW flux. A larger necessary increase in Aqua SW flux is believed to be due to greater pre-flight contamination of the CERES Aqua optics.

Accurate estimation of measurement noise in remote sensing instruments is critically important for the retrieval of geophysical quantities and the analysis of bias and trends. It is difficult to estimate noise directly from observed scene data because it is a combination of many sources, including instrument quiescent noise, scene inhomogeneity and random background fluctuations. Multiple datasets can be used to separate the instrument and scene noise. A noise estimate based on staring at cold space or a calibration source constitutes a lower limit, while noise estimates derived from the difference between scene observations and a model (such as forecast) convolves the true noise with the model uncertainty. Ideally, noise should be estimated directly from the observation of the scene. We have developed a Bayesian hierarchical model to jointly estimate the scene noise, instrument noise and instrument biases from sets of overlapping footprints. Informative prior distributions are constructed from pre-launch test results and inference is done by using Gibbs sampling to sample from the posterior distribution of the instrument parameters. We demonstrate this model by estimating and comparing the relative noise and bias of the Atmospheric InfraRed Sounder (AIRS) instrument on board the Aqua platform to the Tropospheric Emission Spectrometer (TES) aboard the Aura platform over the tropical latitudes using the Real-time, global, sea surface temperature (RTG-SST) analysis as a ground truth.

RADARSAT-1 ScanSAR SWA images of Hurricane Katrina are used to retrieve the surface wind vectors over the ocean. Due to the inadequate spatial resolution of the ScanSAR SWA images, the spectrum method cannot be implemented to estimate the wind direction. Instead, collocated H*wind wind directions are used as wind direction estimates. The wind speed is derived from the σ° by inversion of a C-band HH-polarization Geophysical Model Function (GMF), which is derived from C-band VV-polarization GMF using a polarization ratio model. Because existing polarization models don't fit the ScanSAR SWA data well, a recalibration model is proposed to "recalibrate" the ScanSAR SWA images. The coefficients of the recalibration model are "tuned" using collocated H*wind surface wind fields. To validate the SAR-retrieved wind speed, the mean and the RMS difference between SAR-retrieved and H*wind wind speed estimates are calculated. The mean of difference is small and the RMS for wind speed less than 25 m/s is below 4 m/s, suggesting that the high resolution wind retrieval algorithm can work under hurricane conditions. Except for the influence from rain, the largest errors occur at high wind speed (over 25 m/s), which is mainly due to the saturation of the C-band GMF CMOD5.

MODIS is a cross-track scanning radiometer that makes solar reflective and thermal emissive observations. It has 16 thermal emissive bands (TEB), a total of 160 individual detectors (10 for each spectral band), with wavelengths in the mid-wave infrared (MWIR) and long-wave infrared (LWIR) spectral regions. They are located on two cold focal plane assemblies (CFPA). MODIS TEB detectors were fully characterized pre-launch in a thermal vacuum (TV) environment using a laboratory blackbody calibration source (BCS) at temperatures from 170 to 340K. On-orbit the TEB detectors are calibrated using an on-board blackbody (BB). For nominal on-orbit operation, the on-board BB temperature is controlled at 290K for Terra MODIS and 285K for Aqua MODIS. Each TEB detector's noise equivalent temperature difference (NEdT) is often used to assess its on-orbit performance since this parameter is a key contributor to the calibration uncertainty. Because of its importance, the MODIS TEB detector NEdT is monitored on a daily basis at a fixed BB temperature and fully characterized on a regular basis at BB temperatures from 270 to 315K. In this paper, we describe MODIS TEB NEdT characterization activities, approaches, and associated results. We compare both prelaunch and on-orbit performance with sensor design specifications and examine the impact of detector noise characterization on the TEB calibration uncertainty. For general science applications and future reference purposes, a complete summary of TEB noisy detectors, identified pre-launch and on-orbit, is provided. Since launch in December 1999 and May 2002, Terra and Aqua MODIS have operated for more than 7 and 5 years, respectively. To date, 138 Terra MODIS TEB detectors and 158 Aqua MODIS TEB detectors continue to meet the sensor design NEdT requirements and enable high quality observations.

The Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on the Terra and Aqua satellites have been operating since 2000 and 2002, respectively. To date both instruments have demonstrated good calibration stability for the Thermal Emissive Bands (TEB). Maintaining calibration accuracy is an important issue, as the instrument age, for continued production of high quality science data. In this paper a strategy to track the stability of MODIS TEB measurements from launch to present using a cold ground target is discussed. The land surface in the area surrounding Dome Concordia, Antarctica (75.1 S, 123.4 E) is well characterized and stable in terms of surface temperature and emissivity. A research station at Dome Concordia provides a record of climate variables and the opportunities for satellite validation field campaigns. Both MODIS instruments overpass the site 7-10 times per day, including a near-nadir overpass once every 2-3 days. The long-term data record of near-nadir Dome Concordia MODIS TEB measurements is analyzed relative to the measurements of ground-based (Automated Weather Station) and other satellite (e.g. Atmospheric Infrared Sounder (AIRS)) sensors. This approach allows for the detection of any long-term calibration drift and the calibration consistency between Aqua and Terra MODIS. Additionally, a method to correct the observed cold scene bias for Aqua MODIS versus AIRS is discussed.

During the Tahoe 2006 field effort, the NASA ER-2 aircraft flew 2 nighttime science missions (September 29 and October 13, 2006) over California and the nearby Pacific Ocean. Because of its high cruising altitude (above ~95% of the atmosphere), the ER-2 platform closely simulates satellite-based observations of the earth-atmosphere system. Each Tahoe 2006 mission included overpasses of the Lake Tahoe Validation Network and an underflight of the Aqua satellite. An 8+ minute ER-2 flight segment of clear sky data over the Pacific Ocean on the October 13 flight has been used to assess the MODIS thermal band (bands 20-36) radiometric performance. For the assessment MODIS radiances are simulated using the MAS high spatial resolution and SHIS high spectral resolution radiances (the calibration backbone of the MODIS assessment), and compared to the co-located MODIS observations. The assessment (286 matchups) shows that Aqua MODIS thermal bands continue to perform within or very nearly within their 1% radiometric specification (0.5% for window bands 31, 32; 0.75% for window band 20) with the exception of band 30 (ozone) and band 36 (CO₂). There is low confidence in the ozone band 30 assessment due to lack of information on the ozone profile above the ER-2 flight level; band 36 however, appears to be consistently about 0.7 K warmer than expected. These results are consistent with a previous Aqua MODIS comparison to SHIS and MAS in 2002 and with previously reported1 comparisons of Aqua AIRS and MODIS observations.

MODIS has 20 reflective solar bands (RSB) that are calibrated on-orbit using a solar diffuser (SD) and a solar diffuser stability monitor (SDSM). The MODIS SD bi-directional reflectance factor (BRF) was characterized pre-launch. Its on-orbit degradation is regularly monitored by the SDSM at wavelengths ranging from 0.41 to 0.94μm. During each SD/SDSM calibration event, the SDSM views alternately the sunlight directly through a fixed attenuation screen and the sunlight diffusely reflected from the SD panel. The time series of SDSM measurements (ratios of the SD view response to the Sun view response) is used to determine the SD BRF degradation at SDSM wavelengths. Since launch Terra MODIS has operated for more than seven years and Aqua for over five years. The SD panel on each MODIS instrument has experienced noticeable degradation with the largest changes observed in the VIS spectral region. This paper provides a brief description of MODIS RSB calibration methodology and SD/SDSM operational activities, and illustrates the SD on-orbit degradation results for both Terra and Aqua MODIS. It also discusses the impact on the SD degradation due to sensor operational activities and SD solar exposure time. Aqua MODIS has been operated under nearly the same condition for more than five years. Its SD annual degradation rate is estimated to be 2.7% at 0.41μm, 1.7% at 0.47μm, and less than 1.0% at wavelengths above 0.53μm. Terra MODIS, on the other hand, has experienced two different SD solar exposure conditions due to an SD door (SDD) operation related anomaly that occurred in May 2003 that had led to a decision to keep the SDD permanently at its "open" position. Prior to this event, Terra MODIS SD degradation rates were very similar to Aqua MODIS. Since then its SD has experienced much faster degradation rates due to more frequent solar exposure.

The MODIS (Moderate Resolution Imaging Spectroradiometer) scanner makes subframe measurements in some of its bands to increase the spatial resolution from its standard 1km resolution to 500m or 250m. This is achieved by sampling a detector of a high resolution band at twice (or four times) the sampling rate of the 1km bands. This paper shows that a calibration equation nonlinear with radiance and specific to the individual subframes will reduce striping in the images. The effects are significant for low radiance levels like those encountered over ocean scenes. A preliminary calibration correction is derived with two approaches: first from prelaunch measurements, then from on-orbit data. The results of the two methods are qualitatively similar.

The Moderate Resolution Imaging Spectroradiometer (MODIS) is currently flying on both the Terra and Aqua satellite platforms. The Ocean Biology Processing Group (OBPG) at NASA Goddard Space Flight Center is producing operational ocean color products from the MODIS-Aqua sensor; however, documented uncertainties and instabilities in the prelaunch and on-orbit characterization have inhibited the production of similar products from MODIS-Terra. In particular, the radiometric response of the 412-nm band has degraded by more than 40% over the 7-year mission lifespan, with similar though less extreme changes in the longer wavelengths. Furthermore, the degradation trends are significantly different between the two mirror sides, which is likely a result of asymmetric damage done to the mirror during prelaunch testing. These effects contribute to uncertainty in our knowledge of instrument response versus incidence angle on the mirror and sensitivity with respect to polarization of the observed radiance. In this paper, we examine the impact of apparent MODIS-Terra instrument characterization errors on the derived ocean color products and show that residual errors in the current operational calibration give rise to significant cross-scan artifacts, mirror-side differences, and detector-to-detector striping in the retrieved water-leaving radiances. In addition, we describe OBPG efforts to reduce these artifacts through statistical and vicarious instrument characterization, and show the quality of the resulting water-leaving radiance retrievals relative to those derived from MODIS-Aqua.

The MODIS scan mirror reflectance is a function of angle of incidence (AOI). For the MODIS solar reflective bands (RSB), it is specified that the calibrated response variation versus scan angle (RVS) should be less than 2% and the uncertainty of the RVS characterization should be less than 0.5% within the scan angle range of -45° ~ +45°. During MODIS pre-launch RVS calibration and characterization, a series of laboratory tests were performed to assess the relative response versus scans angle for all MODIS bands. Utilizing a Spherical Integrating Source, SIS, as an illumination source, the test data was collected at various angles of incidence. The characterization of the RVS included a measurement uncertainty assessment, repeatability analysis, RVS modeling and determination. The results show good repeatability on the order of less than 0.5% for all the near infrared (NIR) bands and the visible (VIS) bands. The detector response variation across scan angles for the majority of the NIR and VIS bands meets the instrument specification. The derived RVS model enabled appropriate implementation of on orbit calibration. This paper summarizes the methodologies and the algorithms used in the MODIS pre-launch RVS calibration for the RSB bands, illustrates detector response variation with scan mirror angle of incidence, and demonstrates instrument specification compliance within the scan angle coverage of ±55 degree. As a result, the RVS model and the correction coefficients developed in the pre-launch calibration have been adopted during the MODIS on-orbit calibration.

This paper provides a comprehensive list of prime candidate terrestrial targets for consideration as benchmark sites for the post-launch radiometric calibration of space-based instruments. The key characteristics of suitable sites are outlined primarily with respect to selection criteria, spatial uniformity, and temporal stability. The establishment and utilization of such benchmark sites is considered to be an important element of the radiometric traceability of satellite image data products to SI standards for use in the accurate monitoring of environmental change.

The University of Arizona has recently deployed a set of automated, downlooking radiometers to retrieve surface reflectance of the Railroad Valley test site in Nevada. Results from these radiometers have been combined with atmospheric data from the same site to provide a reflectance-based, vicarious calibration of multiple sensors. The accuracy of the calibrations is similar to those obtained from on-site personnel. Past work has emphasized near-nadir views by the satellite sensors under study to match more closely the view geometry of the automated radiometers to minimize the effect of bi-directional effects in the surface reflectance. Extension to off-nadir views requires an accurate understanding of the surface BRDF. Surface bi-directional reflectance effects have always played a key role in the accuracy of the vicarious calibration of imaging sensors. Such effects are especially important for the large, off-nadir views of sensors such as AVHRR and MODIS. The current work presents a method for retrieving the BRDF using the nadir-viewing data from the automated radiometers throughout the day. The concept of reciprocity is used to derive the reflectance as a function of view angle based on the measurements as a function of solar zenith angle. Comparisons of the results from this approach are compared to MODIS-derived BRDF data as well as ground-based measurements.

A preferred method of ground-based vicarious calibration is the reflectance-based approach, which requires personnel to be present at a test site during sensor overpass. The Remote Sensing Group at the University of Arizona developed an instrumentation suite and methodology in 2004 to measure the surface and atmospheric characteristics in the absence of personnel. Field campaigns typically occur at a rate of once per month during the academic year, and increase during the summer months. The automated approach allows data to be collected during every overpass of large-footprint sensors such as Terra and Aqua MODIS, and AVHRR, which are continuously collecting data. The large-footprint-sensor site at Railroad Valley is 1 km². In the absence of personnel, the surface bidirectional reflectance factor is measured using five nadir-viewing radiometers that are currently located at the site. Their locations are chosen based on the topography of the site in an effort to "completely" sample the 1-km² area. This work quantifies the uncertainty in predicting the surface reflectance of the 1-km² area based on the point measurements of the automated methodology. It also determines if the number of radiometers, and their positions, are suitable to characterize the site in a spatial sense. These uncertainties are determined through the use of portable spectroradiometers, and high-spatial-resolution QuickBird imagery.

A new method of performing vicarious calibration of Visible-Near Infrared (VNIR) sensors has been developed which does not require the manual efforts of a field team to capture surface and atmospheric measurements. Instead, an array of unattended sensors captures the required data on a near continuous basis for recording to a web-based retrieval system. The LSpec (LED Spectrometer) facility, located at Frenchman Flat at the Nevada Test Site, began initial operations in November 2006. The LSpec sensors measure surface reflectance at several VNIR bands, and the accompanying atmospheric measurements allow the production of top-of-atmosphere radiance estimates to calibrate space-borne sensor products. Data are distributed via the Internet, and are available to the calibration community. This paper describes the test site, web-access to the data, and makes use of these data to compute top-of-atmosphere radiance (TOA) and compare to those from the Multi-angle Imaging SpectroRadiometer (MISR) imagery.

We have designed, built, and calibrated a transfer radiometer for the VNIR region of the optical spectrum. The instrument is based on a "trap" detector configuration of large-area silicon detectors. The spectral bandpass of the nine bands between about 410 and 1050 nm is set by interference filters. This paper presents the design, characterization, and calibration of the radiometer.

The Remote Sensing Group (RSG) at the University of Arizona Optical Sciences Center has been performing high accuracy laboratory calibration for over 20 years. This work has been done both in support of our work in vicarious calibration of space-borne and airborne imaging sensors and as a standalone means of achieving NIST-traceable radiometric calibration. The solar radiation-based calibration (SRBC) has in the past been a way for the RSG to verify calibration results and to achieve continued calibration of field-grade instruments. This paper presents multiple SRBC results for multiple laboratory-grade radiometers. These results are compared with laboratory calibrations and studied for their merit as a sole means of high-accuracy calibration.

A cross-calibration methodology has been developed using coincident image pairs from the Terra Moderate Resolution Imaging Spectroradiometer (MODIS), the Landsat 7 (L7) Enhanced Thematic Mapper Plus (ETM+) and the Earth Observing EO-1 Advanced Land Imager (ALI) to verify the absolute radiometric calibration accuracy of these sensors with respect to each other. To quantify the effects due to different spectral responses, the Relative Spectral Responses (RSR) of these sensors were studied and compared by developing a set of "figures-of-merit." Seven cloud-free scenes collected over the Railroad Valley Playa, Nevada (RVPN), test site were used to conduct the cross-calibration study. This cross-calibration approach was based on image statistics from near-simultaneous observations made by different satellite sensors. Homogeneous regions of interest (ROI) were selected in the image pairs, and the mean target statistics were converted to absolute units of at-sensor reflectance. Using these reflectances, a set of cross-calibration equations were developed giving a relative gain and bias between the sensor pair.

NOAA has long term experience in the vicarious calibration of the solar reflectance channels of Advanced Very High Resolution Radiometer (AVHRR) onboard NOAA and Metop-A satellites. It has been providing the monthly operational calibration coefficients for all the operational AVHRRs over the past several years. The objective of this paper is to report our current results of the new version of AVHRR operational calibration algorithm. We use the maximum NDVI data and a thermal channel brightness temperature threshold to select non-vegetation pixels free of cloud and dust-storm. Water vapor correction is implemented for Channel 2 measurement. The integrated precipitable water vapor content is derived based on the linear relationship between the brightness temperature difference of the two AVHRR thermal channels and Terra MODIS water vapor products. The results show that this improved algorithm reduces the uncertainty of NOAA-17 AVHRR channel 1 and 2 calibration parameters.

The Airborne Sensors Initiative (ASI) at Ball Aerospace and Technologies Corp. (BATC) specializes in airborne demonstration of internally-developed instrument concepts and innovative remote sensing technologies. In December 2006, ASI flew an environmental remote sensing suite consisting of the Low Light Imager (LLI) and Prototype Airborne Visible Imaging Spectrometer (PAVIS), both of which are operated using a pushbroom approach. LLI is designed for nighttime or high dynamic range imaging. It is capable of yielding 10⁷ dynamic range and offers quality images amid illumination extending from a ¹/₄ moon to full sunlight and with autonomous operation. PAVIS is an imaging spectrometer based on the Dyson design and exhibits a 200 nm spectral bandwidth tunable within 400 − 850 nm. Developed internally to demonstrate promising remote sensing capabilities, these small, low-mass and low-power instruments are prepared for aircraft flight and are currently being used in the field to acquire scientific data. The LLI/PAVIS instrument suite has been utilized to collect airborne urban and rural imagery, as well as spectral information about the Great Salt Lake area, western Colorado, and ancient lava flows in southern Idaho. Highlights of the instrument design and ensuing data from previous flights are presented herein.

Time-series analysis of Antarctic QuikSCAT data reveals several trends. An annual seasonal cycle in which backscatter power increases during the Austral winter and decreases during the Austral summer, is observed over most of the continent, with varying magnitude. Several areas also show a large ( ~ 10dB) decrease in average backscatter during the Austral summer, suggesting melt events. As expected, seasonal variations are strongly dependent on latitude; the southernmost observable portion of the continent is much less seasonably variable than the coasts. Interanual trends show strong long-term trends superimposed on seasonal cycles in much of the continent. Along the coast of most of the continent, backscatter has consistently increased, on the order of 0.5 dB/year, during the seven-year study period. Other regions, mostly in the West-Antarctic interior show the opposite trend, with average backscatter decreasing on the order of 0.5 dB/year.

The Science Data Processing System (SDPS) application, described herein as an example, has had a long development cycle. The SDPS application incorporates IDL, C++, and Perl programming languages, with significant use of an Oracle Relational Database Management System (RDBMS). The time involved from initial design, 1996, to operational deployment, on July 15^th, 2004, with the launch of the Aura spacecraft, spans several releases of the Oracle RDBMS. New database versions usher in new features and performance enhancements, sometimes requiring modifications to custom application code to take full advantage of improvements in technology. For a project with an aggressive release schedule, major redesigns of the custom code could jeopardize the successful completion of mission criteria. Over time, higher throughput requirements and hardware improvements in the application computing infrastructure revealed database performance bottlenecks due to increased scanning frequency of ever-growing tables and indexes. The Distributed Schema (DS) database redesign successfully addressed the database scalability and performance limitations, with only minor SIPS application changes and no changes to the TES SDPS application.

The Atmospheric Infrared Sounder (AIRS), launched on the EOS Aqua spacecraft on May 4, 2002, has been in routine operations since late August 2002. In this paper we analyze the first four years of AIRS Level 1B data (calibrated radiances) from September 1, 2002 through August 31, 2006 for stability and accuracy of the radiometric and spectral calibration. Both are key to linking the AIRS record to previous and future instruments. The analysis shows that the AIRS absolute radiometric accuracy is better than 200 mK with a stability of better than 10 mK/year. Both upper limits are due to the difficulty of finding ground truth data of sufficient quality. The instantaneous knowledge of the channel frequencies is better than 1 ppmf. Compared to the nominal frequency set adopted in September 2002, AIRS channel frequencies are slowly shifting to higher frequencies at the rate of about 1 ppmf/year. The term "ppmf" means "parts per million in frequency". For all but the most critical climate applications, using the nominal frequency set is sufficient for the radiative transfer code used in atmospheric parameter retrievals.

Clouds and the Earth's Radiant Energy System (CERES) instruments were designed to measure the reflected shortwave and emitted longwave radiances of the Earth's radiation budget and to investigate the cloud interactions with global radiances for the long-term monitoring of Earth's climate. The CERES instrument with the three scanning thermistor bolometers measure broadband radiances in the shortwave (0.3 to 5.0 micrometer), total (0.3 to >100 micrometer) and 8 - 12 micrometer water vapor window regions. The four CERES instruments (Flight Models 1 through 4) aboard Earth Observing System (EOS) Terra and Aqua platforms were instrumental in conducting lunar radiance measurement on a regular basis. Moon-reflected solar radiances were measured with the shortwave sensor while both moon-reflected solar and moon-emitted longwave radiances were measured using the total sensor. The CERES sensors performed lunar measurements at various phase angles ranging from four to ten degrees before and after each full moon phase. Additional measurements were also conducted during the lunar eclipse events. The resulting filtered radiances were normalized to the mean sun-moon distance and the mean earth-moon distance. The lunar radiances measured by the sensors from all CERES instruments for a period of January 2001 to June 2007 were analyzed and compared. The CERES total sensor results showed a variation of about +/- 0.5 percent, while a +/- 2.0 percent variation was seen in shortwave sensor results.

This paper discusses the methodology of Synthetic Aperture Radar (SAR) data analysis for studying various aspects of snow characteristics viz snow dielectric constant, snow wetness and snow density. ENVISAT- Advanced Synthetic Aperture Radar (ASAR), single look complex (SLC) data have been processed for backscattering coefficient image generation. ASAR Backscattering coefficient images have been calibrated and processed into terrain corrected images. Corrected backscattering images are despeckled using Frost filter technique. The estimation of snow pack characteristics is optimal at different incidence angles. The relation between snow characteristics like wetness, and snow density and radar backscatter has been studied and the importance of radar backscatter to infer various snow characteristics has been emphasized. This investigation shows the backscattering coefficient is inversely correlated to snow wetness and density. The correlation between the backscattering coefficients and snow wetness and snow density were observed as 0.8 and 0.92 respectively. 14.74 % and 13.31% part of the study area was found affected by layover and low or grazing local incidence respectively in ENVISAT-ASAR IS6 image. In this study, the wetness range was found to vary from 0.05% to 10.28% by volume and mean absolute error was found to be 0.64% by volume and snow density range varies from < 0.1 to 0.48 gm/cc and mean absolute error for density was found 0.032 gm/cc. At higher elevation to moderate elevation estimated snow wetness was observed to be 0.05 - 4% by volume, increasing to 4-10.28 % by volume at moderate to lower elevation.

The main objective of the study is to estimate snow wetness using ENVISAT ASAR data. Snow surface backscattering can be expressed as a function of permittivity of snow. Coding has been done for backscattering coefficient image generation using ENVISAT- Advanced Synthetic Aperture Radar (ASAR), single look complex (SLC) data with dual (HH and VV) polarization as well as single (HH) polarization data. Incidence angle images were extracted from the ASAR header data using interpolation method. These mages were multi-looked 5 times in azimuth and 1 time in range direction. ASAR backscattering coefficient images have been calibrated and processed into terrain corrected images in Universal Transverse Mercator (UTM), zone 43 north and WGS-84 datum map projection using ERDAS Imagine software. Corrected backscattering images are despeckled using Frost filter technique. For this study Integral equation method (IEM) for first order surface scattering based inversion model has been used. A Software has been developed using integral equation method (IEM) based inversion model to estimate snow permittivity, which can be further related to estimating snow wetness. A comparison was done between inversion model estimated snow wetness and field values of snow wetness in the study region. Comparison with field measurement showed that the correlation coefficient for snow wetness estimated from ASAR data was observed to be 0.94 at 95% confidence interval and standard error is observed as 1.28% by volume at 95% confidence interval. The comparison of ASAR derived snow wetness with ground measurements shows the average absolute error at 95% confidence interval as 2.8%. The snow wetness range varies from 0-15% by volume.

The measurement of snow parameters is important for hydrological modeling. Spatial and temporal changes in snow grain size can help us to characterize the thermal state of snow pack and to estimate the timing and spatial distribution of snowmelt. This paper discusses the methodology of Advanced Synthetic Aperture Radar (ASAR) data analysis for estimating snow grain size. In this investigation, we have used ENVISAT-ASAR image mode SLC data in HH-polarization with incidence angle range 39.1 °- 42.8 ° of 31^st January 2006. Survey of India (SOI) topographical sheet (52H3) in 1:50,000 scale is used for preparation of digital elevation model (DEM) and for the registration of satellite data. Field data were measured synchronous with satellite pass. Envisat-advanced synthetic aperture radar single polarized, single look complex (SLC) data have been processed for backscattering coefficient image generation. Incidence angle image was extracted from the ASAR header data using interpolation method. These images were multi-looked 5 times in azimuth and 1 time in range direction. ASAR Backscattering coefficient images have been calibrated. The scattering and absorption efficiencies of an ice particle are only weakly dependent on the shape of the particle. A Snowflake, although non-spherical in shape, may be treated using the Rayleigh expression for a spherical particle of the same mass provided the Rayleigh condition applies. This study has been done using Rayleigh scattering condition based model. The effect of snow grain size on backscattering coefficient is studied in detail. The comparison of ASAR C-band estimated value with field grain size measurement shows an absolute error of 0.045 mm and relative error 9.6%. Backscattering coefficient increases as the grain size increases with elevation.

The mission of DIOS program is to provide the function of large-swathwidth or in-track stereo imaging with compact electro-optical cameras. Optimized from its predecessor SAC (Small-sized Aperture Camera), DIOS consists of two cameras, each with an aperture of 120 mm diameter, 10 m GSD, and 50 km swath width in the spectral range of 520 ~ 890 nm. DIOS is developed to produce high quality images: MTF of more than 12 %; SNR of more than 100. DIOS can be configured to have cameras side-by-side, providing a swathwidth up to 100 km for a mission of large swathwidth. DIOS will be configured with installation of slanted two cameras for the mission of in-track stereo imaging to produce digital elevation model. In this paper, Dual Imaging Optical Sensor (DIOS) will be introduced with design approach and performance measure. Even though developed for micro satellites, the presentation of development status and test results will demonstrate the potential capability that DISO can provide for world-wide remote sensing groups: short development period, cost-effectiveness, wide application ranges, and high performance.

Funded by the Ministry of Commerce, Industry, and Energy of Korea, Satrec Initiative has initiated the development of the prototype model of a TMA-based electro-optical system as part of the national space research and development program. Its optical aperture diameter is 120 mm, the effective focal length is 462 mm, and its full field-of-view is 5.08 degrees. The dimension is about 600 mm × 400 mm × 400 mm and its weight is less than 15 kg. To demonstrate its performance and versatility, multi-spectral imaging in visible and near-infrared region was chosen as the application of the prototype. In this paper, the progress made so far on the prototype development and the future plan will be presented.

The Geostationary Synthetic Thinned Aperture Radiometer (GeoSTAR) is a new Earth remote sensing instrument concept that has been under development at the Jet Propulsion Laboratory. First conceived in 1998 as a NASA New Millennium Program mission and subsequently developed in 2003-2006 as a proof-of-concept prototype under the NASA Instrument Incubator Program, it is intended to fill a serious gap in our Earth remote sensing capabilities − namely the lack of a microwave atmospheric sounder in geostationary orbit. The importance of such observations have been recognized by the National Academy of Sciences National Research Council, which recently released its report on a "Decadal Survey" of NASA Earth Science activities. One of the recommended missions for the next decade is a geostationary microwave sounder. GeoSTAR is well positioned to meet the requirements of such a mission, and because of the substantial investment NASA has already made in GeoSTAR technology development, this concept is fast approaching the necessary maturity for implementation in the next decade. NOAA is also keenly interested in GeoSTAR as a potential payload on its next series of geostationary weather satellites, the GOES-R series. GeoSTAR, with its ability to map out the three-dimensional structure of temperature, water vapor, clouds, precipitation and convective parameters on a continual basis, will significantly enhance our ability to observe hurricanes and other severe storms. In addition, with performance matching that of current and next generation of low-earth-orbiting microwave sounders, GeoSTAR will also provide observations important to the study of the hydrologic cycle, atmospheric processes and climate variability and trends. In particular, with GeoSTAR it will be possible to fully resolve the diurnal cycle. We discuss the GeoSTAR concept and basic design, the performance of the prototype, and a number of science applications that will be possible with GeoSTAR. The work reported on here was performed at the Jet Propulsion Laboratory, California Institute of Technology under a contract with the National Aeronautics and Space Administration.

The Passive A-Band Wind Sounder (PAWS) was funded through NASA's Instrument Incubator Program (IIP) to determine the feasibility of measuring tropospheric wind speed profiles from Doppler shifts in absorption O₂ A-band. It is being pursued as a low-cost and low-risk alternative capable of providing better wind data than is currently available. The instrument concept is adapted from the Wind Imaging Interferometer (WINDII) sensor on the Upper Atmosphere Research Satellite. The operational concept for PAWS is to view an atmospheric limb over an altitude range from the surface to 20 km with a Doppler interferometer in a sun-synchronous low-earth orbit. Two orthogonal views of the same sampling volume will be used to resolve horizontal winds from measured line-of-sight winds. A breadboard instrument was developed to demonstrate the measurement approach and to optimize the design parameters for the subsequent engineering unit and future flight sensor. The breadboard instrument consists of a telescope, collimator, filter assembly, and Michelson interferometer. The instrument design is guided by a retrieval model, which helps to optimize key parameters, spectral filter and optical path difference in particular.

VENµS is a demonstration mission developed in cooperation between Israël (ISA) and France (CNES). VENµS scientific mission unique feature is to acquire high resolution (5.3m) multi-spectral images (12 bands in the visible and NIR spectrum) continuously every second day with constant viewing angles. At least 50 sites of interest all around the world will be viewed. It aims at demonstrating the relevance of such observation capabilities in the framework of the European Global Monitoring for Environment and Security Program (GMES). The satellite also flies a technological mission that aims at qualifying an Israeli electric propulsion technology (IHET) and demonstrating its mission enhancement capabilities. The satellite will be launched in January 2010. The imaging scientific mission will last 2.5 years with the satellite at 720 km. Next, the technological mission will bring the satellite at 410 km. The scientific mission will then go on for one year with an improved resolution (3m). This paper presents the main geometric and radiometric image quality requirements for the scientific mission. The strong multi-spectral (2m) and multi-temporal (3m) registration requirements constrain the stability of the platform and the ground processing which will refine the geometric physical model using an image matching method based on correlation. The location of the images will take benefits from the capacity of the system to produce Digital Elevation Models at a low 'Base to Elevation' ratio (0.026). These processings are detailed through the description of the level 1 production which will provide users with ortho-images of Top of Atmosphere reflectances. Finally we propose different radiometric (relative and absolute camera sensitivity,...) and geometric (line of sight, focal plane cartography,...) in-flight calibration methods to answer the severe mission requirements.

NOAA plans to build a Geostationary Lightning Mapper (GLM) whose objectives are providing continuous, full-disk lightning measurements for storm warning and science applications. Due to limited telemetry bandwidth, much of the detection processing will be done autonomously. Since the contractor is responsible for the autonomously generated output, which is detection reports - not images, we took a design approach that did not stop with a signal to noise calculation but instead simultaneously considers the effects of hardware configurations and algorithm choices. Key requirements for GLM are the probability of detection (P_D) and probability of false alarm (P_FA). Our approach allows us to provide a system with the best P_D and P_FA performance and the best value. We have accomplished this by developing an analytical model that can find "knees-in-the curve" in our hardware configuration selections and an algorithm prototype that provides realistic end-to-end performance. These tools allow us to develop an optimal system since we have a good handle on realistic performance prior to launch. Our tools rely on descriptions of lightning phenomena embodied in probability densities we developed for the amplitude, temporal and spatial distribution of lightning optical pulses. The "analytic model" uses tabulated integration formulae and conventional numerical integration to implement an analytical solution for the P_D estimate. The average P_D is quickly computed, making the analytic model the choice for rapid evaluation of sensor design parameter effects. The "algorithm prototype" utilizes simulation, consisting of data cubes of time elapsed imagery containing lightning pulses and structured backgrounds, and prototyped detection and false alarm mitigation algorithms to estimate P_D and P_FA. This approach provides realistic performance by accounting for scene spatial structure and apparent motion. We discuss the design and function of these tools and show results indicating the variation of P_D and P_FA performance with changes in sensor and algorithm parameters and how we use these tools to improve our instrument design capabilities.

Traditionally, optical remote sensing payload design satisfies highly defined specifications arrived at by consensus of the scientific constituency. Designs are constrained by required performance such as resolution, Modulation Transfer Function (MTF), and Signal-to-Noise-Ratio (SNR). Payload designers satisfy the specification by performing hardware and cost trades. This process may lack continuous feedback between the performance of the scientific algorithms and the payload design, potentially missing optimal design points. The traditional method has produced separate and specific designs for imagery (over-sampling ratio Q > 0.8) vs. radiometry (Q < 0.8). Radiometers are scientifically precise, with highly accurate scene collection over a tightly defined pixel size exclusive of other scene points, often across several spectral channels. Imagers reveal sharper features, but have considerable "bleeding" of scene radiance into adjacent pixels, causing errors in application of multispectral scientific algorithms. Recently, we created end-to-end models that optimize end scientific data products by considering the payload design and data processing algorithms together, rather than simply satisfying a payload specification. In this process, we uncovered optimal payload design points and insights. We explore end-to-end modeling results that show an optimal single converged payload design, and data processing algorithms that produce simultaneous radiometer and imager products. We show how payload design choices for Instantaneous Field of View (IFOV) and Ground Sampling Distance (GSD) maximize SNR for multiple data products, resulting in an optimized design that increases flexibility of space assets. This approach is beneficial as we move towards distributed and fused image systems.

MODIS is a major instrument for the NASA EOS Terra and Aqua missions, launched in December 1999 and May 2002 respectively. MODIS has 16 thermal emissive bands and they are calibrated using an onboard blackbody (BB) based on a nonlinear second order relationship. While the gains of the MODIS thermal bands are calibrated on a scan-by-scan basis, the offset and non-linear terms are determined either from prelaunch or on-orbit measurements during scheduled BB warm-up and cool-down cycles. A major concern on determination of the offset and non-linear terms from on-orbit BB measurements is that the controlled BB temperature range is relative small compared to the temperature range used in prelaunch tests, which could have impacts on the retrieval of brightness temperatures (BT) well outside the calibration range. In this study, the stability of offset and non-linear terms obtained from BB warm-up/cool-down cycles is presented. Several approaches to derive the on-orbit offset and non-linear terms are used and their impacts on the Earth scene BT estimates are examined. By comparison with BT derived using prelaunch offset and nonlinear terms under the same electronic configuration, it is shown that the current approach of deriving on-orbit offset and nonlinear terms applied in L1B radiance products causes positive BT biases of exceeding 1K at low temperatures for middle- to longwave IR bands. Comparison of MODIS and AIRS (The Atmospheric Infrared Sounder), both on-board Aqua spacecraft, for cold temperature scenes at Antarctica for two long-wave IR bands also indicates that there are temperature-dependent positive BT biases for about the same magnitudes. Results of this study have a significant impact on improving the current approach of setting a₀ and a₂ used to produce MODIS L1B data products.

WindSat is a spaceborne multi-frequency polarimetric microwave radiometer and has the potential of contributing to the retrieval of land variables and complementing efforts directed at the Aqua AMSR-E. In this study, a previously established algorithm was applied to WindSat data to estimate global soil moisture. Comprehensive validation was performed by comparing the retrievals with in situ soil moisture observations from networks located at four soil moisture validation sites. The overall standard error of estimate for surface soil moisture was 0.038 m3/m3. This analysis shows that the WindSat soil moisture retrievals are reasonable and fall within the generally accepted error bounds of 0.04 m3/m3. Larger scale qualitative assessments were performed by analysis of the spatial distribution of soil moisture, which were found to be consistent with the known global climatology. There are other soil moisture algorithms under investigation, however, these result show the potential of the WindSat sensor for soil moisture as well as future operational satellite instruments.

The double-sided paddle wheel scan mirror is the key optical component of the Moderate Resolution Imaging Spectroradiometer (MODIS) on-board the NASA EOS Terra and Aqua satellites. At a constant rotating speed, the scan mirror continuously reflects the Earth's top-of-atmosphere radiances through the instrument nadir aperture door and onto four focal plane assemblies (FPA), which consist of 36 spectral bands. Of those 36 bands, 16 are thermal emissive bands (TEB) with wavelengths ranging from 3.7 to 14.4μm. While this cross-track scanning system provides the Earth scene observations over a range of ±55° viewing angles from the nadir, the on-orbit calibration for TEB is performed by an On-Board Calibrator Blackbody (OBC BB) at a fixed viewing angle. The response versus scan angle (RVS) of the scan mirror is sensitive to the MODIS radiometric calibration. This paper describes how the pre-launch TEB RVS of the Aqua MODIS was characterized at the instrument system level by using ground support equipment, a Blackbody Calibration Source (BCS). The RVS test setup, test procedure, data analysis, derivation of RVS, and the fitting uncertainty are discussed in the paper. A separate paper that gives similar RVS analysis for the MODIS Reflective Solar Bands (RSB) is presented in this proceeding.

The MODIS Protoflight Model (PFM) on-board the Terra spacecraft and the MODIS Flight Model 1 (FM1) on-board the Aqua spacecraft were launched on December 18, 1999 and May 4, 2002, respectively. They are scheduled to view the Moon at a fixed Sun-Moon-MODIS phase angle (-55° for Aqua and 55° for Terra) through the space view (SV) port approximately once a month via a spacecraft roll maneuver to monitor the long-term radiometric stability of their reflective solar bands (RSB). MODIS can also automatically view the Moon in about four months each year without roll maneuvers. The lunar phase angles of the unscheduled lunar views are distributed in a wide range from -75° to -53° for Aqua and 53° to 75° for Terra. Similar to the scheduled lunar observations, the unscheduled lunar observations can be used to monitor the long-term radiometric stability of the RSB. In this report, the coefficients defined to trend degradation of the MODIS system response are derived from the unscheduled lunar observations and compared to those derived from the scheduled lunar views. It is shown that the unscheduled lunar observations can be used to track the radiometric stability of the MODIS RSB with about the same accuracy as the scheduled lunar views.

The design and results of the photon counting laser altimeter simulator are presented. The simulator is designed to be a theoretical and numerical complement for a Laser Altimeter Technology Demonstrator of the space borne laser altimeter for planetary studies built on our university. The motivation of this research is the European Space Agency nomination the photon counting altimeter as one of the attractive devices for planetary research. The proposed device should provide altimetry in the range 400 to 1400 km with one meter range resolution under rough conditions - Sun illumination, radiation, etc. The general altimeter concept expects the photon counting principle laser radar. According to this concept, the simulator is based on photon counting radar simulation, which has been enhanced to handle planetary surface roughness, vertical terrain profile and its reflectivity. The simulator is useful complement for any photon counting altimeter both for altimeter design and for measured data analysis. Our simulator enables to demonstrate the operation of single photon counting detector on altimeter.

A new technology has been developed at the Canada Centre for Remote Sensing (CCRS) for generating North America continental scale clear-sky composites at 250 m spatial resolution of all seven MODIS land spectral bands (B1-B7). The MODIS Level 1B (MOD02) swath level data were used as input to circumvent the problems with image distortion in the mid-latitude and polar regions inherent to the sinusoidal (SIN) projection utilized for the standard MODIS data products. The new data products are stored in the Lambert Conformal Conical (LCC) projection for Canada and the Lambert Azimuthal Equal-Area (LAEA) projection for North America. The MODIS 500m data (B3-B7) were downscaled to 250m resolution using an adaptive regression algorithm. The clear-sky composites are generated using scene identification information produced at 250m resolution and multi-criteria selection which depends on pixel identification. Cloud shadows were also identified and removed from output product. It is demonstrated that new approach provides better results than any scheme based on a single compositing criterion, such as maximum NDVI, minimum visible reflectance, or combination of them. To account for surface bi-directional properties, two clear-sky composites for same time period are produced for the relative azimuth angles within 90°-270° and outside of this interval. Comparison with Landsat imagery and MODIS standard composite products demonstrated advantages of new technique for screening cloud and cloud shadow and providing the high spatial resolution. The final composites were produced for every 10-day intervals since March 2000. The composite products have been used for mapping albedo and vegetation properties as well as for land cover and change detections applications at 250m scale.

An illuminated Solar Diffuser is the calibration source for the VIS/NIR bands on the NPOESS/VIIRS sensor. We completed a set of BRF measurements to fully characterize the distribution of scattered light from the solar diffuser. NPOESS/VIIRS has an overall VIS/NIR radiometric calibration uncertainty requirement of 2%(1 sigma), of which 1.32% was allocated to the characterization of the BRF. In order to meet this requirement, we modified the existing goniometer and measurement procedure used on MODIS. Modifications include sample yoke redesign, periodic measurements of the lamp polarization coupled with stability measurements, modifications to source optics, and stray light reduction. We measured BRF in 6 spectral wavebands for 9 out-of-plane illumination angles and 2 view angles. We achieved NIST traceable measurements with an uncertainty ranging from 1.09% to 1.32%. Our measurements of a smaller Spectralon^TM sample match NIST measurements of the same sample to better than 0.5%. These requirements are nominally the same as achieved on MODIS. As a result of instrument upgrades, we currently meet this overall uncertainty while having included additional uncertainty terms.