The SeaWiFS Project uses monthly lunar calibrations to monitor the on-orbit radiometric stability of SeaWiFS over the course of its mission. Ongoing analyses of the steadily increasing lunar calibration data set have led to improvements in the calibration methodology over time. The lunar measurements must be normalized to a common viewing geometry for the calibration time series to track the radiometric stability of the instrument. Corrections computed from the time and geometry of the observations include Sun-Moon and instrument-Moon distances, oversampling of the lunar image, and variations in the lunar phase angles. The Project has recently implemented a correction for lunar libration that is computed from regressions of the libration angles of the observations against the lunar radiances. Decaying exponential functions of time are fit to the geometry-corrected calibration time series. The observations for bands 1,2,and 5-8 are fit to two simultaneous exponential functions of time, while bands 3 and 4 are fit to single exponential functions of time. The corrections to the radiometric response of the instrument over time are the inverses of these fits. The lunar calibration methodology provides top-of-the-atmosphere radiances for SeaWiFS that are stable to better than 0.07% over the course of the mission, with residual time drifts that are smaller than -0.004% per thousand days. The resulting water-leaving radiances are stable to better than 0.7%, allowing the Project to implement a vicarious calibration of the water-leaving radiances that is independent of time. The calibration methodology presented here will be used to generate the calibration table for the fifth reprocessing of the SeaWiFS global ocean data set.

The Terra MODIS and Aqua MODIS have been successfully operated on-orbit for a total of more than six and a half years, collecting data for the science and applications communities to develop and enhance their understanding of the Earth/atmosphere system and to support studies of the climate and climate changes. Since its launch in December 1999, the Terra MODIS has experienced several changes of its operational configuration either caused by the failure of individual electronics subsystems or purposely switched for better signal response or data quality. Excluding minor anomalies related to instrument reset events during initial on-orbit operation, the Aqua MODIS has been operating in a single configuration since its launch in May 2002. There are approximately 40 science products that are being produced using the calibrated data sets from each instrument. In addition, several products are generated using the combined observations from both instruments. This paper provides an overview of Terra and Aqua MODIS instrument status and summarizes those on-orbit operational activities designed and implemented to provide and support instrument calibration and characterization. The assessments of instrument performance are based on the use of on-board calibrators (OBC) and other activities specially developed and implemented by the MODIS Characterization Support Team (MCST) at NASA/GSFC. Both instruments are performing well. During four and a half years of Terra MODIS on-orbit operation, 11 detectors became noisy and one inoperable out of a total of 490 detectors. Except for band 6 at 1.6m that had many inoperable detectors (identified pre-launch and immediately after launch), there have been no new noisy or inoperable detectors in Aqua MODIS during its two years of on-orbit operation. The sensors' spectral and spatial performance have also been very stable.

MODIS, one of the key instruments for the NASA's Earth Observing System (EOS), is currently operating on both the Terra and Aqua spacecraft making continuous observations in 36 spectral bands from 0.4 to 14.5μm. A complete suite of on-board calibrators (OBC) have been designed for the instruments on-orbit calibration and characterization, including a solar diffuser (SD) and solar diffuser stability monitor (SDSM) system for the radiometric calibration of the 20 reflective solar bands (RSB), a blackbody (BB) for the radiometric calibration of the 16 thermal emissive bands (TEB), and a spectro-radiometric calibration assembly (SRCA) for the spatial (all bands) and spectral (RSB only) characterization. The task of continuously performing high quality on-orbit calibration and characterization of all 36 spectral bands with a total of 490 detectors located on four focal plane assemblies is extremely challenging. The use of a large two-sided paddle wheel scan mirror with a ±55° scan angle range and a retractable pinhole attenuation screen in front of the SD panel for calibrating the high gain bands have resulted in additional unanticipated complexity. In this paper, we describe some of the key issues in the Terra and Aqua MODIS on-orbit calibration and characterization, and discuss the methods developed to solve these problems or to reduce their impact on the Level 1B calibration algorithms. Instrument performance and current issues are also presented.

The QuickBird commercial imaging satellite is a pushbroom system with four multispectral bands covering the visible through near-infrared region of the spectrum and a panchromatic band. The focal plane contains 6972 detectors in each MS band and 27888 detectors in the pan band that must be calibrated. A relative radiometric correction is performed on all image data to account for detector-to-detector non-uniformities and to reduce banding and streaking that would otherwise be seen in the imagery. The goal of the relative radiometric correction, other than to minimize image artifacts, is to scale all image pixel brightness digital numbers (DNs) to top-of-atmosphere spectral radiances so that one set of absolute calibration factors can be applied to all pixels in a given band. A series of uniform imagery collected between February and June of 2004 was radiometrically corrected and analyzed for banding and streaking performance. Banding in QuickBird imagery is less than four DNs in normal desert, ocean, and forest scenes. Desert scenes alone have a percent banding of less than 0.5% in the MS bands and less than 0.7% in the pan band. Banding is less than 2% for typical scenes. Streaking is less than 0.6% for all MS and pan detectors.

The Atmospheric Infrared Sounder (AIRS) is a space-based instrument that measures the upwelling atmospheric spectrum in the infrared. AIRS is one of several instruments on the EOS-Aqua spacecraft launched on May 4, 2002. Typically, instrument polarization is not a concern in the infrared because the scene is usually not significantly polarized. A small amount of polarization is expected over ocean, which can be seen in the AIRS 3.7 mm window channels. The polarization is seen as a signal difference between two channels with the same center frequency but different polarizations. The observations are compared to a model that relies on measurements of instrument polarization made pre-flight. A first look at a comparison of the observations of sea surface polarization to expectations is presented.

The Clouds and the Earth's Radiant Energy System (CERES) is an investigation into the role of clouds and radiation in the Earth's climate system. Four CERES scanning thermistor bolometer instruments are currently in orbit. Flight model 1 (FM1) and 2 (FM2) are aboard the Earth Observing System (EOS) Terra satellite and FM3 and FM4 are aboard the EOS Aqua satellite. Terra was launched in December 1999 and Aqua in May 2002. Both satellites are in high inclination near-polar, sun synchronous orbits. Terra crosses the equator at 10:30 am local time in the descending portion of the orbit. Aqua ascends across the equator at 1:30 pm local time. Each CERES instrument on Terra and Aqua measures in three broadband radiometric regions: the shortwave (0.3 - 5.0 micrometers), total (0.3 - >100 micrometers), and window (8 - 12 micrometers). Several vicarious analyses have been developed to aid in monitoring the health and stability of the instruments' radiometric measurements. One analysis is a three-channel inter-comparison of the radiometric channel measurements for each instrument. This procedure can derive an estimate of the shortwave portion of the total channel radiance measurement. A second analysis compares temporally synchronized nadir measurements for each sensor of two instruments on the same platform. The three-channel inter-comparison along with the direct comparison and onboard internal calibrations have been used to identify and correct drifting in the measurements of the CERES instruments. Although these drifts and the correction of the measurements have been previously documented, this paper is a continuation of the efforts to quantify and correct drifting in the measurements using ground-processing software. Previous papers only reported drift correction to the CERES instruments on the Terra platform. In addition to the Terra instruments, this paper documents drift correction to the CERES instruments on the Aqua platform.

Clouds and the Earth’s Radiant Energy System (CERES) instruments were designed to measure the reflected shortwave and emitted longwave radiances with three scanning thermistor bolometer sensors that measure broadband radiances in the shortwave (0.3 - 5.0 micrometers), total (0.3 - >100 micrometers) and 8 -12 micrometer water vapor window regions. Currently four of the CERES instruments (Flight Models1 through 4[FM1 - FM4]) are flying aboard EOS Terra and Aqua platforms with two instruments aboard each spacecraft. The Terra and Aqua spacecraft are at 705 km near polar, sun synchronous orbits with the equatorial crossing time of 10:30 AM and 1:30 PM. One of the several validation studies for gauging the CERES sensors' performance utilizes the monitoring of tropical ocean longwave measurements for all sky condition. Previous studies on tropical ocean conducted by Earth Radiation Budget Satellite (ERBS) have shown that the mean longwave radiances remain very stable making it a suitable Earth target for validation. The difference in the tropical ocean daytime and nighttime longwave radiances measured by the two longwave measuring sensors on the same instrument are compared, to understand the total sensor’s behavior in various spectral regions. This paper focuses on the results from the tropical ocean measurement analysis called Tropical Mean (TM), calculated for all four CERES instruments aboard Terra and Aqua spacecraft. The TM results along with other validation and calibration studies have helped to detect variations that have occurred in the total sensors of FM2, FM3 and FM4 instruments aboard Terra and Aqua platforms. Further, the TM results has been used to help correct these variations in the ground processing system.

The CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) mission is designed to study the impact of clouds and aerosols on the Earth's radiation budget. Three instruments and their infrastructure make up the payload. They are a two-wavelength, polarization-sensitive lidar, a wide-field camera (WFC) operating at 645 nm, and a three-channel, infrared (IR), imaging radiometer (IIR) built by Sodern in France. The lidar is a follow-on to the short-duration LITE mission that flew on the shuttle.1 The lidar and WFC, built by Ball Aerospace under contract to NASA Langley Research Center, has completed its environmental and performance testing and is being integrated to the spacecraft in preparation for an April 2005 launch. This paper gives an overview of the testing and performance of this payload while being built and integrated at Ball Aerospace.

Following the successful commissioning of the first Meteosat Second Generation (MSG) series, EUMETSAT and the European Space Agency (ESA) are actively preparing the Meteosat Third Generation (MTG) mission to plan for a future operational geostationary meteorological satellite system in the post 2015 time frame. Early user consultation activities of EUMETSAT and ESA for the MTG mission culminated with a user consultation workshop held in November 2001. The User Consultation Process was devoted to the definition and consolidation of end user requirements and priorities in the field of Medium/Short Range global and regional Numerical Weather Prediction (NWP), Nowcasting and Very Short Term Weather Forecasting (NWC) and to the definition of the relevant observation techniques. Studies on potential observation techniques and sensor concepts have been initiated, covering three distinct imagery missions dedicated to operational meteorology, with emphasis on nowcasting and very short term forecasting and two sounding missions: - The high resolution fast imagery mission aiming at 5 minutes revisit time with 0.5 km resolution - The full disk high spectral resolution imagery mission with a large number of spectral channels and with high radiometric performance - The lighting imagery mission, capable of detecting very low energy events with high reliability - The infrared sounding mission supporting NWP through the provision of atmospheric motion vectors and temperature and water vapour profiles - The UV/VIS/SWIR sounding mission dedicated to atmospheric chemistry The paper describes the MTG user requirements and the preliminary instruments concept, with emphasis on the observation missions.

While existing satellite Earth Observing (EO) systems provide many baseline observations, they are lacking an important combination of capabilities in terms of angular sampling, spectral coverage, and spatial resolution. This has an impact on the accuracy of retrievals and the capability to provide accurate regular operational monitoring of surface and atmospheric properties on a large scale (global or continental). The concept of Advanced Multiangular MEdium Resolution System (AMMERS), that addresses the above issues and provides unique capability presently unavailable from other space observing systems, is proposed here. The mission's unique feature is a combination of medium resolution (400m), multi-spectral observations (13 spectral bands in visible, NIR, SWIR, IR, SW and LW), and multi-angular capabilities (7 angles). AMMERS's multiangular features and swath width allow bi-directional angular sampling close to the solar principal plane and in the perpendicular plane. These capabilities are critically important for accurate estimation of surface albedo, vegetation structure, and forest parameters. AMMERS will also be superior to many other missions in retrieving SST, aerosol, clouds parameters, snow, and wild fire mapping.

Recently, a joint Swiss/Belgian initiative started a project to build a new generation airborne imaging spectrometer, namely APEX (Airborne Prism Experiment) under the ESA funding scheme named PRODEX. APEX is a dispersive pushbroom imaging spectrometer operating in the spectral range between 380 - 2500 nm. The spectral resolution will be better then 10 nm in the SWIR and < 5 nm in the VNIR range of the solar reflected range of the spectrum. The total FOV will be ± 14 deg, recording 1000 pixels across track with max. 300 spectral bands simultaneously. APEX is subdivided into an industrial team responsible for the optical instrument, the calibration homebase, and the detectors, and a science and operational team, responsible for the processing and archiving of the imaging spectrometer data, as well as for its operation. APEX is in its design phase and the instrument will be operationally available to the user community in the year 2006.

Medium-sized Aperture Camera (MAC) for earth observation on a small satellite is being developed by Satrec Initiative and ATSB. Designed as a cost-effective high-resolution camera, this push-broom type camera has 1 panchromatic and 4 multispectral channels using all-CCDs-in-one focal plane, and it does not split the channels by prisms. The panchromatic channel has 2.5m, and multispectral channels have 5m of ground sampling distance at a nominal altitude of 685km. The 300mm modified Ritchey-Chretien telescope contains two aspheric mirrors and two spherical correction lenses. MAC is the main payload of RazakSAT (formerly known as MACSAT) to be launched in 2005. RazakSAT is a 180kg (including MAC) small satellite, designed to provide high-resolution imagery of 20km swath width on a near equatorial orbit (NEqO). The mission objective is to demonstrate the capability of a high-resolution small remote sensing satellite system on a near equatorial orbit. This paper describes the status report on the development of the MAC Qualification Model and technical issues.

SAC is a compact camera for imaging in visible-NIR spectral ranges. SAC provides high-resolution images over the wide geometric and spectral ranges: 10 m GSD and 50 km swath-width in the spectral ranges of 520 ~ 890 nm. The missions incorporate various imaging operations: multi-spectral imaging; super swath-width imaging with cameras in parallel; along-track stereo imaging with slanted 2 cameras. In this paper, SAC is introduced with design and performance. Though developed for small satellites, presenting development status and test results will demonstrate the potential capability for worldwide remote sensing groups: short development period, cost-effectiveness, and high performance.

We discuss the design, fabrication and performance of a temperature-tuned solid etalon filter for a 532 nm lidar receiver. This is the first demonstration of a bulk, ZnS (a.k.a. Cleartran) etalon filter. Cleartran provides several advantages including: full FSR tuning with a small temperature range; high thermal conductivity; high numerical aperture; and high reliability (no moving parts or piezoelectrics involved). The filter system, with a FWHM ~28 pm, was tuned at a ratee of ~15 pm/°C across the FSR of 341 pm, and provided a wavelength stability of +/- 0.8 pm.

IN 2005 a lidar instrument will be launched aboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite for measuring the three dimensional distribution of atmospheric clouds and aerosols. A key part of the lidar instrument is a 532 nm tunable etalon, which allows daytime operation. The design rationale and measured optical performance of the etalon and its mounting sytem during assembly and integration are presented.

ACE is a Canadian satellite mission that will provide measurements leading to an improved understanding of the chemical and dynamical processes that control the distribution of ozone in the stratosphere. The ACE instruments are a Fourier transform infrared spectrometer, a UV/visible/near IR spectrograph and a two-channel solar imager, all working in solar occultation mode. ACE was successfully launched on August 12, 2003.

The Atmospheric Chemistry Experiment (ACE) is the mission selected by the Canadian Space Agency for its science satellite, SCISAT-1. ACE consists of a suite of instruments in which the primary element is an infrared Fourier Transform Spectrometer (FTS) coupled with an auxiliary 2-channel visible (525 nm) and near infrared imager (1020 nm). A secondary instrument, MAESTRO, provides spectrographic data from the near ultra-violet to the near infrared, including the visible spectral range. In combination the instrument payload covers the spectral range from 0.25 to 13.3 micron. A comprehensive set of simultaneous measurements of trace gases, thin clouds, aerosols and temperature will be made by solar occultation from a satellite in low earth orbit. The ACE mission will measure and analyze the chemical and dynamical processes that control the distribution of ozone in the upper troposphere and stratosphere. A high inclination (74 degrees), low earth orbit (650 km) allows coverage of tropical, mid-latitude and polar regions. The ACE/SciSat-1 spacecraft was launched by NASA on August 12th, 2003. This paper presents the on-orbit commissioning of the ACE-FTS instrument. Various steps were required to safely and progressively activate each module and sub-system of the instrument. This paper describes each step and its relation with the health and safety of the instrument. The overall strategy and sequence of the commissioning activity is presented. Commissioning results are presented in terms of validation of instrument functionality from an engineering perspective. The characterization of the detector contamination is described as well as methods that were developed to mitigate this issue.

The Atmospheric Chemistry Experiment (ACE) is the mission selected by the Canadian Space Agency (CSA) for its science satellite, SCISAT-1. ACE consists of a suite of instruments in which the primary element is an infrared Fourier Transform Spectrometer (FTS) coupled with an auxiliary 2-channel visible (525 nm) and near infrared imager (1020 nm). A secondary instrument, MAESTRO, provides spectrographic data from the near ultra-violet to the near infrared, including the visible spectral range. In combination the instrument payload covers the spectral range from 0.25 to 13.3 micron. A comprehensive set of simultaneous measurements of trace gases, thin clouds, aerosols and temperature are made by solar occultation from a satellite in low earth orbit. The ACE mission measures and analyses the chemical and dynamical processes that control the distribution of ozone in the upper troposphere and stratosphere. A high inclination (74 degrees), low earth orbit (650 km) allows coverage of tropical, mid-latitude and polar regions. The ACE/SciSat-1 spacecraft was launched by NASA on August 12th, 2003. This paper presents the on-orbit performance of the ACE-FTS instrument. The commissioning activities allowed the activation of the various elements of the instrument and the optimization of several parameters such as gains, integration times, pointing offsets, etc. The performance validation was the last phase of the instrument hardware commissioning activities. The results of the performance validation are presented in terms of on-orbit instrument performance with respect to instrument requirements such as signal-to-noise ratio, transmittance accuracy, and spectral resolution. Results are also compared to ground validation tests performed during the thermal-vacuum campaigns. Performance is presented in terms of validation of instrument from an engineering perspective.

The Atmospheric Chemistry Experiment (ACE) was launched in August 2003 on board the Canadian scientific satellite SciSat-1. The ACE payload consists of two instruments: ACE-FTS, a high resolution (0.02 cm-1) Fourier transform infrared spectrometer and MAESTRO (Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation), a dual UV-visible-NIR spectrograph. Primarily, the two instruments use a solar occultation technique to make measurements of trace gases, temperature, pressure and atmospheric extinction. It will also be possible to make near-nadir observations with the ACE instruments. The on-orbit commissioning of the instruments and spacecraft were undertaken in the months following launch. At the end of this period, a series of science-oriented commissioning activities were undertaken. These activities had two aims: the first was to verify and extend the measurement results obtained during the pre-launch Science Calibration Test campaign and the second was to confirm appropriate parameters and establish procedures for operational measurements (occultation and near-nadir observations and exo-atmospheric calibration measurements). One of the most important activities was to determine the relative location of each instrument field of view and optimize the pointing of the sun-tracker to provide the best viewing for both instruments.

SciSat-1, otherwise known as the Atmospheric Chemistry Experiment (ACE), is a Canadian satellite mission for remote sensing of the Earth's atmosphere. It was launched into low Earth orbit (altitude 650 km, inclination 74 degrees) in August 2003. The primary instrument onboard ACE is a high resolution (maximum path difference ± 25 cm) Fourier Transform Spectrometer (FTS) operating from 2.4 to 13.3 microns (750-4100 cm-1). The satellite also features a dual spectrograph known as MAESTRO with wavelength coverage 280-1000 nm and resolution 1-2 nm. A pair of filtered CMOS detector arrays takes images of the sun at 0.525 and 1.02 nm. Working primarily in solar occultation, the satellite provides altitude profile information for temperature, pressure, and the volume mixing ratios for several dozen molecules of atmospheric interest. Scientific goals for ACE include: (1) understanding the chemical and dynamical processes that control the distribution of ozone in the stratosphere and upper troposphere; (2) exploring the relationship between atmospheric chemistry and climate change; (3) studying the effects of biomass burning in the free troposphere; and (4) measuring aerosols to reduce the uncertainties in their effects on the global energy balance.

The experimental data on O₂ absorption using reflected sunlight and a passive Fabry-Perot technique are presented. The atmosphere's irradiance measurements are an important tool for the remote sensing study. In this work we 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 two different pre-filters. The first pre-filter selects a spectral range around 763 nm which is between the P and R branches, where the absorption coefficient is insensitive to temperature, but is sensitive to pressure changes and therefore to the variations in the O₂ column. The second pre-filter is selecting several absorption bands between 765 and 770 nm, which are more sensitive to temperature changes. The optical setup consists of two channels. Channel one measure the total reflected light, whereas channel two uses a solid substrate Fabry-Perot etalon to restrict measurement to light in the O₂ absorption bands. The ratio of the intensities detected by the two channels is sensitive to O₂ pressure change or temperature change depending of the spectral region and is a function of the air mass, solar zenith angle and altitude. The experimental data presented shows excellent agreement with our theoretical expectations. They were recorded at different gas pressures and temperatures, and also at various weather conditions. The goal of the experiment is to demonstrate that variations of the column density of the O2 can be detected using a solid Fabry-Perot etalon. Results can be used for normalization of the other trace gases column densities, (to measure CO₂ column density) because the Oxygen is well mixed throughout most of the atmosphere (to an altitude of about 100 km) and can help to interpret the influence of scattering from aerosol and clouds, polarization of the reflected light, and the reflection properties of the surface. Some of the major advantages of our optical setup are its compactness, high sensitivity, high signal-to-noise ratio and stability.

For monitoring environmental changes, new passive infrared instruments have become available that allow change detection analyses at resolutions and scales that were impossible just a few years ago. Current instruments have been installed in Antarctica will help to better understand the photochemical transport process and accurately predict ozone depletion and climate changes. During the 2003 polar summer one spectrometer was installed at the McMurdo station and another at the South Pole station, for year-around atmospheric chemistry monitoring. These two instruments use the emission technique to deliver high resolution spectra, from which will derive vertical profiles of many atmospheric tracers involved in the ozone destruction process. The first setup uses one channel to acquire the atmospheric data throw two different angles, the second setup uses two simultaneous channels to acquire the data at the same sky angles. Both instruments integrate two black bodies at different temperatures to calibrate the sky data. The data generated will have multipurpose, first is to provide validation for the new generation of the satellite sensors, like the National Polar-orbiting Operation Environmntal Satellite System (NPOESS), second is to allow photochemical transport modelers to compare outputs with actual measurements, and third is to evaluate the trend of some column abundance measurements like HNO₃, CH₄, O₃, CFCs, H₂O... This paper will present description of the instrumentation, the measurement technique and the automated analysis.

The Ozone Mapping Profiler Suite will produce ozone profiles using the limb scatter technique. While this technique has been used in the 1980s for mesospheric retrievals with data from the Solar Mesospheric Explorer, its use for the stratosphere and upper troposphere is relatively recent. To increase the scientific experience with this method, the Limb Ozone Retrieval Experiment LORE was flown on-board STS107 in 2003. A significant amount of data from thirteen orbits was down-linked during the mission and exists for analysis. LORE was an imaging filter radiometer, consisting of a linear diode array, five interference filters (plus a blank for dark current) and a simple telescope with color correcting optics. The wavelengths for the channels were 322, 350, 602, 675 & 1000 nm and can be viewed as a minimum set of measurements needed for ozone profiling from 50 km to 10 km. The temporal sampling of the channels, along with the shuttle orbital and attitude (e.g. pitch) motions present a challenge in retrieving precise ozone profiles. Presented are the retrieval algorithms for determination of the channel's altitude scale, cloud top height and aerosol extinction. Also shown are a sub-set of flight data and the corresponding retrieved ozone profiles.

Rapid and accurate calibrations of satellite imager sensors are critical for remote sensing of surface, cloud and radiative properties. A post-launch technique has been developed to routinely cross calibrate and normalize the imager visible (VIS) channel on-board operational geostationary (GEO) and low-Earth-orbit (LEO) satellites. As a reference calibration source, this simple approach uses the self-calibrating sensor from the Tropical Rainfall Measuring Mission (TRMM) Visible Infrared Scanner (VIRS) to calibrate other GEO and LEO satellites. The VIRS sensors have been found to be a stable and reliable reference source. This technique uses VIRS to calibrate the eighth Geostationary Operational Environmental Satellite (GOES-8) VIS sensor using collocated data with similar viewing zenith, solar zenith, and relative azimuth angles. GOES-8 is then used as a transfer medium to cross calibrate other GEO and LEO satellites. Post-launch VIS (~0.65 µm) calibration coefficients for GOES-8, -9, -10, -12, Meteosat-7, -8, and NOAA-14 AVHRR satellites are presented. GOES-8 had a non-linear degradation rate of 11% the first year of operational service and 4% in last year before it was decommissioned. GOES-9 degraded linearly at 7.9% per year during 1995-1998. GOES-10 degraded 12% the first year and 1.6% less each year after that. GOES-12 degraded 6% per year. The VIRS visible channel calibration is in good agreement with the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on-board the Terra and Aqua satellites supporting its use as a reference.

A small integrating sphere with two pinhole apertures can be hard-mounted to the nadir-facing surface of a 3-axis stabilized GOES satellite in geostationary orbit. One pinhole can be baffled to produce a circular field-of-fiew (FOV) 18° in diameter, centered at nadir, allowing it to view the Earth's full disk continuously. A second, smaller pinhole can be baffled to produce a rectangular FOV that subtends 1° in the East/West direction and +/- 25° in the North/South direction, centered 22.5° west of nadir. The solar irradiance transmitted through the smaller pinhole will be added to the Earth's irradiance for a brief interval at 2230 hrs, local time, once each night. A detector in the integrating sphere can measure the ratio of the full-disk irradiance to the direct solar irradiance in any desired solar-reflective spectral band, independent of the detector's gain and the sphere's reflectivity. These stable, long-term measurements of the daily and seasonal albedo variations are valuable for climatic studies. This full-disk ratioing radiometer (FDRR) can be placed on a GOES-R satellite and equipped with a six spectral channels matched to the six solar-reflective channels of the Advanced Baseline Imager (ABI). Each ABI channel can then be calibrated by comparing the full-disk albedo derived from every one of its full disk images to that measured simultaneously by the FDRR. The FDRR is small and light, has no moving parts, requires minimal electrical power, has a low data rate, and calibrates the ABI continuously without interrupting its Earth observations or blocking its aperture.

Currently there are two Moderate Resolution Imaging Spectroradiometer (MODIS) instruments operating on-orbit, one on-board the NASA Earth Observing System (EOS) Terra spacecraft launched in December 1999 and the other on the EOS Aqua spacecraft launched in May 2002. Since its launch, each MODIS has been making continuous observations and producing calibrated data sets for the studies of the state of the Earth system and the changes of the global environment. MODIS 11 m and 12 m bands are primarily used for measuring the land and sea surface temperatures. These two bands have higher calibration accuracy requirements of 0.5% at specified typical radiance than most other thermal emissive bands (TEBs) of 1%. All the MODIS TEBs are calibrated on-orbit by an on-board calibrator blackbody (BB). To examine and verify the calibration consistency between Terra and Aqua MODIS in the thermal emissive bands, we have performed inter-comparison of MODIS 11 m and 12 m bands using closely matched thermal infrared (TIR) channels of the Advanced Very High Resolution Radiometer (AVHRR) onboard the NOAA-16 and NOAA-17. Our previous investigations only used the AVHRR LAC (local area coverage) data sets that have very limited availability. In this paper, we present our analysis of comparing the results from using LAC data sets and that from using the GAC (global area coverage) data sets. The use of GAC data sets provides more opportunities for the long-term trending analysis. Our results from August 2002 to July 2004 show that the measured temperature of Terra MODIS at 11 m and 12 m are about 0.20K higher than that from the Aqua MODIS at a brightness temperature range of 250 to 280K. Using the MODIS as an intermediate transfer reference, the results indicate that the 11 m and 12 m channels of the AVHRR on NOAA-16 are about 0.3K and 0.4K warmer than that on NOAA-17 in the same temperature range.

Resolving uncertainties surrounding the nature of future climate change is currently one of the greatest challenges facing mankind. Validating climate model predictions of the currently much miss-represented cloud radiative feedback requires measurements made from orbit of the Earth Radiation Budget (ERB), specifically targeted at clouds. The ERB parameters for measure are the scattered solar or short wave (SW, 0.3-5μm) and the emitted thermal or long wave radiance (LW, 5-100μm). The Clouds and the Earth's Radiant Energy System (CERES), as part of NASA's Earth observing System, uses thermistor bolometer detectors to provide global high spatial resolution ERB measurements from polar orbiting space platforms. The Geostationary Earth Radiation Budget (GERB) experiment is a European Space Agency (ESA) project on board the spin stabilized Meteosat second Generation (MSG) platform. Location in geostationary orbit and the use of an array of thermopile detectors enables sampling of ERB radiances from the entire Earth disc at an optimum 5 minute temporal resolution. Taking full advantage of both GERB's time resolution and CERES's global coverage for climate science requires a radiometric cross calibration and validation between the two satellite programs. This study quantifies the instantaneous sampling errors incurred by the GERB instrument due to geo-location uncertainties and orbit spin axis miss-alignment. The results can therefore be characterized as a function of scene contrast, allowing an appropriate statistical weighting to be employed when making a radiometric comparison between the GERB and CERES instruments.

The AVHRR solar reflectance channels need on-orbit calibration that can only be done vicariously. For over a decade, NOAA/NESDIS has paid particular attention to the vicarious calibration based on the Libyan Desert. A previous algorithm was remarkably precise (<2%) in predicting the long term instrument degradation, but because it omitted the seasonal variation caused by the bidirectional reflectance distribution function of the target, the postlaunch calibration was much less precise (~5%). Careful selection of more uniform target and better detection of contaminated measurements (by clouds, dust storm, and wet surface after rain) further reduced noises in the data used to monitor instrument degradation. Together, these improvements reduced latency of post-launch calibration from 3-4 years to 18 months, with enhanced statistical confidence.

Remote sensing of cloud and radiation properties from National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) satellites requires constant monitoring of the visible sensors. NOAA satellites do not have onboard visible calibration and need to be calibrated vicariously in order to determine the calibration and the degradation rate. Deep convective clouds are extremely bright and cold, are at the tropopause, have nearly a Lambertian reflectance, and provide predictable albedos. The use of deep convective clouds as calibration targets is developed into a calibration technique and applied to NOAA-16 and NOAA-17. The technique computes the relative gain drift over the life-span of the satellite. This technique is validated by comparing the gain drifts derived from inter-calibration of coincident AVHRR and Moderate-Resolution Imaging Spectroradiometer (MODIS) radiances. A ray-matched technique, which uses collocated, coincident, and co-angled pixel satellite radiance pairs is used to inter-calibrate MODIS and AVHRR. The deep convective cloud calibration technique was found to be independent of solar zenith angle, by using well calibrated Visible Infrared Scanner (VIRS) radiances onboard the Tropical Rainfall Measuring Mission (TRMM) satellite, which precesses through all solar zenith angles in 23 days.

The Advanced Spaceborne Thermal Emission and Reflection and Radiometer (ASTER), Multi-angle Imaging Spectroradiometer (MISR) and Moderate Resolution Imaging Spectroradiometer (MODIS) are all onboard the Terra platform. An important aspect of the use of MODIS, and other Earth Science Enterprise sensors, has been the characterization and calibration of the sensors and validation of their data products. The Remote Sensing Group at the University of Arizona has been active in this area through the use of ground-based test sites. This paper presents the results from the reflectance-base approach using the Railroad Valley Playa test site in Nevada for ASTER, MISR, and MODIS and thus effectively a cross-calibration between all three sensors. The key to the approach is the measurement of surface reflectance over a 1-km² area of the playa and results from this method shows agreement with MODIS to better than 5%. The paper examines biases between ASTER and the other two sensors in the VNIR due to uncertainties in the onboard calibrator for ASTER and in the SWIR due to an optical crosstalk effect.

A system to provide radiometric calibration of remote sensing imaging instruments on-orbit using the Moon has been developed by the US Geological Survey RObotic Lunar Observatory (ROLO) project. ROLO has developed a model for lunar irradiance which treats the primary geometric variables of phase and libration explicitly. The model fits hundreds of data points in each of 23 VNIR and 9 SWIR bands; input data are derived from lunar radiance images acquired by the project's on-site telescopes, calibrated to exoatmospheric radiance and converted to disk-equivalent reflectance. Experimental uncertainties are tracked through all stages of the data processing and modeling. Model fit residuals are ~1% in each band over the full range of observed phase and libration angles. Application of ROLO lunar calibration to SeaWiFS has demonstrated the capability for long-term instrument response trending with precision approaching 0.1% per year. Current work involves assessing the error in absolute responsivity and relative spectral response of the ROLO imaging systems, and propagation of error through the data reduction and modeling software systems with the goal of reducing the uncertainty in the absolute scale, now estimated at 5-10%. This level is similar to the scatter seen in ROLO lunar irradiance comparisons of multiple spacecraft instruments that have viewed the Moon. A field calibration campaign involving NASA and NIST has been initiated that ties the ROLO lunar measurements to the NIST (SI) radiometric scale.

Ball Aerospace uses several techniques in radiance calibrations of the SBUV/2 instruments. The instrument Primary Test Fixture (PTF) and Normal Incidence Test Fixture (NITF) both use Spectralon diffusers as radiance targets. Diffuser BRDF (Bidirectional Reflectance Distribution Function) is measured for a central spot at several scatter angles and at several wavelengths. Weighted BRDF is then calculated across the instrument FOV, based on diffuser BRDF measurements, spatial uniformity test data, instrument vignetting, and test geometry. This weighted BRDF curve is then fitted spectrally to determine BRDF at each wavelength of the SBUV/2 instrument. The PTF and NITF have their own BRDF curves, since each fixture has a unique diffuser plate and test geometry. A third test fixture is used for the last SBUV/2 instrument radiance calibration, using a Labsphere Uniform Source System (USS) and an external source for reference. The large aperture of the sphere provides a uniform radiance target with no need for BRDF knowledge. Comparison of instrument calibrations from all three radiance targets shows a small discrepancy of about ±1% among these calibration methods, which indicates that BRDF calculations for both PTF and NITF test diffusers are acceptable.

Long-term (i.e. multi-year) measurements of the Bidirectional Reflectance Distribution Function (BRDF) of three laboratory Spectralon diffuse targets in the ultraviolet are presented. The Spectralon targets were used in the pre-launch radiance calibration of the Solar Backscatter Ultraviolet/2 (SBUV/2) satellite instruments on NOAA 14 and 16. The BRDF data were obtained between 1994 and 2003 using the scatterometer located in the National Aeronautics and Space Administration's Goddard Space Flight Center (NASA's GSFC) Diffuser Calibration Facility (DCaF). The targets were measured at 13 wavelengths between 230 nm and 425 nm and at incident and scatter angles used in the SBUV/2 pre-launch calibration. With the exception of a spurious measurement in 1995, the percent difference in the measured BRDF of the first target, designated H1, was within ±0.7 % from 252nm to 425nm between 1994 and 2000. The percent difference in the measured BRDF of the second target, designated H2, was also within ±0.7 % over the same spectral range between 1997 and 2003. At 230 nm, the H1 and H2 BRDF measurements show larger differences primarily due to reduced signal to noise in the measurements. The combined measurement uncertainty of the reported BRDF measurements is 1.0% (k=1). The comparison also shows how the ultraviolet BRDF of these Spectralon samples changed over time under cleanroom deployment conditions.

Earth observation satellites are commonly equipped with an on-board diffuser. Their use will be pointed out and the errors associated with their use will be explained. The origin of the errors, the speckles formed by scattering on the diffusers, will be dealt with in detail and solutions to minimize these errors will be presented. The use of diffusers, and the types of diffusers will be discussed in combination with their ability to minimise the contrast of the spectral features.

The MODIS instrument relies on solar calibration to achieve the required radiometric accuracy. This solar calibration occurs as the TERRA spacecraft comes up over the North Pole. The earth underneath the spacecraft is still dark for approximately one minute and the sun is just rising over the earth's north polar regions. During this time the sun moves through about 3.3 degrees, the scan mirror rotates about 19 times and about 50 exposures (frames) are taken each time the field of view is directed to the approximate center (sweet spot) of the solar diffuser. For some of MODIS's bands the brightness of the diffuser is reduced, to prevent detector saturation, by means of a retractable pinhole screen, which produces approximately 600 pinhole images of the sun, within the field of view of any one detector. Previous attempts at creating a radiometric model of this, reduced intensity, calibration scenario produced intensity variations on the focal planes with insufficient detail to be useful. The current computational approach, gets around these limitations and is fast enough to permit simulation of the motion of the sun and the scan mirror. The results resemble the observed focal plane temporal and spatial intensity variations well enough to be useful. The computational approach is described and a comparison with observational data is presented.

Two of the GOES instruments, the Imager and the Sounder, perform scans of the Earth to provide a full disc picture of the Earth. To verify the entire scan process, an image of a target that covers an 18o circular field-of-view is collimated and projected into the field of regard of each instrument. The Wide Field Collimator 2 (WFC2) 1 has many advantages over its predecessor, WFC1, including lower thermal dissipation, higher far field MTF, smaller package, and a more intuitive (faster) focusing process. The illumination source is an LED array that emits in a narrow spectral band centered at 689 nm, within the visible spectral bands of the Imager and Sounder. The illumination level can be continuously adjusted electronically. Lower thermal dissipation eliminates the need for forced convection cooling and minimizes time to reach thermal stability. The lens system has been optimized for the illumination source spectral output and athermalized to remain in focus during bulk temperature changes within the laboratory environment. The MTF of the lens is higher than that of the WFC1 at the edge of FOV. The target is focused in three orthogonal motions, controlled by an ergonomic system that saves substantial time and produces a sharper focus.

Detectors have historically been calibrated for spectral power responsivity at the National Institute of Standards and Technology (NIST) using a lamp-monochromator system to tune the wavelength of the excitation source. Silicon detectors can be calibrated in the visible spectral region with uncertainties at the 0.1 % level. However, uncertainties increase dramatically when measuring an instrument's spectral irradiance or radiance responsivity. In addition, the uncertainties are even larger in the UV and IR ranges. We will discuss a new laser-based facility for Spectral Irradiance and Radiance responsivity Calibrations using Uniform Sources (SIRCUS) that was developed to calibrate instruments directly in irradiance or radiance mode with uncertainties approaching those available for spectral power responsivity calibrations. In this facility, high-power, tunable lasers are introduced into an integrating sphere using optical fibers, producing uniform, quasi-Lambertian, high radiant flux sources. Reference standard irradiance detectors, calibrated directly against national primary standards for spectral power responsivity, are used to determine the irradiance at a reference plane. Knowing the measurement geometry, the source radiance can be readily determined as well. The radiometric properties of the SIRCUS source coupled with state-of-the-art transfer standard radiometers whose responsivities are directly traceable to primary national radiometric scales, result in typical combined standard uncertainties in irradiance and radiance responsivity calibrations less than 0.1 % in the visible (larger in the UV and IR). Details of the facility are presented and examples of unique calibrations possible in the facility are given, including system-level responsivity calibrations in support of the National Aeronautics and Space Administration's (NASA's) remote sensing activities.

Advances in earth and space instrumentation will come from future optical systems that provide large, deployable collecting areas of low areal mass density (< 10 kg/sq meter), affordable costs of fabrication ($10k/sq meter), and production times of a few years or less. Laminated optics comprised of an electroformed, replicated nickel optical surface supported by a reinforced shape memory resin composite substrate have the potential to meet the requirements for rapid fabrication of lightweight, monolithic, stowable, large optics, where large is defined to be 8 meters in diameter or larger. The high stiffness of a deployable composite substrate and a high quality, thin, electroformed metal optical surface combine the best properties of these disparate materials to provide a robust yet lightweight mirror system to meet the needs of future missions. The unique properties of shape memory resins in the composite provide a larger range of design parameters for production of usable optics. Results are presented from optical and structural tests of various surface and substrate constructions that may be solutions to the key issues, which are primarily material interface stress control, stability, and deployment repeatability. Initial requirements analysis and material properties measurements that determine both system and individual material target performance are presented.

With the launch of several Earth observing satellites over the last decade, we are now in a "data rich" environment. From NASA's Earth Observing System (EOS) satellites alone, we are accumulating more than 3.5 TB per day of raw data and derived geophysical parameters. The data products are being distributed to a large user community that in-cludes scientific researchers, educators and operational government agencies. Notable progress has been made in the last decade in facilitating access to data. However, to realize the full potential of the growing archives of valuable scien-tific data, further progress is necessary in the transformation of data into information, and information into knowledge that can be used in particular applications. This paper discusses the concept of an Intelligent Archive in the context of a Knowledge Building system (IA-KBS), with six key capabilities: Virtual Product Generation, Significant Event Detec-tion, Automated Data Quality Assessment, Large-Scale Data Mining, Dynamic Feedback Loop, and Data Discovery and Efficient Requesting. Technologies enabling these capabilities are identified. Many of these technologies are in development today by NSF, NASA and industry sponsorship. These can be taken advantage of for evolving the current generation of data and information systems into the visionary IA-KBS.

Polarimetric measurements in the VIS/NIR spectral region improve aerosol microphysical and compositional retrievals. The retrieval approaches exploit the unique polarimetric signatures of aerosols as function of scattering angle, thereby driving the requirement for data collection over a large range of scattering angles. The scattering angle coverage is a function both of the instrument/sun/target geometry and the instrument architectural approach toward acquiring multi-angular data. These two functions are important aspects of a spaceborne, multi-angular polarimetric mission. The instrument design must also consider the impact of retrieval error arising from aerosol spatial variability. For a single-pixel scanning architecture, both the pixel separation as a function of earth rotation beneath the spacecraft and the pixel growth with increasing scan angle can result in significant retrieval errors due to aerosol spatial variability. We have investigated the impact of aerosol spatial inhomogeneity on the performance of a single-pixel, along-track scanning, multi-angular polarimetric instrument operating in a low-earth orbit (LEO) such as the EOS Aqua orbit of 705 km. Possible mitigation strategies to reduce the impact of the spatial inhomogeneity on aerosol property retrieval performance are also reviewed.

SPoRTMap is a system simulation tool for satellite-based polarimetric aerosol measurements. It integrates a large number of the tasks needed to simulate polarimetric Earth observations from satellite sensors: phenomenology model setup and run, sensor geometry setup, integration of sensor radiometric models, interpolation from model grid to sensor field of view, Stokes parameter SNR computations, etc. The architecture of the simulation system is modular to enable replacement of radiative transfer and sensor noise models. Operation of SPoRTMap is illustrated through creation of an orbital simulation using a specific aerosol model. Integration of diverse aerosol models into orbital mosaics is shown.

The Atmospheric Infrared Sounder (AIRS), the Advanced Microwave Sounding Unit (AMSU-A), and the Humidity Sounder for Brazil (HSB) instruments were launched aboard NASA's Aqua spacecraft on May 4, 2002 into near-polar Earth orbit with a 1:30 PM ascending equator crossing. The AIRS instrument measures 2,378 infrared and four visible/near-infrared channels, while the 15-channel AMSU-A and four-channel HSB instrument provide simultaneous observations in the microwave region from 23.8-89 GHz and 150-189 GHz, respectively. Together these instruments produce thousands of measurements per second for a mission expected to last 7 years. This paper describes the challenges of identifying and monitoring, among the approximately 1,500 available engineering and quality assessment parameters, a representative subset for tracking each instrument's performance. A software system has been developed which autonomously extracts key items from the voluminous project database, performs data analysis and creates web-based daily summary reports with links to these archived results. Independently, a second process autonomously monitors these trending data products and notifies team members by e-mail if parameters exceed their trending-specific monitoring limits. Finally, this paper describes how this system has been used to predict long-term instrument performance trends, investigate previous flight anomalies and maintain the instrument within calibration specifications.

The QuickBird commercial imaging satellite is a pushbroom system with four multispectral bands covering the visible through near-infrared region of the spectrum and a panchromatic band. 6972 detectors in each MS band and 27888 detectors in the pan band must be calibrated. In an ideal sensor, a uniform radiance target will produce a uniform image. Unfortunately, raw imagery generated from a pushbroom sensor contains vertical streaks caused by variability in detector response, variability in electronic gain and offset, lens falloff, and particulate contamination on the focal plane. Relative radiometric correction is necessary to account for the detector-to-detector non-uniformity seen in raw imagery. A relative gain is calculated for each detector while looking at a uniform target such as an integrating sphere during ground calibrations, diffuser panel, or large desert target on-orbit. A special maneuver developed for QuickBird called the "Side-Slither" technique is discussed. This technique improves the statistics of a desert target and achieves superior non-uniformity correction in imagery. The "Side-Slither" technique is compared to standard techniques for calculation of relative gain and shows a reduction in the streaking seen in imagery.

A key instrument for the NASA EOS mission, the Moderate Resolution Imaging Spectroradiometer (MODIS) is currently operating on-board the Terra and Aqua spacecrafts. The MODIS has 16 Thermal Emissive Bands (TEB), with each having 10 detectors, covering the wavelengths from 3.7 to 14.4 mm. On-orbit each detector is calibrated by an on-board calibrator (OBC) blackbody (BB). Except for the low gain band used for fire detection, the thermal emissive bands use a quadratic algorithm in the Level 1B (L1B) code for calibration and for retrieval of top of the atmosphere (TOA) scene radiance. The specified calibration uncertainty of 1% applies to most of the TEB at their typical scene radiance levels and for scene-viewing angles inside a ±45° range (relative to instrument nadir). The requirements for two Sea Surface Temperature (SST) bands at 11 mm and 12 mm and for a low gain fire band are 0.5% and 10% respectively. The uncertainty requirements are twice as large at other non-typical radiance levels or at viewing angles outside the ±45º range. This paper reviews the MODIS TEB calibration algorithms and presents the calibration uncertainty analysis, including the methodology and results. Discussions will be focused on the key contributors to the uncertainty computation in the L1B. Results of the estimated uncertainties with the specifications at typical radiance level and at instrument nadir will be provided. A separate paper in this proceeding gives similar analysis for the MODIS Reflective Solar Bands (RSB).

A key instrument for the NASA Earth Observing System (EOS) mission, the Moderate Resolution Imaging Spectroradiometer (MODIS), is currently operating on-board the Terra and Aqua spacecrafts. This paper discusses the calibration uncertainty analysis for the MODIS Reflective Solar Bands. Each MODIS, either on the Terra or on the Aqua spacecraft, has 20 reflective solar bands, making observations at three different nadir spatial resolutions: 250m (B1-2), 500m (B3-7), and 1000m (B8-19, and B26). The 250m, 500m, and 100m bands have 40, 20, and 10 detectors per band, respectively. The reflective solar bands spectral wavelengths are between 0.41 and 2.3 μm. On-orbit, a solar diffuser is used for the reflective solar bands calibration. For the high gain ocean color bands (B8-16), a retractable attenuation pinhole screen is placed in front of the solar diffuser during each calibration. For the reflective solar bands, the specified uncertainty at the typical scene is 2% in reflectance and 5% in radiance. The uncertainty analysis to be presented in this paper will include the approaches and estimated results for Terra MODIS. Aqua MODIS L1B uncertainty is not reported but is extremely similar to Terra. Emphasis will be on the solar diffuser bi-directional reflectance factor characterization at pre-launch since it is a major contributor to the reflective solar bands uncertainty. Other factors include the Earth view response-versus-scan angle, solar diffuser degradation and attenuation screen effect. For the Terra MODIS instrument, the estimated uncertainties based on the instrument characterization and performance will be compared with the specifications.

The paper presents a new method of probabilistic filtering for radar target recognition. The classical Bayesian detector/estimator suffers from the insufficient information about target signature probability distributions and their a priory appearance probabilities. If the number of radar image objects to be classified is not known exactly the appeared unknown target may be wrong classified as one of the known targets. To eliminate this type of errors one can use the known probabilistic windows matched by shape to the recognition signature distributions. The combination of the probability window with a non-linear transform of the signature space is proposed in the paper. Such a combination forms a probabilistic filter. The probabilistic filter output is proportional to the likelihood probability of how the sensed object matches to its statistical model. The theoretical background of the probabilistic filtering method and its application to real X-band radar data are presented in the paper. The proposed method reduces the amount of a priory information required for the recognition and detects well the objects of the same nature independently from their size. For example, the probabilistic filter classifies well the different type of vegetation in the radar images.