The Advanced Land Imager (ALI) is the primary instrument flown on the first Earth Observing mission (EO-1), launched on November 21, 2000. It was developed under NASA's New Millennium Program (NMP). The NMP mission objective is to flight-validate advanced technologies that will enable dramatic improvements in performance, cost, mass, and schedule for future, Landsat-like, Earth Science Enterprise instruments. ALI contains a number of innovative features designed to achieve this objective. These include the basic instrument architecture which employs a push-broom data collection mode, a wide field of view optical design, compact multi-spectral detector arrays, non-cryogenic HgCdTe for the short wave infrared bands, silicon carbide optics, and a multi-level solar calibration technique. During the first ninety days on orbit, the instrument performance was evaluated by collecting several Earth scenes and comparing them to identical scenes obtained by Landsat7. In addition, various on-orbit calibration techniques were exercised. This paper will present an overview of the EO-1 mission activities during the first ninety days on-orbit, details of the ALI instrument performance and a comparison with the ground calibration measurements.

A new era in remote sensing will begin with the launch of the National Polar-orbiting Operational Environment Satellite Systems (NPOESS) Preparatory Project (NPP) spacecraft in 2005, and the multiple operational NPOESS launches in sun-synchronous orbital planes (nominally 13:30, 17:30, or 21:30 local equatorial crossing times) starting in 2008. Users of polar-orbiting environmental satellite data will see a profound improvement in the radiometric quality, spectral coverage, and spatial resolution of routinely available visible and infrared data relative to current operational civilian and military polar-orbiting systems. The improved data will be provided by the NPOESS Visible Infrared Imaging Radiometer Suite (VIIRS). VIIRS will provide Environmental Data Records (EDRs) to meet civilian and national defense operational requirements, including day and night cloud imagery, sea surface temperatures (SST), and ocean color. EDRs will be produced by ground processing of raw data records (RDRS) from the VIIRS sensor. VIIRS will replace three currently operating sensors: the Defense Meteorological Satellite Program (DMSP) Operational Line- scanning System (OLS), the NOAA Polar-orbiting Operational Environmental Satellite (POES) Advanced Very High Resolution Radiometer (AVHRR), and the NASA Earth Observing System (EOS Terra and Aqua) MODerate-resolution Imaging Spectroradiometer (MODIS). This paper describes the VIIRS all-reflective 22-band single-sensor design. VIIRS provides low noise (driven by ocean color for the reflective visible and near-IR spectral bands and by SST for the emissive mid and long-wave IR spectral), excellent calibration and stability (driven by aerosol, cloud, and SST), broad spectral coverage, and fine spatial resolution driven by the imagery EDR. In addition to improved radiometric, spectral, and spatial performance, VIIRS features DMSP OLS-like near- constant resolution, global twice-daily coverage in each orbit plane, and direct heritage to proven design innovations from the successful Sea-viewing Wide Field-of- view Sensor (SeaWiFS) and Earth Observing System (Terra) MODIS.

This paper presents an overview of the Visible and Infrared Imaging Radiometer Suite (VIIRS) design process that achieved exceptional competitive IPO ratings for system optimization, sensor system design, and systems engineering, integration and test (SEIT). A novel aspect of the competition was provision to the sensor competitors of a specification of geophysical measurement requirements called Environmental Data Records (EDRs), rather than a sensor hardware specification. The contractors were required to derive optimal VIIRS hardware specifications from the EDRs and Raytheon's process is the subject of this paper. VIIRS will become the next-generation United States polar-orbiting Operational Environmental Satellite System (MPOESS) Preparatory Project (NPP) spacecraft. Beginning in 2008, the NPOESS VIIRS instrument will be launched into 1370, 1730, and 2130 local-time ascending-node sun-synchronous polar orbits as the single operational source for dozens of civil and defense environmental and weather products, as well as climate research data. VIIRS will replace three different currently operating sensors: the Defense Meteorological Satellite Program (DMSP) Operational Line-scan System (OLS), the NOAA Polar-orbiting Operational Environmental Satellite (POES) Advanced Very High Resolution Radiometer (AVHRR), and the NASA Earth Observing System (EOS Terra and Aqua) MODerate-resolution Imaging Spectroradiometer (MODIS). A critical VIIRS challenge was design optimization to differing requirements from the three user agencies (DoD, NOAA, and NASA) represented by the NPOESS Integrated Program Office.

The Atmospheric Infrared Sounder project will measure global atmospheric water vapor and temperature with unprecedented resolution and accuracy. AIRS is an infrared instrument covering 3.7-15.4 microns in 2378 IR channels. This paper describes the AIRS mission and science objectives, the instrument design and operation, the calibration plan, the in-flight operational scenario and the Science Processing System. All aspects of the program are addressed here to demonstrate that the AIRS program is ready to transition to the flight segment of the program. The AIRS instrument meets the majority of instrument design requirements established in order to meet the scientific objectives. A well-defined operational approach has been established, and a sound calibration plan has been developed to ensure optimal performance throughout the life of the mission.

Spectral characterization of the Atmospheric Infrared Sounder (AIRS) instrument during ground Thermal/Vacuum tests posed a number of difficult challenges due to the high spectral resolution and accurate knowledge requirements. A Fourier transform spectrometer was used in external step-scan mode to characterize the spectral response functions (SRFs) of the 2378 infrared detectors in the focal plane array which is part of the AIRS grating spectrometer. This paper summarizes the test development and characterization results. Special post-test data analysis was needed separately to determine the effects of interference in the order-separating entrance filters, which have a different temperature dependence from that of the otherwise unperturbed SRFs. This separation, which was successfully accomplished, provides calibration of the AIRS SRF shape over the full expected range of instrument temperatures.

The objective of the current research is to study the theoretical uncertainty of the CERES ERBE-like level 1 and level 2 instantaneous filtered and unfiltered radiance data products. The instrument views incident radiation from an Earth scene, which is then focused on a blackened thermistor bolometer, where it is converted to an electrical output. The measured digital counts are converted to a filtered radiance by means of instrument calibration coefficients. The filtered radiance is then converted to an unfiltered radiance with an algorithm that utilizes the instrument's spectral response function. Uncertainties in the calibration sources and the spectral response function of the instrument can negatively affect the quality of the final data products. A statistical study of the data products' sensitivity to various instrument and calibration parameters is performed using high-fidelity first-principle numerical models of the CERES instrument. Once the key parameters are identified, fidelity intervals of the data products are calculated using nominal parameter values and uncertainty distributions.

The Marine Optical Buoy (MOBY) provides values of water- leaving radiance for the calibration and validation of satellite ocean color instruments. Located in clear, deep ocean waters near the Hawaiian Island of Lanai, MOBY measures the upwelling radiance and downwelling irradiance at three levels below the ocean surface plus the incident solar irradiance just above the surface. The radiance standards for MOBY are two integrating spheres with calibrations based on standards traceable to the National Institute of Standards and Technology (NIST). For irradiance, the MOBY project uses standard lamps that are routinely calibrated at NIST. Wavelength calibrations are conducted with a series of emission lines observed from a set of low pressure lamps. Each MOBY instrument views these standards before and after its deployment to provide system responses (calibration coefficients). During each deployment, the stability of the MOBY spectrographs and internal optics are monitored using three internal reference sources. In addition, the collection optics for the instrument are cleaned and checked on a monthly basis while the buoy is deployed. Divers place lamps over the optics before and after each cleaning to monitor changes at the system level. As a hyperspectral instrument, MOBY uses absorption lines in the solar spectrum to monitor its wavelength stability. When logistically feasible during each deployment, coincident measurements are made with the predecessor buoy before that buoy's recovery. Measurements of the underwater light fields from the deployment vessel are compared with those from the buoy. Based on this set of absolute calibrations and the suite of stability reference measurements, a calibration history is created for each buoy. These calibration histories link the measurement time series from the set of MOBY buoys. In general, the differences between the pre- and post-deployment radiance calibrations of the buoys range from +1% to -6% with a definitive bias to a negative difference for the post- deployment values. This trend is to be expected after a deployment of 3 months. To date, only the pre-deployment calibration measurements have been used to adjust the system responses for the MOBY time series. Based on these results, the estimated radiometric uncertainty for MOBY in-water ocean color measurements is estimated to be about 4% to 8% (kequals1). As part of a collaboration with NIST, annual radiometric comparisons are made at the MOBY calibration facility. NIST personnel use transfer radiometers and integrating spheres to validate (verify) the accuracy of the MOBY calibration sources. Recently, we began a study of the stray light contribution to the radiometric uncertainty in the MOBY systems. A complete reprocessing of the MOBY data set, including the changes within each MOBY deployment, will commence upon the completion of the stray light characterization, which is scheduled for the fall of 2001. It is anticipated that this reprocessing will reduce the overall radiometric uncertainty to less than 5% (kequals1).

As part of the Triana mission, the Scripps Earth Polychromatic Imaging Camera (Scripps-EPIC) will view the full sunlit side of Earth from the Lagrange-1 point. The National Institute of Standards and Technology and the Scripps Institution of Oceanography, in collaboration with the contractor, Lockheed-Martin, planned the radiometric calibration of Scripps-EPIC. The measurements for this radiometric calibration were selected based upon the optical characteristics of Scripps-EPIC, the measurement equation relating signal to spectral radiance, and the available optical sources and calibrated radiometers. The guiding principle for the calibration was to perform separate, controlled measurements for each parameter in the measurement equation, namely dark signal, linearity, exposure time, and spectral radiance responsivity.

Airborne radiometric instruments are often used to collect radiance data, whether for producing remote sensing imagery, for use in vicarious calibration, or for atmospheric correction. Reflected radiance from a test site is detected by an Exotech model 100BX radiometer that contains four different spectral filters which coincide with the first four bands of Landsat Thematic Mapper (TM). These filters can be interchanged with filters that correspond to the first three multispectral bands of SPOT. Typically these radiometers are calibrated in a laboratory environment with incandescent radiance sources whose spectral outputs are known by some established standard. In the field, the radiometers are used with a different source than that used for the laboratory calibration, namely the sun. The solar radiation based calibration (SRBC) has been demonstrated to be an accurate calibration method for these instruments. The major advantage of this method is that the source for the calibration is the same source used in acquiring field measurements. In this work, solar radiation based calibration is compared to laboratory radiometric calibration done with a spherical integrating source (SIS) and a lamp source in the Remote Sensing Group (RSG) blacklab for airborne radiometers. Results of measurements taken over Ivanpah Playa on 6 July 2000 and 4 June 2000 by an Exotech model 100BX calibrated with these methods are presented and biases in the three different calibration methods are discussed.

The latest spaceborne scatterometer, SeaWinds on QuikSCAT, estimates near-surface ocean winds at 25 km resolution over the entire globe. The scatterometer wind retrieval process generates several possible wind vector choices or ambiguities at each resolution cell. Routines for selecting a unique wind vector field are generally ad hoc and error prone. In order to assess SeaWinds ambiguity selection and spatial consistency of retrieved winds, a quality assurance (QA) algorithm is presented based on comparing ambiguity-selected winds to a low-order wind field model fit. Regions exceeding error thresholds are rated according to spatial consistency and flagged as possible ambiguity selection errors. Appropriate error thresholds and additional flagging criteria are set through an analysis of false alarms versus missed detections on a manually-inspected training data set. The QA algorithm correctly identifies 97% of the manually flagged regions with a false alarm rate of less than 2%. Applying the algorithm to 16 months of QuikSCAT wind data, we conclude that SeaWinds ambiguity selection is over 95% effective on regions of rms wind speed greater than 3.5 m/s. The QA algorithm indicates that higher noise occurs at nadir and in areas of low wind speed. additionally, fewer estimated ambiguity selection errors occur at nadir and on the swath edges due to a larger ambiguity set in those regions. The percentage of ambiguity selection errors are found to be highly correlated with the number of cyclonic storms passed by SeaWinds and the percentage of wind vector cells corrupted by rain.

While originally designed for making wind vector measurements over the ocean, radar scatterometers are also effective for large-scale monitoring of the Earth's land and ice surfaces. The recently launched SeaWinds scatterometer is the next generation of Ku-band scatterometers and offers many advantages over previous scatterometers including a very wide swath and constant incidence angle measurements. The wide swath of SeaWinds enables much more frequent coverage of the Earth's surface than has previously been possible and enhances the potential of the data in land and ice applications. SeaWinds data has been particularly effective in polar ice applications and SeaWinds data is currently being used for operational sea-ice extent monitoring and large iceberg tracking. Additional applications include monitoring glacial and sea-ice melting and studying the firn structure in Greenland and Antarctica. New applications of SeaWinds are being developed, including high resolution wind retrieval. Several such applications are briefly considered.

SeaWinds on QuikSCAT is the latest of NASA's wind-observing scatterometer missions. It was launched in June of 1999 with the goal of accurately measuring wind fields over all the oceans. It has also proven to be valuable in monitoring ice changes in polar regions. The value of such data necessitates an extremely accurate and precise calibration of both satellite performance and instrument measurements. In order to assure optimal performance a Calibration Ground Station has been constructed, which provides direct measurements of the instrument transmissions. Each time the spacecraft flies overhead, approximately twice a day, the CGS passively captures microwave pulses transmitted from QuikSCAT. The data is then used with various processing and analysis techniques to validate the system performance and calibration. As part of the calibration analysis, a software simulation model of the instrument system has been constructed. This model is able to simulate critical instrument systems and path loss characteristics and thus predict CGS receive data for any given satellite pass. By comparing model-based simulation data with actual recorded CGS data, calibration of parameters such as system timing, power, attitude, and Doppler compensation can be accurately determined. The analysis has been able to validate the Doppler/range compensation algorithm, instrument timing, and other key system operational parameters. The major contributions of the CGS-based analysis are demonstration of pointing accuracy and overall system stability of SeaWinds. By employing a variance minimization technique between simulated and actual data, the QuikSCAT platform is shown to be extremely stable.

Changes in the Greenland ice sheet are considered important indicators of global climate change. These changes can be monitored using space-borne scatterometers which provide frequent coverage of the entire ice sheet. This paper provides a general overview of backscatter measurements over Greenland and the distinguishing attributes of the data sets over the different snow facies including temporal signatures. Seasat-A scatterometer (1978), NSCAT (1996-1997), SeaWinds (1999-present), and ERS AMI (1992-2000) scatterometer data are analyzed to evaluate the long term changes in the ice sheet. An increase in backscatter is observed in the dry snow zone near the dry snow zone/percolation zone boundary. A simple algorithm is applied to determine the length and extent of the melt for the summer of 1999 as observed by SeaWinds and ERS. A comparison between the two sensors shows similar results with the apparent differences attributed to the higher temporal resolution of SeaWinds and the difference in frequencies between the two instruments.

Radiometric calibration of spacecraft sensors using an on-board diffuser has become an accepted method in recent years for sensors operating in the solar-reflective portion of the spectrum. In many of these approaches, the radiance from a sunlit diffuser is used to illuminate the full aperture and full optical path of the sensor. If both the bi-directional reflectance distribution function (BRDF) of the diffuser and the incident solar irradiance are known, the absolute radiance from the diffuser can be used to determine the absolute radiometric calibration of the sensor. In this work, a method for the absolute radiometric calibration using a diffuser made of S13G/LO paint for a silicon-based detector sensor with spectral bands similar to Landsat-7 ETM+ is discussed. The spectral BRDF of a witness sample of the diffuser was measured with the goniometric facility at the Remote Sensing Group of the Optical Sciences Center at the University of Arizona. A measured solar spectral irradiance spectra is used to model the radiance at the sensor entrance pupil. Also presented is a sensitivity analysis of the diffuser-leaving radiance as a function of sensor view and incident solar angle. This sensitivity analysis is used to provide an error estimate for the calibration of the sensor using a diffuser based on the S13G/LO paint.

The MODIS instrument's solar diffuser is used in its radiometric calibration for the reflective solar bands (VIS, NIR, and SWIR) ranging from 0.41 to 2.1 micron. The sun illuminates the solar diffuser either directly or through an attenuation screen. The attenuation screen consists of a regular array of pin holes. The attenuated illumination pattern on the solar diffuser is not uniform, but consists of a multitude of pin-hole images of the sun. This non-uniform illumination produces small, but noticeable radiometric effects. A description of the computer model used to simulate the effects of the attenuation screen is given and the predictions of the model are compared with actual, on-orbit, calibration measurements.

A Solar Diffuser (SD) panel, made of Spectralon, is used for the on-orbit calibration of MODIS reflective solar bands in the spectral range from 0.41 to 2.1 micron. A Solar Diffuser Stability Monitor (SDSM), designed to track the SD degradation during its on-orbit operation, is used at same time during SD calibration by alternatively viewing the Sun though a 1.44% attenuation screen and the Sun-illuminated SD. On-orbit observations have shown serious ripples in the SDSM Sun view response. In this paper, a theoretical model, developed to simulate the SDSM on-orbit performance, is described and the simulation results are compared with the actual on-orbit observations.

Routine observations of the Moon have been acquired by the Robotic Lunar Observatory (ROLO) for over four years. The ROLO instruments measure lunar radiance in 23 VNIR (Moon diameter approximately 500 pixels) and 9 SWIR (approximately 250 pixels) passbands every month when the Moon is at phase angle less than 90 degrees. These are converted to exoatmospheric values at standard distances using an atmospheric extinction model based on observations of standard stars and a NIST-traceable absolute calibration source. Reduction of the stellar images also provides an independent pathway for absolute calibration. Comparison of stellar-based and lamp-based absolute calibrations of the lunar images currently shows unacceptably large differences. An analytic model of lunar irradiance as a function of phase angle and viewing geometry is derived from the calibrated lunar images. Residuals from models which fit hundreds of observations at each wavelength average less than 2%. Comparison with SeaWiFS observations over three years reveals a small quasi-periodic change in SeaWiFS responsivity that correlates with distance from the Sun for the first two years, then departs from this correlation.

This paper describes the properties of two transfer standard sources developed to improve the accuracy of dissemination of spectral irradiance and radiance. The sources both make use of a novel concept, detector stabilization and monitoring, which allow the sources to provide high accuracy calibrations over a period of time more than four times that of conventional sources. Such sources have applications in many technology sectors but they are of particular relevance to the Earth Observation community as they offer high reliability in different environmental conditions and are less susceptible to change on transportation. The radiance source has the additional property of providing an extremely spatially uniform output, <+/- .02% at 380 nm over 80 mm diameter.

The on-orbit identification of the transfer function (TF) of a spaceborne optical telescope is useful for the acceptance test of the instrument, for the on-orbit refocusing and for the restoration of the recorded images. An original method is presented to perform such an identification from a single image. It is based on a physical modeling of the TF via the optical aberrations of the instrument, and on the automatic extraction of sub-images containing patterns that can be described with few parameters, e.g. step functions. The estimation of the TF is performed by minimizing a least-square criterion incorporating all extracted sub-images, as a function of the unknowns, which are the aberrations and the step parameters. Aliasing is explicitly incorporated in the image modeling, so that the TF can be estimated up to the optical cutoff frequency. The method is validated first on simulated images of step functions, then on a realistic, undersampled and noisy simulated image.

The radiometric response of the EOS-AM1 Multi-angle Imaging SpectroRadiometer (MISR) is to be measured throughout the six-year mission. To accomplish this task, MISR makes routine use of an on-board calibrator, aircraft flyovers, field exercises, and comparisons to other on-orbit and aircraft sensors. Analyses of these data results in a deliverable called the Ancillary Radiometric Product (ARP). This file contains the radiometric response parameters for all nine cameras and four spectral bands. The instrument on-board calibrator is exercised bi-monthly, and the next ARP time-series file is created shortly thereafter. This file is used in MISR standard product generation to convert the sensor output into a measure of the incident radiance, and is used to process all MISR data acquired in the subsequent two months. Thereafter the process is repeated and the new ARP time-series file is utilized. Due to improvements in the processing algorithms, updates are allowed to the inactive ARP data files. These revisions would be used should a previously generated MISR data product be reordered and reprocessed, as would be the case should an investigator desire to make use of all science software algorithm upgrades. This paper discusses the investigations and algorithm changes that have occurred in the production of the ARP since launch, and discusses changes to the Level 1B data that might be expected should data be reprocessed.

The Remote Sensing Group at the University of Arizona has used ground-based test sites for the vicarious calibration of airborne and satellite-based sensors. Past work has focused on high-spatial-resolution sensors that are well- suited to the reflectance-, irradiance-, and radiance-based methods. Application of these methods to the Moderate Resolution Imaging Spectroradiometer (MODIS) with its lower spatial resolution pose a challenge for vicarious calibraiton. This work presents a cross-calibration approach using the high spatial resolution sensor Enhanced Thematic Mapper Plus (TEM+) on the Landat-7 platform that allows the reflectance-based results of ETM+ to be scaled to the larger footprint of MODIS. This calibration takes into account the changes in solar zenith angle due to the 40- minute separation in overpass times of the two sensors which view the test sites on the same day with the same view angle. Also included are corrections due to the spectral differences between the sensors. Early results show that MODIS and ETM+ agree to better than 5% in the solar reflective for bands not affected by atmospheric absorption.

The calibration accuracy of the Moderate resolution Imaging Spectro-radiometer (MODIS) on Terra near its one year anniversary of first light has been assessed using ER-2 aircraft underflights during the Terra eXperiment (TX-2001) in the spring, 2001. The ER-2, equipped with the MAS and SHIS instruments, underflew Terra several times viewing clear sky earth scenes of the Gulf of Mexico. MAS and SHIS form a powerful tandem, combining high spatial resolution imaging with high spectral resolution sampling in the midwave to longwave infrared region. The assessment is based on co-located MODIS and MAS fields of view with matching viewing geometry and removes spatial and spectral dependencies. The MAS L1B calibration accuracy is improved by transferring the SHIS calibration accuracy (conservatively 0.5 K) to MAS. The early results of two days from TX-2001 indicate that MODIS bands are performing well, but not optimally. The MODIS MWIR window bands appear to be close to the 0.75 - 1% radiometric accuracy specification for the uniform warm, low reflectance scenes assessed, perhaps suggesting that known electronic crosstalk in MODIS SWIR and MWIR bands is small for such scenes. MODIS LWIR window bands show residuals of about 0.5 K to 0.6 K, larger than the 0.5% radiometric accuracy specification. However with the 0.5 K (window bands) to 1 K (atmospheric bands) uncertainties associated with the current assessment, it is not possible to definitively state whether these MODIS bands are or are not within specification. MODIS LWIR atmospheric CO₂ bands appear to perform near the 1% accuracy specification with the exception of bands 35 and 36, the upper tropospheric CO₂ bands at 13.9micrometers and 14.1micrometers . Different MODIS viewing geometry on the two days seems to suggest that scan mirror reflectance dependence on mirror angles may be influencing the MODIS L1B calibration for some bands, most notably the 8.6micrometers and LWIR CO₂ bands; however this assessment is dependent upon the accuracy of the spectral correction (a function of atmospheric conditions), which will be further investigated in coming months. It was surprising to find large MODIS residuals for several bands when the mirror angle to the earth scene closely matched that of when MODIS views its onboard blackbody.

The accuracy of the MODerate Resolution Imaging Spectroradiometer (MODIS-AM) end data products is affected by the spatial response in the form of the Modulation Transfer Function (MTF). This effect is most noticeable near spatial transition periods where the contrast changes are high. This research effort estimates the MODIS MTF using a simplified model, based on Santa Barbara Research Center's MTF model. The simplified MTF model is incomplete, and, MTF validation laboratory data are used to complete the model by estimating the unknown parameters. The laboratory data were taken using the Internal Alignment Collimator, a line spread function calibration instrument. Using the completed MTF model, a MTF correction filter is derived. The filter corrects the along-scan and along-track optical blurring and the along-scan non-zero integration time. The filter reduces the Point Spread Response (PSR) footprint by sharpening the response. The correction filter is demonstra ted on MODIS level 1B data, using a scene from Mono Lake September 29, 2000 and a scene from the Maricopa Agricultural Center (MAC) September 26, 2000.

The whiskbroom scanner Global Imager (GLI) will be launched on Advanced Earth Observation Satelite 2 (ADEOS-2). It will provide remotely sensed data from the Earth surface from the visible to the thermal infrared. Since the Earth observation data require a careful calibration, different on-board calibration tools have been integrated in the GLI hardware design. For the VIS-SWIR spectral range a special calibration device allows solar and lamp calibration. In this paper a calibration strategy is presented to achieve a high calibration accuracy of the remotely sensed data by means of solar calibration. Therefore the theoretical background, the performed hardware characterization and applied external data basis are presented. Further on it is shown how a stray light simulation analysis using a non- sequential ray-tracing tool will be used to increase the reliability of the solar calibration.

DLR's Modular Optoelectronic Scanner MOS on the Indian Remote Sensing Satellite IRS-P3 has been working now for almost 5 years in orbit. In September 2000 the power supply for driving the internal lamps and the sun calibration equipment failed so that we no longer have actual in-orbit calculation values. However the spectrometers themselves are still working and nadir remote data collection is running. To remedy this situation we have tried to use vicarious calibrations over the Sahara desert. The Great Eastern Erg near the border between Tunisia and Algeria has been selected for this purpose. Because we do not have any ground truth measurements from this area, we have investigated the correlation between the in-orbit sun and internal lamp calibration data and the upwelling radiance data of this area in the VIS/NIR-channels of MOS from May 1996 to August 2000. The vicarious calibration data were corrected with respect to actual sun irradiance only, but not to atmospheric conditions. Nevertheless there is a remarkably high correlation between the in-orbit calculations and these vicarious calculations. This enables us to continue to generate calibration data sets for MOS only by using actual vicarious calibration data in place of the in-orbit calibration data. Additionally the vicarious calibrations can be compared with the extrapolated results of the time trend of the radiometric sensitivity of all spectral channels which we found from the previous in-orbit calibrations. The results of all these investigations are presented in this paper.

The MeteoSat Second Generation (MSG) programme consists of a series of 3 geostationary satellites. The objectives for this programme have been defined by the European meterological community led by The European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) and the European Space Agency (ESA). The first MSG satellite (MSG-1) has been developed by ESA and is scheduled for launch in the year 2002. MSG-2 and MSG-3 will be procured by ESA on behalf of EUMETSAT. The MSG satellites are built by European Industries under ESA contract with Alcatel Space Industries being the prime contractor. EUMETSAT will procure the launch and operate the satellites. The MSG satellites will provide a continuous and reliable collection of environmental data in support of weather forecasting and related meteorological services. The purpose of this paper is to outline the In-Flight calibration of the main payload on-board the MSG satellites which is the imaging radiometer: Spinning Enhanced Visible and Infra-Red Imager (SEVIRI). After a brief description of the satellite and SEVIRI, this paper will focus in discussing the instrument radiance response and its Calibration using both the on-board calibration source and the in-flight foreseen vicarious calibration.

The Geostationary Operational Environmental Satellite (GOES) platform carries an infrared atmospheric sounding instrument which is used to obtain vertical profiles of atmospheric temperature and humidity throughout much of the western hemisphere. These profiles are numerically retrieved from measured nadir-viewing spectral radiances. The opacity of clouds to IR radiance makes such instruments functional only in clear-air regions. Because severe weather is associated with clouded regions, it is highly desirable to obtain soundings through holes in the cloud cover and up to the edge of frontal boundaries. There is much difficulty in performing this task with the existing GOES sounder because cloud cover gives rise to radiance errors in adjacent, and more distant, clear-air fields-of-view. A primary cause for this problem is diffraction, which introduces optical crosstalk between fields-of-view, and which is exacerbated by the large radiance contrast between clouds and clear air. This paper describes a novel application of tapered, or apodized, aperture illumination which may be employed in future GOES sounding instruments to mitigate the effects of diffraction. Tapering the aperture illumination at the edges (or applying this taper at accessible pupils, which are images of the aperture stop) reduces the subsidiary rings of the point-spread function. The benefits of pupil apodization are quantified, as are the penalties incurred by effectively making the aperture smaller. The construction of a graded-transmission spatial filter is described, and its optimal location in a sounding instrument based on a Michelson spectrometer is defined. Finally, the results of measurements taken on a fabricated filter are presented.

The Clouds and Earth Radiant Energy System (CERES) instrument was designed to make measurements of solar radiance reflected from the Earth (0.2 to 0.5 microns) and radiance emitted from the Earch (5.0 to 50+ microns) with 1% accuracies. The CERES design evolved from the Earth Radiation Budget Experiment instrument which had similar objectives. The CERES also had a channel to measure radiance in the 8 to 12 micron window emitted by the Earth for studying the effects of water vapor on the Earth's radiation budget. A CERES instrument flew on the Tropical Rainfall Measuring Mission and 2 are operating on the TERRA spacecraft. One instrument will map the geographical distribution of radiation and the other will measure the anisotrophy of the radiance field. Two CERES instruments will also fly on the AQUA spacecraft. The design features of the telescope and the rationales are described. These aspects of the instrument should be understood by users of the data for a number of purposes. Each channel has its separate telescope to gather radiation onto its detector, which is a thermistor-bolometer. There is a total channel which measures radiances over the range 0.2 to 50+ microns. The shortwave (0.2-5.0 micron) and window (8-12 micron) channel each have filters to provide the desired band. The emitted radiation is computed as the total minus the shortwave radiance.

The development in the past few years of all-mirror telescopes has opened a wide new range of possibilities to instrument designers, with features like high compactness and outstanding optical quality over wide fields of view. However, this design imposes specific constraints on the focal plane: it can no longer accommodate glass beamsplitters and its size increases with the field of view. New CCD detectors with multiple long lines are well-suited to this application, but require a new filters strategy. This paper will detail what ours was in the particular case of a 78-mm long, 4-channel CCD. The choice of the stripe- filters concept was made on the basis of a performance versus cost analysis. Two kinds of assemblies were retained at this stage. The components manufactured by SAGEM-REOSC PRODUCTS in an initial development phase showed good spectral performance with high rejection over a very wide range of wavelengths. Some topics like local defects and straylight needed specific work. The paper focuses on the impact of the defects on the performances and the way they have been dealt with, and on the straylight design strategy with the results obtained in the different cases. In particular, it shows how the detector's design can be partially driven by the straylight requirements.

MOPITT is an instrument aboard NASA's Terra spacecraft. To process the data from raw instrument counts to observations of Carbon Monoxide and Methane a system was established at the National Center for Atmospheric Research (NCAR). This Science Investigator-led Processing System (SIPS) was quickly deployed prior to launch as an alternative to data processing within the Earth Observing System (EOS) Data and Information System (EOSDIS) Core System (ECS). The system was tested a few months before launch and soon became operational. During testing and after launch many lessons were learned due to the divergence between assumptions and reality. The main points to be aware of in order to avoid the worst SIPS problems are: *Don't believe everything you read. *Be flexible. *Test everything. *Build teamwork. *Be consistent. This presentation will provide examples of these principles.

When completed, NASA's EOSDIS Core System (ECS) will be the world's largest Earth science data system, managing almost nine petabytes of data and disseminating more than two terabytes each day. The system's original design assumed that all science data archive, processing and dissemination would be done using high performance subsystems with complex distributed object interfaces between them. These interfaces made it difficult for others to extend the system without incurring the prohibitively high costs of supporting this infrastructure. Over the past three years, most of these interfaces have been replaced with greatly simplified script and file-based interfaces. NASA also has encouraged science and Data Center groups to modify and extend the system's core functionality. As these extensions began to emerge, it was apparent that new configuration management and system deployment methods would be needed to leverage each group's extensions across the ECS Data Centers. NASA has adapted several Open Source development techniques to address this need. This paper will describe how the ECS architecture and supporting development methods have evolved to support Open Source development concepts while at the same time satisfying ECS's challenging requirements. It also will describe how these changes have helped lower the system's overall costs and decrease the time it takes for new capabilities to become operational. We plan to build on the success of these initial changes to encourage additional EOSDIS user participation through many new roles: client and portal providers, data providers, algorithm providers, data processing centers, data service providers, distribution centers and data managers.

The V0 data management and archive system was developed between 1992 and 1997 for use in the Goddard Space Flight Center?s Distributed Active Archive Center (GSFC DAAC). Although originally intended as a prototype system for short-term deployment, its success as a production tool motivated further development and it evolved into a full-fledged system for science processing, data archive and distribution. The software has since been reused successfully for multiple projects, each time paying substantial benefits in the areas of schedule, budget and quality. Currently, it is being adapted to serve as the processing framework for several science missions including the Earth Observing System (EOS) Microwave Limb Sounder (MLS) and Tropospheric Emissions Spectrometer (TES). This paper presents an overview of the system's design and describes its application as a data processing system for the Aura MLS mission.

In this paper we present a new Web-based application for registering multi-sensor satellite images for image fusion operations. It is a distributed processing system which offers automatic or semi-automatic image registration and it is intended to provide a service to the Canadian Geospatial Data Infrastructure (CGDI) users through the GeoConnections Discovery Portal, formerly CEONet. It will be also provided on the web page of A.U.G. Signals Ltd.(www.augsignals.com) which will be connected to CEONet and CGDI. This innovative technology of A.U.G. Signals has all the advantages of current registration techniques, plus is can estimate reference (control) points automatically at high degree of accuracy and with zero false alarms. Users who apply existing remote sensing software tools, such as PCI or IDL/ENVI, with geo-referenced points for registration, may employ the A.U.G. Signals software to further improve the registration accuracy of their images. Geo-referenced control points may also be used with the proposed software. The proposed service is expected to evolve and expand other distributed processing initiatives of current interest, such as the emerging GRID technologies under development in United States and Europe and the Canadian high-speed network CA*Net3 and be part of the US OGC Web based Initiative.

Modern SAR sensors exhibit data rates of the order of hundreds Mbits/s; as a consequence, on board data compression is mandatory. The compression algorithms must be characterized by high computational efficiency and satisfactory compression ratios; on the other hand, losses must be kept within limits that take into account the interpretability of the decompressed data. The compressor presented in this paper is flexible, and allows for compression on 2, 3 or 4 bit/sample, useful respectively for topographic monitoring and interferometric applications. The implementation on a rad tolerant DSP permits to achieve high efficiency levels exploiting parallelization at the instrumentation and possibly board level. Classical SAR raw data compression is based on BAQ (Block Adaptive Quantizer) that yields a fixed compression ratio, or its flexible version FBAQ. This latter is a non-uniform quantizer, in which compression is performed comparing the input samples with proper thresholds. The achievable throughput is limited by the need for multiple comparisons for each data sample. For this reason, a variant of FBAQ is presented, based on the key idea of transforming the input samples so that they exhibit uniform distribution; this feature makes possible to perform the compression via simple truncation. The algorithm has been implemented and optimized from the point of view of the achievable throughput. With respect to FBAQ, it exhibits larger memory requirements (16384 extra words of 32-bit), but significantly improved processing speed without appreciable performance degradation in terms of SQNR and phase error. For example, in the case of 4 bit/sample, a throughput 40% larger than FBAQ can be achieved. The algorithm, implemented on high-frequency, radiation tolerant DSPs, will be able to match the requirements of modern SAR for most practical applications.

Radiances from current polar orbiting infrared (IR) and microwave (MW) sounders are used to infer temperature and moisture profiles in the troposphere in a physical retrieval algorithm. Specification of the tropopause and the surface are necessary boundary conditions in the profile retrieval. Good definition of the tropopause has been elusive via radiometric approaches. The Global Positioning System (GPS) provides an opportunity to derive very accurate upper atmospheric temperature profiles by using radio occultation (RO) techniques. In this paper we show that the combination of radiometric (IR and MW) and geometric (RO) information yields improved tropospheric temperature and moisture profiles when compared to those inferred from either system alone. RO and IR/MW measurements are simulated from the National Oceanic and Atmospheric Administration, National Environmental Satellite, Data, and Information Service (NOAA/NESDIS) NOAA88 global radiosonde data set. Retrievals are performed using a statistical regression approach. Surface data are set as the lowest level of a radiosonde profile. A variety of simulation tests will be presented to illustrate the impact of surface and tropopause information on the temperature and humidity retrievals.