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Reflectance measurements with spectroradiometers in the solar wavelength region (0.4-2.5 [micro]m) are frequently conducted in the laboratory or in the field to characterize surface materials of artificial and natural targets. The spectral surface reflectance is calculated as the ratio of the signals obtained over the target surface and a reference panel, yielding a relative reflectance value. If the reflectance of the reference panel is known, the absolute target reflectance can be computed. This standard measurement technique assumes that the signal at the radiometer is due completely to reflected target and reference radiation. However, for field measurements in the 2.4-2.5-[micro]m region with the Sun as the illumination source, the emitted thermal radiation is not a negligible part of the signal even at ambient temperatures, because the atmospheric transmittance, and thus the solar illumination level, is small in the atmospheric absorption regions. A new method is proposed that calculates reflectance values in the 2.4-2.5-[micro]m region while it accounts for the reference panel reflectance and the emitted radiation. This technique needs instruments with noise-equivalent radiances of 2 orders of magnitude below currently commercially available instruments and requires measurement of the surface temperatures of target and reference. If the reference panel reflectance and temperature effects are neglected, the standard method yields reflectance errors up to 0.08 and 0.15 units for 7- and 2-nm bandwidth instruments, respectively. For the new method the corresponding errors can be reduced to approximately 0.01 units for the surface temperature range of 20-35[degrees]C. OCIS codes: 280.0280, 120.4640, 120.6780, 120.6810.

Identification of clouds over earth's polar regions is difficult from satellite radiometric measurements in the visible and infrared (IR) atmospheric window regions because of the high albedos of snow- and ice-covered surfaces in the visible and the low-temperature contrast between the surface and the troposphere in the IR. The Moderate Resolution Imaging SpectroRadiometer (MODIS) on the Terra Spacecraft has a near-IR channel located within the strong water vapor absorption regions close to 1.38 [micro]m. This channel was originally designed for remote sensing of high-altitude clouds in the tropical and mid-latitude regions. In this paper, we report that this channel is also quite useful for detecting high clouds in polar regions during the daytime. Comparisons with IR emission techniques for polar cloud detections are also presented. Index Terms--Atmosphere, cirrus cloud, remote sensing.

The pattern-matching algorithms originally developed for Multi-angle Imaging SpectroRadiometer (MISR) (flying on the Earth Observing System (EOS) Terra platform) cloud retrieval have also proven useful in independently providing quality assurance of the coregistration of multiangle measurements with the nadir view. Two new techniques developed to test the coregistration are described in this paper along with results of the misregistration detection on both historical and current data. No ground-control points are strictly necessary for these calculations--just simultaneous clear-sky land imagery for three cameras and knowledge of the terrain altitude. The difficulty of registration increases with the obliquity of the view angle, so our emphasis is on coregistering to the nadir view. This paper also provides proxy validation of the stereo-matching algorithms for clear-sky land scenes. Index Terms--Coregistration, Multi-angle Imaging SpectroRadiometer (MISR), multiangle, stereo-matching, winds.

Ground processing of data from the Multi-angle Imaging SpectroRadiometer (MISR) instrument, part of NASA's Earth Observing System (EOS), exploits new and unique science algorithms not previously used operationally. A range of data products from Level 1 through Level 3 is being produced. Because of MISR's unprecedented design, extensive prototyping was required from a relatively early stage. The data throughput is large, necessitating an innovative software design approach that maximizes performance. The systematic science processing software was developed at the Jet Propulsion Laboratory (JPL), with data processing occurring at the NASA Langley Research Center using the EOS Core System (ECS), a collaborative arrangement that works we!!. With the availability of actual mission data following launch on the Terra spacecraft in December 1999, MISR's computational needs have become better known, and many improvements have been made to both the science software and the production system to achieve a successful overall data processing capability. This paper provides information about MISR data for the science user, and describes the nature and scope of implementation and operations activities. Index Terms--Algorithms, data processing, data products, ground system.

The Multi-angle Imaging SpectroRadiometer (MISR) instrument consists of nine cameras, four spectral bands each, and an on-board calibrator (OBC). Experiments using the latter allow camera radiometric coefficients to be updated bimonthly. Data products are thus calibrated to a stable radiometric scale, even in the presence of instrument response changes. The camera, band, and pixel-relative calibrations are accurately determined using the OBC. Conversely, as the OBC itself is subject to response degradation, MISR also conducts annual field vicarious calibration (VC) campaigns. The first of these, conducted June 2000 at a desert site in Nevada, has been used to establish the present absolute radiometric scale. Validation of this radiometric scale, using AirMISR, shows consistency to within 4%. Following these studies, however, it was determined that MISR radiometry is subject to scene-dependent effects due to ghosting that, for the Nevada test sites, reduces the apparent radiance by 3 %. Correction for this effect is required in order to avoid radiometric errors over sites that do not exhibit the same background contrast. Additional studies are in progress, with plans to correct for scene-contrast effects in future Level 1B1 processing. Index Terms--Calibration, Multi-angle Imaging SpectroRadiometer (MISR), radiometry.

The Multi-angle Imaging SpectroRadiometer, one of five science instruments aboard NASA's Terra spacecraft, was launched into earth orbit in December 1999. Acquisition of earth imagery began in February 2000, and the quality of the data is excellent. Overall, MISR has been performing superbly, though the instrument exhibits several idiosyncrasies, some of which were anticipated prior to launch. Details regarding the in-flight performance of the instrument system are presented. Index Terms--Earth, imaging, multiangle, remote sensing.

The Multiangle Imaging Spectroradiometer makes use of an onboard calibration system that includes two Spectralon panels that are used to reflect sunlight into the cameras. During preflight testing, these panels were quantified in terms of their bidirectional reflectance distribution function, which was measured as a function of the source-incident and detector view angles and at laser wavelengths of 442.0, 632.8, and 859.9 nm. Principal plane measurements are presented in which polarizations of the source and detector are analyzed. These data are unique and valuable in modeling Spectralon reflectance properties and for experiments in which polarization sensitivities are important.

An Airborne Multi-angle Imaging SpectroRadiometer (AirMISR) instrument has been developed to assist in validation of the Earth Observing System (EOS) MISR experiment. Unlike the EOS MISR, which contains nine individual cameras pointed at discrete look angles, AirMISR utilizes a single camera in a pivoting gimbal mount. The AirMISR camera has been fabricated from MISR brassboard and engineering model components and, thus, has similar radiometric and spectral response as the MISR cameras. This paper provides a description of the AirMISR instrument and summarizes the results of engineering flights conducted during 1997. Index Terms - Earth, remote sensing.

A precision reflectance characterization facility, constructed specifically for the measurement of the bidirectional reflectance properties of Spectralon panels planned for use as in-flight calibrators on the NASA Multiangle Imaging Spectroradiometer (MISR) instrument is described. The incident linearly polarized radiation is provided at three laser wavelengths: 442, 632.8, and 859.9 nm. Each beam is collimated when incident on the Spectralon. The illuminated area of the panel is viewed with a silicon photodetector that revolves around the panel (360 [degrees]) on a 30-cm boom extending from a common rotational axis. The reflected radiance detector signal is ratioed with the signal from a reference detector to minimize the effect of amplitude instabilities in the laser sources. This and other measures adopted to reduce noise have resulted in a bidirectional reflection function (BRF) calibration facility with a measurement precision with regard to a BRF measurement of [+ or -]0.002 at the 1[Sigma] confidence level. The Spectralon test piece panel is held in a computer-controlled three-axis rotational assembly capable of a full 360 [degrees] rotation in the horizontal plane and 90 [degrees] in the vertical. The angular positioning system has repeatability and resolution of 0.001 [degrees]. Design details and an outline of the measurement methodology are presented.

The multi-angle imaging spectroradiometer (MISR) instrument is designed to provide global imagery at nine discrete viewing angles and four visible/near-infrared spectral bands. The MISR standard products include vegetation canopy green leaf area index (LAI) and fraction of photosynthetically active radiation absorbed by vegetation (FPAR). These products are produced using a peer-reviewed algorithm documented in the EOS-AM1 (Terra) special issue of the Journal of Geophysical Research. This paper presents results on spatial distributions of LAI and FPAR of vegetated land surfaces derived from the MISR LAI/FPAR algorithm with bidirectional reflectance data from the polarization and directionality of the Earth's reflectance (POLDER) instrument over Africa. The results indicate that the proposed algorithm reflects the physical relationships between surface reflectances and biophysical parameters and demonstrates the advantages of using multi-angle data instead of single-angle data. A new method for evaluating bihemispherical reflectance (BHR) from multi-angle measurements of hemispherical directional reflectance factor (HDRF) was developed to prototype the algorithm with POLDER data. The accuracy of BHR evaluation and LAI/FPAR estimation is also presented. To demonstrate the advantages of using multi-angle data over single-angle data of surface reflectance, we demonstrate that: 1) the use of multi-angle data can decrease the dispersion and saturation of LAI, and increase the localization and quality of retrieved LAI and FPAR, 2) the use of multi-angle data can improve the accuracy of LAI retrievals in geometrically complex canopies such as shrubs, and 3) the use of multi-angle data can help determine biome or land cover types correctly (by using the minimum value of LAI dispersion). For many other cases, we demonstrate that the use of multi-angle data does not lead to misevaluation, even if the land cover type is misidentified. Index Terms--Fraction of photosynthetically active radiation absorbed by vegetation (FPAR), leaf area index (LAI), multi-angle imaging spectroradiometer (MISR), multi-angle remote sensing, polarization and directionality of the Earth's reflectance (POLDER), terra.