3 October 1998 Bidirectional reflectance factor (BRF) characterization of the MODIS flight solar diffuser
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Abstract
The Moderate Resolution Imaging Spectroradiometer (MODIS) will be one of the primary instruments observing the earth on the Earth Observing System (EOS) scheduled for launch in late 1999. The solar diffuser BRF characterization is required for MODIS on-orbit reflectance calibration. The system reflectance calibration accuracy requirement is 2 percent covering a spectral region of 400 to 2300 nm. An internal flow down specification of 1 percent was allotted to characterization of the BRF. The SBRS scattering goniometer will be described. The source is a quartz-halogen lamp. Multiple field stops, aperture stops, and baffle masks were experimentally optimized to reduce scattered light to acceptable levels. In addition the room was made 'light tight'. Glan Thompson and Wollaston polarizers were used in the illuminating and viewing arms, respectively. Three sets of detectors were used to cover the 400 to 2300 nm range: PMT, Ge, and PbS. The rotary and translation stages used to move the solar diffuser, polarizers, optical filters, and detectors being computer controlled, which permitted measurements to be made remotely. This scattering goniometer is a relative device, so the flight solar diffuser is characterized by measuring it relative to a diffuser which was characterized by NIST. The transfer to the NIST standard was done before and after solar diffuser characterization. BRF measurements were made at five wavelengths and nine illumination angles with one out-of-plane observation angle. Multiple BRF measurements were made to determine repeatability and spatial uniformity. Measured BRF data will be presented.
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Milutin M. Pavlov, Milutin M. Pavlov, Michael L. Byers, Michael L. Byers, Joe A. Walker, Joe A. Walker, } "Bidirectional reflectance factor (BRF) characterization of the MODIS flight solar diffuser", Proc. SPIE 3439, Earth Observing Systems III, (3 October 1998); doi: 10.1117/12.325631; https://doi.org/10.1117/12.325631
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