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28 December 1999 Radiometric calibration of spacecraft using small lunar images
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The Moon is the only object that is accessible to Earth- orbiting imaging systems, whose brightness is within the dynamic range of most such systems, and whose spectral radiance is potentially knowable to a fraction of a percent. As such, it is a desirable target for radiometric calibration. Several spacecraft teams have begun using or are planning to use lunar observations as part of their calibration process. We examine the data reduction steps that can be used to extract the lunar irradiance from low resolution images of the Moon and qualitatively assess the attendant uncertainties. Images of the Moon provide a precise measure of scattered- light sensitivity. The response integrated over an image is compared to a lunar irradiance model being developed from terrestrial multi-band photometric observations over the 350 - 2500 nm range. For SeaWiFS images, wherein the Moon is about 6 by 20 pixels, the uncertainty in extracting the total lunar signal from the image is about 1% for most bands. A significant source of uncertainty is knowledge of the spacecraft inertial pitch rate, which is currently derived form image analysis. The very low noise in some of the detectors limits knowledge of the zero radiance level to 1/2 of a Data Number. A program is underway to accurately determine at several wavelengths the brightness variations of the Moon associated with Sun-Moon-observer Geometry. Comparisons with Earth-based lunar radiometric observations for relative responsivity (changes of spacecraft instrument gain with time) are consistent to about 1/2 the formal uncertainty. At present, the largest errors in using these data for absolute radiometric calibration are in the lunar radiance model.
© (1999) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Hugh H. Kieffer, James M. Anderson, and Kris J. Becker "Radiometric calibration of spacecraft using small lunar images", Proc. SPIE 3870, Sensors, Systems, and Next-Generation Satellites III, (28 December 1999);

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