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4 November 2004 Use of the Moon as a reference for satellite-based climate change measurements
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The United States Geologic Survey (USGS) has developed a lunar irradiance model for comparison with on-orbit sattelite instruments. The comparisons are given as the percent difference of the satellite measurements from the model-generated lunar irradiances. For users of the USGS lunar model, details of the inner operation of the model are unknown. That operation is not examined here. Rather, we examine the outputs of the model. We treat the model-generated lunar irradiances as independent data sets, with each covering only a limited range of phase angles in the comparison with an individual satellite instrument. We correct the model irradiances to standard Sun-Moon and Moon-instrument distances and to fixed values for the phase and libration angles. These same corrections can be applied to the measuements by the comparison satellite instrument. For the model outputs examined here, the time trends in the corrected irradiances differ from zero change by less that 0.0014% per thousand days, and the residual scatter in the results is 0.013% (1σ). There are no apparent oscillations in the time series. At this level, the lunar model should provide an adequate reference for instruments that measure long-term climate change. The model outputs here correspond to the bands from the Sea-viewing Wide Field-of-View Sensor (SeaWiFS) instrument and to the phase angle range for the SeaWiFS lunar measurements, which is from 5° to 10°, both before and after full phase. Similar results have been obtained for model outputs corresponding to lunar measurements from the Moderate Resolution Imaging Sectroradiometer (MODIS) instruments onboard the Terra and Aqua spacecraft. This technique is applicable to other instruments that measure at wavelengths from 400 nm to 2500 nm since, in addition to the relative spectral responses of the instrument's bands, the only requirements for the model are the time and location of the instrument's lunar measurements.
© (2004) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
James J. Butler, Gerhard Meister, Frederick S. Patt, and Robert A. Barnes "Use of the Moon as a reference for satellite-based climate change measurements", Proc. SPIE 5570, Sensors, Systems, and Next-Generation Satellites VIII, (4 November 2004);


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