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The Moon plays an important role in the radiometric stability monitoring of the NASA Earth Observing System's (EOS)
remote sensors. The MODIS and SeaWIFS are two of the key instruments for NASA's EOS missions. The MODIS
Protoflight Model (PFM) on-board the Terra spacecraft and the MODIS Flight Model 1 (FM1) on-board the Aqua
spacecraft were launched on December 18, 1999 and May 4, 2002, respectively. They view the Moon through the
Space View (SV) port approximately once a month to monitor the long-term radiometric stability of their Reflective
Solar Bands (RSB). SeaWIFS was launched on-board the OrbView-2 spacecraft on August 1, 1997. The SeaWiFS
lunar calibrations are obtained once a month at a nominal phase angle of 7°. The lunar irradiance observed by these
instruments depends on the viewing geometry. The USGS photometric model of the Moon (the ROLO model) has been
developed to provide the geometric corrections for the lunar observations. For MODIS, the lunar view responses with
corrections for the viewing geometry are used to track the gain change for its reflective solar bands (RSB). They trend
the system response degradation at the Angle Of Incidence (AOI) of sensor's SV port. With both the lunar observation
and the on-board Solar Diffuser (SD) calibration, it is shown that the MODIS system response degradation is
wavelength, mirror side, and AOI dependent. Time-dependent Response Versus Scan angle (RVS) Look-Up Tables
(LUT) are applied in MODIS RSB calibration and lunar observations play a key role in RVS derivation. The
corrections provided by the RVS in the Terra and Aqua MODIS data from the 412 nm band are as large as 16% and
13%, respectively. For SeaWIFS lunar calibrations, the spacecraft is pitched across the Moon so that the instrument
views the Moon near nadir through the same optical path as it views the Earth. The SeaWiFS system gain changes for
its eight bands are calibrated using the geometrically-corrected lunar observations. The radiometric corrections to the
SeaWiFS data, after more than ten years on orbit, are 19% at 865 nm, 8% at 765 nm, and 1-3% in the other bands. In
this report, the lunar calibration algorithms are reviewed and the RSB gain changes observed by the lunar observations
are shown for all three sensors. The lunar observations for the three instruments are compared using the USGS
photometric model. The USGS lunar model facilitates the cross calibration of instruments with different spectra
bandpasses whose measurements of the Moon differ in time and observing geometry.
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