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The shortwave and shortwave part of the total-wave sensors are calibrated using the solar radiances reflected from the MAM's. Each MAM consists of baffle-solar diffuser plate systems, which guide incoming solar radiances into the instrument fields of view of the shortwave and total wave sensor units. The MAM diffuser reflecting type surface consists of an array of spherical aluminum mirror segments, which are separated by a Merck Black A absorbing surface, over-coated with SIOx (SIO2 for PFM). Thermistors are located within each MAM plate and the total channel baffle. The CERES MAM is designed to yield calibration precisions approaching .5 percent for the total and shortwave detectors. The Terra FM1 and FM2 shortwave channels and the FM1 and FM2 total channels MAM calibration systems showed shifts in their solar calibrations of 1.5, 2.5, 1.5 and 6 percent, respectively within the first year. The Aqua FM3, and FM4 shortwave channels and the FM3 and FM4 total channels MAM calibration systems showed shifts in their solar calibrations of 1.0, 1.2, 2.1 and .8 percent, respectively within the first year. A possible explanation has attributed the MAM reflectance change to on-orbit solar ultraviolet/atomic oxygen/out-gassing induced chemical changes to the SIOx coated MAM assembly during ram and solar exposure. There is also changes to the sensor telescope shortwave filters as well as the Total channel mirrors and/or sensors. The Soumi NPP FM5 is still after 2.5 years displaying a stability of less than .5 percent. In this presentation, lessons learned from the ERBE MAM and application of knowledge of how the space environment affected the CERES FM1-4 solar calibrations will be presented along with on-orbit measurements for the thirteen years the CERES instruments have been on-orbit. |
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