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The Clouds and the Earth's Radiant Energy System (CERES) spacecraft scanning thermistor bolometers were used to
measure earth-reflected solar and earth-emitted longwave radiances, at satellite altitude. The bolometers measured the
earth radiances in the broadband shortwave solar (0.3 - 5.0 micrometers) and total (0.3->100 micrometers) spectral bands
as well as in the (8 - 12 micrometers) water vapor window spectral band over geographical footprints as small as 10
kilometers at nadir. In May 2002, the fourth and fifth sets of CERES bolometers were launched aboard the Aqua
spacecraft. Ground vacuum calibrations defined the initial count conversion coefficients that were used to convert the
bolometer output voltages into filtered earth radiances. The mirror attenuator mosaic (MAM), a solar diffuser plate, was
built into the CERES instrument package calibration system in order to define in-orbit shifts or drifts in the sensor
responses. The shortwave and total 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, overcoated with
silicon dioxide. Temperature sensors are located in each MAM plate and baffle. The CERES MAM wass designed to
yield calibration precisions approaching .5 percent for the total and shortwave detectors. In this paper, the MAM solar
calibration procedures are presented along with on-orbit results. Comparisons are also made between the Aqua,Terra
and the Tropical Rainfall Measurement Mission (TRMM) CERES MAM solar calibrations.
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