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CERES-GERB
COMPARISON
CAMPAIGN



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Collecting data for comparing CERES/GERB measurements has been done at the summer and winter solstice since 2003. A CERES instrument (Terra-FM2) is always turned in the direction of the GERB viewing geometry. This alignment ss necessary to avoid using a bidirectional reflectance function (BRDF) twice on comparing CERES/GERB radiances. It is clear that errors in the BRDFs would go straight into the inter-comparison of the instruments. Matching of the viewing zenith angle (VZA) for shortwave and longwave radiances is done at the time of processing data from both instruments.

CERES plots show how the scanning plane orientation changes as Terra flies south (descending orbit). For the trial runs we used a coarse, 1-min relative azimuth angle (RAZ) adjustment to reduce the number of uploaded commands. During the campaign, we implemented a variable time step scheme to provide a uniform coverage for the GERB viewing geometry. Typical implementation will require about sixty commands for the RAZ adjustment per orbit.

First SEVIRI Image (© EUMETSAT)
CERES scan types 		CERES Overflight Pass
(Satellite Projection)

Plot of Total Filtered Radiances Upward.
CERES-GERB_Overpass
25 January, 2003

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Daily Overflight Plots