Spatial sampling error of a scanning radiation budget radiometer

Simulations of ERBE (Earth Radiation Budget Experiment) scanner measurements were performed to investigate the spatial sampling error of regional averaged radiation fluxes. Meteosat data with a spatial resolution of 0.04 deg were used for the description of the true radiation field. Regional means were calculated by weighting and arithmetically averaging the simulating ERBE scanner measurements. The optimal estimate can be derived by taking a phase shifted spatial filter as a weighting function. The phase shift of the distribution of weights varies with scan angle of the region and is related to the phase shift of the point spread function. Analyses of sampling error of the arithmetic estimates for different scene types show in most cases overestimations of short wave and underestimations of long wave fluxes. The total error of the arithmetic estimate varies between 5 and 31 W/sq m in the short wave region, and between 2 and 20 W/sq m in the long wave region.