Satellite Measurements of Reflected Solar Energy and the Energy Received at the Ground

Abstract

A method is described for comparing satellite measurements of reflected solar radiation with pryheliometric measurements at the ground and with measurements from airplanes. When data from accurate, well-calibrated satellite instruments become available, this method can be used to compute the solar energy absorbed directly in the atmosphere. In the meantime the method is applied to solar radiation measurements from TIROSIII, although these data are of doubtful accuracy. TIROSIII measured the solar energy reflected by the planet Earth. Several of these measurements, taken over the United States near noon on 12 July 1963 are described. The corresponding ?albedos? which varied from 0.65 over a bright overcast area to 0.05 over some cloudless areas, may be too low. The reflected energy is correlated with pyrheliometer measurements at the ground at 31 stations. The correlation coefficient was ?0.9. The relationship between the satellite measurement and the ground pyrheliometer measurements is further compared with similar measurements made from airplanes in previous years. It is this comparison which suggests that the satellite measurements of albedo may he too low. From the satellite measurements and the ground pyrheliometer measurements, the solar energy absorbed by the atmosphere itself can be computed after reasonable assumptions about the ground albedo are made. These absorptions sometimes exceed 35 per cent of the solar energy entering the top of the atmosphere; the values appear to be too large and are a consequence of the relatively low satellite values of measured reflectivity over cloudy areas.