Methods of Estimating Infrared Flux and Surface Temperature from Meteorological Satellites

Abstract

The TIROS II meteorological satellite carried a multiple channel radiometer of medium resolution (about 5 deg). Two of the channels were designed to measure the upward radiation in the ?window? at 8?12 microns, and over the broad spectral region of 7?30 microns. To deduce surface temperatures and total upward flux values from the measurements in these two channels, additional operations must be carried out on the data. As a basis for these transformations, the specific spectral intensity over the entire infrared region was calculated at five zenith angles for each of 106 atmospheric models. In the 7?30 micron channel, an empirical relation was found to transform measured values to total intensity; and, from the limb-darkening exhibited by the 106 individual models, a method of calculating flux was formulated; in this case, the results contain inaccuracies of only about two per cent attributable to the method used. In the 8?12 micron channel, the influence of ozone and water vapor was determined for the model atmospheres, and curves were developed for the direct transformation from measured values to surface temperature; however, if a knowledge of the water vapor content of the viewed column is lacking, errors in the inferred surface temperature can range from near zero to 10 deg or more. A series of radiative flux maps over Europe, calculated from the 7?30 micron data, have values whose magnitudes are in accord with other estimates and measurements. Corrected satellite 8?12 micron data are compared with shelter temperatures for several stations in a cloudless area; the range of the satellite data from 3.5 deg higher to 5.0 deg lower than the shelter data is discussed.