Nimbus 7 earth radiation budget wide field of view climate data set improvement: 1. The Earth albedo from deconvolution of shortwave measurements

Abstract

A deconvolution technique to recover the daily average earth albedo from a set of wide field of view (WFOV) satellite measurements is presented. For each shortwave observation in space a corresponding synthetic WFOV integral is formulated to simulate the satellite value. This is done by including the known earth‐sun‐satellite geometry and a compromise diurnal model, depicting reflection from the earth‐atmosphere system as isotropic and occurring at an effective top of the atmosphere (TOA), and by representing the unknown albedo field as a truncated series of spherical harmonic functions. The series expression for the albedo reduces the measurement integral to a linear equation in the now unknown expansion amplitudes. A typical sampling period leads to many such Satellite measurements and their associated linear representations. This system of linear equations will generally be overdetermined and is solved in a least squares sense for the expansion amplitudes and resulting albedo field. Simulation studies show that a maximum of about 289 pieces of information can be extracted from a set of Nimbus 7 WFOV satellite measurements. These correspond to the number of linearly independent modes of variation definable in the TOA albedo expansion. Zonally, variations through eight waves may be resolved and, meridionally, through 16 nodes. When compared to the current WFOV archived albedo product, the deconvolved albedo field achieves about a 20% reduction in the global rms regional reflected flux density errors. This error reduction is attained within a data collection period containing as few as 6 sampling days and remains constant for longer periods. Global mean measurements are, of course, not changed. An application of these results is used to derive the mean, daily average TOA albedo field for January 1983. An unusually strong and extensive albedo maximum is noted over the south central Pacific Ocean. It has a central maximum of 0.42 and corresponds to the El Niño/Southern Oscillation event of 1982–1983.