The Constrained Inversion of Nimbus-7 Wide Field-of-View Radiometer Measurements for the Earth Radiation Budget

Abstract

The results of a constrained, wide field-of-view (WFOV) radiometer measurement deconvolution are presented and compared against higher resolution results obtained from the Earth Radiation Budget (ERB) Experiment on the Nimbus-7 satellite and from the Earth Radiation Budget Experiment (ERBE). The method is applicable to both longwave and shortwave observations and is specifically designed to treat the problem of anisotropic reflection and emission at the top of the atmosphere (TOA), and low signal-to-noise ratios that arise regionally within the observation field. The latter occur, for example, near the earth's terminator where measured WFOV shortwave signals contain increasing percentages of instrument and modeling errors. Ridge regression and meridional smoothing are used to quell the resulting ?local? instability and permit the recovery of a global solution. An optimized retrieval is obtained by tuning the constraints until the recovered solution matches, as well as possible, a known higher resolution product or, lacking that, until unacceptable features in the recovered field no longer appear. The latter approach leads to a set of weight factors that depend on the length of the sampling period and on the desired parameter field, but not on the calendar date. A 1-year study dataset, July 1983 through June 1984, as well as data for the individual months of April 1980 and 1985 have been processed using a preliminary version of these algorithms. Representative deconvolved fields of mean daily longwave flux and albedo are shown for monthly and 8-day inversion periods. When compared to ERB scanner data (April 1980) within 63° of the equator, the WFOV deconvolved solution reduces the RMS error of the WFOV archived results by 31% for longwave flux and 10% for shortwave flux. When compared to the ERBE data of April 1985 over the same domain, error reductions of 25% and 5% are obtained, respectively, for the longwave and shortwave fluxes.