SURFACE LONGWAVE FLUXES FROM SATELLITE-OBSERVATIONS - A CRITICAL-REVIEW

Several different techniques have been proposed for estimating the net longwave radiation at the Earth's surface from satellite observations Many of these show considerable promise over ocean surfaces, although their accuracies are limited to the order to 20-30 W m(-2) for indivi dual satellite observations given the current uncertainties in satelli te estimates of the vertical distribution of coater vapor, cloud cover , cloud base altitude, and near-surface temperatures. The uncertaintie s over land surfaces are higher due to the larger uncertainties in est imating the surface temperature and emissivity. All of the flux estima tion techniques suffer from an absence of absolute calibration, and li ttle information is available to estimate the uncertainties of surface longwave radiation budgets over extended times for large areas. Never theless, this is an area of active research, and a narrowing of the un certainties is expected to occur with the results of current and plann ed field programs.