Surface longwave fluxes from satellite observations: A critical review

Several different techniques have been proposed for estimating the net longwave radiation at the Earthʹs 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 individual satellite observations given the current uncertainties in satellite estimates of the vertical distribution of water vapor, cloud cover, cloud base altitude, and near-surface temperatures. The uncertainties over land surfaces are higher due to the larger uncertainties in estimating the surface temperature and emissivity. All of the flux estimation techniques suffer from an absence of absolute calibration, and little information is available to estimate the uncertainties of surface longwave radiation budgets over extended tisrnes for large areas. Nevertheless, this is an area of active research, and a narrowing of the uncertainties is expected to occur with the results of current and planned fiei!d programs.