Remote Sensing of Precipitable Water over the Oceans from Nimbus 7 Microwave Measurements

Abstract

Nimbus 7 Scanning Multichannel Microwave Radiometer (SMMR) brightness temperature measurements in the 21 and 18 GHz channels are used to sense the precipitable water in the atmosphere over oceans. The difference in the brightness temperature (T21 ? T18), both in the horizontal and vertical polarization, is found to be essentially a function of the precipitable water in the atmosphere. An equation, based on the physical considerations of the radiative transfer in the microwave region, is developed to relate the precipitable water to (T21 ? T18). It is shown from theoretical calculations that the signal (T21 ? T18) does not suffer severely from the noise introduced by variations in sea surface temperature, surface winds and liquid water content in non-raining clouds. The rms deviation between the estimated precipitable water from SMMR data and that given by the closely coincident ship radiosondes is about 0.25 g cm?2. Global maps of precipitable water over oceans derived from SMMR data reveal several salient features associated with ocean currents and the large-scale general circulation in the atmosphere.