Linear retrieval and global measurement of precipitable water from the SEASAT SMMR data

Abstract

The Seasat Scanning Multichannel Microwave Radiometer (SMMR) measurements in the 18.0, 21.0 and 37.0 GHz channels, both horizontal and vertical polarizations, are primarily used for precipitable water, cloud liquid water content and rainfall rate determination. Linear regressions using a leaps and bounds procedure are used for the retrieval of precipitable water. The radiation simulated for all the ten SMMR channels with varied global environmental parameters were used for subset selection for water vapour retrieval. Only subsets with channels having uniform grid size (18, 21 and 37 GHz) were used for the analysis. A total of eight subsets using two to five frequencies of the SMMR are examined to determine their potential in the retrieval of atmospheric water vapour content. Our analysis indicates that the information concerning the 18 and 21 GHz channels are optimum for the water vapour retrieval. An attempt to use all the SMMR channels simultaneously gives no significant improvement. A comparison with the radiosonde observations gave an rms accuracy of 0.4 g/cm2. The rms accuracy of retrieved precipitable water using different subsets was within 10 percent.