1989 年 9 巻 1 号 p. 53-67
As a joint research with National Space Development Agency of Japan (NASDA) for past several years, the authors had been involved in the development of a retrieval algorithm for water vapor and cloud liquid contents using the Microwave Scanning Radiometer (MSR) to be on board the MOS-1 and in the estimation of the MSR data obtained in the airborne MSR verification experiment conducted by NASDA in 1984 through 1985. The frequency used is 23.8 GHz and 31.4 GHz. In succession to the joint research, MOS-1 Verification Program has been conducted using the MSR data of the MOS-1 satellite launched in February 1987. The estimation of the land-radiation effect on antenna temperature through antenna sidelobes and of the accuracy of the water vapor content retrieved from the MSR data have been made. As for cloud liquid content, its in-situ data is not practically available for the comparison with.the MSR data and therefore water vapor content alone was discussed.
First of all, for more than 200 km of offshore distance, the increase of antenna temperature due to land radiation was found to be correctable using a function of the offshore distance. Because in this offshore distance, the increased antenna temperature measured by the MSR are considered to be almost equal to the calculated increase. Seasonal variation of the land radiation can be neglected. Consequently, the data taken within 600 km of off-shore distance, which have been so far considered erroneous because of influence of land radiation, can be used as close as 200 km offshore.
Next, considerable amount of equivalent bias errors in MSR antenna temperature were found at both frequencies when all the bias errors in the retrieval algorithm are treated as equivalent errors in the measured temperature. Possible causes of the equivalent bias errors are discussed. By correcting MSR antenna temperatures for the equivalent bias errors, the retrieved water vapor content was found to be close to the calculated values of radiosonde data at Chichijima, Minamidatojima and Hachi-jojima. After the correction, the root-mean-square accuracy of the MSR-derived water vapor content is 2.8 kg/m2 which corresponds to 8 percent of the averaged water vapor content. This rms deviation is found to be relatively reasonable comparing with the estimation of receiver noise, random cloud distribution and sea-surface roughness.