Research On Problems Of Polarimetric Microwave Radiometer Calibration And Wind Vector Retrieval

Polarimetric microwave radiometer, a new type remote sensing instrument, can measure not only target's power, but also its polarizability. Polarimetric radiometer can use all information about electromagnetic wave, including frequency,phase,amplitude and polarization. The thesis focuses on problems of polarimetric microwave radiometer calibration and wind vector retrieval, and explores their relationship. It intends to establish calibration system of the polarimetric radiometer for its quantitative application and provide theory and methods for future hardware system design and wind vector retrieval.The theory of polarimetric microwave radiometer calibration and the design considerations of the fully polarimetric calibration standard are demonstrated. The design of the fully polarimetric calibration standard is completed. The uncertainties associated with the practical implementation of it for real ocean surface wind vector remote sensing are discussed. Original idea of calibrating polarimetric radiometer on satellite is presented. The vicarious calibration method is used to revise Windsat's first and second Stokes brightness temperatures'systematic bias. According to the zero magnitude of the third and fourth Stokes brightness temperatures at wind speed below 2m/s, Windsat's third and fourth Stokes brightness temperatures'systematic bias is corrected.Windsat, the world's first microwave polarimetric radiometer in space, was launched by U.S. Its on-orbit data and Maximum Likelihood Estimation (MLE) algorithm are utilized to retrieve ocean wind vector. The results preliminarily test the capability of polarimetric radiometer remote sensing ocean surface wind vector from space: compared with NCEP, the wind speed error is 1.15m/s, the wind direction error above 5m/s is 21°, compared with buoy, the corresponding errors are 1.4m/s and 20.5°respectively. The cause and distribution of wind direction 180°ambiguity are investigated. The ability to measure wind vector in atrocious weather conditions such as typhoon with polarimetric radiometer is evaluated.The calibration errors and main parameters of polarimetric radiometer have significant influences on the accuracy of wind vector retrieval. A new scanning geometry with fore and aft twice look to remove wind direction ambiguous solutions is set up. Scan azimuth and calibration cell of on-board polarimetric radiometer in one scan cycle are assigned.