海洋目标的HY-2A卫星微波散射计在轨辐射定标研究

HY-2A卫星微波散射计主要用于测量海表面的风速和风向,为了满足其风速和风向的测量精度要求,必须对其进行在轨辐射定标。本文基于散射计在开阔大洋的观测数据,利用经过定标的seawinds散射计后向散射系数数据,分析了海洋目标定标法的定标精度,结果表明定标精度可以达到0.15 dB,且模式函数对定标结果的影响为系统偏差,说明海洋目标定标法需要选用高精度的模式函数。然后,采用相同的海洋目标定标算法,实现了HY-2A卫星微波散射计的在轨辐射定标,获得HY-2A卫星微波散射计VV极化的定标系数为-1.79 dB,HH极化的定标系数为-1.73 dB。最后,利用NDBC浮标观测数据,检验HY-2A卫星微波散射计反演的风矢量精度,证明获得的定标系数可以明显提高HY-2A卫星微波散射计反演风矢量的精度。

In-orbit radiometric calibration of the HY-2A microwave scatterometer through open ocean measurements

The microwave scatterometer onboard HY-2A ocean satellite primarily measures surface wind speed and direction over the global oceans. A precise in-orbit radiometric calibration of the scatterometer is crucial to accurately measure both wind speed and direction. This study is the first to perform the in-orbit radiometric calibration of the seawinds scatterometer on the QuikSCAT spacecraft by using global open ocean backscatter measurements. The ocean calibration method is analyzed and discussed on the basis of the result of weawinds that was precisely calibrated. Results show that the accuracy of the ocean calibration method is approximately 0.15 dB for a specific Geographic Model Function (GMF). The deviation among different GMFs in ocean calibration is caused by systematic bias. The GMF must be accurate enough to realize the absolute calibration of the scatterometer. The calibration method and results from seawinds are used as a basis to implement the radiometric calibration of the HY-2A microwave scatterometer. Our results suggest that the calibration coefficients for the HY-2A microwave scatterometer are -1.79 dB for VV polarization and -1.73 dB for HH polarization. The wind vectors of the HY-2A microwave scatterometer are also validated by wind observations from NDBC ocean buoys. The accuracy of retrieving wind speed and direction is significantly improved after applying the obtained calibration coefficients.