星载SAR亚马逊雨林辐射定标仿真研究

Simulation of Radiometric Calibration of Spaceborne SAR by Amazon Rainforest

辐射定标是准确、定量描述星载合成孔径雷达(SAR)系统性能的重要手段．星载SAR在轨运行期间,天线方向图较之发射前可能存在较大的失真,从而严重影响所获取的SAR图像数据质量,因此准确测量在轨飞行时天线俯仰向方向图特性并予以补偿是星载SAR辐射定标的主要内容之一．利用具有均匀后向散射系数特性的分布目标进行外定标是测量双程俯仰向天线方向图的最佳方案,而亚马逊雨林是全球最稳定、最均匀、最平坦的分布目标,后向散射系数几乎不随入射角变化,是公认的理想测试场地．鉴于目前我国尚无自行采集的星载SAR图像数据,我们对星载SAR回波功率仿真、天线方向图模型参数估算进行了深入、系统的研究,利用仿真的亚马逊雨林SAR功率图像成功地实现了星载SAR俯仰向天线方向图在轨测试关键环节的模拟,对我国的星载SAR辐射定标研究具有一定的理论意义和重要的工程实用价值．

Radiometric calibration is a powerful means to quantify the SAR （Synthetic Aperture Radar） system performance. Compared with that before launching, there is a considerable distortion of the antenna elevation pattern after the spaceborne SAR is in orbit, which will debase the quality of SAR images greatly. An accurate measurement of the antenna elevation pattern is an important aspect of spaceborne SAR radiometric calibration. The external calibration of distributed targets based on the uniform backscattering is an optimal choice to measure the double-way antenna elevation pattern. Amazon rainforest is the most stable, most uniform and flattest distribute external target in the world. With a backscattering almost independent of the incidence, Amazon rainforest is regarded as an ideal radiometric calibration site. However, because the SAR data sets collected by our own spaceborne SAR are still unavailable at present, the estimation of unknown parameters of SAR antenna pattern model based on the simulated spaceborne SAR power image has been investigated in this paper. A successful computer simulation of how to determine the antenna elevation pattern in orbit by simulated Amazon rainforest SAR power images has been made, which is significant for the radiometric calibration of spaceborne SAR in our country.