Institute of Remote Sensing and Geographic Information System, School of Earth and Space Science, Peking University, Beijing 100871, China.
State Key Laboratory of Information Engineering in Surveying, Mapping and Remote Sensing, Wuhan University, Wuhan 430079, China.
Sensors (Basel). 2019 Mar 27;19(7):1493. doi: 10.3390/s19071493.
GaoFen-3 (GF-3) is the first Chinese civilian multi-polarization synthetic aperture radar (SAR) satellite, launched on 10 August of 2016, and put into operation at the end of January 2017. The polarimetric SAR (PolSAR) system of GF-3 is able to provide quad-polarization (quad-pol) images in a variety of geophysical research and applications. However, this ability increases the complexity of maintaining image quality and calibration. As a result, to evaluate the quality of polarimetric data, polarimetric signatures are necessary to guarantee accuracy. Compared with some other operational space-borne PolSAR systems, such as ALOS-2/PALSAR-2 (ALOS-2) and RADARSAT-2, GF-3 has less reported calibration and image quality files, forcing users to validate the quality of polarimetric imagery of GF-3 before quantitative applications. In this study, without the validation data obtained from a calibration infrastructure, an innovative, three-hierarchy strategy was proposed to assess PolSAR data quality, in which the performance of GF-3 data was evaluated with ALOS-2 and RADARSAT-2 data as references. Experimental results suggested that: (1) PolSAR data of GF-3 satisfied backscatter reciprocity, similar with that of RADARSAT-2; (2) most of the GF-3 PolSAR images had no signs of polarimetric distortion affecting decomposition, and the system of GF-3 may have been improved around May 2017; and (3) the classification accuracy of GF-3 varied from 75.0% to 91.4% because of changing image-acquiring situations. In conclusion, the proposed three-hierarchy approach has the ability to evaluate polarimetric performance. It proved that the residual polarimetric distortion of calibrated GF-3 PolSAR data remained at an insignificant level, with reference to that of ALOS-2 and RADARSAT-2, and imposed no significant impact on the polarimetric decomposition components and classification accuracy.
高分三号（GF-3）是中国第一颗民用多极化合成孔径雷达（SAR）卫星，于 2016 年 8 月 10 日发射，2017 年 1 月底投入运行。GF-3 的极化 SAR（PolSAR）系统能够提供多种地球物理研究和应用的四极化（quad-pol）图像。然而，这种能力增加了维持图像质量和校准的复杂性。因此，为了评估极化数据的质量，极化特征是保证准确性所必需的。与其他一些运行中的星载 PolSAR 系统，如 ALOS-2/PALSAR-2（ALOS-2）和 RADARSAT-2 相比，GF-3 报告的校准和图像质量文件较少，这迫使用户在进行定量应用之前验证 GF-3 的极化图像质量。在本研究中，在没有从校准基础设施获得验证数据的情况下，提出了一种创新的、三级策略来评估 PolSAR 数据质量，其中使用 ALOS-2 和 RADARSAT-2 数据作为参考来评估 GF-3 数据的性能。实验结果表明：（1）GF-3 的 PolSAR 数据满足后向散射互易性，与 RADARSAT-2 相似；（2）大多数 GF-3 PolSAR 图像没有影响分解的极化失真迹象，并且 GF-3 系统可能在 2017 年 5 月左右得到了改进；（3）由于图像采集情况的变化，GF-3 的分类精度从 75.0%变化到 91.4%。总之，所提出的三级方法具有评估极化性能的能力。它证明了校准后的 GF-3 PolSAR 数据的残余极化失真仍然处于微不足道的水平，与 ALOS-2 和 RADARSAT-2 相比，对极化分解分量和分类精度没有显著影响。
