基于极化相干矩阵的河流水质污染监测初探

利用遥感手段监测水质污染具有监测范围广、实时性强的优点。本研究选择中国南方地区水质变化明显的河流区域作为研究对象，利用C波段星载极化合成孔径雷达(极化SAR)卫星RADARSAT-2提供的数据，对基于极化SAR的河流水质污染监测技术进行了初步研究。首先介绍了电磁波的极化现象以及极化SAR的基本原理；其次结合一次同步测量实验，提取河流区域，并对极化SAR数据与水质常见监测指标的监测数据进行对比分析，通过对10个采样点18组数据的分析发现，极化相干矩阵中的T 22元素与部分水质指标(如五日生化需氧量BOD₅等)具有较强的相关性，从而反映水质的污染状况；并通过实测数据和最小二乘法，拟合得到了利用T]矩阵元素反演BOD₅的经验公式，拟合系数达到0.82。最后通过对地表散射模型和菲涅尔系数的分析，从理论上探讨了极化相干矩阵中部分元素与水体物理性质存在相关性的原因。初步理论分析和实验数据表明，T 22元素能够反映水体的污染状况。

Primary exploration on monitoring of river pollution based on polarimetric coherence matrix

Monitoring water pollution using remote-sensing techniques has the advantage of large scale coverage and real-time processing. The rivers with prominent gradient of water quality in South China were selected as a case study, and the polarimetric SAR (POLSAR) data obtained by C-band spaceborne POLSAR system RADARSAT-2 was utilized to investigate the potential of monitoring the river pollution based on POLSAR data as the primary exploration. We fi rstly introduced the polarimetry of electromagnetic wave and the principle of POLSAR. Then based on a simultaneous measurement with POLSAR scanning, we extracted the river region and compared the pollution status with POLSAR data. By analyzing the measured water quality index of 18 samples in 10 measuring spots, we found that the T22 element in the polarimetric coherence matrix is highly correlated to some water quality indexes, such as the 5-day biochemical oxygen demand (BOD₅), therefore it can refl ect the pollution in river. Using least square estimation on the measured data, we obtained the retrieval model for BOD₅ from coherence matrix, with the correlation coeffi cient of 0.82. Finally from the analysis of the random surface scattering model and the Fresnel Coeffi cient, we investigated the underlying reason for the relevance between T22 element and the physical property of water. It is indicated from the preliminary theoretical analysis and experimental result that T22 element is capable of refl ecting the water pollution status.