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 firstly 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 （BOD 5）

therefore it can reflect the pollution in river.Using least square estimation on the measured data

we obtained the retrieval model for BOD 5 from coherence matrix

with the correlation coefficient of 0.82.Finally from the analysis of the random surface scattering model and the Fresnel Coefficient

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 reflecting the water pollution status.