Polarimetric decomposition with RADARSAT-2 for rice mapping and monitoring

Synthetic aperture radar for paddy rice crop mapping is operational in many countries in southeast Asia due to the unique temporal backscatter signature when the rice grows above the water surface. Although the rapid increase of up to 10 dB or more allows for the identification and subsequent mapping of the rice crop extent the saturation of the backscatter signal during the later growth stages makes yield determination difficult. The development of polarimetric decomposition techniques may improve the capability to estimate rice production as the phase centre of the backscatter is expected to change as the crop matures and the water distribution in the plant parts changes. These changes can potentially be related to crop yield using growth models. This capability for monitoring growth stage and enhancing yield estimation is explored with a multitemporal RADARSAT-2 polarimetric data set of a rice growing region in China. The Freeman-Durden, the Cloude-Pottier, and the Touzi decompositions were used for classification and then evaluated as a function of the growth stage, which was monitored in the rice paddies during the image acquisition period. The Touzi decomposition produced the best classification accuracy when six or more parameters were used in the classification, but all polarimetric decompositions produced suitable accuracies for rice mapping. This indicated only one date of imagery is needed for rice identification when polarimetric data are available. The results also demonstrated some sensitivity to the growth stage in the polarimetric decompositions, especially with the Freeman-Durden and the Touzi parameters. A controlled experiment is planned to further develop the methodology for using polarimetric decompositions for rice monitoring and yield estimation.