Potential of X-Band Images from High-Resolution Satellite SAR Sensors to Assess Growth and Yield in Paddy Rice

The comprehensive relationship of backscattering coefficient (sigma(0)) values from two current X-band SAR sensors (COSMO-SkyMed and TerraSAR-X) with canopy biophysical variables were investigated using the SAR images acquired at VV polarization and shallow incidence angles. The difference and consistency of the two sensors were also examined. The chrono-sequential change of sigma(0) in rice paddies during the transplanting season revealed that sigma(0) reached the value of nearby water surfaces a day before transplanting, and increased significantly just after transplanting event (3 dB). Despite a clear systematic shift (6.6 dB) between the two sensors, the differences in sigma(0) between target surfaces and water surfaces in each image were comparable in both sensors. Accordingly, an image-based approach using the "water-point" was proposed. It would be useful especially when absolute sigma(0) values are not consistent between sensors and/or images. Among the various canopy variables, the panicle biomass was found to be best correlated with X-band sigma(0). X-band SAR would be promising for direct assessments of rice grain yields at regional scales from space, whereas it would have limited capability to assess the whole-canopy variables only during the very early growth stages. The results provide a clear insight on the potential capability of X-band SAR sensors for rice monitoring.