Novel clustering schemes for full and compact polarimetric SAR data: An application for rice phenology characterization
Citation
Dey, S., Bhattacharya, A., Ratha, D., Mandal, D., McNairn, H., Lopez-Sanchez, J.M., Rao, Y.S. (2020). Novel clustering schemes for full and compact polarimetric SAR data: An application for rice phenology characterization. ISPRS Journal of Photogrammetry and Remote Sensing, [online] 169 135-151. http://dx.doi.org/10.1016/j.isprsjprs.2020.09.010
Plain language summary
This study develops a method to estimate the growth stage of rice, using fully polarimetric (FP) and compact polarimetric (CP) Synthetic Aperture Radar (SAR) satellite imagery. Two new scattering parameters (θFP and θCP) are introduced, which range in response from -90 degrees to +90 degrees. These two new parameters use the Barakat degree of polarization and Span (total scattering power of the radar). When used with measures of scattering entropy (H-FP and H-CP), these parameters (θFP and θCP) can characterize the microwave scattering from rice fields in terms of how diffuse/random the scattering is, and whether scattering occurs as a single or double bounce of the radar wave. The new scattering parameters are used with entropy to create two-dimensional plots and to cluster radar scattering into 12 zones. This method was developed and validated using RADARSAT-2 data over a research site in Vijayawada (India). These radar parameters track the development of rice crops and the 12 zones can be correlated to the rice growth stage. The results of this research indicate that the full capability of Compact Polarimetric modes, as available from the RADARSAT Constellation Mission, could be exploited to track crop growth development for crops of importance to Canada.
Abstract
Information on rice phenological stages from Synthetic Aperture Radar (SAR) images is of prime interest for in-season monitoring. Often, prior in-situ measurements of phenology are not available. In such situations, unsupervised clustering of SAR images might help in discriminating phenological stages of a crop throughout its growing period. Among the existing unsupervised clustering techniques using full-polarimetric (FP) SAR images, the eigenvalue-eigenvector based roll-invariant scattering-type parameter, and the scattering entropy parameter are widely used in the literature. In this study, we utilize a unique target scattering-type parameter, which jointly uses the Barakat degree of polarization and the elements of the polarimetric coherency matrix. Likewise, we also utilize an equivalent parameter proposed for compact-polarimetric (CP) SAR data. These scattering-type parameters are analogous to the Cloude-Pottier's parameter for FP SAR data and the ellipticity parameter for CP SAR data. Besides this, we also introduce new clustering schemes for both FP and CP SAR data for segmenting diverse scattering mechanisms across the phenological stages of rice. In this study, we use the RADARSAT-2 FP and simulated CP SAR data acquired over the Indian test site of Vijayawada under the Joint Experiment for Crop Assessment and Monitoring (JECAM) initiative. The temporal analysis of the scattering-type parameters and the new clustering schemes help us to investigate detailed scattering characteristics from rice across its phenological stages.