Target decomposition using dual-polarization sentinel-1 SAR data: Study on crop growth analysis

Abstract

Decomposition of synthetic aperture radar data has been carried out using fully polarised microwave bands. Considering the economical point of view, fully polarimetric SAR data is expensive to use for many applications like soil and agriculture, where, it is important to monitor frequently. With the advancement of human civilization, new agricultural techniques and crops are being developed to meet global food demand. With the development of crop growth, crop texture and dielectric properties varies, which is depicted in the backscattering values along with the crop growth. In this study, Sentinel-1 SAR data is used, which is freely available in dual polarimetric mode with a temporal revisit of 12 days with respect to the transmitter polarizations. In this work, we attempt to decompose the targets from dual polarised SAR data using entropy and alpha bands of H-A-α decomposition. The entropy and alpha band clusters are obtained by using K-means unsupervised classification is utilized for target decomposition. The clustering process is repeated 30 times for 100 iterations to obtain the optimum grouping of pixels. The clusters are plotted on the H-α plane to get an H-α plot of dual-polarization SAR data for target decomposition. The obtained H-α plot is used to identify the crop stages and its scattering mechanism at different growth stages. Crops grown in selected crop fields during the considered period include ginger, tobacco, rice, cabbage, and pumpkin. An attempt is made by plotting the time-series trends of early and late-planted crops with peak mature stages in terms of backscattering analysis, and the results were compared to the H-α plot to gain a better understanding of crop growth scattering mechanisms at various growth stages. Although the backscattering values for the VH and VV polarizations of crops are different, the temporal backscattering study showed the same trend for both polarizations with good similarity of VH polarization than VV for analyzing crop growth stages. The crop growth scattering mechanism on the H-α plane produced similar results to the temporal analysis.