Kharif rice growth and area monitoring in Gosaba CD block of Indian Sundarbans region using multi-temporal dual-pol SAR data

Agriculture in the Indian Sundarbans is mainly dominated by kharif rice-based cropping systems. The cropping intensity of this region largely depends on growing cycle of kharif rice. The present study aimed to determine the spectral pattern of kharif rice and estimate the rice grown area in the Gosaba CD block of Indian Sundarbans in 2017, 2018, and 2019 years using multi-temporal Sentinel-1 Synthetic Aperture Radar data. To estimate the rice grown area, a simple binary classification was carried out using the carefully selected threshold values of co (VV) and cross-polarized (VH) backscatter coefficients ( $$\sigma^\circ $$ σ ∘ ) obtained during the growth cycle of rice. The results revealed that the $$\sigma^\circ $$ σ ∘ obtained at the transplanting stage was lower. $$\sigma^\circ $$ σ ∘ gradually increased with the advancement of the crop. The cross- polarized backscatter values were higher than the co-polarized backscatter values as the vertical canopy structure attenuated co-polarized signals. The Radar vegetation Index (RVI) showed a bell-shaped profile attaining its peak during the middle of October which coincided with the grain filling stage of the crop. About 41, 40, and 45% of the total study area were covered by kharif-rice in 2017, 2018, and 2019, respectively. The advancement of the rice crop over the study area was clearly shown by the spatial variation of the RVI in the rice growing areas and this would help to implement necessary management actions in the rice fields as well as to decide the sowing site and time for the winter crops for cropping intensification.