Behaviour of NISAR L and S band Backscatter for Soil Moisture and Crop Water Monitoring in India’s Mixed Cropping Landscapes

Understanding crop water status and soil moisture dynamics in heterogeneous agricultural landscapes remains a major challenge for microwave remote sensing, especially when multiple crop types coexist within a single pixel. With the NISAR mission providing fully polarimetric L- and S-band SAR observations, there is a unique opportunity to evaluate its retrieval capability in complex mixed-cropping systems.

In this study, we conduct an intensive field campaign across irrigated and rainfed plots in southern India to assess how NISAR L- and S-band backscatter responds to variations in vegetation water content (VWC) and surface soil moisture (SSM) under heterogeneous conditions. Each satellite-aligned pixel in the study region typically contains 4-5 crop types with distinct canopy structures and rooting characteristics. For selected NISAR acquisition dates, we measure VWC through destructive sampling of each crop species present within the pixel. Concurrently, surface soil moisture is measured using both handheld probes and permanently installed soil moisture sensors deployed across the heterogeneous fields to capture intra-pixel variability.

By combining in-situ VWC, multi-depth soil moisture observations, and crop-wise metadata with co-located NISAR L- and S-band backscatter, we evaluate (i) the sensitivity of each band to mixed vegetation conditions, (ii) the ability to distinguish irrigated vs. rainfed water-use patterns, and (iii) the impact of intra-pixel crop diversity on retrieval accuracy. This work provides one of the first ground-based evaluations of NISAR performance in complex Indian agroecosystems and contributes toward developing improved retrieval approaches for crop water assessment and soil moisture estimation in heterogeneous landscapes.