Validation of SMAP and EOS-04 Soil Moisture Products Over Karnataka’s Heterogeneous Agricultural Landscapes Using Ground Measurements

Soil moisture is a crucial parameter that influences various environmental and socioeconomic processes, including flood and drought mitigation, sustainable agricultural productivity, and industrial applications. This study analyses soil moisture dynamics using data from 25 sensing stations distributed across various regions of Karnataka State. These sensing stations were installed under the REWARD (Rejuvenating Watersheds for Agricultural Resilience through Innovative Development Programme) project funded by World Bank. These stations encompass diverse topographic, soil, rainfall, and crop characteristics. High-frequency data collected from these stations at 15-minute intervals is aggregated into daily averages to analyse soil moisture responses to rainfall, recovery times, and depth-wise correlations between 5 cm and 50 cm. This study also validates soil moisture products from SMAP and EOS-04 satellites using ground-based measurements at these 25 locations. The validation was performed for both raw satellite data and data filtered using the Soil Wetness Index (SWI). The Soil Wetness Index (SWI) filter is applied as a background layer to effectively capture soil moisture dynamics across different spatial scales. The accuracy of soil moisture retrievals is evaluated for SMAP products at spatial resolutions of 9 km, 1 km, and 400 m, as well as for EOS-04 data at a 500 m resolution. When the SWI filter is applied, the remotely sensed retrievals show the strongest agreement with in-situ measurements across cultivated crop areas throughout the year. The findings from this study enhance the understanding of soil moisture dynamics and offer actionable recommendations for selecting the best satellite soil moisture products and optimizing soil moisture modelling. These insights are valuable for agricultural planning, water resource management, and disaster mitigation strategies in regions with diverse environmental conditions.