Soil moisture

Soil moisture work retrieves near-surface soil water so agriculture, drought, flood, weather, climate, and water-cycle users can track wetness, anomalies, and freeze-thaw state.^[1][2] NASA SMAP measures water in the top layer of soil and freeze-thaw state, with global soil-moisture mapping every 2-3 days.^[1] SMAP uses L-band microwave measurements; its radar failed after early operation while its radiometer continues extended operations.^[1][3] Soil-moisture outputs commonly include surface retrievals, anomaly layers, freeze-thaw status, and trend products for field-context to global hydrology monitoring.^[1][2] Passive microwave retrieval is central to broad-area monitoring, while radar backscatter, GNSS reflectometry, and fused optical, SAR, meteorological, and vegetation context support higher-resolution interpretation and gap-filled products.^[1][3][2]