Instrumenting every smallholder plot is economically impossible. Blind random sampling wastes budget on redundant soil-irrigation strata. Sparse design treats ground truth as an information budget: sensors calibrate C-band SAR flooded-paddy backscatter where the radar model is most uncertain, collapsing cost per hectare by roughly two orders of magnitude versus dense IoT.
Why water-level sensors, specifically
Safe Alternate Wetting and Drying is defined by water-table depth (commonly ~15 cm threshold). Direct water-level measurement is the agronomic ground truth for AWD adoption; methane chambers remain the flux calibration reference for the emissions model.