High-Resolution Soil Moisture—A European Airborne Campaign Using NASA Goddard’s Scanning L-Band Active Passive (SLAP)

A summer 2021 European airborne field campaign—the Land surface Interactions with the Atmosphere over the Iberian Semi-arid Environment (LIAISE) campaign—presented an opportunity to explore passive soil moisture sensing with footprints as small as 100x200m, contributing a key measurement to LIAISE and providing a valuable opportunity to gain detailed insight into the water/energy/carbon exchanges at such plot-scale resolution over a 17 x 5 km area. NASA Goddard’s Scanning L-band Active Passive (SLAP) sensor—an airborne simulator of the Soil Moisture Active Passive (SMAP) satellite—made nine soil moisture flights near Lleida, Spain during 15—29 July. Soil moisture imagery and histograms demonstrate sensitivity to spatial and temporal patterns spanning irrigated and non-irrigated areas and their response to both irrigation and precipitation events followed by drydowns. Comparisons with point-scale ground truth at two sites–one within the irrigated zone and one in the non-irrigated zone–are good. Soil moisture differences are within the error bars of the ground truth values and within one standard deviation of the SLAP moisture values except for the afternoon flight of July 24. The overly dry retrieved values of that flight were likely the result of the extremely dry surface conditions and the simplified uniform ancillary data values used for this analysis. Future analyses using higher-fidelity ancillary data will explore these differences.