Airborne SAR soil moisture estimates over forests replicating NISAR observations

Airborne SAR observations of soil moistureconditions are analyzed over deciduous and evergreenforest in the US Northeast during the 10-day spring and 14-day summer periods in 2022. During the summer, thedynamic range of HH is about 1 dB, deemed associatedmostly with soil moisture changes. Larger changes in  isfound between the two seasons, indicating the vegetationchange, and also in spring when the attenuation by canopyis weak. In spring, the sensitivity of σ0 to soil moisturedecreased in time, suggesting the impact of dryingvegetation. In many sites, σ0 correlates highly with in situsoil moisture, consistently between ascending anddescending viewing geometry on flat terrain and, on slopesonly when imaged at similar incidence angles. Theconsistency benefits NISAR’s retrieval by allowing morefrequent consistent retrievals of soil moisture. The accuracyof soil moisture retrieval from 8 sites is 0.066 m3/m3 inunbiased rmse. The results are very encouraging as anindependent test of the retrieval algorithm under thechallenging conditions of surface slope or forest vegetation.Deficiencies in the retrieval algorithm is represented mostlyas the bias error. In comparison, the temporal range of theretrieval is the most useful property for applications andmatches well with in situ observations.