Incidence angle diversity on L-band microwave radiometry and its impact on consistent soil moisture retrievals

Incidence angle diversity of space-borne L-band radiometers needs to be taken into account for a consistent estimation of surface soil moisture (SM). In this study, the Land Parameter Retrieval Model (LPRM) is applied to SMOS brightness temperatures to calibrate the effective scattering albedo (w) and the soil roughness (h 1 ) parameter against ERA5-land SM. The analysis is carried out for SMOS data at three different incidence angles ( 32.5±5°, 42.5±5° and 52.5±5° ) focusing in 2016 on the three main land cover types of the Iberian Peninsula according to the Climate Change Initiative (agricultural, forest and grassland). The parameterization shows an increasing trend of w and h 1 with rise of incidence angle. The SM retrieval have been evaluated with in situ SM measurements of the REMEDHUS network on rainfed crop fields. Both compare well at the three incidence angles, obtaining high correlations (0.81-0.85), an ubRMSE around 0.04 m 3 m -3 and low bias (0-0.015 m 3 m -3 ).This research was funded by the Spanish Ministry of Science, Innovation and Universities, through the coordinated project LBand (MCIU/AEI/FEDER, UE): ESP2017-89463-C3-R, the Unidad de Excelencia María de Maeztu MDM-2016-0600, the Centro de Excelencia Severo Ochoa CEX2019-000928-S, and the CSIC Plataforma Temática de Teledetección. M. Piles is supported by a Ramón y Cajal contract and the project RTI2018-096765-A100 (MCIU/AEI/FEDER, UE). The authors are grateful to MIT for supporting this research with the MIT-Germany Seed Fund “Global Water Cycle and Environmental Monitoring using Active and Passive Satellite-based Microwave Instruments”.Peer ReviewedPostprint (published version