Concept and Assessment of the University of Luxembourg Cygnss-Based Soil Moisture Product

Global Navigation Satellite System Reflectometry (GNSS-R) represents an emerging concept to retrieve geophysical parameters. In this contribution, we describe and assess the University of Luxembourg (UL) large-scale near-surface soil moisture product. The model applies Cyclone GNSS (CYGNSS) observations to retrieve daily soil moisture content at 9 km, using a linear regression and Soil Moisture Active Passive (SMAP) as reference. It selects a subset of the delay-Doppler maps (DDMs) to estimate surface reflectivity, which are normalized with respect to incidence angle using a strategy that accounts for the spatial variations of surface roughness. Our assessment of almost three years of data showed a median unbiased root-mean-square error (ubRMSE) of 0.043 cm
³
cm
^-3
with respect to SMAP and of 0.056 cm
³
cm
^-3
with respect to 224 in-situ sites. Our product is available upon request.