Estimating surface soil moisture over Sahel using ENVISAT radar altimetry

• Published in: Remote Sensing of Environment
• Main Authors: Fatras, Christophe, Frappart, Frédéric, Mougin, Éric, Grippa, Manuela, Hiernaux, Pierre
• Other Authors: Géosciences Environnement Toulouse (GET), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Centre National de la Recherche Scientifique (CNRS), PNTS "Potentialités des altimètres radars spatiaux pour l'hydrologie en zone sahélienne. Perspectives pour la mission SWOT"
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2012
• Subjects: Surface soil moisture; Radar altimetry; Backscattering coefficient; Sahel; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Sea ice
• Online Access: https://hal.science/hal-00743876; https://hal.science/hal-00743876/document; https://hal.science/hal-00743876/file/Fatras_et_al_RSE_2012_corr.pdf; https://doi.org/10.1016/j.rse.2012.04.013

International audience This paper analyses the potential of the radar altimeter onboard ENVISAT for estimating surface soil moisture in the semi-arid Gourma region in Northern Mali. To this end, the relationships between observed backscattering coefficients derived from 4 retracking algorithms, namely Ocean, Ice-1, Ice-2 and Sea-Ice, and ground data, including soil type, topography, vegetation and soil moisture are investigated. The considered period is 2002-2010. Results show a strong linear relationship between the backscattering coefficients and surface soil moisture measured at six different stations along the satellite track. The best results are obtained with the Ice-1 and Ice-2 algorithms. In these cases, correlation coefficients are higher than 0.8 with RMSE smaller than 2%. Vegetation effects are found to be small due both to the nadir-looking configuration of the radar altimeter and to the low vegetation cover. Finally, the relationship between soil moisture and normalized backscattering coefficient is used to retrieve soil moisture from the altimeter data. These estimates are then compared to soil moisture estimations obtained from the METeorological Operational (METOP) Advanced SCATterometer (ASCAT). These results highlight the high capabilities of Ku-band altimeters to provide an accurate estimation of surface soil moisture in semiarid regions.