Evaluation of SMOS soil moisture retrievals over the central United States for hydro-meteorological application |
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| Institution: | 1. Department of Forest Resource Management, Swedish University of Agricultural Sciences, SLU Skogsmarksgränd, Umeå SE-90183, Sweden;2. USDA Forest Service, Pacific Northwest Research Station, USA;3. Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, P.O.Box 5003, Å NO-1432s, Norway;4. NASA/Goddard Space Flight Center, Greenbelt, MD20771, USA;5. USDA Forest Service, Northern Research Station, USA;6. School of Forestry and Environmental Studies, Yale University, New Haven, CT, USA;1. CNR IRPI, via Madonna Alta 126, 06128, Perugia, Italy;2. Università degli Studi di Perugia, Dipartimento di Fisica e Geologia, via A. Pascoli, 06123, Perugia, Italy;3. CNR IRPI, via Cavour 6, 87036, Rende (CS), Italy;4. CNR IRPI, via Amendola 122 I, 70126 Bari, Italy;5. Università degli Studi di Napoli Federico II, Dipartimento di Scienze della Terra dell''Ambiente e delle Risorse, Largo San Marcellino 10, 80138, Napoli, Italy |
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| Abstract: | Soil moisture has been widely recognized as a key variable in hydro-meteorological processes and plays an important role in hydrological modelling. Remote sensing techniques have improved the availability of soil moisture data, however, most previous studies have only focused on the evaluation of retrieved data against point-based observations using only one overpass (i.e., the ascending orbit). Recently, the global Level-3 soil moisture dataset generated from Soil Moisture and Ocean Salinity (SMOS) observations was released by the Barcelona Expert Center. To address the aforementioned issues, this study is particularly focused on a basin scale evaluation in which the soil moisture deficit is derived from a three-layer Xinanjiang model used as a hydrological benchmark for all comparisons. In addition, both ascending and descending overpasses were analyzed for a more comprehensive comparison. It was interesting to find that the SMOS soil moisture accuracy did not improve with time as we would have expected. Furthermore, none of the overpasses provided reliable soil moisture estimates during the frozen season, especially for the ascending orbit. When frozen periods were removed, both overpasses showed significant improvements (i.e., the correlations increased from r = ?0.53 to r = ?0.65 and from r = ?0.62 to r = ?0.70 for the ascending and descending overpasses, respectively). In addition, it was noted that the SMOS retrievals from the descending overpass consistently were approximately 11.7% wetter than the ascending retrievals by volume. The overall assessment demonstrated that the descending orbit outperformed the ascending orbit, which was unexpected and enriched our knowledge in this area. Finally, the potential reasons were discussed. |
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| Keywords: | Hydro-meteorology Passive microwaves NLDAS-2 Soil moisture deficit SMOS Ascending Descending Xinanjiang (XAJ) |
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