Root-zone soil moisture estimation from assimilation of downscaled Soil Moisture and Ocean Salinity data |
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| Affiliation: | 1. Department of Civil Engineering, Monash University, Building 60, Melbourne, 3800 Victoria, Australia;2. Center for the Study of the Biosphere from Space (CESBIO), Toulouse, France;1. Centre d''applications et de recherches en télédétection (CARTEL), Département de géomatique appliquée, Université de Sherbrooke, Canada;2. Centre d''Études Spatiales de la BIOsphère, France;1. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA;2. Massachusetts Institute of Technology, Cambridge, MA 02139, USA;3. Science System and Application, Inc, United State Department of Agriculture, Beltsville, Maryland, USA;4. United State Department of Agriculture, Beltsville, Maryland, USA;5. University of Guelph, Canada;6. USDA ARS Southeast Watershed Research, Tucson, AZ, USA;7. University of Texas at Austin, Texas, USA;8. USDA ARS Hydrology and Remote Sensing Laboratory, Beltsville, MD, USA;9. USDA ARS Southwest Watershed Research, Tucson, AZ, USA;10. University of Valencia, Spain;11. University of Southern California, California, USA;12. USDA ARS Grazinglands Research Laboratory, El Reno, OK, USA;13. Comisión Nacional de Actividades Espaciales (CONAE), Argentina;14. Monash University, Australia;15. Goddard Space Flight Center (GSFC), NASA, 8800 Greenbelt, MD 20771, USA;1. State Key Laboratory of Hydroscience and Engineering, Department of Hydraulic Engineering, Tsinghua University, Beijing 100084, China;2. State Key Laboratory of Resources and Environmental Information System, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China;3. College of Resources and Environment Science, China Agricultural University, Beijing 100094, China;4. National Meteorological Information Center, China Meteorological Administration, Beijing 100081, China |
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| Abstract: | The crucial role of root-zone soil moisture is widely recognized in land–atmosphere interaction, with direct practical use in hydrology, agriculture and meteorology. But it is difficult to estimate the root-zone soil moisture accurately because of its space-time variability and its nonlinear relationship with surface soil moisture. Typically, direct satellite observations at the surface are extended to estimate the root-zone soil moisture through data assimilation. But the results suffer from low spatial resolution of the satellite observation. While advances have been made recently to downscale the satellite soil moisture from Soil Moisture and Ocean Salinity (SMOS) mission using methods such as the Disaggregation based on Physical And Theoretical scale Change (DisPATCh), the assimilation of such data into high spatial resolution land surface models has not been examined to estimate the root-zone soil moisture. Consequently, this study assimilates the 1-km DisPATCh surface soil moisture into the Joint UK Land Environment Simulator (JULES) to better estimate the root-zone soil moisture. The assimilation is demonstrated using the advanced Evolutionary Data Assimilation (EDA) procedure for the Yanco area in south eastern Australia. When evaluated using in-situ OzNet soil moisture, the open loop was found to be 95% as accurate as the updated output, with the updated estimate improving the DisPATCh data by 14%, all based on the root mean square error (RMSE). Evaluation of the root-zone soil moisture with in-situ OzNet data found the updated output to improve the open loop estimate by 34% for the 0–30 cm soil depth, 59% for the 30–60 cm soil depth, and 63% for the 60–90 cm soil depth, based on RMSE. The increased performance of the updated output over the open loop estimate is associated with (i) consistent estimation accuracy across the three soil depths for the updated output, and (ii) the deterioration of the open loop output for deeper soil depths. Thus, the findings point to a combined positive impact from the DisPATCh data and the EDA procedure, which together provide an improved soil moisture with consistent accuracy both at the surface and at the root-zone. |
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