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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/hess-2019-471
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/hess-2019-471
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 09 Oct 2019

Submitted as: research article | 09 Oct 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Hydrology and Earth System Sciences (HESS).

Validation of SMAP L2 passive-only soil moisture products using in situ measurements collected in Twente, The Netherlands

Rogier van der Velde1, Andreas Colliander2, Michiel Pezij3, Harm-Jan F. Benninga1, Rajat Bindlish4, Steven K. Chan2, Thomas J. Jackson5,*, Dimmie M. D. Hendriks6, Denie C. M. Augustijn3, and Zhongbo Su1 Rogier van der Velde et al.
  • 1Department of Water Resources, University of Twente, Enschede, 7500 AE, The Netherlands
  • 2Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
  • 3Department of Water Engineering and Management, University of Twente, Enschede, 7500 AE, The Netherlands
  • 4NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
  • 5Hydrology and Remote Sensing Laboratory, USDA ARS, Beltsville, MD 20705, USA
  • 6Department of Subsurface and Groundwater Systems, Deltares, Utrecht, 3508 AL, The Netherlands
  • *retired

Abstract. The Twente region in the east of the Netherlands has a network with twenty soil monitoring stations that has been utilized for validation of the Soil Moisture Active/Passive (SMAP) passive-only soil moisture products. Over the period from April 2015 until December 2018, seven stations covered by the SMAP reference pixels have fairly complete data records. Spatially distributed soil moisture simulations with the Dutch national hydrological model have been utilized for the development of upscaling functions to translate the spatial mean of point measurements to the domain of the SMAP reference pixels. The native and upscaled spatial soil moisture means have been adopted as in situ references to assess the performance of the SMAP i) Single Channel Algorithm at Horizontal Polarization (SCA-H), ii) Single Channel Algorithm at Vertical Polarization (SCA-V), and iii) Dual Channel Algorithm (DCA) soil moisture estimates. In the case of the Twente network it was found that the SCA-V soil moisture retrieved SMAP observations collected in the afternoon had the best agreement with the in situ references leading to an unbiased Root Mean Squared Error (uRMSE) of 0.059 m3 m−3. This is larger than the mission target accuracy of 0.04 m3 m−3, which can be attributed to large over- and underestimation errors (> 0.08 m3 m−3) in particular at the end of dry spells and during freezing, respectively. The strong vertical dielectric gradients associated with rapid soil freezing and wetting causes the disparity in soil depth characterized by SMAP and in situ that leads to the large mismatches. Once filtered for frozen conditions and antecedent rainfall the uRMSE improves to 0.043 m3 m−3.

Rogier van der Velde et al.
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Validation of SMAP L2 passive-only soil moisture products using in situ measurements collected in Twente, The Netherlands R. van der Velde, A. Colliander, M. Pezij, H.-J. F. Benninga, R. Bindlish, S. K. Chan, and D. M. D. Hendriks https://doi.org/10.17026/dans-x3c-5cvq

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Short summary
NASA’s SMAP satellite provides estimates of the amount of water in the soil. With measurements from a network of twenty soil monitoring stations the accuracy of these estimates has been studied for a four-year period. We found a good agreement between satellite and in-situ estimates, and yet large mismatches in situations with rapidly changing water contents, e.g. soil freezing, rainfall. This can be used to improve model simulations for more skillful management of available natural resources.
NASA’s SMAP satellite provides estimates of the amount of water in the soil. With measurements...
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