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Volume 22, issue 9 | Copyright

Special issue: Integration of Earth observations and models for global water...

Hydrol. Earth Syst. Sci., 22, 4605-4619, 2018
https://doi.org/10.5194/hess-22-4605-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 03 Sep 2018

Research article | 03 Sep 2018

Joint assimilation of soil moisture retrieved from multiple passive microwave frequencies increases robustness of soil moisture state estimation

Anouk I. Gevaert1, Luigi J. Renzullo2, Albert I. J. M. van Dijk2, Hans J. van der Woerd3, Albrecht H. Weerts4,5, and Richard A. M. de Jeu6 Anouk I. Gevaert et al.
  • 1Earth and Climate Cluster, Department of Earth Sciences, VU University Amsterdam, Amsterdam, the Netherlands
  • 2Fenner School of Environment and Society, Australia National University, Canberra, Australia
  • 3Institute for Environmental Studies (IVM), VU University Amsterdam, Amsterdam, the Netherlands
  • 4Deltares, Delft, the Netherlands
  • 5Department of Environmental Sciences, Wageningen University, Wageningen, the Netherlands
  • 6VanderSat B.V., Haarlem, the Netherlands

Abstract. Soil moisture affects the partitioning of water and energy and is recognized as an essential climate variable. Soil moisture estimates derived from passive microwave remote sensing can improve model estimates through data assimilation, but the relative effectiveness of microwave retrievals in different frequencies is unclear. Land Parameter Retrieval Model (LPRM) satellite soil moisture derived from L-, C-, and X-band frequency remote sensing were assimilated in the Australian Water Resources Assessment landscape hydrology model (AWRA-L) using an ensemble Kalman filter approach. Two sets of experiments were performed. First, each retrieval was assimilated individually for comparison. Second, each possible combination of two retrievals was assimilated jointly. Results were evaluated against field-measured top-layer and root-zone soil moisture at 24 sites across Australia. Assimilation generally improved the coefficient of correlation (r) between modeled and field-measured soil moisture. L- and X-band retrievals were more informative than C-band retrievals, improving r by an average of 0.11 and 0.08 compared to 0.04, respectively. Although L-band retrievals were more informative for top-layer soil moisture in most cases, there were exceptions, and L- and X-band were equally informative for root-zone soil moisture. The consistency between L- and X-band retrievals suggests that they can substitute for each other, for example when transitioning between sensors and missions. Furthermore, joint assimilation of retrievals resulted in a model performance that was similar to or better than assimilating either retrieval individually. Comparison of model estimates obtained with global precipitation data and with higher-quality, higher-resolution regional data, respectively, demonstrated that precipitation data quality does determine the overall benefit that can be expected from assimilation. Further work is needed to assess the potentially complementary spatial information that can be derived from retrievals from different frequencies.

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We assimilated three satellite soil moisture retrievals based on different microwave frequencies into a hydrological model. Two sets of experiments were performed, first assimilating the retrievals individually and then assimilating each set of two retrievals jointly. Overall, assimilation improved agreement between model and field-measured soil moisture. Joint assimilation resulted in model performance similar to or better than assimilating either retrieval individually.
We assimilated three satellite soil moisture retrievals based on different microwave frequencies...
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