Triple collocation-based estimation of spatially correlated observation error covariance in remote sensing soil moisture data assimilation

Kai Wu; Hong Shu; Lei Nie; Zhenhang Jiao

doi:10.1117/1.JRS.12.016039

19 March 2018 Triple collocation-based estimation of spatially correlated observation error covariance in remote sensing soil moisture data assimilation

Kai Wu, Hong Shu, Lei Nie, Zhenhang Jiao

Author Affiliations +

Journal of Applied Remote Sensing, Vol. 12, Issue 1, 016039 (March 2018). https://doi.org/10.1117/1.JRS.12.016039

Abstract

Spatially correlated errors are typically ignored in data assimilation, thus degenerating the observation error covariance R to a diagonal matrix. We argue that a nondiagonal R carries more observation information making assimilation results more accurate. A method, denoted TC_Cov, was proposed for soil moisture data assimilation to estimate spatially correlated observation error covariance based on triple collocation (TC). Assimilation experiments were carried out to test the performance of TC_Cov. AMSR-E soil moisture was assimilated with a diagonal R matrix computed using the TC and assimilated using a nondiagonal R matrix, as estimated by proposed TC_Cov. The ensemble Kalman filter was considered as the assimilation method. Our assimilation results were validated against climate change initiative data and ground-based soil moisture measurements using the Pearson correlation coefficient and unbiased root mean square difference metrics. These experiments confirmed that deterioration of diagonal R assimilation results occurred when model simulation is more accurate than observation data. Furthermore, nondiagonal R achieved higher correlation coefficient and lower ubRMSD values over diagonal R in experiments and demonstrated the effectiveness of TC_Cov to estimate richly structuralized R in data assimilation. In sum, compared with diagonal R, nondiagonal R may relieve the detrimental effects of assimilation when simulated model results outperform observation data.

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Kai Wu, Hong Shu, Lei Nie, and Zhenhang Jiao "Triple collocation-based estimation of spatially correlated observation error covariance in remote sensing soil moisture data assimilation," Journal of Applied Remote Sensing 12(1), 016039 (19 March 2018). https://doi.org/10.1117/1.JRS.12.016039

Received: 15 October 2017; Accepted: 9 February 2018; Published: 19 March 2018

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