A method for retrieving soil moisture in Tibet region by utilizing microwave index from TRMM/TMI data

Abstract

According to simulation analysis of the advanced integral equation model (AIEM), there is a good linear relationship between emissivity and soil moisture under conditions of given roughness. The normalized difference of emissivities at 19.35 GHz and 10.65 GHz with vertical polarization can partly eliminate the influence of roughness and the squared correlation coefficient is about 0.985. This paper uses the normalized brightness temperature for retrieving soil moisture in Tibet from TRMM/TMI data. This method avoids parametrizing the land surface temperature which is a key parameter for the computation of emissivity. We make some sensitivity analysis for the atmosphere which is the main influence factor for our method. The analysis results indicate that our method is very good for clear days but is not very good when there is rainfall. We evaluate our algorithm by using the ground truth data obtained from GAME‐Tibet and the retrieval error of soil moisture is about 0.04m³ m⁻³ relative to experimental data. The analysis indicates that the relationship obtained from the theoretical model should be revised through the local ground measurement data because the method is still influenced by roughness and vegetation. After making a regression revision, the retrieval error of soil moisture is under 0.02m³ m⁻³. Finally, we retrieve the soil moisture in Tibet from TRMM/TMI data, and the distribution trend of retrieval results is consistent with the real world.

Acknowledgment

The authors would like to thank the following people for their various help with this study: Jiancheng Shi, University of California, Santa Barbara, A. K. Fung, University of Texas, Kun‐Shan Chen, Center for Space and Remote Sensing Research, National Central University. They would also like to thank the anonymous reviewers for their valuable comments, which greatly improved the presentation of this paper.

Thanks are also due to NASA for providing TRMM/TMI data, the Department of Civil Engineering University of Tokyo, providing the GAME‐Tibet POP/IOP Dataset CD. This work was sponsored by the National Natural Science Foundation of China (Grant No: 90302008&40571101); basic research work of Central Scientific Research Institution for Public Welfare; Project 863 of China: (Grant no. 2006AA10Z241&2007AA10Z230) and Sponsored by the Open Fund of Key Laboratory of Resources Remote Sensing and Digital Agriculture, MOA.