Abstract
Soil moisture monitoring is a significant aspect of environmental and agricultural studies, and Global Navigation Satellite System Interferometric Reflectometry (GNSS-IR) has emerged as a promising technology for this purpose. Traditionally, GNSS-IR is mainly employed for bare soil experiments, and the effectiveness of bare soil retrieval algorithm will be reduced due to the influence of vegetation and meteorological, etc. To address the limitations of the bare-soil retrieval algorithm, a multi-feature soil moisture retrieval approach was proposed. This approach integrated multiple factors including GNSS signals, cumulative precipitation, effective reflection height, and Normalized Microwave Reflection Index (NMRI), and then multi-layer perceptron (MLP) was employed to build retrieval models. In this study, measurements from the Plate Boundary Observatory (PBO) H2O networks and a self-built site in Henan, China were used for experiments and validation, and the geographical environment of stations are various. The experimental results demonstrated several key findings: (1) The delay phase is not sensitive to the variations in soil moisture before and after precipitation, but by integrating the cumulative precipitation data, the accuracy of the model could be improved. (2) The introduction of NMRI and reflection height can help remove the influence of vegetation and penetration depth. (3) Compared between three retrieval models (i.e., unary linear regression, multiple linear regression, and MLP), the decrease in the mean absolute error (MAE) of MLP is up to 96% most and the mean coefficient of determination (R2) is all above 0.98. Meanwhile, this study proved that the proposed method could fully utilize satellite reflection signals from all directions and better reflect the fluctuation of soil moisture.
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Data and codes availability statement
The GNSS site data were provided under the PBO Observation Program of the United States, and the measured soil moisture data were obtained from http://xenon.colorado.edu/portal. The authors gratefully acknowledge the PBO, IGS, and its analysis center for providing GNSS data.
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Funding
This work is funded by Key Laboratory of Land Satellite Remote Sensing Application, Ministry of Natural Resources of the People’s Republic of China (Grant Nos. KLSMNR-K202310, KLSMNR-G202207) and the National Natural Science Foundation of China (Grant Nos. 42077003, 41904018) and the Open Project Program of The Key Laboratory of Cognitive Computing and Intelligent Information Processing of Fujian Education Institutions, Wuyi University (KLCCIIP202202) and the Postgraduate Research & Practice Innovation Program of Jiangsu Province (Grant No. SJCX22_0553). This work is also partially sponsored by the China Scholarship Council.
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HX and FS wrote the main manuscript text and FZ revised article details. All authors reviewed the manuscript.
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Xian, H., Shen, F., Guan, Z. et al. A GNSS-IR soil moisture retrieval method via multi-layer perceptron with consideration of precipitation and environmental factors. GPS Solut 28, 122 (2024). https://doi.org/10.1007/s10291-024-01668-w
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DOI: https://doi.org/10.1007/s10291-024-01668-w