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Article

Simulations and Analysis of GNSS Multipath Observables for Frozen and Thawed Soil under Complex Surface Conditions

by
Chao Gao
1,
Weihua Bai
2,3,4,5,6,*,
Zhiqiang Wang
1,
Xuerui Wu
7,8,
Lijun Liu
2,3,5,6,
Nan Deng
2,3,4,5,6 and
Junming Xia
2,3,4,5,6
1
Beijing Institute of Tracking and Telecommunications Technology, Beijing 100094, China
2
National Space Science Center, Chinese Academy of Sciences (NSSC/CAS), Beijing 100190, China
3
Beijing Key Laboratory of Space Environment Exploration, Beijing 100190, China
4
School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 100049, China
5
Joint Laboratory on Occultations for Atmosphere and Climate (JLOAC), NSSC/CAS and University of Graz, Beijing 100190, China
6
Key Laboratory of Science and Technology on Space Environment Situational Awareness, CAS, Beijing 100190, China
7
School of Resources, Environment and Architectural Engineering, Chifeng University, Chifeng 024000, China
8
Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, China
*
Author to whom correspondence should be addressed.
Water 2021, 13(14), 1986; https://doi.org/10.3390/w13141986
Submission received: 29 June 2021 / Revised: 14 July 2021 / Accepted: 16 July 2021 / Published: 20 July 2021
(This article belongs to the Special Issue Remote Sensing Application on Soil Moisture)
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Abstract

The transition of the freeze–thaw state of the land surface soil occurs every year with the season and is closely related to the human living environment. The freezing and thawing changes of the ground surface have important effects on hydrological activities, meteorological conditions, and ecological gas dynamics. Traditional monitoring methods have their limitations. In the past two decades, the emerging GNSS-R/IR (Global Navigation Satellite System-Reflectometry/Interference Reflectometry) technology has provided a new method for monitoring the surface f state; however, fewer works have paid attention to the scattering mechanism models in the current study. In this paper, a forward GNSS multipath model suitable for a complex cold surface is developed. The dielectric constant model with different surface parameters is added. The calculation of snow layer attenuation is employed to take the snow cover into consideration. Based on the first-order radiation transfer equation model, a polarization synthesis method is used to obtain the circularly and linearly polarized vegetation specular scattering characteristics. The surface characteristics and antenna model are coupled. A more detailed forward GNSS multipath model of frozen and thawed soil under complex surface conditions is established. The model is used to simulate and analyze the forward GNSS multipath (Signal to Noise Ratio (SNR), phase and pseudorange) responses of frozen and thawed soil under complex surface conditions (soil salinity, snow and vegetation coverage). Studies have shown that when the soil changes from freezing to thawing due to the change in the phase of the water in the soil, the dielectric constant and BRCS (bi-static radar cross-section) increase, causing the increase in the amplitude of the multipath observation. The higher the salinity content, the larger the amplitude of the multipath observation. The attenuation of the snow cover and the vegetation layer will lead to the reduction of the multipath observation amplitude. For the first time, the model developed by this paper reveals the GNSS multipath observation response of frozen and thawed soil under complex surface conditions in detail, which can provide some theoretical support for subsequent experimental design and data analysis.
Keywords: GNSS-R/IR; soil freeze–thaw process; salinity; snow; vegetation; multipath GNSS-R/IR; soil freeze–thaw process; salinity; snow; vegetation; multipath

Share and Cite

MDPI and ACS Style

Gao, C.; Bai, W.; Wang, Z.; Wu, X.; Liu, L.; Deng, N.; Xia, J. Simulations and Analysis of GNSS Multipath Observables for Frozen and Thawed Soil under Complex Surface Conditions. Water 2021, 13, 1986. https://doi.org/10.3390/w13141986

AMA Style

Gao C, Bai W, Wang Z, Wu X, Liu L, Deng N, Xia J. Simulations and Analysis of GNSS Multipath Observables for Frozen and Thawed Soil under Complex Surface Conditions. Water. 2021; 13(14):1986. https://doi.org/10.3390/w13141986

Chicago/Turabian Style

Gao, Chao, Weihua Bai, Zhiqiang Wang, Xuerui Wu, Lijun Liu, Nan Deng, and Junming Xia. 2021. "Simulations and Analysis of GNSS Multipath Observables for Frozen and Thawed Soil under Complex Surface Conditions" Water 13, no. 14: 1986. https://doi.org/10.3390/w13141986

APA Style

Gao, C., Bai, W., Wang, Z., Wu, X., Liu, L., Deng, N., & Xia, J. (2021). Simulations and Analysis of GNSS Multipath Observables for Frozen and Thawed Soil under Complex Surface Conditions. Water, 13(14), 1986. https://doi.org/10.3390/w13141986

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