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Sensors 2017, 17(6), 1291;

A Forward GPS Multipath Simulator Based on the Vegetation Radiative Transfer Equation Model

1,2,* , 1,2
Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, China
Key Laboratory of Planetary Sciences, Chinese Academy of Sciences, Shanghai 200030, China
National Space Science Centers, Chinese Academic of Sciences, Beijing 100190, China
Author to whom correspondence should be addressed.
Academic Editors: Mehrez Zribi and Nicolas Baghdadi
Received: 1 April 2017 / Revised: 25 May 2017 / Accepted: 26 May 2017 / Published: 5 June 2017
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Global Navigation Satellite Systems (GNSS) have been widely used in navigation, positioning and timing. Nowadays, the multipath errors may be re-utilized for the remote sensing of geophysical parameters (soil moisture, vegetation and snow depth), i.e., GPS-Multipath Reflectometry (GPS-MR). However, bistatic scattering properties and the relation between GPS observables and geophysical parameters are not clear, e.g., vegetation. In this paper, a new element on bistatic scattering properties of vegetation is incorporated into the traditional GPS-MR model. This new element is the first-order radiative transfer equation model. The new forward GPS multipath simulator is able to explicitly link the vegetation parameters with GPS multipath observables (signal-to-noise-ratio (SNR), code pseudorange and carrier phase observables). The trunk layer and its corresponding scattering mechanisms are ignored since GPS-MR is not suitable for high forest monitoring due to the coherence of direct and reflected signals. Based on this new model, the developed simulator can present how the GPS signals (L1 and L2 carrier frequencies, C/A, P(Y) and L2C modulations) are transmitted (scattered and absorbed) through vegetation medium and received by GPS receivers. Simulation results show that the wheat will decrease the amplitudes of GPS multipath observables (SNR, phase and code), if we increase the vegetation moisture contents or the scatters sizes (stem or leaf). Although the Specular-Ground component dominates the total specular scattering, vegetation covered ground soil moisture has almost no effects on the final multipath signatures. Our simulated results are consistent with previous results for environmental parameter detections by GPS-MR. View Full-Text
Keywords: GNSS-R; multipath; radiative transfer equation model; vegetation; simulation GNSS-R; multipath; radiative transfer equation model; vegetation; simulation

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Wu, X.; Jin, S.; Xia, J. A Forward GPS Multipath Simulator Based on the Vegetation Radiative Transfer Equation Model. Sensors 2017, 17, 1291.

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