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

Xuerui Wu,Shuanggen Jin,Junming Xia

doi:10.3390/s17061291

Abstract

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.

Highlights

Global Navigation Satellite Systems (GNSS) have reached a new era with wider applications than navigation, timing and positioning, e.g., GNSS-Reflectometry (GNSS-R)
We begin with the comparisons between bare soil and vegetation on GPS multipath observables, where the main features of vegetation moisture content and sizes are illustrated
Wheat is selected as a representational vegetation for simulations: its stem and leaf are modeled as dielectric cylinder and disks, respectively

Summary

Introduction

Global Navigation Satellite Systems (GNSS) have reached a new era with wider applications than navigation, timing and positioning, e.g., GNSS-Reflectometry (GNSS-R). Compared to traditional remote sensing techniques, GNSS-R has advantages of exploiting pre-existing transmission sources with wide spreading applications from meso-scale ocean remote sensing to soil moisture and vegetation detections on the land surface [1]. In order to receive the reflected signals, a special receiver should be designed, such as the modified. The SAM sensor (An innovative GNSS-R system for Soil Moisture retrieval) used in the LEiMON (Land Monitoring with Navigation Signals) experiments [4]. Sensors 2017, 17, 1291 simulator for bare and vegetated soils was developed [5]. Egido et al has carried out experimental activities for soil moisture and vegetation biomass study [6,7]. A specially designed GPS receiver named SMIGOL

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Results

Discussion

Conclusion