Signal-to-Noise Ratio Analyses of Spaceborne GNSS-Reflectometry from Galileo and BeiDou Satellites

Yang Nan,Bofeng Guo,Shuangcheng Zhang,Jingnan Liu,Weiqiang Li,Shirong Ye

doi:10.3390/rs14010035

Abstract

In recent years, Global Navigation Satellite System Reflectometry (GNSS-R) technology has made considerable progress with the increasing of GNSS-R satellites in orbit, the improvements of GNSS-R data processing technology, and the expansion of its geophysical applications. Meanwhile, with the modernization and evolution of GNSS systems, more signal sources and signal modulation modes are available. The effective use of the signals at different frequencies or from new GNSS systems can improve the accuracy, reliability, and resolution of the GNSS-R data products. This paper analyses the signal-to-noise ratio (SNR) of the GNSS-R measurements from Galileo and BeiDou-3 (BDS-3) systems, which is one of the important indicators to measure the quality of GNSS-R data. The multi-GNSS (GPS, Galileo and BDS-3) complex waveform products generated from the raw intermediate frequency data from TechDemoSat-1 (TDS-1) satellite and Cyclone Global Navigation Satellite System (CYGNSS) constellation are used for such analyses. The SNR and normalized SNR (NSNR) of the reflected signals from Galileo and BDS-3 satellites are compared to these from GPS. Preliminary results show that the GNSS-R SNRs from Galileo and BDS-3 are ∼1–2 dB lower than the GNSS-R measurements from GPS, which could be due to the power of the transmitted power and the bandwidth of the receiver. In addition, the effect of coherent integration time on GNSS-R SNR is also assessed for different GNSS signals. It is shown that the SNR of the reflected signals can be improved by using longer coherent integration time (∼0.4–0.8 dB with 2 ms coherent integration and ∼0.6–1.2 dB with 4 ms coherent integration). In addition, it is also shown that the SNR can be improved more efficiently (∼0.2–0.4 dB) for reflected BDS-3 and Galileo signals than for GPS. These results can provide useful references for the design of future spaceborne GNSS-R instrument compatible with reflections from multi-GNSS constellations.

Highlights

Global navigation satellite system reflectometry (GNSS-R) is a L-band bistatic radar technique to retrieve geophysical parameters by receiving GNSS signals reflected from the earth’s surface
It is clearly shown that the mean signal-to-noise ratio (SNR) of TDS-1 Global Navigation Satellite System Reflectometry (GNSS-R) measurements is ∼2–4 dB lower than those from the Cyclone Global Navigation Satellite System (CYGNSS)
The main objective of this study is to characterize if the reflected signal from the other GNSS systems, e.g., Galileo and BDS-3, can be received with enough SNR with the current GNSS-R instrument configurations

Summary

Introduction

Global navigation satellite system reflectometry (GNSS-R) is a L-band bistatic radar technique to retrieve geophysical parameters by receiving GNSS signals reflected from the earth’s surface. The use of reflected GNSS signals for sensing the Earth’s surface was proposed in [1,2]. With the technological innovations of receiving platform and transmitting platform, GNSS-R has developed continuously. At the part of receiving platform, after some successful ground-based [3,4] and airborne platform [5,6] experiments, spaceborne. GNSS-R satellite missions have been launched one after another. The feasibility of GNSSR at Low Earth Orbit (LEO) is firstly verified on UK Disaster Monitoring Constellation (UK-DMC) mission developed by Surrey Satellite Technology Ltd

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Conclusion