Feasibility of Code-Level Altimetry Using Coastal BeiDou Reflection (BeiDou-R) Setups

With the development of the Chinese BeiDou satellite navigation system, the applications of BeiDou-reflected (BeiDou-R) signals will play a key role in Global Navigation Satellite System-reflected (GNSS-R) signals. In this paper, we describe the theory of code-level ocean surface altimetry using BeiDou-R signals. Two BeiDou-R coastal experiments (lake and ocean experiments in China) were performed using direct right-handed circularly polarized (D-RHCP) antenna, reflected left-handed circularly polarized (R-LHCP) antenna, and reflected right-handed circularly polarized (R-RHCP) antenna. This is the first research on BeiDou-R ocean altimetry performance analysis. The lake experiment demonstrated the potential availability of water surface altimetry using BeiDou-R signals. We found that the resulting error (0.11 m) from the BeiDou geostationary Earth orbit (GEO) satellite signals was much smaller than that (1.61 m) from the inclined geosynchronous orbit (IGSO) satellite signals, and thus verified that R-LHCP signals from high-elevation satellites were more suitable for altimetry. The ocean surface altimetry was performed on China East Sea for 28 h. The predicted results of ocean surface height using R-LHCP signals from BeiDou GEO satellites were in good agreement with the field measured data, and the root-mean squared (rms) height precision can reach 0.37 m. A better performance of GEO observations compared to IGSO observations was found for coastal setups. In case of airborne setups with different multipath settings, the result may be different.