BDS/GNSS multipath reflectometry (BDS/GNSS-MR) based altimetry with new signals: Initial assessment and comparison

Abstract

The BeiDou Navigation Satellite System with global coverage (BDS-3) was officially launched on July 31, 2020. In addition to the legacy B1I and B3I signals from the regional system (BDS-2), BDS-3 provides several new signals, i.e., B1C, B2a, B2b and B2a + b, with advanced technologies and global availability, which brings new opportunities for ground-based BDS multipath reflectometry (BDS-MR) altimetry. Previous studies focused on the MR altimetry performance of the legacy signals using signal-to-noise ratio (SNR) observations, but the new BDS signals have not been investigated. In this contribution, all types of BDS-3 SNR data collected from seven International GNSS Service (IGS) stations are analyzed signal by signal in terms of SNR quality and altimetry performance, while the legacy BDS B2I and Global Positioning System (GPS) L2C signals are also selected for comparison. Seven globally distributed IGS stations are first investigated for the quality of SNR observations, and then two optimally selected land stations are used to assess BDS-MR based altimetry performance, while a coastal station is used to assess BDS-MR for sea level retrieval performance. It is found that the quality of SNR observations varied site by site due to the differences in environment and equipment, but in general, the new signals except B1C show a higher level of SNR. Then, no detectable biases among each signal are found for land altimetry, while new signals could yield higher amplitude when performing spectral analysis. In coastal sea level altimetry, only two new signals B1C and B2a are available at the selected IGS station, and it is observed that the retrieval performance of BDS B2a is comparable to that of B2I, B3I and GPS L2C with root-mean-square errors (RMSEs) of about 21 cm, while that for B1I and B1C is slightly poorer with RMSEs of 29.68 cm and 26.66 cm respectively.