Objectives The B2a is a new signal of BeiDou-3(BD-3) with high-bandwidth and high pseudorange measurement precision, therefore, it is suitable for GNSS-R water surface altimetry. There were few studying based on the BD-3 reflected signal, due to the BD-3 system just began to provide worldwide services in the past two years.
Methods The National Space Science Center (NSSC) has developed a GNSS-R receiver with independent intellectual property supporting the BD-3 B2a capture and tracking functions, which can obtain and track both direct and reflected B2a signals. B2a signals are difficult to capture due to its long PRN code. One B2a assistant approach is proposed and implemented that the shorter B1I signals are first obtained and tracked, then the B2a signals can be correctly captured using B1I auxiliary information with shorter acquisition time. One cross calibration system is included by the receiver, which can effectively eliminate the system biases caused by the delays of different cables and receiver channels.
Results During the shore-based experiment carried out at Huairou in Beijing in 2019, the correlation waveforms of the BD-3 B2a, BD-2 B1I and GPS L1 C/A reflected signals were accumulated. The water surface height was successfully retrieved and the systematic biases was eliminated effectively. The water surface height results show that the inversion precision based on BD-3 B2a reaches 5.9 cm with the non-coherent integration time of 30 s.
Conclusions The height precision has been improved by 13 cm than BD-2 B1I signal and 20 cm than GPS L1 C/A signal. This verification experiment expands the application research of BD-3 system in GNSS-R water surface altimetry and lays the foundation for the development of subsequent tasks.
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