A shipborne experiment using a dual-antenna reflectometry system for GPS/BDS code delay measurements
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ORIGINAL ARTICLE
A shipborne experiment using a dual-antenna reflectometry system for GPS/BDS code delay measurements Fan Gao1 · Tianhe Xu1
· Nazi Wang1 · Yunqiao He1 · Xiaowen Luo2
Received: 10 April 2019 / Accepted: 12 August 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Global navigation satellite system-reflectometry (GNSS-R) has great potential to be a novel technique for altimetry, which can be used to derive sea surface heights (SSH). Shipborne altimetry is an important method to measure local SSH with high spatial resolution. In order to test the feasibility of shipborne dual-antenna GNSS-R reflector height retrieval, we developed a GNSS-R receiver system and performed experiments on a research vessel. In this study, direct and reflected GPS/BDS signals were collected using the same setup, and processed to estimate the reflector heights on the basis of path-delay measurements. A strategy of obtaining the GPS/BDS code-level path delay based on 10-ms coherent integration waveforms was adopted. We analyzed the relationship between the path-delay error and the error of the estimated reflector height, and we pointed out that the error in the path delay was amplified when the satellite elevation was low. We also performed reflector height retrieval based on BDS-3 signals for the first time. We evaluated the precisions of the BDS-R and GPS-R derived reflector heights with 30° and 50° cut-off elevations. The results show that the standard deviation of solutions at different cases is around 1.0 m and precisions are slightly better for a 50° cut-off angle compared with a 30° cut-off angle. In general, the mean values of different cases are close, with differences of several centimeters for the experiments. Keywords GNSS-Reflectometry · Altimetry · BDS-3 · Code-level altimetry · Shipborne GNSS-R
1 Introduction Altimeter sea surface height (SSH) measurements with high temporal and spatial resolutions are required for observing mesoscale/sub-mesoscale sea level change signals and improving marine geoid (Traon and Dibarboure 1999; Pujol et al. 2013; Andersen and Knudsen 2009). At present, the mature techniques used to observe SSH are tide gauges, geodetic global navigation satellite system (GNSS) buoys, and radar altimetry satellites (Watson 2005; Wunsch and Stammer 1998). Of these, either spatial or temporal resolution is very limited, for a variety of reasons (Penna et al. 2018). Coastline-based tide gauges provide high temporal resolution but poor spatial resolution. Geodetic GNSS buoys can only provide pointwise measurements in very limited
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Tianhe Xu [email protected]
1
Institute of Space Science, Shandong University, 180 Wenhuaxi Road, Weihai 264209, China
2
Second Institute of Oceanography, Ministry of Natural Resources, 36 Baochubei Road, Hangzhou 310012, China
sea areas (Xu et al. 2016). Monostatic radar altimetry satellites observe the global sea surface topography with lower temporal and spatial resolution because of their repeat orbit mission phases. Moving geodetic GNS
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