Abstract
Global Navigation Satellite System—Acoustic (GNSS-A) positioning is the main technique for seafloor geodetic positioning. A transceiver lever arm offset and sound velocity bias in seawater are the main systematic errors of the GNSS-A positioning technique. Based on data from a sea trial in shallow water, this paper studies the functional model of GNSS-A positioning. The impact of the two systematic errors on seafloor positioning is analysed and corresponding processing methods are proposed. The results show that the offset in the lever arm measurement should be parameterised in the observation equation. Given the high correlation between the vertical lever arm offset and the vertical coordinate of the seafloor station, a sample search method was introduced to fix the vertical offset correction. If the calibration of the sound velocity profiler cannot be ensured, the correction parameter of the sound velocity bias should be solved. According to the refined functional model and corrections, the position of a seafloor station in shallow water can be determined with a precision of better than 1 cm.
Highlights
The Global Navigation Satellite System—Acoustic (GNSS-A) positioning technique combines the GNSS sea surface dynamic positioning technique and the underwater acoustic positioning technique [1,2], which is the important basis of marine science research and engineering surveys
The accuracy of the seafloor position obtained by the GNSS-A positioning technique is limited by systematic errors, which mainly include the offset error of lever arms between shipborne devices and the bias of sound velocity measured in seawater [10,11]
If errors exist in the transceiver lever arms, but no error exists in the sound velocity, the three offset components of the lever arms can be solved together with the 3-D position of the seafloor station
Summary
The Global Navigation Satellite System—Acoustic (GNSS-A) positioning technique combines the GNSS sea surface dynamic positioning technique and the underwater acoustic positioning technique [1,2], which is the important basis of marine science research and engineering surveys. The accuracy of the seafloor position obtained by the GNSS-A positioning technique is limited by systematic errors, which mainly include the offset error of lever arms between shipborne devices and the bias of sound velocity measured in seawater [10,11]. For a sound velocity error, researchers in marine geodesy arrange the acoustic transponder array on a seafloor circle with the radius of water depth and can estimate the position changes of the array centre (virtual reference station) with centimetre-level accuracy by using shipborne GNSS and acoustic equipment [26,27]. Using shallow sea trial data, the GNSS-A positioning model was verified, and the transceiver lever arm offset and sound velocity bias were effectively corrected. The positioning accuracy of the seafloor station reached the centimetre level
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