Investigation on total adjustment of the transducer and seafloor transponder for GNSS/Acoustic precise underwater point positioning

Abstract

Global navigation satellite system/acoustic (GNSS/A) underwater positioning technique has drawn increasing attention in the fields of marine scientific research and engineering application. The conventional positioning strategy of GNSS/A is to fix the positions of sea-surface transducer, in other words, the positions of the transducer determined by GNSS positioning at different epochs are regarded as accurate and unbiased, and then estimate the underwater transponder's coordinate with acoustic ranging data. However, there inevitably exists bias in the estimation of transducer's positions, and the precision varies at different epochs. Ignoring precision differences of the transducer's positions will lead to a worse estimation of the transponder's coordinate. In this contribution, we propose a total adjustment (TA) method, where the positions of both sea-surface transducer and seafloor transponder are treated as unknown parameters, and the transducer's positions determined by GNSS positioning at different epochs are introduced as virtual observations. In order to reduce the computation load caused by large increase of estimation parameters, an equivalent transformation is applied to observation equations to remove estimation parameters for the transducer's positions at different epochs. To evaluate the performance of the proposed total adjustment method, a series of simulation tests and a sea-trail experiment were carried out. Testing results show that, as compared with the traditional method, the positioning accuracy with the proposed method can be improved by about 10%–33% in the simulation tests and 15% in the field test.