Evaluation of an off-the-shelf acoustic system for precision positioning of seabed transponders

In this study, a commercial off-the-shelf acoustic system with ranging accuracy of 20 centimeters is employed to conduct an experiment of positioning seabed transponders. The feasibility of using a GPS/acoustic system with off-the-shelf transponders to achieve centimeter-level positioning accuracy was evaluated. In order to verify the relative positioning accuracy between seabed transponders, a seafloor acoustic transponder (SAT) system was developed. Three transponders were mounted on the SAT system to form a triangle with known baselines. In addition, a data acquisition and logging system was developed to integrate with a motion reference unit (MRU) and a fiber optic gyro (FOG) for collecting the heading information of the SAT system. A field experiment to verify the relative positioning accuracy between transponders was carried out. The collected GPS/acoustic observations and sensor data were then used to estimate the positions of the three transponders based on an optimization technique combined with ray trace calculations. The transponder positioning result shows that the root mean square slant range residuals are in good agreement with the inherent ranging accuracy of the acoustic system. The experimental results also show that the mean value of the acoustic slant range residuals is about 3 centimeters and the relative positioning error between transponders is less than 3 centimeters. Furthermore, the heading of the SAT system derived from the position estimates of the three transponders is in good agreement with the measurement obtained by the MRU and FOG on the SAT system.