Assessment of Underwater Positioning Accuracy of Acoustic Modems Using Real-Time Kinematic GNSS

Accurate ground truth data is crucial for developing and evaluating new localization and navigation techniques for autonomous underwater vehicles (AUVs). This paper presents a Real-Time Kinematic (RTK)-GNSS-based experimental setup for assessing the performance of underwater positioning systems in real-world scenarios. We demonstrate its application for static and dynamic testing using acoustic modems with an underwater vehicle and two buoys. Based on extensive error analysis, we derived a method to estimate the acoustic ranging error as well as the positioning errors when using the trilateration technique. We have verified our method by evaluating test data collected with the proposed experimental setup. The results of the static ranging test show that an accuracy below 10 centimeters can be achieved; while in the dynamic test case with a velocity up to 0.7 m/s and range up to 30 m, the real-time positioning error is well below 3 meters. Overall, these are promising results considering that low-cost acoustic modems are used for acoustic ranging, and the positions are determined by the trilateration method without any error compensation or prediction models.