Evaluation of Acoustic Ranging Performance of UAV-Based GNSS-A Observation System by Water Tank Experiment

Global Navigation Satellite System-Acoustic ranging combination (GNSS-A) is a technique that combines GNSS positioning with acoustic ranging between a sea surface platform and a seafloor station to determine the absolute position of the seafloor station. A key step in GNSS-A observations is waveform identification for acoustic signals. In this study, we employ a UAV-based GNSS-A system to conduct detailed acoustic ranging performance tests in a water tank. We used two types of sonars (hemispherical and cylindrical), and systematically investigated the resulting biases in detected arrival times. Our findings reveal that sonar design significantly influences the ranging bias, protective dome structures can introduce additional signal distortions, and fraction-cycle biases depending on the transmission angle persist even after integer-cycle corrections. These results highlight the necessity of improved correction schemes to achieve higher acoustic ranging accuracy.