Experimental investigation on underwater acoustic ranging for small robotic fish

GPS-free localization is essential for navigation and information tagging in small robotic fish-based aquatic mobile sensor networks. Constraints on size, weight, and onboard computing power, together with noisy underwater environment, have made underwater localization a particularly challenging problem. In this paper a comprehensive experimental study is presented on underwater acoustic ranging methods based on time difference of arrival (TDOA). Performances of four methods are characterized and analyzed, including threshold-crossing, tone-detection, correlation integral, and sliding-window fast Fourier transform (FFT) methods. The study facilitates the understanding of capabilities and limitations of different underwater ranging methods and provides important insight into choice of hardware and algorithms for localization of networks of small aquatic robots.