Robust Underwater Localization of Buoyancy Driven microFloats Using Acoustic Time-of-Flight Measurements

TL;DR

This paper introduces a robust, low-cost underwater localization method for buoyancy-driven microFloats using bidirectional acoustic ToF measurements, significantly improving accuracy and robustness in coastal environments.

Contribution

It presents a novel bidirectional acoustic ToF framework with nonlinear trilateration and filtering, enhancing underwater localization accuracy and robustness without heavy smoothing.

Findings

Median error below 4 meters relative to GPS

Reduced mean error from 139.29 m to 12.07 m

Improved trajectory alignment with GPS paths

Abstract

Accurate underwater localization remains a challenge for inexpensive autonomous platforms that require highfrequency position updates. In this paper, we present a robust, low-cost localization pipeline for buoyancy-driven microFloats operating in coastal waters. We build upon previous work by introducing a bidirectional acoustic Time-of-Flight (ToF) localization framework, which incorporates both float-to-buoy and buoy-to-float transmissions, thereby increasing the number of usable measurements. The method integrates nonlinear trilateration with a filtering of computed position estimates based on geometric cost and Cramer-Rao Lower Bounds (CRLB). This approach removes outliers caused by multipath effects and other acoustic errors from the ToF estimation and improves localization robustness without relying on heavy smoothing. We validate the framework in two field deployments in Puget Sound, Washington, USA. The localization pipeline achieves median positioning errors below 4 m relative to GPS positions. The filtering technique shows a reduction in mean error from 139.29 m to 12.07 m, and improved alignment of trajectories with GPS paths. Additionally, we demonstrate a Time-Difference-of-Arrival (TDoA) localization for unrecovered floats that were transmitting during the experiment. Range-based acoustic localization techniques are widely used and generally agnostic to hardware-this work aims to maximize their utility by improving positioning frequency and robustness through careful algorithmic design.