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.

翻译：对于需要高频位置更新的低成本自主平台而言，精确的水下定位仍是一项挑战。本文提出了一种适用于近岸水域浮力驱动微型浮标的稳健、低成本定位流程。我们在前人研究基础上，引入双向声学飞行时间定位框架，该框架同时整合浮标至浮体与浮体至浮标的双向传输，从而增加可用测量数据量。该方法将非线性三边测量与基于几何代价及克拉美-罗下界的定位估计滤波相结合，通过剔除多径效应及其他声学误差导致的飞行时间估计异常值，在不依赖重度平滑处理的前提下提升了定位稳健性。我们在美国华盛顿州普吉特湾的两处实地部署中验证了该框架。定位流程相对于GPS位置的中位数定位误差低于4米。滤波技术使平均误差从139.29米降至12.07米，并提升了轨迹与GPS路径的吻合度。此外，我们针对实验中持续发射信号但未回收的浮标展示了到达时间差定位方法。基于距离的声学定位技术已广泛应用且通常与硬件无关——本研究旨在通过精细的算法设计提升定位频率与稳健性，从而最大化其应用效能。