Underwater localization is essential for marine exploration and autonomous underwater operations, yet existing radio frequency and optical approaches are limited by rapid attenuation or limited visibility. Acoustic sensing remains the most practical choice, but conventional acoustic systems typically rely on large arrays or multiple synchronized anchors, resulting in high hardware costs and complex deployment. This paper introduces a novel low-cost passive acoustic metasurface, MetaBlue , explicitly designed for underwater localization, which, when attached to an ordinary ultrasonic transmitter, transforms it into a directional "super-transmitter." The metasurface embeds direction-dependent spectral patterns into the transmitted waveform, enabling accurate angle-of-arrival (AoA) estimation using only a single hydrophone. For ranging, we present a new EM-acoustic mixed time-of-arrival (ToA) method that leverages the acoustic transducer's inherent low-frequency EM leakage as a timing reference, enabling precise ranging without shared clocks. This allows complete 3D localization with a single low-cost anchor. We evaluate the system across diverse real-world underwater settings, including pools, tanks, and outdoor environments. Experiments show that our design achieves an average AoA error of 8.7 degree and 3D localization error of 0.37 m at distances over 10 m. Even with a single anchor, the system maintains 0.73 m precision.

翻译：水下定位对于海洋探索与自主水下作业至关重要，然而现有的射频与光学方法受限于快速衰减或有限能见度。声学传感仍是最实用的选择，但传统声学系统通常依赖大型阵列或多个同步锚点，导致硬件成本高昂且部署复杂。本文介绍了一种新颖的低成本被动声学超表面MetaBlue，专为水下定位设计，当附着于普通超声发射器时，可将其转换为定向“超级发射器”。该超表面将方向相关的频谱模式嵌入发射波形中，使得仅使用单个水听器即可实现精确的到达角估计。针对测距，我们提出了一种新的电磁-声学混合到达时间方法，该方法利用声学换能器固有的低频电磁泄漏作为时间参考，无需共享时钟即可实现精确测距。这使得仅需单个低成本锚点即可完成完整的三维定位。我们在多种真实水下环境（包括水池、水箱和户外环境）中对系统进行了评估。实验表明，我们的设计在超过10米的距离上实现了平均8.7度的到达角误差和0.37米的三维定位误差。即使仅使用单个锚点，系统仍能保持0.73米的定位精度。