Miniaturized frequency-diversity FPGA-DAS system for small-size object hydro-acoustic detection

Distributed acoustic sensing (DAS) technology plays a significant role in marine biological monitoring, fisheries research, underwater scientific investigations, and underwater search and rescue. However, conventional full-scale DAS systems are restricted to shore-based infrastructure and cannot be deployed in remote open-sea areas or isolated islands and reefs. To address this limitation, this study proposes a miniaturized DAS technology with low power consumption based on a field programmable gate array (FPGA). Frequency diversity is adopted to suppress interference fading to ensure system reliability. A four-stage pipeline acceleration algorithm is designed to realize real-time demodulation of multi-channel diversity signals. By multi-domain clock homology, the low-frequency phase noise introduced by clock asynchrony is suppressed fundamentally. Through isolated integrated packaging, thermal and vibration isolation for the passive optical components is achieved, resolving phase variations caused by the connection of exposing passive and active components in the external environment. Experimental results demonstrate that the proposed DAS system exhibits a stable millihertz-level very low-frequency (VLF) response capability. The sea trial successfully captured the signals of the diver's movement (0.05-0.1 Hz). To the best of our knowledge, this is the first time that diver detection and 1 mHz frequency response are realized by such a miniaturized DAS, less than half the size of an A4 sheet, with a low power consumption of 30 W. This study provides a feasible technical pathway for remote open sea monitoring that was previously difficult to realize.