Abstract
Distributed Acoustic Sensing (DAS) is increasingly being explored for passive acoustic monitoring of many phenomena, including earthquakes, storms and detecting and tracking ships and whales. It has recently been reported that DAS may also be used to communicate acoustically underwater from low-power submerged sources to shore using incoherent frequency-hopped modulated packets. This new mode of underwater communication to shore could be of significant interest to smart sensors and autonomous vehicles that need to report compact bursts of time-critical information. It is therefore important to understand the conditions under which such communication packets might be well received, as a function cable construction, burial in sediment, acoustic frequency and angle of incidence of the acoustic wave to the cable. This paper reports a preliminary investigation into the latter factors, using data from a recent experiment conducted in Trondheim Fjord, described in a previous paper. We find that suitable conditions extend over a wide range of incidence angles between 30 – 75 degrees grazing angle to the cable used in that experiment over at least a bandwidth of several kHz. The results suggest that this new mode of underwater communication could offer significant benefits to teams of smart systems monitoring, inspecting or patrolling near or around pipelines, power cables, offshore wind or other installations that have fibre optic cables.