 The aim of this project is to monitor underwater acoustic fields over large areas using distributed optical fiber sensor systems. Typically, sub-C acoustic sensing is performed with point sensors, and when large areas need to be monitored, arrays of these sensors are connected together. In optical fibers, each one meter long section corresponds to one sensor. Therefore, 40 kilometers of fiber can provide an equivalent output to 40,000 point sensors. And the beauty of this approach is that all of them can be monitored at a single end by a system which looks like this. This system was developed within my group at the Optoleutronic Research Center in Southampton. The initial experiments were carried out at the A.B. Wood tank at the Institute of Sound Evaporation at the University of Southampton, which you can see in the top right corner. This tank is about 5 meters deep. We plan to perform further experiments in the towing tank at the engineering, which is nearly 100 meters long. This graph summarizes the measurement performed using the optical fiber underwater, and it is possible to observe that the optical fiber experience vibrations in the sections between 1560 meters, 90100 meters, and at 110 meters, with frequency in the region of 1000 Hz. The ultimate aim is to reconstruct the 3D acoustic field from these measurements. The next test will be performed at the Empress Deck. Just outside the National Oceanographic Center in downtown Southampton, we plan to have optical fibers on the seabed and monitor both traffic on top of that. And why do we do that? Because the optical fiber network is vast and a significant fraction of it is underwater. In this map, you can see that there are significant sections under the Irish Sea, some of them go under the North Sea, and some of them are under the channel. It is therefore possible to place our units where the cables land and monitor from those locations 50 kilometers under the water from single locations. We hope then to be able to use these to monitor mammals movements, nautical traffic, and possibly even sea level.