The issue is the thermocline which reflects sounds back either back to the surface or back to the ocean floor You need to get your hydrophone below the thermocline layer Also the pinger is not very noisy meaning you need to get the hydrophone within 1 nautical mile 6 076 feet of the pinger What they end up doing is towing the hydrophone about 1000 feet above the ocean floor At 1000 feet you are able to scan a swath that s 11 978 feet wide assuming the ocean floor is flat and level talk