High-resolution multibeam deepwater cable route survey in high-relief seafloor area

In support of monitoring for nuclear tests, a Hydroacoustic Data Acquisition System (HDAS) monitoring system is to be installed at Ascension Island. The system consists of two hydrophone arrays linked by fibre optic cable to the island. A survey to select cable routes from PanAm Beach on Ascension Island to the proposed hydrophone sites was conducted in the summer of 2002. The survey utilised various acoustic sensors, single beam and multibeam echo sounders, sidescan sonar and sub-bottom profilers, operating from very shallow, near surf-zone depths, to full ocean depth. Backscatter data was included in the multibeam echo sounder data acquisition. The survey employed a small survey launch for the shallow water work, depths less than 100 meters, and a 1200-ton survey ship for the deep-water work. A land survey of the beach and a diver swim survey in the surf zone, completed the end-to-end survey. Data were processed in near real time to allow for rapid assessment and revision of the survey route.