1 School of Electrical and Electronic Engineering, Newcastle University, Merz Court, Newcastle upon Tyne NE1 7RU, UK 2Department of Electronics, University of York, Heslington, York YO10 5DD, UK 3 Institut Mines-Telecom, Telecom Bretagne, UMR CNRS 6285 Lab—STICC, Universite Europeenne de Bretagne, Technopole Brest Iroise, CS 83818, 29238 Brest Cedex, France 4Acoustic Research Laboratory, National University of Singapore, 12A Kent Ridge Road, Singapore 119223 5Department of Information Engineering, University of Padova, Via G. Gradenigo, 6/B, 35131 Padova, Italy 6Applied Ocean Physics and Engineering, Woods Hole Oceanographic Institution, MS No. 9, Bigelow 404, Woods Hole, MA 02543, USA