OFDM for Underwater Acoustic Communications

Chapter 1Introduction

1.1 Background and Context

1.1.1 Early Exploration of Underwater Acoustics

The Earth is a water planet, with two-thirds of the surface covered by water. Exploration of the mysterious underwater world has never ceased in human history. As early as BC, Aristotle had noted that sound could be heard in water as well as in air. In AD , Leonardo da Vinci wrote: “If you cause your ship to stop and place the head of a long tube in the water and place the other extremity to your ear, you will hear ships at great distances” [268]. In , Charles Sturm and Daniel Colladon made the first accurate measurement of sound speed in water at Lake Geneva, Switzerland. The first practical application of underwater sound appeared in the s: the underwater bells equipped on lightships were simultaneously sounded with a fog horn to measure the offshore distance based on the difference of the airborne and waterborne arrivals, and meanwhile the stereo headphones were also used for directions [397]. With the sinking of Titanic in , L. F. Richardson successively filed a patent of echo ranging ...