Acoustic Waves

On land the five sense of living beings sight hearing touch smell and taste play complementary roles. Two of these sight and hearing are essential for long range interaction, while the other three have essentially short range functionality. But things are different under water sight loses all meaning as a long range capability, as does indeed its technological counterpart, radar. So by default, sound waves carry out this long range sensing under water. The most highly developed and intelligent forms of underwater life e.g. whales and dolphins over a time scale of millions of years have perfected  very sophisticated range-finding, target identification, and communication systems using ultrasound. On the technology front, ultrasound also really started with the development of underwater  transducers during World War I.  Water is a natural medium for the effective transmission of acoustic waves over large distances and it is indeed for the case of transmission in opaque media, that ultrasound comes into its own. (jacket)