Greg says he'll get the Port Nicholson's platinum, even if he has to lift the ship out of the water.
A basic Side Scan Sonar System is shown above. It consists of a topside processing unit, a cable for electronic transmission and towing, and a subsurface unit (a tow fish) that transmits and receives acoustic energy for imaging. Side scan sonar is a method of underwater imaging using narrow beams of acoustic energy (sound) transmitted out to the side of the tow fish and across the bottom. Sound is reflected back from the bottom and from objects to the tow fish. Certain frequencies work better than others, high frequencies such as 500kHz to 1MHz give excellent resolutions but the acoustic energy only travels a short distance. Lower frequencies such as 50kHz or 100kHz give lower resolution but the distance that the energy travels is greatly improved.
The tow fish generates one pulse of energy at a time and waits for the sound to be reflected back. The imaging range is determined by how long the tow fish waits before transmitting the next pulse of acoustic energy. The image is thus built up one line of data at a time.
Hard objects reflect more energy causing a dark signal on the image; soft objects that do not reflect energy as well show up as lighter signals. The absence of sound such as shadows behind objects show up as white areas on a sonar image.
