Yamba SSS image

Klein 595 Side Scan Sonar

The main tool used in our search for shipwrecks is a Klein 595 side scan sonar, with a hundred meters of Kevlar reinforced cable and a dual frequency towfish.

Side scan sonars are designed to provide high-resolution acoustic images of the seafloor. They work by charging capacitors in the towfish (a torpedo-shaped object towed submerged behind the boat) through the tow cable. On command from the recorder on the boat, this stored power is dumped from the capacitors to the towfish transducers, which emit acoustic pulses of two different frequencies.

These pulses propagate out through the water, and hit solid objects. Returning echoes are received a very short time later by the transducers, the time delay being proportional to the distance to the reflected object, and returning echo signals are amplified on a “time varied gain curve”, then transmitted up the tow cable to the recorder, which further processes the signals, digitizes them, and calculates the position to display them in the image.

Scott and Steve’s system consists of a 595 Graphic Recorder and dual frequency towfish. The Graphic Recorder is interfaced with a data acquisition processor, which is equipped with a full suite of Seasone software.

The towfish can operate simultaneously with pulse “pings” at 100kHz and 500 kHz; 500 kHz gives the highest resolution, but with limited range, and 100 kHz gives increased range, but less resolution. The two frequencies ping simultaneously, which gives us maximum “ping rate”, increasing the probability of detection.

At 100 kHz, the unit is theoretically capable of viewing 750 meters either side of the towfish, although typically the range used is about a third of this.