Underwater Discovery Using Side SonarPeter Gan, Tony Castagna, Peter Straub- Benthic SIRE

2009Richard Stockton College

What is side sonar? Side sonar is a new way to do underwater surveys with

remarkable accuracy and precision. Side sonar is a towfish that is towed behind a boat and uses sound or sonar, which can take a picture of the sea floor with very high resolution. The towfish puts out sound waves that are pings, which travel downward through the water column, and reflects off of the bottom. The towfish records the time it takes for the sound waves to travel back to the towfish. The towfish shows a ongoing map of the bottom of the sea floor to a personal computer that is on the boat. These recordings can be used in all types of clarities of water, it can even work in dark and murky water mainly because of its use of sound.

The Klein 3900 has two features a low and high resolution. The low range (445kHz) is usually used first to locate the objects that are being searched for because it will have a wider range of 150 meters. Once the object is located with the global positioning system (GPS) coordinates, a pass over the object in high resolution (900 kHz) will provide a more detailed picture of the object however the range drops down to 50 meters.

Side Sonar Applications: The Klein 3900 side scan has many applications that

can assist in research of the marine environment. One of the first applications the side sonar can be used for is the mapping of the topography of the bottom of the oceans, bays and lagoons of the local region. The tow fish has such great resolution that it can actually tell the different types of sediments and bottom types of the waterways. This information can be used for clam beds, oyster beds, erosion problems, unknown marine obstructions, and other applications.

The towfish can also be used to find lost items in our waterways. Side sonar has been used to find downed planes, drowning victims, lost scallop dredges, and almost anything that needs to be found. The side sonar can also be used to find lost “ghost” crab and fish pots that can be needlessly killing thousands of fish, crabs, lobsters, and terrapin turtles.

Finally one of the best applications of the side sonar is its ability to take images of artificial reefs and shipwrecks. There are literally thousands of these sites all over the waterways of the world. The side sonar creates an easy and affordable way to explore these sites. Previously in the past there was “snags “ that fishermen and scallopers have found but never knew what they were. Know with the side sonar we can see the sites that are good wrecks which will have abundant marine habitat and the ones we can see that are smaller and of no interest.

Many of the wrecks may have some historical significance since some of them were torpedoed or hit mines during World War II. Divers still visit these wrecks and continue to find artifacts. These shipwrecks are also a mini environment of life, consisting of plankton, crabs, sea bass, tautog, ling, summer flounder, lobsters, anemones, and northern star coral. With all of this life on these wrecks, it attracts fishermen, scuba divers and researchers to explore these wrecks. One advantage of the side sonar is its ability to determine the varies types of wrecks . It can easily be seen if a particular wreck is wooden or metal by the evidence of boilers or steel ribs.

A. Towing sonar, B) sonar equipment, C) sonar interpretation. Images courtesy of NJSCUBA.net & L-3 Klein Associates

Deploy towfish NJ wreck sites SIRE crew

Anemone- Astra

Lobster- Almirante

Coral- Almirante

Side scan images, NJ wrecks

AB C

NJSCUBA.net

Acknowledgement: Thank you to Steve Evert and crew of R.V. Gannet for support