Sonar – How Does it Work? What Does it Reveal?


What is side scan sonar? And how does it help find shipwrecks?

SONAR (Sound Navigation And Ranging) refers to the use of underwater sound waves to detect objects. Typically towed behind a ship, a sonar unit sends out sound waves and records the strength of the returning echo. Rocks, obstructions and man-made objects stand out from the surrounding seabed, as their smooth or irregular shapes typically reflect sound more easily than the ocean bottom and any object rising from the ocean floor will create a “shadow” behind it, further clues to the shape and size.

SonarEndurance Exploration Group’s first shipwreck project is the Connaught, a large side-wheel steamer lost in 1860 with a cargo of gold coins. Endurance rediscovered the shipwreck site in the waters off Boston using side-scan sonar in 2013 after mapping over 700 square miles and finding twenty-five potential shipwreck targets. In summer 2014, Endurance returned with a remotely-operated underwater vehicle (ROV) and successfully identified the final resting place of the steamship Connaught.



ConnaughtFirstFootage Returning in 2015, Endurance surveyed the site with 500 kHz high-resolution side scan sonar from multiple angles to map the shipwreck hull and debris field. Check out the new images below:

HighResConnaughtSonar2 HighResConnaughtSonar1

So what did Endurance learn from these high-resolution sonar passes?

The wreck is still largely intact; with an “acoustic shadow” indicating that the machinery may still be over 50 feet tall. The bow section appears almost fully separated from the main body of the wreck, the possible result of a massive explosion when freezing water first reached the high-pressure boilers. There was a bit of chop on the waves during the day of the survey, resulting in the horizontal lines across the imagery.

So what’s next? There are a number of operational stages to this salvage mission. We’re currently removing sonar and anchor deployment gear and replacing it with a sophisticate Remotely-Operated Vehicle (ROV) equipment. This changeover will allow us to begin subsea operations, starting with a full video and image survey of the site. Once complete, we’ll begin removing overburden and sediment while we work to locate the Connaught’s lost gold shipment and other valuables. Stay tuned—more updates soon!

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