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What Is Side Scan Sonar?

side scan sonar FILEminimizer

 

This blog was copied from an article that was originally posted on NOAA’s Ocean Service Education page. The image above is the side scan sonar towfish ANAMAR used in a survey off the coast of Fernandina Beach, Florida.

What Is Side Scan Sonar?

Side scan sonar creates a picture or an image of the sea floor.  It measures the strength of how "loud" the return echo is and paints a picture.

Hard areas of the sea floor like rocks reflect more sound and have a stronger or louder return signal than softer areas like sand. Areas with loud echoes are darker than areas with quiet echoes. Objects or features that rise above the sea floor also cast shadows in the sonar image where no sound hit. The size of the shadow can be used to estimate the size of the feature.

Pictured below is a shipwreck ANAMAR found in the Atlantic a few years ago using sidescan sonar.

shipwreck ANAMAR found

 

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Potentially Polluted Shipwrecks Along U.S. Shores Undergo Remediation

Potentially Polluted Shipwrecks Along U.S. Shores Undergo Remediation

NOAA’s Findings on Potentially Polluting Shipwrecks Found in U.S. Waters

In 2010 Congress appropriated $1 million in funds toward identifying the most significant polluted shipwrecks along U.S. waters. With the help of the Remediation of Underwater Legacy Environmental Threats (RULET), U.S. Coast Guard, Regional Response Teams (RRTs) and NOAA, a complete investigation was conducted listing 20,000 vessels wrecked in U.S. waters. Of the 20,000 wrecked vessels, the RULET database narrowed down 573 wrecks within the U.S. Exclusive Economic Zone (U.S. EEZ) that could pose a substantial oil pollution threat. Another investigation was launched and of the 573 potential threats, 107 were found to be capable of causing substantial pollution. Eliminations were calculated due to the violent nature of the shipwrecks, structural reductions and demolitions already conducted due to navigational hazards, etc. Further investigations were conducted based on vessel contents, condition, environmental sensitivity, and other factors. NOAA then used a series of vessel-related risk factors based on current knowledge and best professional judgment to assess physical integrity and pollution potential as well as other factors that may impact potential removal operations if such operations were undertaken. Vessels that scored low were screened out and 87 remained on the priority list. Fifty-three of the 87 remaining ships were sunk in an act of war, 10 in a collision, 5 in a fire, 4 in a grounding, 10 in a storm, and 5 were sunk in an unknown or other cause. During recovery activities, a number of historical and cultural concerns with the wartime wrecks also surfaced, as some are gravesites and most contain ammunitions and other hazardous cargos.

All 87 vessels received a proper companion screening report, each of which contained an overall score and preliminary vessel-specific recommendations for further action, ranging from awareness within the local response community, to monitoring, to further assessment and planning for underwater remediation. More details are contained in NOAA’s published March 2013 online report.

 
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