Page 19: of Maritime Reporter Magazine (July 1998)

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Deepsea Diving

The Hawaii MR1 is a portable side-scanning sonar system that simultaneously collects digital bathymetry and acoustic imagery over a wide section of seafloor.

The sonar itself is housed in a 16.4 ft. (5 m) long "towfish" which weighs 3,500 lbs. in air. In wafer, the towfish is towed behind the ship at a depth of 328 ft. (100 m) using a 2,200 lb. depressor weight. The tow- ing configuration allows the MR1 sonar to operate far from the noisy ship and below the surface mixed layer where the water temperature gradient causes acoustic rays to bend. In this quiet environment, MR1 transmits a "ping" every nine seconds, records the returning echo and sends the digital data up to the ship through the tow cable.

On the survey vessel, the acoustic data is processed to yield water depth and echo strength for each ping.

The images are displayed on computer monitors in real time, and combined with the ship's GPS navigation, generate precise charts of the seafloor.

To hunt for USS Yorktown, MRl's acoustic imagery was analyzed in search of the high-amplitude echoes indicative of the carrier's steel hull. The search area was centered on an area of sedimented abyssal plain, where the strong echoes from the ship were in contrast to the weak echoes of the surrounding sediment.

Operated by the Hawaii Mapping Research Group at the School of Ocean and Earth Science and Technology (SOEST) at the University of Hawaii, the MR1 was designed for exploration of the deep ocean.

It was selected as the reconnaissance tool in the ini- tial search for Yorktown due to its ability to rapidly -——. 1 scan for strong echoes over wide areas of seafloor, which allowed for the seafloor battlefield to be rapidly assessed for evidence of the sunken destroyer.

World War II veteren and USS Yorktown suvivor Bill Surgi helped the expedition to identify the wreck from video images relayed from the ocean floor. the ships I've ever seen on the ocean floor," said

Dr. Ballard, who hopes to one day create an underwater sea museum which can be accessed from the information highway, and is always on the look out for the perfect specimen to demon- strate how well the seas can preserve sunken ships. "With this expedition we've gone deeper than ever before and we've searched a greater area than ever before. It's a thrill to come back with images of this great American warrior."

The USS Yorktown expedition can be seen as part of the National Geographic Explorer series, to be called Battle for Midway, and is scheduled to air on TBS in the first part of 1999.

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