Army Corps of Engineers sonar maps Ohio River bottom

Barry Vessels explains a sonar to collect data from the Ohio River bottom to 5th and 6th Grade Magnate School students from Glasgow, Ky. The data helps barge captains in navigation. "Sometimes it feels like you are collecting data while riding a roller coaster that is pitched in every direction," said Barry Vessels, Lead Marine Information Specialist/Navigation, Army Corps of Engineers, Louisville. On the computer screen: The Marine Team use multibeam sonar that has 240 sonar beams collecting point cloud data along the bottom surface of the riverbed at 15 times a second. It uses a fan pattern from the 240 beams, with each sonar beam or sound wave sent out at ½ a degree cone. Think of a "fish finder" used on a fishing boat. That fishing boat sends out a single sonar beam typically at a 14-degree cone. The narrower cone of the survey grade sonar has a much smaller footprint showing finer detail of the object it strikes on the bottom. As the boat travels, it collects 240 points along the fan with a footprint that has a width about 3 times the depth. At 10 feet deep, the fan footprint along the bottom will be about 30 feet wide with the 240 point spread across even spaced. The sonar sends the data to the computer at an adjustable rate with most surveys using 15-20 times a second.

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