When people are attempting to clean up oil spills at sea, one of the key things they need to know is the amount of oil that's been spilled – among other things, this will determine the amount of dispersant or other agents that are used. In order to make that process easier and more accurate, scientists from the Virginia Institute of Marine Science have developed a remotely operated vehicle (ROV) that does the job by measuring the thickness of oil slicks from below the surface.
Ordinarily, oil slick thickness is assessed by people in boats or aircraft, looking down on the spill from above. According to project leader Paul Panetta, however, doing so can be quite difficult. For one thing, it's hard for them to know – or get to – the location where the slick is at its thickest.
That's where the ROV comes in.
Moving underwater beneath the oil, it's equipped with four sonic transducers. Using these, it sends sound waves up into the underside of the slick. Each of those waves is first partially reflected by the density boundary between the water and the oil, and then again by the boundary between the oil and the air (or in the case of spills in the Arctic, the oil and the ice).
Once those reflected sound waves return back down to the ROV, its software analyzes the slight time lag between the two reflections. By doing so, it can precisely ascertain the thickness of the slick, ranging from several centimeters down to less than half a millimeter.
In its current prototype form, the ROV moves on tank-like tracks along the bottom of testing pools, and is linked to a human operator by a control tether. It's also equipped with two video cameras for navigation, and with a thermometer. The latter is necessary due to the fact that temperature affects the speed at which sound travels through both water and oil, and the ROV's software needs to be able to compensate for that variable.
Down the road, however, its sensing system could be installed on free-swimming ROVs, or even non-piloted AUVs (autonomous underwater vehicles).
You can see the ROV being tested, in the video below.
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