Airborne lasers measure oil slicks at sea

17 Jun 2002

Later this year, three lasers mounted in an aircraft will measure the thickness of an oil slick bobbing on the sea.

The demonstration by Conseil national de recherches Canada - National Research Council Canada (CNRC-NRC) is to prove the versatility of laser ultrasonics.

As the aircraft flies at heights less than 100 metres above the slick, the first laser will reflect its beams off the slick to measure the orientation of its surface relative to the aircraft.

When the aircraft and the slick are correctly oriented, the second laser will fire a high power pulses at the oil. As the pulses strikes it will heat the slick's surface and the resulting expansion will send an ultrasonic wave through the oil.

The ultrasonic wave will reflect off the water supporting the oil and pass back through the slick where it will eventually make the surface vibrate. The third laser will reflect its beam off the vibrating surface and back into an interferometer. Data analysis of the interferometer's signal will reveal the time of flight of the ultrasonic pulse through the slick thus revealing the thickness of the layer.

CNRC-NRC thinks the technique will make it simpler to gather evidence of ships dumping oil illegally at sea.

Laser ultrasonics is well established in the aircraft industry which uses pairs of lasers to measure faults in composite materials. The steel industry is interested in the technique to measure the wall thickness of steel pipes as they are manufactured.

Other applications of laser ultrasonics are likely to appear in measuring plasma coatings and thin films, predicting the quality of paper from the pulp in the mill, measuring the temperature of silicon wafers or molten metal, or the distribution of stones and flaws in concrete. JB