Airborne Laser Terrain Mapper Experiment (ALTM)


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Detailed topographic maps of very high accuracy are produced by airborne laser altimeter terrain mapping. The unique capabilities of this new technique yield more comprehensive and precise topographic information than traditional methods. Airborne laser altimeter data can be used to accurately measure the topography of the ground, even where overlying vegetation is quite dense. The data can also be used to determine the height and density of the overlying vegetation, and to characterize the location, shape, and height of buildings and other manmade structures.

The method relies on measuring the distance from an airplane, or helicopter, to the Earth’s surface by precisely timing the round-trip travel time of a brief pulse of laser light. The travel-time is measured from the time the laser pulse is fired to the time laser light is reflected back from the surface. The reflected laser light is received using a small telescope that focuses any collected laser light onto a detector. The travel-time is converted to distance from the plane to the surface based on the speed of light. Typically a laser transmitter is used that produces a near-infrared laser pulse that is invisible to humans. The laser light reaching the ground surface is completely safe. It can not cause any eye damage to a person who might be looking up at the plane as it flies overhead.

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