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Planetary Laser Altimetry
A laser altimeter is an instrument that measures the distance from an orbiting spacecraft to the surface of the planet/asteroid that the spacecraft is orbiting. The distance is determined by measuring the complete round trip time of a laser pulse from the instrument to the planet's/asteroid's surface and back to the instrument.The distance to the object can be determined by multiplying the round-trip pulse time by the speed of light and dividing by two. With a well-known attitude and position of the instrument/spacecraft the location on the surface illuminated by the laser pulse can be determined. The series of the laser spot, or footprint, locations provides a profile of the surface.
 
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