A New Application of Lidar Technology Lidar, or laser altimetry, is an emerging remote-sensing technology already used in Earth and planetary science applications. Laser altimeters were used in the early 1970's on three Apollo missions. Only in the last decade have technological advances resulted in the development of reliable and accurate spaceborne sensors. These include the Mars Observer Laser Altimeter and the Shuttle Laser Altimeter. Lidars send a short pulse of light energy from a laser at a target. The time it takes for each pulse to complete a roundtrip to and from the target is converted into a direct measure of the elevation of the target. VCL's Multi-Beam Laser Altimeter goes one step further by also recording the "waveform" of the returned signal. The unique shape of the waveform reveals where—in the space between the ground and the tree tops—the foliage, trunk, and branches are concentrated. VCL is the first multi-beam, waveform-recording lidar to fly in space. LIDAR stands for light detection and ranging. Lidar sensors measure elevation by bouncing laser light off of a surface and measuring the time the light pulse takes to return. The above diagram shows how the Vegetation Canopy Lidar measures forest height by detecting reflected laser light. (Image by Robert Simmon) The VCL lidar holds five lasers that each send 242 pulses per second at the Earth's surface. Each beam covers an area 75 feet across. By spacing the five beams a little over a mile apart, each VCL orbit will sample an area 5 miles across. The VCL science team is using the airborne Laser Vegetation Imaging Sensor (LVIS), built at NASA's Goddard Space Flight Center in Greenbelt, Md, to acquire VCL-like data that they will use to fine-tune their data analysis methods. LVIS uses one laser, but it maps 100 percent of an area more than a half mile wide at a single pass. A rotating mirror reflects each laser pulse out from the aircraft at a slightly different angle to hit a series of consecutive areas in a strip across the flight path. next: Applications to Forest Management Needs back: Science Objectives		Vegetation Canopy Lidar Science Objectives A New Application of Lidar Technology Applications to Forest Management Needs Lidar Lasers: A Safe Technology

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