The remote detection technology of light detection and ranging, or lidar, uses light in the form of laser pulses to determine variable distances by measuring the time it takes the pulses to reflect off objects or surfaces and return to its receiver. Unlike radio detection and ranging, or radar, lidar uses light instead of radio waves to generate images of scanned surfaces, bodies of water and the atmosphere.
A lidar system consists of a laser and optics working as a mirror with scanning and rotating mechanisms to reflect the laser from its source. A photodetector serves as the receiver for the return pulse; timing electronics measure the time between the pulse and return. A positioning system measures the altitude and position of the application from the GPS and inertial measurement unit, and a computer performs calculations and records data.
Lidar uses green or near-infrared light to scan an area downwards or side to side from an application and flashes up to 400,000 laser pulses per second. The distance between the lidar system and the target is equal to one-half of the time between sending the laser pulse and receiving the reflection and multiplied by the speed of light.
In aerial applications, ground elevation is determined by taking the aircraft’s altitude calculated by the GPS receiver, then subtracting the distance from the light traveling to the ground.