laseraltimeters

Laser altimeters are precision instruments used to measure altitude above the Earth's surface by emitting short laser pulses and recording the time delay until the reflected light returns to the sensor.

Most operate on the time-of-flight principle: the distance is derived from the round-trip travel time of photons and the speed of light. Some systems employ phase-based (continuous-wave) techniques or photon-counting receivers to detect very weak returns, enabling higher sensitivity or long-range operation.

A typical laser altimeter consists of a laser transmitter, a receiver telescope, a photodetector, timing and ranging electronics, and a navigation unit such as a GNSS receiver combined with an inertial measurement unit. Many platforms also use scanners or multiple beams to sample a swath and generate elevation data over an area.

Platforms include airborne systems on aircraft and helicopters, and spaceborne systems on satellites or the International Space Station. Wavelengths vary by design: common choices include near-infrared and green light, with some systems optimized for atmospheric transmission or canopy penetration.

Applications encompass topographic mapping, digital elevation models, forestry measurements (such as canopy height), floodplain assessment, and coastal or bathymetric surveys in shallow water.

Limitations include sensitivity to surface reflectivity, atmospheric scattering, weather and cloud cover, and geometry between the plane, surface, and satellite. Footprint size, incidence angle, and data processing affect accuracy, which typically ranges from sub-meter to decimeter scales under favorable conditions.

Notable laser altimeter programs include ICESat and ICESat-2 for ice and land elevation, GEDI for forest structure from the ISS, and various airborne lidar surveys.