Laser altimeters historically were the first active sensing devices used on airborne platforms, measuring range information in form of single distances since the mid-1960s.
Even though laser scanners made it possible to retrieve information in a more rapid and denser coverage since the mid-1990s, laser altimeters remain of importance in the scientific community. Especially, the mapping of ice-covered surfaces, water bodies and flat land areas is still performed using laser altimeters.
Laser altimeters are either airborne or spaceborne and are often used together with microwave (radar) profiler in order to calibrate the radar instruments. Whereas airborne laser altimeters are preferred for forestry application, e.g. for analyzing vertical vegetation structure, spaceborne laser altimeters are additionally used for multiple other applications. In particular, spaceborne laser profiler are of high interest for studying surface roughness of ice sheets or for mapping desert topography. Furthermore, spaceborne laser profilers are also useful in atmospheric science for retrieving cloud structure and analyzing different aerosol layers. The requirements for airborne and spaceborne laser altimeters are different. In particular, for spaceborne altimeters, both the distance travelled by the laser pulse and the platform speed are much higher than for airborne instruments, inducing the need of larger optics and more powerful laser instruments. First spaceborne laser experiments were conducted onboard the space shuttle in the mid-1990s, first aiming atmospheric research with a near infrared laser. After successful trial, the space shuttle laser altimeter was fine-tuned and follow-up missions focused on mapping terrain relief and vegetation canopies. Later missions, such as GLAS (IceSAT), ATLAS (IceSAT-2) and GEDI (ISS), used either near-infrared or green (or both) laser light and focused on improving ground coverage while allowing smaller footprints of the laser beam on ground. The revisit cycle of spaceborne laser altimeters allow the determination of regional elevation changes, e.g. monitoring of ice–sheet thickness or vegetation height, which is highly relevant for the scientific community and climate modelers.