Laser Altimeter

"An instrument that uses a lidar to measure the height of the platform (spacecraft or aircraft) above the surface. The height of the platform with respect to the mean Earth’s surface is used to determine the topography of the underlying surface." (National Aeronautics and Space Administration, 2018)

Sources

"Remote Sensors". Earthdata, National Aeronautics and Space Administration. Last modified December 11, 2018.
https://earthdata.nasa.gov/user-resources/remote-sensors.
Accessed February 13, 2019.