Radar

"An active radio detection and ranging sensor that provides its own source of electromagnetic energy. An active radar sensor, whether airborne or spaceborne, emits microwave radiation in a series of pulses from an antenna. When the energy reaches the target, some of the energy is reflected back toward the sensor. This backscattered microwave radiation is detected, measured, and timed. The time required for the energy to travel to the target and return back to the sensor determines the distance or range to the target. By recording the range and magnitude of the energy reflected from all targets as the system passes by, a two-dimensional image of the surface can be produced." (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.

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