Another active sensor system, similar in some respects to radar, is lidar (light detection and ranging).
The radar data collected by RADARSAT could be valuable for mapping and monitoring wetlands, because radar is an active sensor creating its own illumination source, and data can be collected for areas covered with clouds or even at night.
An active sensor sends out a signal and measures the response (e.g. radar), whereas a passive sensor measures the earth's natural response to the sun (e.g. light wavelengths).
Here satellites use different sensor packages to passively measure the reflectance from parts of the electromagnetic spectrum or radio waves that were sent out from an active sensor such as radar.
radar systems generate and collect radiation - they are active sensors
objects with large differences in their electrical properties may be discriminated, and the size of the
object compared to the wavelength of the radar system is also important ...
Applications to actual remotely sensed data acquired from airborne and satellite remote sensing systems (passive and active sensors) indicate that multiquadrics, ...
 See also: Resolution, Class, Sensor, Imagery, Surface
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