Definitions for "Active system"
A remote sensing system that transmits its own electromagnetic emanations at an object(s) and then records the energy reflected or refracted back to the sensor.
remote sensing system that transmits its own electromagnetic energy, then measures the properties of the returned radiation. Active systems require more power to operate than passive systems, but can be designed to have greater sensitivity. Examples of active systems are radar, lidar, and acoustic sounders.
A solar heating or cooling system that requires external mechanical power to move the collected heat.