What is the definition of Active Sensors in remote sensing?

Active sensors are defined as instruments that provide their own source of electromagnetic radiation to gather information about an object or area. This type of sensor emits energy, typically in the form of microwave or laser signals, and measures the energy reflected or backscattered from the surface being observed. The ability to generate their own energy enables active sensors to capture data regardless of the natural illumination conditions, making them highly versatile for applications such as radar and LiDAR.

The other options do not accurately describe active sensors. For instance, sensors that operate without any energy would be passive sensors, which rely on external sources of light, like the sun. Additionally, an emphasis solely on detecting light excludes other forms of electromagnetic radiation utilized by active sensors. Lastly, stating that active sensors are exclusive to thermal imaging overlooks the range of electromagnetic waves these sensors can work with, as active sensors can function across various spectrums and are not limited to thermal frequencies.