What function do active sensors serve in remote sensing?

Active sensors play a crucial role in remote sensing by emitting their own energy to illuminate an area and then measuring the reflected or backscattered energy that returns to the sensor. This process allows them to create detailed images and gather information about the Earth's surface or atmosphere, independent of natural light conditions. For instance, active sensors can work effectively during nighttime or in areas obscured by clouds, making them versatile tools for capturing data across various environments.

The ability to output radiation and collect return data is what distinguishes active sensors from passive sensors, which rely on external sources of illumination, like the sun. By utilizing emitted energy, active sensors can also manipulate the wavelength and intensity of the emitted signal to optimize the retrieval of specific data, such as altitude, surface roughness, or material composition. This functionality makes active sensing crucial for applications in earth observation, environmental monitoring, and disaster management.