Sensing element

(Or sensor.) The component of an instrument that converts an input signal into a quantity that is measured by another part of the instrument.

Active sensor: An electro-optical sensor that also illuminates (or irradiates) a target or other object and senses the reflected (or scattered) energy coming from the target (for example, radar).

Passive sensor: An electro-optical sensor that perceives the emitted or reflected natural energy from a target or other object.

Semiactive sensor: An electro-optical sensor that perceives the reflected energy from a target or other object; however, the reflected energy is created by illumination or irradiation by an unnatural source, such as a laser.

Electro-optical sensor: The component of an electro-optical system that converts input electromagnetic energy of a specific wavelength or band of wavelengths into electrical energy measured by another part of the component. Examples include a photographic camera.

Term edited 3 October 2025.