The interaction of the electromagnetic radiation produced with a specific wave length to illuminate a target on the terrain for studying its scattered radiance, is called:

Remote Sensing: It is an art and science of obtaining information about an object without physical contact with that object.

The main principle of remote sensing is as follow:

Different objects reflect or emit different amounts of energy in different bands of the electromagnetic spectrum. The amount of energy reflected or emitted depends on the properties of both the material and the incident energy (angle of incidence, intensity, and wavelength).

Detection and discrimination of objects are done through the uniqueness of the reflected or emitted electromagnetic radiation from the object.

Depending on the source of electromagnetic energy, remote sensing can be classified as passive or active remote sensing.

In the case of passive remote sensing, the source of energy is naturally available such as the Sun. Solar energy reflected by the targets at specific wavelength bands is recorded using sensors. As a simple analogy, passive remote sensing is similar to taking a picture with an ordinary camera.

In the case of active remote sensing, energy is generated and sent from the remote sensing platform towards the targets. The energy reflected back from the targets are recorded using sensors located on the remote sensing platform.