In the broadest sense, remote sensing is the measurement or acquisition of information of an object or phenomenon, by a recording device that is not in physical or intimate contact with the object.
It is the utilization at a distance (as from aircraft, spacecraft or satellite, or from a ship) of any device for gathering information about the environment. The technique can make use of devices such as a camera, laser, radar, sonar, seismograph or a gravimeter. Remote sensing normally includes digital processes but can as well be done with non-digital methods.
One unique characteristic of this kind of data collection is that it makes use of the emitted or reflected electromagnetic radiation of the examined object in a certain frequency domain (infrared, visible light, microwaves). This is possible due to the fact that the examined objects (plants, houses, water surfaces, air masses ...) reflect or emit radiation in different wavelengths and in different intensity according to their current condition.