Basic principles of remote sensing

Remote Sensing as it has been accepted today in the scientific literature is comparatively a young branch of science. But the act of remote sensing is perhaps as old as the origin of life on our planet. Remote sensing is the sensing of an object or a phenomenon from a remote distance. But then, how remote is remote for remote sensing? Consideration of this type is highly relative and depends on the characters of the signals and the sensors, and also on the attenuation properties of the signal transmission channel. One may also like to know whether there can be sensing without physical contact between the sensor and the object. You may say yes, but the real answer to this question is a big NO. This is because of the fact that under all circumstances the objects to be sensed and the sensor are always intimately bathed in an interacting field, namely the gravitational field, the electromagnetic field and / or the pressure field. These fields are not fictitious but are as real as a lump of matter is. Thus, whatever may be the distance between the sensor and the sensed, they are always in contact with each other through the field. What then is the special significance of the contact sensing? In fact, during the so-called contact sensing no true material contact is established since the planetary / surface electrons of the two bodies can not touch each other, being both negatively charged they repel one another and keep themselves at a distance. What happens in reality is that during the so-called contact sensing the fields of both the bodies influence each other so markedly that it results in an appreciable amount of interaction force / pressure, which is sensed or measured. Now, without going any further with the passionate philosophical discussion on what is remote sensing, we may content ourselves saying that practically remote sensing is the science and technology for acquiring information about an object or a phenomenon kept at a distance. Basically it is a non destructive physical technique for the identification and characterization of material objects or phenomena at a distance.