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remote sensing — English
The obtaining of data about an object from a distance by means of a specialised instrument – a sensor – that is not physically in touch with the object. The instrument could be a camera, sonar devise, mechanical scanner, radar system, laser sensor, electronic sensor, or an electromagnetic radiation sensor mounted in an Earth-orbiting satellite. All natural and synthetic objects with a temperature higher than absolute zero (that is, nil on the Kelvin scale, or -273,16˚C) emit electromagnetic energy and certain sensors can detect these emissions. Different objects emit different wavelengths of electromagnetic energy and we can build different sensors that can detect different wavelengths of radiation. An ordinary camera like the one in your cellphone can detect a very limited span of radiation wavelengths, namely those that are in the visible part of the spectrum – the same ones we can see with our own eyes. Laser instruments can emit wavelengths outside the visible spectrum with the result that we cannot see the beam unless it is reflected by some medium. This is used to spectacular effect in theatre productions and pop concerts, but it is mostly used for bona fide scientific, military and medical purposes. (Sonar imagery is often used in the military and medical fields, but that is something entirely different. Sound waves are emitted by an instrument and the same instrument detects the waves as they bounce back from the object they were aimed at. With sonar technology a baby can be safely viewed within its mother’s uterus.) It is important to note that an ordinary airphoto can be interpreted without processing of the data captured on it. However, this is not the case with satellite imagery which has to be processed before it can be interpreted.
