Definition and origins of remote sensing

‘Remote sensing’ is, broadly but logically speaking, the collection of information about an object without making physical contact with it. This is a simple definition, but too vague to be really useful, so for the purposes of this book we restrict it by confining our attention to the Earth's surface and atmosphere, viewed from above using electromagnetic radiation. This narrower definition excludes such techniques as seismic, geomagnetic and sonar investigations, as well as (for example) medical and planetary imaging, all of which could otherwise reasonably be described as remote sensing, but it does include a broad and reasonably coherent set of techniques, nowadays often described by the alternative name of Earth Observation. These techniques, which now have a huge range of applications in the ‘civilian’ sphere as well as their obvious military uses, make use of information impressed in some way on electromagnetic radiation ranging from ultraviolet to radio frequencies.

The origins of remote sensing can plausibly be traced back to the fourth century bc and Aristotle's camera obscura (or, at least, the instrument described by Aristotle in his Problems, but perhaps known even earlier). Although significant developments in the theory of optics began to be made in the seventeenth century, and glass lenses were known much earlier than this, the first real advance towards our modern conception of remote sensing came in the first half of the nineteenth century with the invention of photography.