Remote Sensing of the Terrestrial Environment. Principles and Progress

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Abstract
The theoretical and technical basis of remote sensing is first reviewed. The potential of remote sensing techniques for geographical research is then discussed in the light of previous work and of the authors' comparative use of five types of imagery in the Isle of Man. The most geographically significant aspects of remote sensing involve the perception and recording of terrestrial phenomena by equipment carried in aircraft or satellites and the subsequent analysis of the data so obtained. Terrestrial remote sensing depends upon the fact that surface features and certain other phenomena are recognizable by distinct 'signatures' which result from their differential response to electromagnetic energy. Different remote sensing systems are designed to sample energy within various bands of the electromagnetic spectrum. Passive, direct systems employ cameras and films, and sample the visible and near-infrared parts of the spectrum. They include conventional panchromatic, true-colour and false-colour photography. Passive, indirect systems, such as infrared linescan (IRLS), record terrestrial radiation and are valuable for the study of thermal phenomena. Active, indirect systems, such as sideways-looking airborne radar (SLAR), generate their own energy and record its transformation. SLAR is capable of all-weather reconnaissance and can operate by day or night. At present terrestrial remote sensing equipment is normally carried in aircraft, but its extension to orbiting satellites promises to provide continuous, repeating observations of most of the earth's surface. The potential value to geographers of the range of data that can now be obtained by remote sensing techniques is enormous and, as these techniques become more widely available, the assumptions and methods of much geographical field work will require radical revision.

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