Satellite monitoring of desertification: Background overview

Environmental monitoring of arid and semi-arid regions relies highly on Earth Observation satellites to repeatedly and regularly survey these vast areas. This introductory paper reviews the basic principles of long term monitoring and available imagery. Detailed monitoring relies on long series of images taken by optical sensors from Landsat and Spot satellites. Basically, these satellites measure the variations of solar light reflected by the land surface. Their use is based on relationships established between such measurements and land surface composition. To detect changes affecting the surfaces, the quality of image processing is crucial in terms of geometric correction, radiometric intercalibration and conversion into ground reflectance. Two studies are cited which illustrate the use of change detection: 30 years’ monitoring of rangelands in Tunisia, and irrigation extension in Morocco. Recommendations and perspectives are discussed in the context of the wealth of new remote sensing data and more powerful hardware and software for image processing.