A new information source: very high resolution
For a long time, it was only the military that had access to very high resolution satellite images. Recently, however, access has become much wider and many civilian or even commercial applications have been developed. Today a number of satellites offer images of this kind, with an increasingly precise resolution close to 50 centimetres. These images provide a useful complement to aerial photography as they permit the repeated observation of a quite large area over a number of spectral bands. The limits of high resolution instruments such as LANDSAT TM and SPOT HRV have become apparent in many applications, particularly in urban areas. On the other hand, very high resolution image proved to be particularly useful especially in support of decision-making at local or regional level. A new fi eld has opened up to show how and to what extent data supplied by very high resolution sensors can meet the growing demand for geotopographic information and thereby contribute to the improved management of urban and semi-urban areas.