Very high resolution images (e.g. GeoEye, QuickBird, IKONOS etc.) have a spatial resolution of 2.5 m and below where single buildings, shadows, roads, vehicles, individual trees and even individual persons are recognisable. Applications include urban planning, forestry, agriculture, hydrology and cartography as well as terrain modelling. The fine resolution supports mapping scales of up to 1: 5,000.
The pixel size of high resolution images can be considered to range from 5 m to 30 meters (e.g. Landsat). These images are used for detailed land cover and land use mapping from regional to national scales.
Moderate resolution images are characterised by a spatial resolution in the order of 100 m and above (e.g. Meris, Modis). The satellites offer a high revisit rate and allow frequent monitoring of land cover and environmental phenomena. Thus they afford to infer major Earth surface transformation processes.
Imaging radar systems, most commonly active microwave sensors, allow day and night time operation under virtually all atmospheric conditions. They can “see” through haze, light rain and snow, clouds, and smoke.
Application fields include forest and agriculture, geology, ice monitoring, flood & subsidence monitoring, maritime applications as well as terrain modeling.