Information Contents of High Resolution Satellite Images

Large scale topographic maps do include more details like small scale maps. Corresponding to this, the required details have to be visible in the used images. Not only the pixel size, also the image quality, the spectral range and the number of spectral bands and the sensor type are important for the object identification. Even if space photos are scanned with a small pixel size, this must not correspond to the information contents; the photo grain may limit the information contents of digitized photos. Today the majority of space images are based on CCD line or array sensors, so the ground pixel size is better defined like for photos. The ground sampling distance (GSD) – the distance of the pixel centres on the ground – must not be the same like the size of the physical pixels projected to the ground. We do have the influence of the optics, the actual situation of the atmosphere and a numerical over or under sampling. In addition the image quality, especially the contrast, is depending upon the grey value range which goes from 6 bit or 64 different grey values to 12 bit or 4096 different grey values. Very high resolution images must be equipped with a time delay and integration (TDI) technology or the image motion has to be reduced by a permanent rotation of the satellite during imaging. Both techniques can influence the image quality. In the test area Zonguldak, Turkey, the effective information contents of several sensors like TK350, KVR1000, ASTER, SPOT V, IRS-1C, KOMPSAT-1, IKONOS and QuickBird have been analysed for the generation of topographic maps.