Optical surveys of space debris in GEO

Optical observations in astronomy have been revolutionized by the use of solid state CCD detectors. Their enhanced sensitivity combined with digital image processing opened new prospects for automated sky surveys. Such techniques may be used for space debris surveys. Ground based optical surveys of the geostationary ring and the geostationary transfer orbit region outperform Radar observations in terms of minimum detectable object size, even when using telescopes of moderate size. On the other hand, automated optical surveys - given the large data volume produced by the sensors - ask for a high degree of on-line processing. Furthermore carefully planned observation scenarios are mandatory. We discuss different detection techniques and survey types. Optical surveys may yield a wide variety of results. In the simplest case a correlation with catalogued objects on the basis of observed positions is performed. It is also possible to aim for precise orbits, visual magnitudes, albedo, geometrical size, attitude motion, etc. The techniques will be illustrated by results from three surveys conducted with the 1 m Zimmerwald Laser and Astrometry Telescope (ZIMLAT) in the geostationary orbit region.