A surveillance device makes use of a fixed point in space such as a stabilized blimp, and a downward-looking high-resolution scanning camera. One or more line scan devices are arranged in a radial fashion on a rotating disk, together with associated lenses, so as to repeatedly scan an area of interest. To allow for manageable data bandwidth and to focus on objects of interest, the data from successive scans is compared so as to show primarily the moving objects, with occasional full-scan reference images included.