An optical scanning system includes a frame having a central axis along which is mounted a first elevation mirror for receiving an incident light and reflecting the incident light along a first optical path, a telescope for receiving the reflected incident light and outputting an output light, a visible linear array imager for receiving the output light from the telescope, and a folding mirror positioned to receive part of the output light from the telescope and directing it to a linear array infrared imager. The optical scanning system scans large areas of sky using multiple linear sensors in order to detect, identify and track low and slow flying manned and unmanned aircraft as well as to surveil large areas of terrain.