With the A900s, Persistent Surveillance is done using the Tiling method - we fly 1,000 metres above the ground (3,280 ft) and monitor one square kilometre. The cameras then divide the 1km2 into 9 tiles and every 5 seconds new images are taken and compared with prior ones. Any change detected is identified and classified according to the type of object. Everything from small UAVs to larger objects are recorded.