Any equipment which detects, and may indicate and/or record objects and activities, by means of energy or particles emitted, reflected, or modified by objects. Under the Treaty on Open Skies, equipment of a category specified in Article IV of the Treaty that is installed on an observation aircraft for use during the conduct of observation flights. The categories of equipment specified in Article IV are: optical and framing cameras; video cameras with real-time display; infra-red line-scanning devices; and sideways-looking synthetic aperture radar.