Photographic reconnaissance permits searches of the territory of another country for objects of interest, usually missile sites or troop movements. Electronic reconnaissance is used to record and playback radar and other electromagnetic radiation emanating from another country. Other uses of satellites are to detect launching of missiles or nuclear explosions using infra-red techniques. Multi-spectral analysis gathers subtle clues about the actual physical makeup of observed objects, and penetrates natural barriers detecting anything camouflaged or decoyed. Satellite surveillance constitutes an infringement of national sovereignty which may be tolerated or which may be the cause of provocations leading to the destruction of 'enemy' satellites, and thus possibly, leading to war.