One of the new sensors developed for the F-35 is the AN/AAQ-37 electro-optical DAS (Distributed Aperture System). This is a more powerful set of infrared (heat sensing) detectors placed on the aircraft so that objects producing heat can be sensed in all directions. The air force calls this “passive spherical awareness”. This is similar to the anti-missile systems carried on many aircraft. These use four or more heat sensors mounted on an aircraft and a computer that takes the sensor data and decides which detected heat is actually an approaching missile. If a missile is detected, a flare is launched, to draw the missile away from the aircraft. An alternative, and increasingly more common, defense is a laser, which delivers a dose of distracting heat to the missiles heat detector.
DAS uses more sensitive heat detectors, which can spot a ballistic missile being launched over 1,200 kilometers away or another aircraft 30 or more kilometers away. Recent tests discovered that DAS could detect ground fire (tank guns, artillery, or rocket launchers). This was an unexpected bonus, as it allows DAS equipped aircraft to quickly identify these weapons on the ground. If any of these are enemy systems, they can be immediately attacked with smart bombs because DAS can also calculate the GPS coordinates of what it spots on the ground.
The main purpose of DAS is to spot aerial targets without revealing yourself by transmitting a signal (as radar does). This is called passive sensing and enables the user to get the first shot in with a missile. For obvious reasons the air force did not reveal what the exact detection ranges were.