Jane's Fighting Nodes Sources: USAF, Jane's, interviews.

The JSTARS is a large radar surveillance aircraft operated by the U.S. Air Force. JSTARS stands for Joint Surveillance Target Attack Radar System.

Role of the JSTARS

The JSTARS aircraft is designed to provide U.S. and allied forces a complete picture of the disposition of enemy ground forces and other ground traffic on a battlefield. It is used to locate and track troop or vehicle movements, both for threat detection as well as to vector attacking forces onto their targets. Flying behind the front lines, the JSTARS uses a large radar to detect movement on the ground at a distance.

The Technology

SAR has been around for a while; the JSTARS takes it to an extreme. It is outfitted with a 40-foot 'canoe-shaped' radome below the fuselage which houses the radar antenna; the antenna can be used to look in either direction, and can be slewed by phased array techniques. According to the USAF:

Radar operating modes include wide area surveillance, moving target indicator (MTI), sector search MTI and synthetic aperture radar. The antenna can be slued to either side of the aircraft to provide a 120 degree field of view covering nearly 19,305 square miles (50,000 square kilometers) and is capable of detecting targets at ranges from 164,049 to 820,248 feet (50 to 250 kilometers) from the aircraft. In addition to being able to detect, locate and track large numbers of ground vehicles the radar has some limited capability to detect helicopters, rotating antennas and low slow-moving fixed wing aircraft.

Well and good. But how? Well, bear in mind I don't actually know for sure; this is just an educated guess. The radar systems on JSTARS are optimized for ground imaging and targeting. The side-facing radome indicates that the system uses phased array radar, probably in two modes. One mode would simply be used to map the ground the system is looking at, both for informational purposes as well as to 'remove' it from the targeting information. The second mode would likely detect and measure Doppler changes in the frequency of any returned radar energy, in order to determine if the object that reflected said energy is moving. That's another reason to image the ground in general; the aircraft itself is moving, and imaging the ground will give the system a baseline Doppler shift to compare point target differences to.

If the system detects a frequency shift in the returned signal, it's likely that there is an additional 'pass' by the radar array which concentrates its energy on the regions of all Dopplered targets from the previous sweep. Radar's efficacy and accuracy is directly indexed to the amount of radar energy the system can receive from the target's reflected signature; this, in turn, is directly related to the amount of energy put out by the radar towards the target in the first place. An increased 'dwell time' for the likely targets means that the system will have a much greater level of return from those areas, and can make more detailed observations about the shape and behavior of said targets.

The Aircraft

JSTARS is built on an extensively modified version of the U.S. Air Force's favorite commercial large airframe, the Boeing 707-300. There are multiple workstations inside for everything from communications and detection to battle management and traffic control. The E-8C can be refueled in midair in order to extend its mission endurance. It contains crew amenities such as sleeping spaces and galleys in order to allow the operators to remain aloft for long missions.

The Specs: (source USAF)