Airborne surveillance radars serve two purposes. They assist the detection of air targets and the detection of targets on the ground and sea surface. These radars equip Airborne Early Warning (AEW) aircraft, principally fixed- and rotary-wing platforms. Airborne surveillance radars furnish maritime surveillance aircraft and/or intelligence, surveillance and reconnaissance platforms. In this latter role they equip fixed- and rotary-wing aircraft and unmanned aerial vehicles.
Airborne Early Warning (AEW) Radars
AEW aircraft use airborne surveillance radars to detect air targets like aircraft or missiles. Some AEW radars may have a residual capability to detect and track targets on the ground and sea. Illustrative of this were the Royal Navy’s erstwhile AgustaWestland/Leonardo ASAC.7 Sea King helicopters. These carried the Thales’ Searchwater-2000 radar. Likewise, Boeing’s E-3 Sentry series of AEW jets equipped with the Westinghouse/Northrop Grumman AN/APY-1/2 radar can detect and track targets on the sea surface.
Detect & Track AEW Radars
AEW radars detect and track hostile air targets. This lets controllers onboard the aircraft direct friendly airpower towards these targets and manage their interception. The same radar can manage the direction of friendly aircraft and coordinate blue force air operations. These missions can include close air support and battlefield interdiction, combat air patrols, refuelling and combat support. The advantage of an AEW radar is its range of target detection and tracking. For example, such a radar equipping an aircraft flying at 30,000 feet/ft (9,144 metres) would have a range of circa 212 nautical miles (392 kilometres). Choices of radar are governed by the radar’s role, power and antenna size, among other factors. As a result, radars furnishing AEW platforms tend to use L-band (1.215 gigahertz/GHz to 1.4GHz), S-band (2.3GHz to 2.5GHz/2.7GHz to 3.7GHz), C-band (5.25GHz to 5.925GHz) and X-band (8.5GHz to 10.68GHz).
Airborne Maritime Surveillance Radar
Airborne surveillance radars also have a key role to play detecting targets on the ground and sea. Both the ground and maritime environments can be very ‘cluttered’. Clutter refers to the spurious echoes a radar receives as its transmissions hit objects on the ground and surface. For example, the sea has wave crests, which can sometimes be relatively large. A radar will detect these wave crests and display them on the screen. Likewise, the ground has a plethora of objects causing clutter from buildings to vegetation and vehicles. Clutter can cause a small target like a boat or car to be masked by larger objects on the screen. For this reason, many airborne surveillance radars frequencies of X-band (8.5GHz to 10.68GHz) and above.
The narrowness of these beams allows targets to be picked out in sharp detail. As X-band beams are very narrow, a radar can take several transmissions to compose a picture of a car, for example. This is because the antenna will be relatively small compared to lower frequency radars. X-band transmissions can create a soda straw-like view of a target. Therefore, the aircraft carrying the radar must physically move the antenna over a given area to create a detailed picture of the target. This is the principle behind Synthetic Aperture Radar (SAR). The movement of the aircraft over a particular area artificially creates a larger antenna. SAR pictures are so detailed that they rival photographs. However, unlike photographs, they can be composed in all weathers, day or night as radar is unaffected by such conditions.
Airborne Surveillance Radars & MTI Software
These airborne surveillance radars also include Moving Target Indicator (MTIs) software. This detects when targets like vehicles or vessels are moving. MTIs are useful in helping battle management on the ground and in the maritime environment. The United States Air Force’s Boeing E-8C Joint Surveillance Target Attack Radar System is equipped with the Northrop Grumman AN/APY-7 radar. This radar used its SAR and MTI capabilities to track Iraqi Army vehicles during Operation Desert Storm. Waged by a US led coalition in 1991, Desert Storm evicted Iraq from its occupation of Kuwait. Information from the E-8C was particularly useful in helping vector coalition airpower towards these targets during combat.