A recent development, synthetic aperture radar (SAR), was used during the Gulf War to detect disposition and movement of Iraqi forces. SAR systems used by coalition forces included the advanced synthetic aperture radar system -2 (ASARS-2), on the U-2 and the APG-70 on the F-15E.
An important advantage of SAR is its ability to penetrate clouds, smoke and fog to provide useful information, day or night, irrespective of weather conditions to give high-quality, extremely detailed ground mapping and moving target indication (MTI) for border surveillance and reconnaissance.
| The wide area moving target mode (WAMTI) that takes indiviidual moving targets and super-imposes them on a cartographic map |
The Hughes integrated synthetic aperture radar (HISAR), is an affordable airborne stand-off reconnaissance/surveillance system designed to provide high-resolution SAR imagery in real time displayed on a workstation on-board an aircraft. This real-time display provides flexibility to accomplish a pre-planned mission or to re-task radar to adapt to targets of opportunity as they are discovered.
HISAR was designed to support military and civil applications ranging from border surveillance and the monitoring of military exercises and build-ups, to drug interdiction and environmental monitoring.
A major advantage of HISAR is flexibility that results from its mode design. Baseline HISAR modes include wide-area search to provide a rapid overview of a large area. An operator can map land areas as large as 110km x 70km in seconds with resolutions of 15m-50m depending on range to the target.
Baseline HISAR modes also include strip map for border or coastline surveillance or environmental monitoring. In this mode, HISAR maps a continuous swath at an aircraft's speed up to 37km wide and 110km away from the ground track. The resolution of the pixels is 6m x 6m. MTI is also available in this mode.
Spot mode takes advantage of SAR's ability to see a target area in great detail over extreme distances. It provides a picture of an area 2.5km x 2.5km with a resolution of 1.8 x 1.8. Typically, the wide area search or the strip map with MTI would be used to identify areas or targets of interest and spot would be used to gather greater details of the area.
Air-to-air is similar to airborne early-warning systems. HISAR-equipped aircraft can detect low- flying aircraft and helicopters and track multiple targets, displaying their relative direction and velocity. The range is 70km for a 2m2 target.
Sea surveillance mode provides rapid surveillance of surface vessels in open seas. An operator can map a 300-degree area as large as 100km x 70km in 20 seconds.
Moving target indication (MTI) utilises pulse Doppler technique. HISAR can detect ground movers in the strip map mode and measure accurately their position, radial speed and indicate them as symbols on an SAR image. Trucks and cars and small boats and ships also can be detected.
The US government thinks the HISAR concept is valid. In head-to-head competitions HISAR derivatives were selected by the air force and army for Tier II Plus and ARL-M programmes.
| The strip map mode |
| The strip map mode at full resolution |
| The spot mode at full resolution |
