THE SENSORS, display and communications units fitted to the Dash 8 maritime-patrol aircraft (MPA) are typical of the large range of such equipment on offer.
There were two choices of radar considered: the travelling-wave-tube (TWT) type, or the power-hungry, but cheaper, magnetron variety. The latter has longer range, but 75% of the target detection ability. A TWT radar, with pulse compression, sustains high target detection probability in rough seas, at up to 60% of its maximum range; a magnetron radar has a dip in performance - down to one-third, at 15-25% maximum range.
This Dash 8 MPA's TWT radar was a "lightweight" version of Texas Instruments' APS-134 Sea View. A ship with a 3,750m2 (40,500ft2) surface area can be detected up to the full 280km range, but an area of only 5m2 should be seen at up to 95km - from 2,000ft. So each search swathe can be as wide as 175km.
Its display carried an outline of the coast - a highly detailed zigzagging thin line - derived from the world database provided by the US Defense Mapping Agency, and related to aircraft position by the global-positioning system.
Two radar modes optimise operation in high sea clutter: "Search 2" at longer ranges, with coastline display; and "Search 1" for small close-range targets. With a 360¡ scan, targets not seen ahead, because of sea state, may well be picked up on a rearward scan. The radar quickly detects the target's track or drift on the water. Up to 32 can be tracked concurrently - more, according to customer needs. Speed, accurate to a knot, is shown on a data panel to the right; on the left is a full list of all tracked targets, with tracking status. Targets, reference points, vectors to targets, waypoints and reference lines are selected by a roller-ball, similar to that used by air-traffic controllers.
The Wescam TV/IR equipment uses mature and proven technology. Its cameras come into play at closer range - about 10km out of cloud and precipitation. Infra-red performance varies with temperature, so two options are available, using the 3-5µu or 8-12µm bands; the first is twice as good in extreme hot and humid conditions, but in the moderate or cold surroundings, the latter out-performs. The UNS 125mm flat-panel liquid-crystal-display screen can remotely display the console picture.
The mount of the 400mm-diameter turret (housing two sensors - from among daylight or low-light TV and IR) has six-axis vibration isolation and active stabilisation in four axes. It can be automatically or manually steered to a radar target. A wing-pod searchlight, a further option, can be slaved to it in elevation and in a wide forward arc.
The turret can be slewed through 180¡ in azimuth in about 10s. The IR image may be presented on part of the radar screen, and a video recorder stores images from both IR and TV cameras.
Source: Flight International
