Plan position indicator

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Image:H2S - Pembroke And Milford Haven.jpg

The Plan Position Indicator, known as PPI, is the most common way to represent radar data.

The signal represented is the reflectivity at only one elevation of the antenna, so it is possible to have many PPI at one time, one for each antenna elevation. The radar is usually represented in the center of the display, so the distance from it can be drawn as concentric circles. As the radar antenna rotates, a radial trace on the PPI sweeps in unison with it about the center point.

Usually, north is represented at the top of the image, except in the case of ship and aircraft radars, where the top represents the front part of the ship or aircraft, i.e., its heading (direction of travel) and this is usually represented by a lubber line.

The Plan Position Indicator was devised at the Telecommunications Research Establishment, UK and was first introduced in the H2S radar blind-bombing system of World War Two.

The PPI is used in many domains involving radars, including air traffic control, meteorology, on board ships and aircrafts, etc... In meteorology, a competing display system is the CAPPI (Constant Altitude Plan Position Indicator) when a multi-angles scan is avalaible. Using computers to process data, modern sonar installations can mimic radar PPI displays too. (block diagram)fr:Plan Position Indicator