A plan position indicator (PPI) is a type of

radar display A radar display is an electronic device to present radar data to the operator. The radar system transmits pulses or continuous waves of electromagnetic radiation, a small portion of which backscatter off targets (intended or otherwise) and retu ...

that represents the radar antenna in the center of the display, with the distance from it and height above ground drawn as concentric circles. As the radar antenna rotates, a radial trace on the PPI sweeps in unison with it about the center point. It is the most common type of radar display.

Description

The radar antenna sends pulses while rotating 360 degrees around the radar site at a fixed elevation angle. It can then change angle or repeat at the same angle according to the need. Return echoes from targets are received by the antenna and processed by the receiver and the most direct display of those data is the PPI. The height of the echoes increases with the distance to the radar, as represented in the adjacent image. This change is not a straight line but a curve as the surface of the Earth is curved and ''sinks'' below the

radar horizon The radar horizon is a critical area of performance for aircraft detection systems that is defined by the distance at which the radar beam rises enough above the Earth's surface to make detection of a target at low level impossible. It is associ ...

. For fixed-site installations,

north North is one of the four compass points or cardinal directions. It is the opposite of south and is perpendicular to east and west. ''North'' is a noun, adjective, or adverb indicating direction or geography. Etymology The word ''north ...

is usually represented at the top of the image. For moving installations, such as small ship and aircraft radars, the top may represent the bow or nose of the ship or aircraft, ''i.e.'', its

heading Heading can refer to: * Heading (metalworking), a process which incorporates the extruding and upsetting processes * Headline, text at the top of a newspaper article * Heading (navigation), the direction a person or vehicle is facing, usually s ...

(direction of travel) and this is usually represented by a

lubber line A lubber line, also known as a lubber's line, is a fixed line on a compass binnacle or radar plan position indicator display pointing towards the front of the ship or aircraft and corresponding to the craft's centerline (being the customary direc ...

. Some systems may incorporate the input from a gyrocompass to rotate the display and once again display north as "up". Also, the signal represented is the

reflectivity The reflectance of the surface of a material is its effectiveness in Reflection (physics), reflecting radiant energy. It is the fraction of incident electromagnetic power that is reflected at the boundary. Reflectance is a component of the respon ...

at only one elevation of the antenna, so it is possible to have many PPIs at one time, one for each antenna elevation.

History

The PPI display was first used prior to the start of the

Second World War World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposi ...

in a

Jagdschloss A ''Jagdschloss'' is a hunting lodge in German-speaking countries. It is a '' schloss'' set in a wildlife park or a hunting area (such as a forest, field or by a lake) that served primarily as accommodation for a ruler or aristocrat and his ent ...

experimental radar system outside

Berlin Berlin ( , ) is the capital and List of cities in Germany by population, largest city of Germany by both area and population. Its 3.7 million inhabitants make it the European Union's List of cities in the European Union by population within ci ...

. The first production PPI was devised at the

Telecommunications Research Establishment The Telecommunications Research Establishment (TRE) was the main United Kingdom research and development organization for radio navigation, radar, infra-red detection for heat seeking missiles, and related work for the Royal Air Force (RAF) ...

, UK and was first introduced in the

H2S radar H2S was the first airborne, ground scanning radar system. It was developed for the Royal Air Force's Bomber Command during World War II to identify targets on the ground for night and all-weather bombing. This allowed attacks outside the ran ...

blind-bombing system of

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposing ...

. Originally, data was displayed in real time on a cathode ray tube, and thus the only way to store the information received was by taking a photograph of the screen.

Philo Taylor Farnsworth Philo Taylor Farnsworth (August 19, 1906 – March 11, 1971) was an American inventor and television pioneer. He made many crucial contributions to the early development of all-electronic television. He is best known for his 1927 invention of t ...

, the American inventor of all-electronic television in September 1927, contributed to this in an important way. Farnsworth refined a version of his picture tube ( cathode ray tube, or CRT) and called it an "Iatron;" generically known as a

storage tube Storage tubes are a class of cathode-ray tubes (CRTs) that are designed to hold an image for a long period of time, typically as long as power is supplied to the tube. A specialized type of storage tube, the Williams tube, was used as a main mem ...

. It could store an image for milliseconds to minutes and even hours. One version that kept an image alive about a second before fading proved to be useful for radar. This slow-to-fade display tube was used by

air traffic controller Air traffic control specialists, abbreviated ATCS, are personnel responsible for the safe, orderly, and expeditious flow of air traffic in the global air traffic control system. Usually stationed in air traffic control centers and control ...

s from the very beginning of radar usage. With the development of more sophisticated radar systems, it became possible to digitize data and store it in memory, allowing access at a later date.

Uses

The PPI is used in many domains involving display of range and positioning, especially in radars, including

air traffic control Air traffic control (ATC) is a service provided by ground-based air traffic controllers who direct aircraft on the ground and through a given section of controlled airspace, and can provide advisory services to aircraft in non-controlled airs ...

, ship navigation,

meteorology Meteorology is a branch of the atmospheric sciences (which include atmospheric chemistry and physics) with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progress in meteorology did no ...

, on board ships and aircraft etc. PPI displays are also used to display

sonar Sonar (sound navigation and ranging or sonic navigation and ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, measure distances (ranging), communicate with or detect objects on o ...

data, especially in underwater warfare. However, because the speed of sound in water is very slow compared to microwaves in air, a sonar PPI has an expanding circle that starts with each transmitted "ping" of sound. In meteorology, a competing display system is the CAPPI (Constant Altitude Plan Position Indicator) when a multi-angle scan is available. Using computers to process data, modern

and lidar installations can mimic radar PPI displays too.

Bibliography

* Sir Bernard Lovell ''ECHOES OF WAR : The Story of H2S Radar'' * ''Adapted fro
Microwave Radar At War (1)
There is an open source verification for this text on the home pag

'' * A. P. Rowe: ''One Story of Radar'' - Camb Univ Press - 1948 * Dudley Saward, ''Bernard Lovell: A Biography'' - Robert Hale - 1984 * Norman Longmate ''The Bombers: the RAF offensive against Germany, 1939-1945'', Hutchins & Co, (1983), * E. G. Bowen ''Radar Days'' * David Atlas, ''Radar in Meteorology: Battan Memorial and 40th Anniversary Radar Meteorology Conference'', published by

American Meteorological Society The American Meteorological Society (AMS) is the premier scientific and professional organization in the United States promoting and disseminating information about the atmospheric, oceanic, and hydrologic sciences. Its mission is to advance th ...

Boston Boston (), officially the City of Boston, is the state capital and most populous city of the Commonwealth of Massachusetts, as well as the cultural and financial center of the New England region of the United States. It is the 24th- mo ...

, 1990, 806 pages, , AMS Code RADMET. * Yves Blanchard, ''Le radar, 1904-2004: histoire d'un siècle d'innovations techniques et opérationnelles '', published by Ellipses,

Paris Paris () is the Capital city, capital and List of communes in France with over 20,000 inhabitants, most populous city of France, with an estimated population of 2,165,423 residents in 2019 in an area of more than 105 km² (41 sq mi), ma ...

France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of overseas regions and territories in the Americas and the Atlantic, Pacific and Indian Oceans. Its metropolitan area ...

, 2004 * Brown, Louis. ''A Radar History of World War II: Technical and Military Imperatives'', Philadelphia, Pa.: Institute of Physics Publishing, 1999. * R. J. Doviak et D. S. Zrnic, ''Doppler Radar and Weather Observations'', Academic Press. Seconde Edition,

San Diego San Diego ( , ; ) is a city on the Pacific Ocean coast of Southern California located immediately adjacent to the Mexico–United States border. With a 2020 population of 1,386,932, it is the eighth most populous city in the United State ...

Cal., 1993 p. 562. * Roger M. Wakimoto and Ramesh Srivastava, ''Radar and Atmospheric Science: A Collection of Essays in Honor of David Atlas'', publié par l'American Meteorological Society, Boston, August 2003. Series: Meteorological Monograph, Volume 30, number 52, 270 pages, ; AMS Code MM52.

References

{{Reflist Radar Radar meteorology Meteorological instrumentation and equipment