science

Plan position indicator

Plan position indicator is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Plan position indicator rather than just read about it. In short: A plan position indicator (PPI) is a type of radar display 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.

Key takeaways

Plan position indicator belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Plan position indicator to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Plan position indicator from memory before moving on to harder problems.

Reference excerpt

A plan position indicator (PPI) is a type of radar display 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. For fixed-site installations, 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 (direction of travel) and this is usually represented by a lubber line. 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 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 in a Jagdschloss experimental radar system outside Berlin. The first production PPI was devised at the Telecommunications Research Establishment, UK and was first introduced in the H2S radar blind-bombing system of World War II. Originally, data was displayed in real time on a cathode-ray tube (CRT), and thus the only way to store the information received was by taking a photograph of the screen. Philo Taylor Farnsworth, 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 (CRT) and called it an "Iatron;" generically known as a storage tube. 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 controllers 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, ship navigation, meteorology, on board ships and aircraft etc. PPI displays are also used to display sonar 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 sonar and lidar installations can mimic radar PPI displays too.

Bibliography Sir Bernard Lovell ECHOES OF WAR : The Story of H2S Radar ISBN 0-85274-317-3 Adapted from Microwave Radar At War (1) . There is an open source verification for this text on the home page Greg Goebel / In The Public Domain. 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), ISBN 0-09-151580-7 E. G. Bowen Radar Days ISBN 0-7503-0586-X David Atlas, Radar in Meteorology: Battan Memorial and 40th Anniversary Radar Meteorology Conference, published by American Meteorological Society, Boston, 1990, 806 pages, ISBN 0-933876-86-6, AMS Code RADMET. Yves Blanchard, Le radar, 1904-2004: histoire d'un siècle d'innovations techniques et opérationnelles , published by Ellipses, Paris, France, 2004 ISBN 2-7298-1802-2 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 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, ISBN 1-878220-57-8; AMS Code MM52.

References

Illustrations

Plan position indicator: Simplified animation of a Plan Position Indicator radar display — Simplified animation of a Plan Position Indicator radar display

Worked examples

Example 1 — a first encounter with Plan position indicator

Start with the simplest possible case. Write down what Plan position indicator claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Plan position indicator before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Plan position indicator ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Plan position indicator

In research: Plan position indicator appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Plan position indicator in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Plan position indicator is common in secondary-school and first-year university syllabi. It links to neighbouring topics Meteorological instrumentation and equipment, Radar, Radar meteorology, so understanding it makes those chapters shorter.
In everyday life: Look for Plan position indicator outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Plan position indicator in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Plan position indicator means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Plan position indicator out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Plan position indicator in simple terms?

Why does Plan position indicator matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Plan position indicator?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Plan position indicator.