Misplaced Pages

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114-446: Modern systems typically use some sort of raster scan display to produce a map-like image. Early in radar development, however, numerous circumstances made such displays difficult to produce. People developed several different display types. Early radar displays used adapted oscilloscopes with various inputs. An oscilloscope generally receives three channels of varying (or oscillating) voltage as input and displays this information on

228-707: A C-scope display on the CRT. In the post-war period the Mk. X became one of the UK's most widely used fighter radars, largely because a lack of foreign exchange to purchase newer designs, and the poor economy in general which required the RAF to have a "make do" attitude. The Mk. X would go on to equip the first jet-powered night fighters, including the Vampire NF.10 and Meteor NF.11 . Small numbers remained in service as late as 1957. For

342-508: A Junkers Ju 88 A-5 near Chichester . Several advanced versions of the Mk. IV were also produced, which offered direct readings for the pilot and options to allow use in single seat aircraft. However, these developments were overtaken by the rapid improvements in microwave systems, and both the Mark V and Mark VI saw only limited production and service. In February 1940, John Randall and Harry Boot at Birmingham University successfully ran

456-411: A cathode ray tube . The oscilloscope amplifies the input voltages and sends them into two deflection magnets and to the electron gun producing a spot on the screen. One magnet displaces the spot horizontally, the other vertically, and the input to the gun increases or decreases the brightness of the spot. A bias voltage source for each of the three channels allows the operator to set a zero point. In

570-736: A friendly fire incident, killing him and destroying the only prototype. This so greatly delayed the program that the Air Ministry asked Jackson to test the US SCR-720 unit as a stop-gap measure. This proved to be able to pick the bomber from the window, and work on the Mk. IX was given low priority while the UK version of the SCR-720, known as the Mk. X, was purchased. With the night fighter force certain of its ability to continue operating successfully if needed, Bomber Command received clearance to begin using window on 16 July 1943. Work on

684-469: A B-scope displaying range vs. elevation, rather than range vs. azimuth. They are identical in operation to the B-scope, the name simply indicating "elevation". E-scopes are typically used with height finding radars , which are similar to airborne radars but turned to scan vertically instead of horizontally, they are also sometimes referred to as "nodding radars" due to their antenna's motion. The display tube

798-582: A Mosquito NF.II was upgraded to the Mk. VIII, serving as the pattern for the Mosquito NF.XII. Starting in December, Beaufighter units were upgraded to the similar Mk. VIIIA, an interim type awaiting production quantities of the VIII. Although the precise origins of the concept are unknown, on 8 March 1941 Lovell mentions the concept of "lock-follow" for the first time in his notes. This was a modification to

912-406: A circular screen and scanned the beam from the center outwards. The deflection yoke rotated, causing the beam to rotate in a circular fashion. The screen often had two colors, often a bright short persistence color that only appeared as the beam scanned the display and a long persistence phosphor afterglow. When the beam strikes the phosphor, the phosphor brightly illuminates, and when the beam leaves,

1026-469: A delay so it would appear slightly to the right of the other. The operator would then swing the antenna back and forth until both blips were the same height. This was sometimes known as a K-scope . A slightly modified version of the K-scope was commonly used for air-to-air (AI) and air-to-surface-vessel (ASV) radars. In these systems, the K-scope was turned 90 degrees so longer distances were further up

1140-400: A focused electron beam . By association, it can also refer to a rectangular grid of pixels. The word rastrum is now used to refer to a device for drawing musical staff lines. The fundamental strategy underlying the raster data model is the tessellation of a plane, into a two-dimensional array of squares, each called a cell or pixel (from "picture element"). In digital photography ,

1254-506: A further adaptation of the J-scope in the "spiral time base", which moved the blip both around the face and outward from the center. This produced a time base that was 7 feet (2.1 m) long, allowing very highly accurate measurements of range. To improve the accuracy of angle measurements, the concept of lobe switching became common in early radars. In this system, two antennas are used, pointed slightly left and right, or above and below,

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1368-661: A ground-mapping display. The AI.18R added modes to support the Red Top missile . The AI Mark 20 was an X-band radar developed by EKCO Electronics for single seat fighters. Code named "Green Willow" by the MoS, it was intended to be a backup system to the AI.23 being developed for the English Electric Lightning (see below). It is believed that the 1953 contract was awarded to EKCO due to their already existing work on

1482-440: A helical scan instead of spiral. The radar antenna was spun around a vertical axis through an entire 360 degrees 10 times a second, with the transmitter switching off when the antenna was pointed back towards the aircraft. This provided a 150 degree scan in front of the aircraft. As it spun, the antenna slowly nodded up and down to provide altitude coverage between +50 and -20 degrees. The resulting scanning pattern naturally produced

1596-522: A horizontal "slice" of the airspace on both sides of the aircraft out to the tracking angles of the radar. B-scope displays were common in airborne radars in the 1950s and 60s, which were mechanically scanned from side to side, and sometimes up and down as well. The spot was swept up the Y-axis in a fashion similar to the A-scope's X-axis, with distances "up" the display indicating greater range. This signal

1710-723: A lock at as much as 75° in roll. The dish was unique in that it included a fibreglass ring around the outer rim as a stiffener. Mk. 18 was able to detect the English Electric Canberra at 28 nautical miles (52 km) at altitudes over 20,000 feet (6,100 m) and a closing speed of 900 knots (1,700 km/h). It could detect the Boeing B-47 at 38 nautical miles (70 km) under the same conditions, and could lock-follow after closing to about 25 nautical miles (46 km). When set to its longest range, 100 miles (160 km), it also offered sea surface search, and

1824-780: A memo on the topic in 1936, indicating that the Germans would likely begin a night campaign if the daylight campaign went as poorly as he believed it would due to Chain Home. The obvious solution would be to mount a small radar on the aircraft, one able to cover the range between the Dowding system's 5-mile accuracy and the average visual spotting range, about 500 to 1,000 feet (150–300 m). As early as August 1936 "Taffy" Bowen , one of Robert Watson-Watt 's hand-picked radar development team, personally requested that he be allowed to start research into an airborne radar set for this role. This

1938-431: A pair of antennas arranged at right angles. Using a device known as a radiogoniometer , the operator could determine the bearing of the target, and by combining their range measurement with the bearing, they could determine a target's location in space. The system also had a second set of antennas, displaced vertically along the receiver towers. By selecting a pair of these antennas at different heights and connecting them to

2052-425: A printer setting of 1200 DPI. Raster-based image editors, such as PaintShop Pro , Corel Painter , Adobe Photoshop , Paint.NET , Microsoft Paint , Krita , and GIMP , revolve around editing pixels , unlike vector-based image editors, such as Xfig , CorelDRAW , Adobe Illustrator , or Inkscape , which revolve around editing lines and shapes ( vectors ). When an image is rendered in a raster-based image editor,

2166-408: A radar display, the output signal from the radar receiver is fed into one of three input channels in the oscilloscope. Early displays generally sent this information to either X channel or Y channel to displace the spot on the screen to indicate a return. More modern radars typically used a rotating or otherwise moving antenna to cover a greater area of the sky, and in these cases, electronics, slaved to

2280-423: A raster approach. Each on-screen pixel directly corresponds to a small number of bits in memory. The screen is refreshed simply by scanning through pixels and coloring them according to each set of bits. The refresh procedure, being speed critical, is often implemented by dedicated circuitry, often as a part of a graphics processing unit . Using this approach, the computer contains an area of memory that holds all

2394-514: A receiver fit to a Handley Page Heyford bomber, with an antenna consisting of a wire strung between the fixed landing gear . A working transmitter was first fit to the Heyford and flew in March 1937. In spite of this success, the system's antennas were still too large to be practical, and work continued on versions working at shorter wavelengths. A new system working at 1.25 m (220 MHz)

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2508-520: A separate squegging oscillator was used to produce pulses of the carrier signal using a timer. This timer also muted down the receiver, solving the ringing issue. Minimum range was reduced to about 400 feet. The resulting AI Mk. IV went into production in July 1940 and all units were sent to newly arriving Bristol Beaufighters . The Beaufighter/AI Mk. IV achieved its first victory on the night of 15/16 November 1940, when an aircraft from No. 604 destroyed

2622-399: A very different meaning, and this can be misleading. Because, through the dithering process, the printer builds a single image pixel out of several printer dots to increase color depth , the printer's DPI setting must be set far higher than the desired PPI to ensure sufficient color depth without sacrificing image resolution. Thus, for instance, printing an image at 250 PPI may actually require

2736-402: Is based on a (usually rectangular, square-based) tessellation of the 2D plane into cells, each containing a single value. To store the data in a file, the two-dimensional array must be serialized. The most common way to do this is a row-major format, in which the cells along the first (usually top) row are listed left to right, followed immediately by those of the second row, and so on. In

2850-415: Is displayed by drawing a second "blip" offset from the target indicator by a short distance, the slope of the line between the two blips indicates the elevation relative to the radar. For instance, if the blip were displaced directly to the right this would indicate that the target is at the same elevation as the radar. The offset is created by dividing the radio signal into two, then slightly delaying one of

2964-460: Is lost, although certain vectorization operations can recreate salient information, as in the case of optical character recognition . Early mechanical televisions developed in the 1920s employed rasterization principles. Electronic television based on cathode-ray tube displays are raster scanned with horizontal rasters painted left to right, and the raster lines painted top to bottom. Modern flat-panel displays such as LED monitors still use

3078-571: Is the AI.24 radar of the Tornado ADV . These radars were often given common names as well, and generally better known by these; the AI.24 is almost universally referred to as "Foxhunter". Other widely used post-war examples include the AI.18 used on the de Havilland Sea Vixen , and the AI.23 Airpass on the English Electric Lightning . This article will use Mk. or AI. depending on which is most commonly used in available references. In order to provide

3192-530: Is the G-scope , which overlays a graphical representation of the range to the target. This is typically represented by a horizontal line that "grows" out from the target indicator blip to form a wing-like shape. The wings grew in length at shorter distances to indicate the target was closer, as does the aircraft's wings when seen visually. A "shoot now" range indicator is often supplied as well, typically consisting of two short vertical lines centered on either side of

3306-424: Is then stored for each pixel. For most images, this value is a visible color, but other measurements are possible, even numeric codes for qualitative categories. Each raster grid has a specified pixel format , the data type for each number. Common pixel formats are binary , gray-scale , palettized , and full-color , where color depth determines the fidelity of the colors represented, and color space determines

3420-550: Is to detect ships and other sea-suface vessels, rather than aircraft; both AI and ASV are often designed for airborne use. The term was first used circa 1936, when a group at the Bawdsey Manor research center began considering how to fit a radar system into an aircraft. This work led to the AI Mk. IV radar , the first production air-to-air radar system. Mk. IV entered service in July 1940 and reached widespread availability on

3534-512: Is vector, rendering specifications and software such as PostScript are used to create the raster image. Three-dimensional voxel raster graphics are employed in video games and are also used in medical imaging such as MRI scanners . Geographic phenomena are commonly represented in a raster format in GIS . The raster grid is georeferenced , so that each pixel (commonly called a cell in GIS because

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3648-638: The Bristol Beaufighter by early 1941. The Mk. IV helped end the Blitz , the Luftwaffe ' s night bombing campaign of late 1940 and early 1941. Starting with the AI Mk. VII , AI moved to microwave frequencies using the cavity magnetron , greatly improving performance while reducing size and weight. This gave the UK an enormous lead over their counterparts in the Luftwaffe , an advantage that

3762-666: The Exif standard. High-resolution raster grids contain a large number of pixels, and thus consume a large amount of memory. This has led to multiple approaches to compressing the data volume into smaller files. The most common strategy is to look for patterns or trends in the pixel values, then store a parameterized form of the pattern instead of the original data. Common raster compression algorithms include run-length encoding (RLE), JPEG , LZ (the basis for PNG and ZIP ), Lempel–Ziv–Welch (LZW) (the basis for GIF ), and others. For example, Run length encoding looks for repeated values in

3876-510: The Fairey Fireflash missile illumination radar. AI.20 was significantly simpler than the AI.23, being much closer in design to an upgraded AI.17 than the much more advanced AI.23. It used a simple spiral scan system driven at 10,000 RPM, scanning out to 45 degrees and then back every 2.25 seconds. Testing started in 1955, and the AI.20 demonstrated its ability to lock-on to a Hawker Hunter sized target at 7 miles (11 km) 95% of

3990-592: The Fairey Firefly , which had the size to carry a radar operator and the performance to operate as a fighter. Some were also used on the Mosquito. Considerably later, a single Meteor, EE348 , was fit with an APS-4 in a nose mounting as a test vehicle. The APS-6 was a modification of the APS-4 specifically for the interception role. It replaced the side-to-side scan with a spiral-scan system largely identical to

4104-571: The Fleet Air Arm , the TRE developed a series of AI radars operating at the even shorter 3 cm wavelength, the X band , which further reduced the size of the antennas. The original model was the Mark XI, followed by the improved Mark XII and lightened Mark XIII. It is not clear if any of these models saw service, and few references mention them even in passing. These designations were given to

4218-526: The H2S radar project and was replaced by Arthur Ernest Downing. This delayed the project just long enough that it got caught up in a great debate that broke out in the summer of 1942 about the use of window , today known as chaff . Window caused false returns on radar displays that made it difficult to tell where the bombers were amid a sea of blips. Bomber Command had been pressing to use window over Germany to reduce their losses, which were beginning to mount as

4332-430: The pulse repetition frequency of the radar. This spread out the blips across the display according to the time they were received. Since the return time of the signal corresponds to twice the distance to the target divided by the speed of light , the distance along the axis directly indicates the range to any target. This was usually measured against a scale above the display. Chain Home signals were normally received on

4446-614: The visible spectrum ; the large CCD bitmapped sensor at the Vera C. Rubin Observatory captures 3.2 gigapixels in a single image (6.4 GB raw), over six color channels which exceed the spectral range of human color vision. Most computer images are stored in raster graphics formats or compressed variations, including GIF , JPEG , and PNG , which are popular on the World Wide Web . A raster data structure

4560-446: The "picture" part of "pixel" is not relevant) represents a square region of geographic space. The value of each cell then represents some measurable ( qualitative or quantitative ) property of that region, typically conceptualized as a field . Examples of fields commonly represented in rasters include: temperature, population density, soil moisture, land cover, surface elevation, etc. Two sampling models are used to derive cell values from

4674-508: The 1990s. PPI displays are actually quite similar to A-scopes in operation, and appeared fairly quickly after the introduction of radar. As with most 2D radar displays, the output of the radio receiver was attached to the intensity channel to produce a bright dot indicating returns. In the A-scope a sawtooth voltage generator attached to the X-axis moves the spot across the screen, whereas in the PPI

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4788-426: The A-scope was the amplified return signal received from the radar, which was sent into the Y-axis of the display. Returns caused the spot to be deflected downward (or upward on some models), drawing vertical lines on the tube. These lines were known as a "blip" (or "pip"). The X-axis input was connected to a sawtooth voltage generator known as a time base generator that swept the spot across the display, timed to match

4902-672: The AI.20 primarily in the details of the operation and visual presentation. This was later upgraded to the Mark 2 model that equipped the V-force for most of its lifetime. As the Javelin ran into delays, it was decided to increase the useful life of the existing Meteor and Vampire night fighters with a new radar. After considering three US designs, they chose the Westinghouse AN/APS-57 . Its 200 kW transmitter improved range to as much as 25 miles (40 km) although this

5016-551: The FAW.6. The last AI.17-equipped Javelin FAW.9's ended their service in Singapore in 1968. Having lost the contest for the Javelin, GEC submitted an updated version of the Mk. 16 for the contest for the de Havilland Sea Vixen . This produced the Mk. 18. Mk. 18 operated in the X band with a 180 kW peak power, using a 29 inches (740 mm) parabolic dish that could be pointed ±100° in azimuth, +50/-40° in elevation, and could keep

5130-531: The German defensive network improved. Fighter Command was concerned that if Bomber Command used it over Germany, the Germans would return the favour and use it over the UK. A series of tests carried out in September 1942 by Wing Commander Derek Jackson suggested that some changes to the display systems might solve the problems with window on the Mk. VIII. At this point it was suggested that the Mk. IX might ignore

5244-419: The Mk. IV, but as the timebase now spun, they drew short arcs on the display during the period the antenna was pointed in that direction. Like the Mk. IV, the distance from the center of the CRT indicated the range. As the target moved closer to the centreline of the aircraft, the beam spent more time painting the target, and the arc spread out, becoming a ring when dead ahead. First introduced in March 1941, it

5358-482: The Mk. IX continued, but it never saw operational service. In testing in 1944 it was found to be marginally better than the US SCR-720, but with the SCR-720 expected to arrive at any moment, the demand for another radar was not pressing. Instead, the Mk. IX was given more time to mature. Further development led to more testing in 1948, but it was again passed up for production and cancelled the next year. The Mark X

5472-639: The Mk. VII, requiring very large amount of aircraft space for the install. Conversions on the Beaufighter began in December 1941. This run was followed by the production Mark VIII that included the new "strapped magnetron" of 25 kW, improving range to about 5.5 miles (8.9 km). This version also had several major clean-ups in the electronics, support for IFF Mark III which caused a sunrise pattern to appear when aimed at friendly aircraft, and beacon tracking allowing it to home in on ground-based transmitters emplaced by friendly units. In September 1942

5586-494: The Mk. X to soldier on while a definitive jet-powered night fighter evolved. This effort underwent similar delays and setbacks before finally emerging as the Gloster Javelin . Two radar sets competed for the design, the Mk. 16 and Mk. 17. The later went into production, and is better known as the AI.17. General Electric Company 's Mark 16 was one of two similar designs competing to equip the Gloster Javelin . The contest

5700-740: The NF.14, which started deliveries in June. Likewise the de Havilland Venom received the Mk. 21 to become the Venom NF.3, also entering service in June, but was withdrawn by the end of 1957. The Sea Venom flew the Mk. 21 until 1959, and in second-line duty until 1970. The Mark 22 was the British version of the US AN/APQ-43 , This consisted of two radar antennas driven from a common magnetron transmitter. One used spiral-scan to search for targets, while

5814-627: The US AN/APS-4 and AN/APS-6 radars, small under-wing X band radars used primarily by naval aircraft. The APS-4 was originally developed as the ASH, a forward-aimed surface-search system. It was packaged into an underwing pod so it could be used on single-engine aircraft like the TBM Avenger . It proved to have a useful interception function, and was modified to be able to scan up and down as well as just side to side. The Fleet Air Arm mounted it on

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5928-406: The aircraft starting to the left of the approach line and then being guided toward it. Raster graphics In computer graphics and digital photography , a raster graphic represents a two-dimensional picture as a rectangular matrix or grid of pixels , viewable via a computer display , paper , or other display medium. A raster image is technically characterized by the width and height of

6042-503: The array, and replaces them with the value and the number of times it appears. Thus, the raster above would be represented as: This technique is very efficient when there are large areas of identical values, such as a line drawing, but in a photograph where pixels are usually slightly different from their neighbors, the RLE file would be up to twice the size of the original. Some compression algorithms, such as RLE and LZW, are lossless , where

6156-409: The boresight of the system. The received signal would differ in strength depending on which of the two antennas was more closely pointed at the target, and be equal when the antenna was properly aligned. To display this, both antennas were connected to a mechanical switch that rapidly switched between the two, producing two blips in the display. In order to differentiate them, one of the two receivers had

6270-472: The data that are to be displayed. The central processor writes data into this region of memory and the video controller collects them from there. The bits of data stored in this block of memory are related to the eventual pattern of pixels that will be used to construct an image on the display. An early scanned display with raster computer graphics was invented in the late 1960s by A. Michael Noll at Bell Labs , but its patent application filed February 5, 1970,

6384-412: The dimmer long persistence afterglow would remain lit where the beam struck the phosphor, alongside the radar targets that were "written" by the beam, until the beam re-struck the phosphor. The specialist Beta Scan Scope was used for precision approach radar systems. It displays two lines on the same display, the upper one (typically) displaying the vertical approach (the glideslope ), and the lower one

6498-478: The example at right, the cells of tessellation A are overlaid on the point pattern B resulting in an array C of quadrant counts representing the number of points in each cell. For purposes of visualization a lookup table has been used to color each of the cells in an image D. Here are the numbers as a serial row-major array: 1 3 0 0 1 12 8 0 1 4 3 3 0 2 0 2 1 7 4 1 5 4 2 2 0 3 1 2 2 2 2 3 0 5 1 9 3 3 3 4 5 0 8 0 2 4 3 2 8 4 3 2 2 7 2 3 2 10 1 5 2 1 3 7 To reconstruct

6612-407: The field: in a lattice , the value is measured at the center point of each cell; in a grid , the value is a summary (usually a mean or mode) of the value over the entire cell. Raster graphics are resolution dependent, meaning they cannot scale up to an arbitrary resolution without loss of apparent quality . This property contrasts with the capabilities of vector graphics , which easily scale up to

6726-427: The first cavity magnetron , eventually generating 1 kW at 9.8 cm (3,060 MHz). Supported by GEC, the device quickly developed into a practical 10 kW system, and several test units were available by May 1940. Microwave wavelengths are so much shorter than the Mk. IV's 1.5 m, fifteen times, that the dipole antennas required for reasonable gain were only a few inches long. This dramatically reduced

6840-435: The gunsight, as well as computer-calculated cueing information that located both the target and the proper position to fly to engage based on the selected weapon. For instance, when using missiles, the system guided the aircraft not toward its target, but a point behind it where the missile could be fired. This gave the system its name, AIRPASS , an acronym for aircraft interception radar and pilot's attack sight system. AI.23

6954-499: The headquarters staff at the University of Dundee attempted to develop their own solutions to the problem. This led to considerable strife and in-fighting between the two groups. The AI group was eventually broken up at the end of March 1940, leaving Bowen out of the AI effort. A solution was eventually provided by EMI who had developed a new type of transmitter that was not based on the common self exciting principle. Instead,

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7068-401: The horizontal approach. A marker indicates the desired touchdown point on the runway, and often the lines are angled towards the middle of the screen to indicate this location. A single aircraft's "blip" is also displayed, superimposed over both lines, the signals being generated from separate antennas. Deviation from the centerline of the approach can be seen and easily relayed to the pilot. In

7182-428: The image in pixels and by the number of bits per pixel . Raster images are stored in image files with varying dissemination , production , generation , and acquisition formats . The printing and prepress industries know raster graphics as contones (from continuous tones ). In contrast, line art is usually implemented as vector graphics in digital systems. Many raster manipulations map directly onto

7296-536: The image is composed of millions of pixels. At its core, a raster image editor works by manipulating each individual pixel. Most pixel-based image editors work using the RGB color model , but some also allow the use of other color models such as the CMYK color model . Aircraft interception radar Aircraft interception radar , or AI radar for short, is a British term for radar systems used to equip aircraft with

7410-414: The image, the upper portion of the display shows the vertical situation, and the lower portion the horizontal. In the vertical, the two diagonal lines show the desired glideslope (upper) and minimum altitude approach (lower). The aircraft began its approach below the glideslope and captured it just before landing. The proper landing point is shown by the horizontal line at the left end. The lower display shows

7524-418: The infamous 1957 Defence White Paper , but by this time the interim English Electric Lightning design, the P.1, had progressed to the point where development was undertaken anyway (along with TSR.2). This led to continued development of the AI.23 for this aircraft (and Mk. 20, see above), and it was given the official designation "ARI 5897". The system was mounted entirely in a single bullet-shaped housing that

7638-439: The linear distance along it. This arrangement allows greater accuracy in reading the range with the same sized display as an A-scope because the trace uses the full circumference rather than just the horizontal distance (so the time base is π times longer. For instance, on a typical . An electro-mechanical version of the J-scope display remained common on consumer boating depth meters until the 1990s. W. A. S. Butement developed

7752-453: The mathematical formalisms of linear algebra , where mathematical objects of matrix structure are of central concern. The word "raster" has its origins in the Latin rastrum (a rake), which is derived from radere (to scrape). It originates from the raster scan of cathode-ray tube (CRT) video monitors , which draw the image line by line by magnetically or electrostatically steering

7866-628: The maximum possible warning time of an incoming raid, the RAF's Chain Home (CH) radar stations had been positioned as far forward as possible, right on the coastline. These systems could only see targets in front of them, over the English Channel . Tracking over land fell to the Royal Observer Corps (ROC) using visual means. In testing it was found that the two different reporting systems provided information that varied enough to make tracking targets confusing and error prone, and

7980-497: The means to find and track other flying aircraft. These radars are used primarily by Royal Air Force (RAF) and Fleet Air Arm night fighters and interceptors for locating and tracking other aircraft, although most AI radars could also be used in a number of secondary roles as well. The term was sometimes used generically for similar radars used in other countries, notably the US. AI radar stands in contrast with ASV radar , whose goal

8094-509: The mechanical motion of the antenna, typically moved the X and Y channels, with the radar signal being fed into the brightness channel. The original radar display, the A-scope or A-display , shows only the range, not the direction, to targets. These are sometimes referred to as R-scopes for range scope . A-scopes were used on the earliest radar systems during World War II , notably the seminal Chain Home (CH) system. The primary input to

8208-415: The middle of the display. To make an interception, the pilot guides his aircraft until the blip is centered, then approaches until the "wings" fill the area between the range markers. This display recreated a system commonly used on gunsights , where the pilot would dial in a target's wingspan and then fire when the wings filled the area inside a circle in their sight. This system allowed the pilot to estimate

8322-496: The most appropriate image resolution for a given printer-resolution can pose difficulties, since printed output may have a greater level of detail than a viewer can discern on a monitor. Typically, a resolution of 150 to 300 PPI works well for 4-color process ( CMYK ) printing. However, for printing technologies that perform color mixing through dithering ( halftone ) rather than through overprinting (virtually all home/office inkjet and laser printers), printer DPI and image PPI have

8436-425: The naming was not universal. Size of A-scope displays vary, but 5 to 7 inch diagonal was often used on a radar display. The 7JPx series of CRTs (7JP1, 7JP4 and 7JP7) was originally designed as an A-scope display CRT. A B-scope or b-scan provides a 2-D "top down" representation of space, with the vertical axis typically representing range and the horizontal axis azimuth (angle). The B-scope's display represented

8550-541: The one in the Mk. VIII. It also included a switch that reduced the scanning pattern to a 15 degree cone in front of the aircraft, producing a C-scope view used during the final approach. This was paired with a new and much smaller display, allowing it to be fit to smaller single-seat aircraft. It was widely used on the F6F Hellcat and F4U Corsair . With Mk. IX cancelled in 1949, the Ministry of Supply (MoS) allowed

8664-474: The original pixel values can be perfectly regenerated from the compressed data. Other algorithms, such as JPEG, are lossy , because the parameterized patterns are only an approximation of the original pixel values, so the latter can only be estimated from the compressed data. Vector images (line work) can be rasterized (converted into pixels), and raster images vectorized (raster images converted into vector graphics), by software. In both cases some information

8778-407: The output of two such generators is used to rotate the line around the screen. Some early systems were mechanical, using a rotating deflection coil around the neck of the display tube, but the electronics needed to do this using a pair of stationary deflection coils were not particularly complex, and were in use in the early 1940s. Radar cathode ray tubes such as the 7JP4 used for PPI displays had

8892-455: The plane is the visual field as projected onto the image sensor ; in computer art , the plane is a virtual canvas; in geographic information systems , the plane is a projection of the Earth's surface. The size of each square pixel, known as the resolution or support , is constant across the grid. Raster or gridded data may be the result of a gridding procedure. A single numeric value

9006-409: The quality of the device rendering them. Raster graphics deal more practically than vector graphics with photographs and photo-realistic images, while vector graphics often serve better for typesetting or for graphic design . Modern computer-monitors typically display about 72 to 130 pixels per inch (PPI), and some modern consumer printers can resolve 2400 dots per inch (DPI) or more; determining

9120-461: The radar could only see targets directly in front of the antenna, unlike the Mk. IV which could see anything in the entire volume in front of the aircraft. To solve this problem, the dish was mounted on a bearing system from Nash & Thompson that allowed it to be rotated in a spiral pattern. The cockpit display was modified to spin the timebase at the same speed as the antenna, 17 times a second. The display still produced blips similar to those on

9234-469: The radiogoniometer, they could determine the vertical angle of the target, and thus estimate its altitude. Since the system could measure both range and altitude, it was sometimes known as an HR-scope , from "height-range". Early American , Dutch and German radars used the J-scope , which resembled a circular version of the A-scope. These display range as an angle around the display face, as opposed to

9348-399: The range of color coverage (which is often less than the full range of human color vision ). Most modern color raster formats represent color using 24 bits (over 16 million distinct colors), with 8 bits (values 0–255) for each color channel (red, green, and blue). The digital sensors used for remote sensing and astronomy are often able to detect and store wavelengths beyond

9462-402: The range to the target. In this case, however, the range is being measured directly by the radar, and the display was mimicking the optical system to retain commonality between the two systems. The PPI display provides a 2-D "all round" display of the airspace around a radar site. The distance out from the center of the display indicates range, and the angle around the display is the azimuth to

9576-480: The receiver causing it to oscillate or ring for a period. While this powerful signal was dying down, reflections from nearby aircraft were lost in the noise. Numerous solutions had been attempted, but were of limited use. Starting in late 1939 the development team was asked to fit the existing Mk. III design, of limited use, to aircraft. This ended further attempts to address the minimum range issue while they worked on installations. While their development effort ended,

9690-403: The same target into a single track. Telephone operators, or "tellers", would then forward this information to group headquarters who would re-create the map, and then from group to the sector HQs who would give instructions to the fighter pilots. Due to delays in the flow of information between the various centres, and inherent inaccuracies in the reports coming from multiple sources, this system

9804-486: The scope instead of further to the right. The output of one of the two antennas was sent through an inverter instead of a delay. The result was that the two blips were displaced on either side of the vertical baseline, both at the same indicated range. This allowed the operator to instantly see which direction to turn; if the blip on the right was shorter, they needed to turn to the right. These types of displays were sometimes referred to as ASV-scopes or L-scopes , although

9918-634: The second used conical scanning for tracking at close range. This was one of the earliest radars to offer track while scan (TWS) operation, although it did so through the use of what was essentially two radars. The APQ-43 was one of three designs also considered for updated versions of the Meteor and Venom, the others being the AN/APQ-35 which also had two-dish TWS, and the AN/APS-57. The -35 and -43 proved too large to install in these aircraft, forcing

10032-474: The selection of the -57 as the Mk. 21. The two TWS units proved interesting, and the -43 was considered for the Javelin. These were used in small numbers in the FAW.2 and FAW.6 models. Ferranti 's Mark 23 was an X band design originally designed for the modified Fairey Delta 2 proposed for the Ministry of Supply's Operational Requirement F.155 for a modern interceptor aircraft . Work on F.155 ended with

10146-565: The sheer volume of information could be overwhelming. Hugh Dowding addressed this through the creation of what is today known as the Dowding system , networking together the radars and observation centres by telephone to a central station. Here, in the Fighter Command 's "filter room" at RAF Bentley Priory , operators would plot the map coordinates sent to them on a single large map, which allowed them to correlate multiple reports of

10260-440: The signals so it appears offset on the display. The angle was adjusted by delaying the time of the signal via a delay, the length of the delay being controlled by a voltage varying with the vertical position of the antenna. This sort of elevation display could be added to almost any of the other displays, and was often referred to as a "double dot" display. A C-scope displays a "bullseye" view of azimuth vs. elevation. The "blip"

10374-436: The size of the system, allowing it to fit entirely in the nose of the aircraft. While a team under Herbert Skinner developed the electronics, Bernard Lovell was put in charge of examining the use of a parabolic dish to improve the directionality of the signal. The resulting beam was so sharply focussed, spanning about 10 degrees, that it easily avoided ground reflections at even low altitudes. The narrow beam also meant that

10488-455: The spiral-scan system that allowed it to track targets automatically without further manual operation. This became known as AIF. "Freddie" Williams joined the effort, and by the autumn of 1941 the system was basically functional and plans began to introduce it as the Mark IX. Several unrelated events conspired to greatly delay further progress. On 1 January 1942 Lovell was sent to work on

10602-419: The target. The current position of the radar antenna is typically indicated by a line extending from the center to the outside of the display, which rotates along with the antenna in realtime. It is essentially a B-scope extended to 360 degrees. The PPI display is typically what people think of as a radar display in general, and was widely used in air traffic control until the introduction of raster displays in

10716-471: The time, excellent performance for that era. Nevertheless, as AI.23 began successful trials the same year, further work on AI.20 was cancelled. The next year the MoS published a requirement for a new tail warning radar for the V bomber force, replacing the original Orange Putter , and quickly chose the AI.20 as its basis. This was developed into the ARI-5919 Red Steer , which differed from

10830-423: The two-dimensional grid, the file must include a header section at the beginning that contains at least the number of columns, and the pixel datatype (especially the number of bits or bytes per value) so the reader knows where each value ends to start reading the next one. Headers may also include the number of rows, georeferencing parameters for geographic data, or other metadata tags, such as those specified in

10944-435: The war. Practical ASV radars were operational in 1940, but the AI developments proved much more difficult. It was not until 1939, with the war obviously looming, that the team was once again moved back to AI development full-time. A lingering problem was that the minimum range remained around 1,000 feet, too long to allow easy interception. This was due to the transmitter signal not turning off sharply, leaking through to

11058-399: The window completely, as the light metal strips rapidly dispersed from the target being tracked, faster than the radar could follow. Further testing by Jackson demonstrated the opposite was true, and that the Mk. IX almost always locked-on to the window instead. Arthur Downing quickly implemented several changes to fix this problem. He was personally operating the system when he was shot down in

11172-595: Was a version of the Airpass dedicated to low-level flying, especially target detection, fitted to the Blackburn Buccaneer . Further development led to the terrain following radar used in the BAC TSR.2 . Many other variants were proposed for a wide variety of projects. The final radar in the UK series of AI designs to see deployment was the Mark 24, better known as "Foxhunter". Foxhunter was developed for

11286-469: Was abandoned at the Supreme Court in 1977 over the issue of the patentability of computer software. During the 1970s and 1980s, pen plotters , using Vector graphics , were common for creating precise drawings, especially on large format paper. However, since then almost all printers create the printed image as a raster grid, including both laser and inkjet printers. When the source information

11400-510: Was able to detect and track a Bear-sized bomber at 40 miles (64 km), allowing the Lightning to accomplish fully independent interceptions with only the minimum of ground assistance. A version with fully automated guidance that would have flown the aircraft into range and fired its missiles automatically was cancelled in 1965. Further development of Airpass led to AI.23 Airpass II, code named "Blue Parrot" and also known as ARI 5930. This

11514-408: Was accurate to perhaps 5 miles (8.0 km). Within 5 miles the fighters would normally be able to spot their targets visually and complete the interception on their own. Interception rates over 80% was common, and on several occasions the system succeeded in getting every fighter launched into position for an attack. While the Dowding system proved invaluable inputs during daylight attacks, it

11628-564: Was approved, and the small aircraft interception team set up shop in Bawdsey Manor 's two towers. At the time, radar development was in its infancy and the other teams were working with long- wavelength transmitters operating around 7 meters. An efficient antenna requires it to be about 1 ⁄ 2 the wavelength or more, which demanded antennas at least 3 metres (9.8 ft) long, impractical for an aircraft. Additionally, available transmitters were large, heavy and fragile. The first AI experiments thus used ground-based transmitters and

11742-574: Was decided to produce another version of the Javelin with the US AN/APQ-43, which on paper appeared to be a better system. In RAF service the APQ-43 became the AI.22, and produced the Javelin FAW.2. In practice, the two systems offered similar performance and the AI.17 quality issues were soon addressed. Future versions of the Javelin mostly mounted the AI.17, although the AI.22 was also used on

11856-464: Was displayed indicating the direction of the target off the centreline axis of the radar, or more commonly, the aircraft or gun it was attached to. They were also known as "moving spot indicators" or "flying spot indicators" in the UK, the moving spot being the target blip. Range is typically displayed separately in these cases, often using a second display as an L-scope. Almost identical to the C-scope

11970-486: Was essentially useless against night raids. Once the enemy aircraft passed the coastline they could not be seen by the radars, and the ROC could not see at night except under ideal conditions with bright moonlight, no cloud cover, and considerable luck. Even when tracks could be developed, the difficulty of spotting a target from the cockpit of an aircraft while flying it at night proved to be equally difficult. Henry Tizard wrote

12084-434: Was eventually won by AI.17. AI.17 was essentially a version of the Mk. IXC with a number of detail cleanups and a 200 kW magnetron, as well as the ability to cue the "Blue Jay" missile that was then under development. It could detect a Javelin-sized target at about 20 nautical miles (37 km; 23 mi). AI.17 entered service with the Javelin in early 1956. Early sets had considerable reliability problems and it

12198-487: Was found that the ground reflection created a sort of artificial horizon on the bottom of the display, a surprising side-effect which proved very useful. However, the limited power of the magnetron, about 5 kW, provided range of about 3 miles (4.8 km), not a great improvement over the Mk. IV. Performance of the system at low altitude was so improved over the Mk. IV that it was decided to make an initial run of 100 units out of what were essentially prototype systems as

12312-447: Was generally rotated 90 degrees to put the elevation axis vertical in order to provide a more obvious correlation between the display and the "real world". These displays are also referred to as a Range-Height Indicator , or RHI , but were also commonly referred to (confusingly) as a B-scope as well. The H-scope is another modification of the B-scope concept, but displays elevation as well as azimuth and range. The elevation information

12426-408: Was mixed with a varying voltage being generated by a mechanical device that depended on the current horizontal angle of the antenna. The result was essentially an A-scope whose range line axis rotated back and forth about a zero point at the bottom of the display. The radio signal was sent into the intensity channel, producing a bright spot on the display indicating returns. An E-scope is essentially

12540-519: Was rarely achieved in practice. It also included various beacon homing modes, as well as an air-to-surface mode for detecting ships. This was modified to add a British strobe unit and variable pulse repetition frequency , becoming the Mark 21. The Mk. 21 was first used on the Meteor NF.12 and flew for the first time on the 21 April 1953, entering service in January 1954. Small improvements produced

12654-442: Was ready by August 1937 and fitted to Avro Anson K6260 at RAF Martlesham Heath . This unit demonstrated the ability to detect aircraft at the range of about 1 mile (1.6 km) in the air-to-air mode, but also demonstrated the ability to detect ships on the ocean at ranges up to 3 miles (4.8 km). This ability led to the split between AI and air-to-surface-vessel (ASV) radar systems, both of which would be widely used during

12768-423: Was suspended within the Lightning's circular nose air intake. The AI.23 was the world's first operational aircraft interception monopulse radar system. The monopulse method allows higher resolution and is far more resistant to common forms of jamming . AI.23 also included all of the features of earlier AI radars, and more. Among the highlights were an automatic lock-follow system which fed ranging information to

12882-402: Was the UK version of the SCR-720. This was originally promised for delivery in the summer of 1942, but ran into delays and only started arriving in December 1943. These were fit to the Mosquito to produce the NF.XVII and later versions. Conversions at operational units began in January 1944, and the Mk. X remained in service through the rest of the war. Compared to the Mk. VIII, the SCR-720 used

12996-498: Was to exist for the remainder of World War II . By the end of the war, over a dozen AI models had been experimented with, and at least five units widely used in service. This included several US-built models, especially for the Fleet Air Arm. The AI naming convention was used in the post-war era as well, but these generally dropped the "Mk." when written in short form and used numbers instead of Roman numerals . A good example

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