radar display

8/8/2019 Radar Display

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AN AIRBORNE MULTIMODE RADAR DISPLAY PROCESSOR

John Felsman and Joseph W. lannielloNorden Systems, Inc.P.O. Bo x 5300Norwalk, CT06856

ABSTRACTModem tactical, multimode airborne radar systems developforward looking land and sea images for mapping and weapondelivery, and providearepresentationof otheraircraft n surroundingairspace for air combat. A large quantity of information must bepresented to the pilot and other onboard personnel in a real-time,accurate, andclear presentation. A ProgrammableSignal Processor(PSP) performs the processing to detect targets and develop mapimages; however, these systems. nclude a specialized hardwareunit, the Display Processor Unit (DPU), as an adjunct to the PSP toformat the information nto images for presentation on a TV likedisplay monitor. The DPU also displays special symbols and alpha-numeric information which may be provided from other aircraftsystems.This paper describes a DPU that develops display images fora multimode airborne radar system. The DPU described has aunique feature that allows display updates for a periodof time whenthe radar is not transmitting. Once the radar image is formed, theinformation provided by the avionics system can reposition thedisplay mage. in his mode he aircraft is ess vulnerable o detectionby electronic counter measures. This feature also provides a signifi-cant improvement n display clarity during normal operation.The multimode airborne radar display modes, the equipmentthat generates the displays, and the technology used are also

described.TACTICAL AIRBORNE DISPLAY MODES

A modem multimode airborne radar system supports all as-pects of the aircraft mission, including:a.

b.

C

d.e.f.

Navigation modes that help find the route to and from thetargeted area.Terrain clearance and terrain avoidance modes that en-able the aircraft to safely fly at low altitudes to avoiddetection by ground based radars.High resolution air-to-ground modes that enable identifi-cation of buildings and moving vehicles.Weapon delivery modes that guide ordnance to targets.Air combat modes for defense against other aircraft.Air-to-sea modes that enable ship detection and identifi-cation.

These modes requiredifferentprocessing and presentationsofthe radar returns to support the pilot and onboard personnel in themission. The various display presentations are described herein.

Pian Position Indicator (PPI) Ground MapModeFigure I llustrates a typical Plan Position Indicator display forgroundmap modes. The display portrays a map mage of the groundbeing scanned by the radar. The display can be divided into threemajor components, display markers and symbology, active radarvideo, and scrolled video. The display markers consist of variouscursor ndications, range marks, and reference ines. These markersprovide reference indications for the radar video. Radar video ispresented in two distinct regions on the display. The area in theactive PPI sector receives dynamically updated radar video. Thearea below the active PPIsector contains previously scanned radarvideo which, because of the aircraft motion, has 'scrolled" below theactive PPI sector. The scrolled video allows the pilot to maintain areference to the previously scanned image and enables a displaypresentation when the radar is not transmitting.

EXTENSION RANGE AZIMUTHLINE .SCAN MARKERS MARKERSCENTER (EVERY (EVERY30CURSOR

I 7

PPI RANGE.160 NMIACTIVEPPI IMAGERY

SECTOR

Figure1. Navigation Display - Depressed Center PPI Origin

367CH3030-4/91 OOOO-0367 $1 OO 0 1991 IEEE

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AZIMUTH 360 DEGREEAZCURSOR MARKER SCAN RANGE MARKERSEXTENSION (EVERY30 CENTER (EVERYLINE DEGREES) A M CURSOR 50NMI)

CROSS RANGECURSOR RANGE MARKERSEXTENSION MARKERS EVERY

LINES EVERY 10 NMI 10 NMI

~.\ PPIRANGE160 NMI/SCROLLED FIXED 120I IMAGERY DEGREEACTIVE PPIf SECTOR

Figure2. Navigation Display - Centered PPI OrlginFigure 2, Navigation Display with PPI origin centered. en-hances the general navigational view of the radar. The apex of theactivescanhas been moved o the center of the display. The displaymarkers are extendedto include the additional viewing area and thescrolled region at the bottom half of the display.Figure3presentsan additional refinement in the PPI display.The image has been magnified o display detailed targeting infor-

mation. The PPI apex has moved below the displayed portion of themonitor, butthe hree basicdisplayelements remain. Markersdefinethe target, the radarcontinues to display active radar video data, andthe scrolled video regions are smaller but continue to provide usefulreference information.Terrain Avoidance/Terraln Clearance (TAITC) Modes

The Terrain Clearance Display represented n Figure4allowsthe pilot to fly at low altitudes avoiding both radar detection andground obstacles. The display is implemented with the horizontalaxis corresponding otheazimuth field of view forward of the aircraftand the vertical axis corresponding to the elevation angle of theterrain as viewed by an observer on the ground. The pilot views theimageasa set of contours that correspond to the ground elevationat discrete ranges. Each range contour is assigned a gray scalevalue. Additional range highlighting emphasizes he most mportantranges. The altitude contour and horizon line allow the pilot toreference the aircraft to the display.Terrain Clearance PPI (TCPPI) Mode

The TCPPI mode has the appearance of the standard PPIshown in Figures 1, 2 and3 except that the video displayed is onlythose returns that extend above a clearance plane"over which thepilot wishes to fly. For example, if the pilot sets the clearance plane

\8 RANGE SCALE: 40NMI STOREDF SCAN ANGLE: 26.7 DEGREES IMAGERYCURSOR: 90 NW+QDEGREES

Figure3. Magnlfled PPI Display

DARKEST 3RD CONTOURHORIZON SHADE (8) SELECTABLYLINE (10NMI) CODEDI- IZIMUTH

1STCONTOUR BUCK RANGE LIGHTESTPERMANENTLY RADAR HIGHLIGHT SHADE (1)CODED (0.5 NMI) ALTITUDE BARS (0.5 NMI)CONTOURFigure4. Terraln Clearance Display

to 200feet only those returns n the field of view that are in he regionbetween the aircraft and 200 feet below the aircraft are displayed.This enables the pilot to avoid obstacles and safely maneuvertheaircraft at low altitudes.

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Figure 5. HRGWGMTI Display SAR with Overlay ofDetected Moving Targets

High Resolution Ground Map and Moving Target indication(HRGM/GMTI) ModeFigure5illustrates a HRGWGMTI mode. Synthetic ApertureRadar (SAR) processing s used odevelop a high resolution map as

a background display with an overlay of detected moving targets.TheSA R processing provides a high resolution image of the field ofview, while accurately positioning moving argets on the map image.The azimuth and range resolution of the background map are suchthat roads, rivers, coastlines, railroads, buildings, etc. can be dearlyidentified. The MTI overlay displays moving vehicles-both fastandslow movers. Both the azimuth (horizontal) and range (vertical)coordinates are distances measured in tens of feet. The imagepresented s a spot lighted area not directly forward of the aircraft butatan azimuth position with its Center between15 o65degrees of theflight path.Air Combat Modes

Similar to the Ground Map PPI displays, the Air Surveillancedisplay presents data using the PPI format. The marker functionsand names have changed, but remain essentially the same. Figure6 summarizes he details.The Airborne Targeting Display, Figure 7, mapsthe radar videoonto a format where both range and azimuth map into Cartesiancoordinates. Azimuth, in degrees, is expressed along the bottom ofthe display, and range is expressed vertically. Various markers andcursers allow target referencing.

Air-to-Sea (A-scan) ModesThe purpose of this mode s to image ships for identification bythe pilot or other onboard personnel. The radar processing isdesignated Inverse SAR (ISAR) and uses the motion of the shipbeing targeted to develop a high resolution image. The displaygenerator provides a split screen to enable the operator to displaystored mages of ships to allow identification. Either image canalsobe displayed on the ull screen. The operator is able to freeze theradar image to aid in identification. Figure 8 illustrates a typicalASCAN scene.

DiSPLAY GENERATOR ARCHITECTUREThe display generatorhas two primary functions; conversion ofthe radar image data from the radar scan rate and format to a ratecompatiblewith licker free presentation on aTVtypedisplaymonitorandthe presentationof symbolson hedisplay. Thissection describesthe architecture of a twochannel implementation of a prototypeDPU. The next section describes operation of the elements that areused to implementthe DPU.

OPENING CIRCULARAZIMUTH TARGET MLOUM

Az ACTlVE PPI RANGEMARKERSUNE EVERY(50NMI)EXTENSION SECTOR

g PPI RANGE: 16 0 NMIf (SELECTABLE:120.80,40 DEGREES)PPISCAN ANGLE:80DEGREESFigure6. Airborne Surveillance Display(Depressed Center PPI)

The DPU is mplemented n three basic sections, as illustratedin Figure 9. The Interface Section processes and distributes thebasic radar video and control. Two identical sections implement hevideo memory subsystem. One section is dedicated o channel oneand the other dedicated to channel two. The final section indudesmany of the miscellaneous unctions such as the symbol memories,ASCAN and TC display generation, and video mixing and timing.Partitioning he system in his manner reduces he design tothefewest number of unique modules and provides a degree of faulttolerance. Criticaldisplay modes operating na ailed channel can beswitched over to the remaining channel.The allocation of module interconnecting data paths in thesystem further increases the flexibility and reliability of the DisplayProcessor. Separating the control paths from the radar video datapaths reduces the speaal control required o manage multiplexingthese functions. In addition, control messagescan be sent to themoduleswithout ntempting thedata low. Reliability senhancedbyreducing the number of interconnects between modules.The outputs from the video memory modules are routed o thevideo mixer module. Depending on the operating modes, eitherchannel can be displayed on one or both of the video outputchannels,mixedwith heothervideo sourcesforsplit screen displays,

or blanked for self-test operations.DISPLAY GENERATOR IMPLEM ENTATiON

This section contains a detailed description of the operation ofthe elements of a display processor. Figure 10 shows a blockdiagram of these elements.

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