1959 IRE TRANSACTIONS ON MILITARY ELECTRONICS 105

A Land-Mass Radar Simulator Incorporating Ground and ContourMapping and Terrain Avoidance Modes*

W. P. JAMESONt AND R. M. EISENBERGt

Summary-This paper describes a method of simulating the ra- Ultrasonicdar displays of an airborne radar system. The simulator employs a . . . hscan-programmed vidicon tube and a low-power light source in con- This iS an extensively used technique utilzing thejunction with a three-dimensional terrain model to simulate radar propagation of ultrasonic waves in water. The simulatedreturn from land-mass formations, cultural areas, and target com- radar reflection pattern is produced by the sound wavesplexes. All effects of a moving aircraft, including velocity, heading, reflected from the surfaces of a three-dimensional terrainaltitude, position, and attitude, are included in the simulation.

This device will produce the displays for ground mapping, contour model Te onsthe boto of a shalonk omapping and terrain clearance radar systems. It may be employed water. The transducer and pickup are positioned towith an operational flight simulator or as a self-containe*Fradar mis- simulate the aircraft position over the area of interest.sion trainer for radar navigation and blind bombing operations. The water must be carefully filtered and purified to

keep it free from foreign matter. The temperature mustbe maintained at a specific level to assure a constant

D9sURING \Vorld War II, the need for simulation propagation velocity.of airborne radar systems for training purposes The propagation velocity of sound in water at a givenwas recognized. Through the ensuing years the temperature and the propagation velocity of electro-

programs initiated to develop radar simulation tech- magnetic waves in space are physical constants whichniques have resulted in the creation of several accept- allow a direct, fixed analogy to be established. The re-able systems. sultant scale ratio for the terrain model is 210,000 toAs the development of radar systems has advanced, one. The ultrasonic system is limited to this scale ratio

many of these techniques have been taxed beyond their where the indicator sweeps cannot be changed. Rangecapabilitie s and have failed to keep abreast of the actual resolution is poor at short ranges due to severe inter-system design. Thus the stimulus is provided for launch- ference effects, therefore limiting the low altitude simu-ing new programs to arrive at a reasonable solution to lation capability. Many of these problems could bethe many problems encountered in the simulation of solved, but the limited scale ratios and the space re-comlplex, high performance radar systems. quirements for this system make it unattractive for

Increasingly heavy emphasis is being placed upon development as a simulator for today's high performance"high-fidelity" radar simulation because of the problems radar systems.encountered in the training of a radar operator withactual equiipment. Aside from the expense of operating Pre-Programmed Tape or Film Stripan airborrne system under actual conditions, the problem Actual video signals in a radar receiver may be re-is one of training an operator to perform many tasks corded on tape or film during an actual flight, thenefficientlv. This is particularly true of the pilot of a played back in a device which will produce the indicatorsingle place fighter-bomber aircraft who must performn displays. This method is seriously limited since no vari-the duties of a pilot, navigator, radar operator, radio ables may be introduced into the problem while maini-operator, and bombardier during the course of a single taining the validity of the radar information. Themission. An operationial flight simulator for aniy size simulation is accurate for one preselected flight path.aircraft must teach the pilot or crew to perform all these Such a device may be useful in premission briefing totasks in an efficient manner and teach him to interpret familiarize a radar observer with the radar pattern of athe informiation presented by the radar system and particular target complex, but could not be used success-automatic navigation systems accurately and rapidly. fully as an operational radar simulator.In a sense it should be possible for a pilot and crew to"pre-fly" an actual missioni to help assure the success AMlatched Photoplateof an operation. The matched photoplate has one great advantage over

all systems devised to date. This advantage lies in itsRADAR SIMULATON TECHNIQUE ability to store huge land-mass areas in a small space.

M\anly systems usinlg various techniques have been Two photoplates are used to accomplish the informationproduced to simulate grounld surveillance radar sets. storage. One plate contains terrain elevation informa-The followving is a brief description of some of these de- tion, the other stores the reflectivity (at one altitude)vices: information. This pair of plates is scanned synchronously

by two similar light-optical systems. Television camera* Manuscript received by the PG.MIL, April 15, 1959. type tubes are used to convert the light variations intot Nuclear Products-Erco Division of ACE Industries, Inc., River- elcrclsgaswihaethnue oceth aa

dale, Md. eetia lnl hc r hnue ocet h aa

106 IRE TRANSACTIONS ON MILITARY ELECTRONICS July

indicator displays. Shadow effects are produced syn- limited only by the photoelectric devices utilized anidthetically by a computer receiving the terrain elevation the terrain model. Techniques for producing highlyvideo and terrain reflectivity video as inputs. accurate terrain models are well known. Methods

Scale ratios of three million or four million to one may whereby the models may be modified and kept currenitbe used. Thus large areas of the earth's surface may be have been developed and are being improved. Theserepresented on two relatively small photoplates. There models may be constructed to be compatible with a

are several disadvantages which exist at present. These given simulation technique so as to produce many of theinclude heating problems due to the high intensity light desirable radar effects not possible with other land-masssources, optical alignment problems, some of which storage means. The scale ratios which may be used witharise from the large scale ratios, poor integration of these systems in the present state of development areelevation and cardinal effects in regard to aspect vs not as high as those attainable with a matched photo-radar reflectivity, and poor low altitude simulation. plate, but it is believed that the many desirable features

of some of these light reflective systems make them theLight Reflective Systems most attractive for use in the radar simulationi fieldMany of the systems being developed and in use as at the present time.

simulators for the higher performance radar sets areclassed as light reflective systems. This general class of DESCRIPTION OF THE SCAN PROGRAMMEDsystems achieves a good balance between performance, VIDICON TECHNIQUEaccuracy of simulation, simplicity, durability, and The system described herein is capable of simulatingflexibility. The systenm to be described in the following three modes of operation of a radar system. Thesesections of this paper is classed as a light reflective three modes are Ground Mlapping, Contour Mapping,system. and Terrain Avoidance (or Terrain Clearance). Fig. 1

All have in common the inethod of land-mass storage. is a block diagram of the system configuration for simu-Their differences lie mainly in the means used for propa- lating the ground mapping mliode of operation.gation of the light and converting the reflected light Ground Mapping Simulationpatterns to video signals.A three-dimensional terrain model is mounted on a General Description: Anl assembly consistinig of a light

flat bed or frame. The model is cast or formed of a source, prism, and light pickup device is mounted on a

plastic material. Cultural areas and target complexes gantry arranged so that the assembly can be positionedare painted on the map surface as a pattern of spotted in X and Y coordinates over a three-dimensional terrain

gray areas or may be cast in relief as blocks of plastic model in accordance with signals representing the posi-painted the proper color or gray shade corresponding to tion of the simulated radar carrying aircraft. The

the radar reflectivity of the object or objects. Water assembly is capable of being rotated, in accordance with

appears as a glossy black surface while land areas are the simulated aircraft headinlg, about a pivot pointpainted a flat gray or are textured with fine grit to yield located near the center rear edge of the prism as shown inthe desired reflective properties. Figs. 1 and 2. The light source is provided with a verticalA gantry mechanism carrying the light optical devices drive to enable its altitude above the terrain model

rides over the map with the light source or light pickup datum plane to be varied in accordance with altitude

device having a position corresponding to the simulated signals. The X- Y positioni of light source relative to theairborne radar position. The carriage supplies horizontal prism is fixed. The front of the light source is at the

motion and a portion of the light optical system is moved previously mentioned assembly pivot center line. The

vertically to simulate altitude. light beam emanating from the light source is shaped so

The light may be propagated in a shaped high in- as to evenly illuminate a scaled area on the map surface

tensity beam which scans the map surface in accordance equal to, or greater than, the azimuth and range searchwith the simulated radar antenna scan program. An- area of the radar being simulated. A representative area

other technique utilizes a flying spot-scanner light source of illumination is indicated in Fig. 3.for light programming. The light pickup, analogousto As indicated in Fig. 1, the area of interest, i.e., thethe radar receiver, receives the light reflected from the area to be presented oni the simulated radar indicator,map surfaces, and the resultant video signals are used is focused by the lenis of the camera onto the photo-to modulate the intensity of the indicator swveeps to cathode of a vidicon camera tube. The photo-cathode isproduce the radar display. This paper describes a tech- commutated by the electronl beam in the vidicon whichnique utilizing a scan programmed light pickup with is deflected inl accordanlce with a PPI sector scan pro-a light source which floods a specified map surface area. gram. The scanning pattern on the vidicon faceplate isA wide range of scale ratios may be used with these indicated in Fig. 4 which also depicts anl A scan presenta-

techniques. There are no great problems encountered tion of the video output fromn the vidiconl for the azimuthin handling the propagation medium. The life of the position indicated. The low level video signals obtainedscanning components is relatively high. The range reso- from the camera tube are amplified by means of suitablelution and lowv altitude simulation capabilities are video amplifiers, clamped to a reference level, and

1959 Jameson and Eisenberg: A Land-Mass Radar Simulator 107

SPECIAL

PRISM'-, LENS\

I PRE-AMPLIFIER

/ SOURCE t vdl < I f 1 T R TO INDICATOR

DEFLECT ION

ITERRAINATNA 0CRUT5=> U1 TS | ~ ~~XBEAIRING SHAFT OA D g AD LMCDELEACMTIP SN1ECCI E INCeA L/ | AZIMUTHIL

APIIE - REOLERRSO|I RI LCURSOR CONTROL

PUSINLNIGr-L SYNHRNDA IZGPLESR NLNIG N FOCURSORS AND SWEEPS TIME SHAPE PULSE JTLrL

SWEEP EA

Fig. 1.

~MAP

;I- LONGITUDINAL RADAR LAND MASS GENERATORCARRIAGE

-;; || |||__ _ - MAPTRANSVERSE CARRIAGE

iROTATION IAND PROJECTION a.

SLIP RING ASSEMBLY

-ltv + - r 1Ill-t t eo /~~~~~~~~~C BRUSH BLOCK

-$-i| ] -2 _ _ 0 0 // g ~~~~~~~~~~FLEXIBLECORD.10'-9" APPROX.

ROTATION AND BEARING HOUSINGPROJECTION\ i1 > T.V. CAMERA ALTITUDE GREATER GUIDE ROD

THAN10,000 FT. 0

/ I -It-F

108 IRE TRANSACTIONS ON MILITARY ELECTRONICS July

applied to the grid or cathode of the radar indicatortube. The PPI scan is generated by resolving a sweep

MAP AREA SEARCH AREA of suitable waveform into its X and Ycomponents aboutILLUMINATED the azimuth bearing representing the aircraft heading.

A similar scanning system is utilized to sweep theradar indicator tube screen in synchronism with thevidicon sweep. The video signals applied to the radarindicator CRT cause intensification of the trace at thecorrect position thereby painting on the indicator theimage present on the photo-conductive faceplate of the

_SOURCE WVith a terrain model constructed according to radarreturn prediction data, the presentation on the radarindicator is an accurate simulation of the presentationthat would be observed on an actual airborne radar setover the terrain. Although a PPI sector display is de-scribed here, this is not meant to infer that this is theonly type of display which may be simulated with thistechnique. Any type of scan utilized by search radarsystems is applicable to this systemn.

4-LIGHT The sweeps, gating pulses, unblanking and clampingSOURCE pulses, and range marks are generated in a synchronizer

unit. The design of the circuits in this synchronizermay be arranged to accommodate various pulse repeti-

5 ~~~~~~~MAPSECTION

SIDEVIEWS

tion rates, range mark spacing, altitude delay circuits,and sweep expansion circuits so that any radar setperformance may be accurately simulated. Fig. 5 is asimplified block diagram of typical synchronizer andvidicon sweep circuits for the simulation of a groundmapping radar system including distance mark genera-tion and range cursor generation.

Various effects such as jamming, noise, or the additionSCAN /ZIMof electronically-generated air targets are introduced

PAT TERN into the system by means of the video mixer as indicatedin Fig. 1.

Simulation of Changes in Range Coverage: Changesin range coverage (an operator selected function) areeffected by changes in the lens field of view. The lensesare mounted in a turret on the camera. The turret isremotely switched from the range selection control on

Cs, \\ )/ + /the radar operator's set control. A wide angle lens isused for the longest range coverage. When shorter rangeoperation is selected, a lens with a narrower field of viewis positioned in optical alignment with the vidicon and

IMAGE FOCUSED / ... .ON VIDICON / \ X prism. Since the field of view is narrowed concentrically,

FACE PLATE

the prism must be tilted slightly about its lateral axisto return the rearmost edge of the field of view to the

SWEEP ORIGIN AIRCRAFT / \ zero ground range point. Fig. 6 shows the field of viewPRESENT POSITION PLUSALTITUDE DELAY / \ of two lenses and demonstrates the rearward shift

{1 ~~~~~necessary to accomplish the scanning pattern com-R ANGE b ~~~pensation .

\ / ~~~~~~TheLight Source: The light source used with this< / ~~~~~technique consists of a lamp and housing, a collimating

PRSNAINoptical assembly, and a "light pipe." The lamp is aOF INDICATED SWEEP relatively low power incandescent bulb. The light pipe

Fig. 4. is constructed of a lucite plastic rod 18 inch in diameter.

1959 Jameson and Eisenberg: A Land-Mass Radar Simulator 109

VIDICON YOKE

E ~~PHANTASTRONlPRF SWEEP C. RESOLVER1 ? T1 XL I~~~~~~~~~~~~~Y-SWEEP

RANGE DISTANCE MARK GENERATORCURSORCONTROL

C.F. SQUARER DIFF. RANGE CURSOR

S L ~~~~~~RANGECURSOR GENERATOR

Fig. 5.

beam with its many optical elements. The light lossesOF SHORT RNGSE do not necessitate a high intensity lamp to transmit theLE4lS WITHOUTCOZPENSATION \necessary light through multiple optical interfaces to

the map surface. Second, the vidicon tube possessesexcellent photosensitivity. Some of the vidicons now inproduction are capable of producing satisfactory videosignals with as little as 0.2 foot-candles of illuminationon the faceplate of the tube. The heating problemsattendant to high intensity shaped beam sources arethereby eliminated allowing the light source to travel inclose proximity to the map surfaces without danger of

FN\IELDOFVIEWOf causing damage to the plastic material. Since the lightsource will be very close to the surfaces during low

\IOINT TOITS CO,e,NAL POSITION altitude operation, a means of preventing physicalZERO GROUND RANNE damage due to a collision with the map is provided.

Fig. 7 is a sketch of a portion of the light source showingFig. 6-Field of view compensation for range coverage lenses. th colso. wthcntuce sa nerlprPi =raiige of coverage of wide angle (long range) lens. P2=range the collision switch constructed as an integral partof coverage of narrow angle (short range) lens. of the light source assembly. The lucite rod passes

through a rubber grommet at the upper end of itssupport housing. At the lower end of this support hous-

This lucite rod is shaped at its lower end to disperse ing, a ring of metal feelers, similar to finger stock ma-the light in the pattern indicated in Fig. 3. This ap- terial, is fastened so as to just clear the lucite rod. Atproach was used to allow the light source to travel in this point on the lucite rod a metal band is fasteneddepressioyns in the terrain model surface, thereby en- and connected to a collision relay circuit through ap-hancing the low altitude simulation. A low-power light propriate wiring. A wire connected to the metal feelersmay be used as a source for two reasons. First, this completes the circuit should the lucite rod bend andtechnique does not depend upon a programmed light touch the feelers. This will occur if the lower end of the

110 IRE TRANSACTIONS ON MILITARY ELECTRONICS July

LAMPHOUSING

cl--P GROMMET ECTION

\[}/ WIRES TOLOCK-UP RELAY (a)

FINGER STOCK \CONTACTS TARGET

BLOCK

METAL BAND F

LUCITE ROD \"LIGHT PIPE'\ U~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~.......

Fig. 7-Light source collision switch.(b)

rod strikes the map surface with a force greater thanapproximately 5 grams. Actuation of the collision relay TARGET

wvill lock the horizontal and vertical drive servos and \require that the light source be slewed upward before &the servos can be reactivated. When the radar simulator \lvis used as a part of an operational flight simulator, this \ =collision signal may be used to energize the crash systemindicating a collision with the earth's surface. (c)Map Construction: The map is constructed of a plastic * AGEO HT AEI XGEAE

material and cast from a master mold. The target com-plexes are stored in relief with blocks of the map ma- Fig. 8.terial representing targets and groups of targets. Wateris represented by a glossy black surface. A class "one" may, at low angles, become an outstanding or "classor highly reflective target is painted a flat white on one" return. The construction of such a target typethe faces of the target blocks. Three shades of gray are is indicated in Figs. 8(a)-(c).used to represent targets of lower reflectivity classifica- Fig. 8(a) is a low altitude, rear corner view of ation and terrain. Texturing is used where applicable faceted target block. Fig. 8(b) is a high altitude, frontalto create rough surface terrain reflectivity. The resultant approach view of the target, and Fig. 8(c) is a lowmodel is athree-dimensional radar prediction map of a altitude, frontal approach view. The front face of theportion of the earth's surface. Target complex areas block is painted white. This type of target will produceare constructed as inserts so that they may be remnoved excellent cardinal effects. That is, a return will be ob-and replaced by mnodifled target areas. Small changes served onlywhen approaching the target from the propermay be made on the mnodel's surface by hand if the direction. Groups of these target blocks representing aproper tools are used. The target complex inserts are target complex will create a reflectivity pattern whichfaired into the surrounding map contours so that the will vary as a function of approach bearing.line of demarkation is not visible to the camera. The Low Altitude Simulation: Further examnination ofentire map is braced on its under side so as to prevent Fig. 8 will indicate that the angle of the target facet cansagging. A map of this type measuring 11 feet by 5 feet, be varied so as to produce "no show"' effects at highwith necessary integral bracing and mounting provi- angles with good return at low angles or vice versa.sions, weighs approximately 200 pounds. Indexing When the simulated aircraft is at high altitudes, themarks are provided on the edge of the map with an camera and prism are oriented as shown in Fig. 9(a).alignment pin mounted in the exact center of the map The view then is essentially perpendicular to the mapbase to mate with a bushing in the map bed. surface, and the vertical sides of the target blocks are

Target Storage and Effects: The storage of targets (in not seen by the camera. At lower altitudes, the prism isrelief) aids in the creation of proper target aspect, rotated to decrease the angle of incidence as shown incardinal effects, and shadowing. A target having a low Fig. 9(c). In order to continue observing the same mapmagnitude radar return with a high angle of incidence area, the camera is moved back as the prism is rotated

1959 Jameson and Eisenberg: A Land-Mass Radar Simulator 111

CAMERA altitude limit a servo motor begins moving the assem-iblydown and aft. The lower limit of the assembly motionis reached as the aircraft descends through the loweraltitude limit (2000 to 500 feet depending upoIn the

LIGHT / / 1 lens field of view and the system geoiimetry). At anvPATTERN

LIGHT SOURCE AT f/ I MEDIUM ALTITUDE fligh altitude below this limit the assembly rell-aiiisfixed in its lower position. Note that the light sourcedoes not move with the camera and prismnassemiibly butcontinues to servo to a position simulatiiig the aircraft'saltitude. This camera assembly motioni is ani auxiliary

\i5/TARGETBLOCK motion used to create good low altitude simiulation.SHADOWED AREAS Shadowing Effects: Shadowing effects are realistically

(a) produced as the light source is raised anid lowered as aCAMERA function of simulated altitude, as indicated by Fig.

LIGHT PRISM \ 7 9(a)-(c). The camera sees only the surfaces of the miiapPAT TERN - m | which are illuminated. Therefore, the video output of

targets and terrain is obtained only when they are notLIGHT SOURCE AT in the shadowe areas.HIGH ALTITUDE

i h hdwdaes

Range Resolution: The results of tests performiied onthis system have indicated a resolution capability of800 lines. The scale range resolution while simulating a

radar range of 80 nautical miles is then 608 feet. Thisapproaches the ideal range resolution capability of anlairborne ground mapping radar systemii with a pulse

TARGET fO / 'width of 1 NSCC. The range resolution of the simulator\/ ~~~~~TARGET BLOCK

SHADOWED ARES improves when shorter radar ranges are simulated.

(b) Operational Flight Simulator Tie-In: Wheni this radarsimulation device is to be used as a portioni of a flight

CAMERA and tactics simulation system, the gantry motion, lightAT LOWERPOSITION source motion, and the camiera motion are programmed

PRISM from the flight simulator's position, bearing and altitudeTILTEDflgtpsto, adatueLIGHT computers where:

PATTERN V7\ = Aircraft horizontal velocity= Aircraft heading=Orientation of the map major axis

K = Scaling factor of the terrain model/Lo=Longitudinal carriage rate

LIGHT SOURCE LA= Lateral carriage rate.AT LOW ALTITUDE

tThe longitudinal carriage motion is described by theSHADOWED - expression LO= 1V, cos (7'-l/m) K. The lateral carriage

AREASnmotioni is according to the expression LA= Vn Sill(c) (7/'-Q,Vm~)/K. The vertical motion of the light source is

Fig. 9-(a) Shadow effect at simutlated medium altitude; (b) shadow according to the expressionieffect at simulated high altitude; (c) shadow effect of simulatedlow altitude. dI

L =- Kso as to miainitaini the samne miiap area focused oni the dtphotocathode. Since the aforementioned action would whereresult in a, larger area being observed, the camera is1 1 . 1 n 1 1 r . 1 .........thLh= Rate of vertical motion of the light sourceloweredl so as to maintain the same field Of view. Th dhdneaeofcag farcatattdmotion of the entire assemblly iS accomplishedt smoothly KSaigfco ftetranmdlas a functiona of altitude. At altitudes above 10,000 to ..... =cln atro h erllrldl15,000 feet (the exact altitude depenlds upon the map ......Theturning rate d),/1dt computed for the simulatedscaling and systeml geometry), the assembly is main- ......aircraft drives the camera, prism, and light source as-tamIed at a fixed height above the model's datum plane. ......semblies about their turninlg axes at the rate of turnl ofAs the simrulated aircraft descends through this upper ......thesimulated aircraft.

112 IRE TRANSACTIONS ON MILITARY ELECTRONICS July

The radar set controls and indicator controls, withappearance anid function identical to that of the actual __hradar system, are located in the simulator cockpit orsimulated aircraft radar operator's station. , 'A plot of the simulated aircraft's track over the A, , A.

earth's surface is recorded during a "mission," thus t-allowing a post mission critique for training purposes.

Use As a Radar Display Interpretation Trainer: In -addition to its use as an operational radar training de- - Atvice, this system may be installed so as to provide class- -- PLANE

vice, ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~tZERO ALT ITUDE

room traininig in the skill of reading and interpretingthe displays of a radar system.A repeat indicator may be provided for a remote loca- Fig. 10.

tion with the necessary set and indicator controls. Apreprogrammed flight track will provide the carriage h0 distance between flight path and clearancemotions for the radar simulator. A group of radar oper- plane betators or pilots may then be instructed in the display plane, pilot setinterpretations and the correlation of the data presented Po computed ground range from aircraft to inter-on the radar indicator with that presented on standard section of clearance plane and zero altitudeaeronautical charts or radar prediction charts. P =instanetaneous radar ground range (sweep volt-

It is conceivable that this device may also be utilized age)to prepare flight crews for actual operations over ul- p=distance from Po to Pfaila teri. 0 =aircraft pitch angle

ht = terrain altitude at distance pi

Terrain Clearance and Contour Mapping Simulation 7=0.

General Description of Actual Radar Operation: During Equations relative to the geometry of the problem are:the terrain clearance mode of operation of a radarsvstem, a clearance plane parallel to the flight path of 1t0the aircraft is established by the operator at some alti- cos ytude above or below the aircraft. Only the terrain he= h-heprotruding above the clearance plane is displayed on theradar indicator. This enables the pilot of an aircraft to P0=tan 4'iadjust his let-down or climb-out flight path angle to hr = tan Op,assure his clearing the terrain by a predetermined p = p - paltitude.

During the contour mapping mode of operation a = -0 ± 90clearance planie parallel to the earth plane is established hta = tan Opiby the operator at some altitude above or below the htr = hl - hla.aircraft. As in the case of terrain clearance, only thatterrain protruding above the clearance plane is dis- The equations solved in order to obtain a voltageplayed. This provides means for identifying check-points proportional to the instantaneous altitude of the pro-and for locating possible let-down areas on the terrain. jected clearance plane (htr) are:

Terrain Avoidance Simulator Technique: The geom- = -etry of the terrain avoidance problem is shown in Fig.10. Definitions of symbols are as follows: ho

lie =h = aircraft altitude cos yh= vertical distance below projected aircraft flight hta- tan Opi

path to projected clearance planeh=altitude of projected clearance plane at a point lirle -h-at.

directly below aircraft As shown in Fig. 11 the terrain altitude along thehtr=instantaneous altitude of projected clearance radar sweep must be determined. Special equipment, in

plane. htr. decreases with range addition to that utilized in the ground mapping mode,hta =instantaneous vertical distance from projected is used to accomplish this. Fig. 12 shows a method which

clearance plane to a plane parallel to the datum uses a photo transparency whose emulsion density isplane at an altitude equal to hc inversely proportional to terrainl altitude. The area of

1959 Jameson and Eisenberg: A Land-Mass Radar Simulator 113

this earth's surface represented by this transparency is -T-

identical to that of the area depicted by the terrainmodel in use for the ground mapping problem. A flyingspot-scanner, positioned horizontally in synchronismwith the camera, prism, and light source assembly onthe terrairn model gantry, and deflected in the same , _ h-hGATEscan program as that of the vidicon tube, is mounted AND

on one side of the transparency. A photomultiplier tube iE e l lis positioned in the same manner on the opposite sideof the transparency. The output of the photomultiplier _lfor each swveep made by the flying spot is a waveform TERRAIN AVOIDANCEwhose instlantaneous amplitude at any point on the Twaveform is proportional to the terrain altitude at that

S

samne poinlt in range on the map surface.Fig. 13 shows a method whereby an opaque print and

CONTOUR VIDEO LEVEL h, ...

vidicon camera are used, in lieu of the transparency andflying spot-scanner, to derive the terrain altitude voltage. Fig. 11.The terrain elevation information is stored on the printas varying shades of gray, the highest terrain being DEFLECTIONdepicted by white and the lowest being depicted by COILSblack.The conitour video obtained by either of the two FLYING SPOT CRT

aforementioned means are compared to the voltageproportional to htr. Any video voltage having an ampli-tude greater than that of htr is squared and utilized to _ TRANSPARENCYgate the video from the three-dimensional scanninghead into the indicator video amplifier chain. Duringthe terrain avoidance mode, the pickup head sweep ismodified to display slant range. PHOTO VIDEO CONTOUR

MULTIPLIER TUBE AMP. VIDEOContour Mapping Simulator Technique: The geometryof the contour mapping problem is identical to that Fig. 12.of terrain avoidance with the exception that the effectsof pitch anigle are eliminated. This establishes the clear-

DEFLECTIONance plane parallel to the ground plane, i.e., ht,=h-h,. SIGNALS >-1Mounting of Additional Equipment: This additional CONTOUR

equipment may be mounted in a number of ways, the LIOOD VIDEOchoice of mnounting being determined by the space avail- LIGHTable. The transparency or opaque print may be mounted /'under the terrain model bed or suspended above theterrain model carriages with the light source and pickup N OPAQUEdriven directly by the terrain model gantry. These PRINT

auxiliary devices could also be mounted vertically on Fig. 13.the side of the gantry or in a separate cabinet with servodrives for the light source and pickup devices receiving In operation the amplitude of the actual contour in-their inptuts directly from the gantry servos. formation voltage is compared to the preset clearaniceThe choice of either the transparency or opaque print altitude signal, and when the contour information signial

techniques is dependent largely upon the space available. is greater than the desired clearance signal, the videoIt will be noted from Figs. 12 and 13 that the transpar- from the terrain model camera is gated into the opera-ency requiires the use of devices mounted on either side tor's radar indicator permitting this video to be dis-of the plate wvhile the opaque print need only have com- played. By this means only the video from objects aboveponents oln one side. The cost of either of these elevation the clearance plane are displayed to the operator.storage mledia is a function of the scale ratios requiredwith the larger scale ratio being the more expensive CONCLUSIONchoice. Special data are not required to fabricate these The technique described in the preceding paragraphsplates or prints since existing terrain elevation data provides a solution to many of the problems which havecan be utilized. made other techniques unattractive.

114 IRE TRANSACTIONS ON MILITARY ELECTRONICS July

The maintenianice requirements of the system are kept ACKNOWLEDGMENTto a minimunm through the use of a noncritical propaga- The authors wish to acknowledge the suggestionis oftion medium and a technique which does not require Ross Gafvert of the Fighter Simulator Branchhigh intensity light sources with their attendant heat (WCLEQF), Aeronautical Accessories Laboratory,problems. Wright Air Development Center, Wright-Patterson Air

Reliability is attained through the utilization Of Force Base, Ohio.proven pulse circuitry. The authors also wish to thank the engineers of the

Fidelity of simulation of the radar presentation is Aero Service Corporation, Philadelphia, Pa., for themade possible through the use of a high resolution, light assistance they have rendered in selecting the designsensitive device and methods to achieve good altitude parameters for the terrain model used with thiseffects, and a target aspect realism not available by simulator.other knownimeans.

Flexibility is realized through providing a means for BIBLIOGRAPHYchanging the target complex areas of a terrain model. [1] E. C. Hollinger, "Advanced Radar Simulator Techniques Using a

Photo Plate Map Storage," WADC Tech. Rep. No. 58-138,Further, the entire map may be replaced and aligned ASTIA Document No. ADiS1150; April, 1958.rapidly to represent other known areas of interest. [2] E. C. Hollinger, "A Light Reflective Method for Simulation of

rapi ~~~~~~~~~~~~~~AirborneRadar," WADC Tech. Rep. No. 58-139, ASTIA Docu-Modification for new radar characteristics is simply a ment No. AD151150; April, 1958.matter of replacing those portions of the light source. [3] E. C. Hollinger, "Study of Matched Photo Plate and Light Re-

flective Map Systems," WADC Tech. Rep. No. 58-140, ASTIAsweep, and gating circuitry affected. Document No. AD151147; May, 1958.

Thirty-Two Aircraft Radar Track Simulator*L. PACKERt, M. RAPHAELt, AND H. SAKSt

Summary-This paper describes a Radar Track Simulator which parisons show that the aircraft is being illuminated bygenerates the track of thirty-two aircraft in x, y, and h coordinates the simulated radar beam, the digitally-generated videoaccurate to one-hundreth of a mile and produces video accurate to pulses are gated through to the output sections of theone-hundreth of a mile in range, one milliradian in azimuth and twomilliradians in elevation. The output video signals are modified by equipment. Since the range is generated by the digitalthe radar beam pattem, aircraft scintillation noise, radar receiver equipment, it is accurate to 0.01 mile in range up to a

noise, fading of video signal with range, and blip-scan effects to pro- maximum of 500 nautical miles. The azimuth angle isduce a realistic display. accurate to one milliradian, except when the simulated

radar has wide beamwidths (beamwidths larger thanINTRODUCTION 8°). The elevation angle accuracy is two milliradians up

T HE track and radar simulator to be described to a maximum of 60°.generates the track of thirty-two aircraft in x, y, The gated video pulse is sent from the digital sectionand h coordinates. Manual inputs determining the of the equipment to the 64 output channels, 32 for the

x, y, and h rates for these aircraft are converted from search and 32 for the height section. Aircraft scintilla-analog form to digital form by means of a central tion noise as well as beam pattern and blip-scan infor-analog-to-digital converter. The digital x, y, and h mation is used to operate on the video pulse. At thisnumbers are initegrated digitally aid provide continuous point, the video pulse has been converted to an RFinformation of the position of each of the aircraft. A signal having the proper amplitude and duration to cor-continuous computation is performed to convert the respond to the particular type radar being simulated.x, y, and h numbers for the aircraft to p (range), sin /3 The outputs of the 32 search channels are mixed to-(elevation angle), and sin or cos of 6 (bearing angle). gether at the simulated RF frequency, heterodyned, andDigital comparisons are then continuously made be- then passed through an IF strip where the receiver noisetween the bearing angle of the aircraft and the antenna is generated and the signal attenuation with range isazimuth angle. Analog comparisons are made between accomplished. The IF strip output is detected and isthe antenna elevation angle (of a three-coordinate fed to a PPI or other equipment having similar signalradar) and the aircraft elevation angle. When the com- inputs. A similar radar receiver sectionl is also provided

for the three-coordinate radar.

* Manuscript received by the PGMIL, April 15, 1959 .T ev.fteipttret r otoldb h

t General Applied Science Labs., Inc., Hempstead, L. I., N. Y. Target Control Unit to be described later in this paper.