SPECIAL REPORT 91-003 TECHNICAL … REPORT 91-003 TECHNICAL ADVANCEMENTS IN SMULATOR-BASED WEAPONS TEAM ... This increased tacticE ... 5 Timing Sequence for …

SPECIAL REPORT 91-003

TECHNICAL ADVANCEMENTSIN SMULATOR-BASED

WEAPONS TEAM TRAINING t

AR19


TECHNICAL ADVANCEMENTSIN SIMULATOR-BASED

WEAPONS TEAM TRAINING

APRIL 1991

Albert H. MarshallRonald S. Wolff DTIC

Robert T. McCormackEdward J. Purvis ELECTE

S APR25 19911DE

NAVAL TRAINING SYSTEM CENTERADVANCED SIMULATION CONCEPTS DIVISION

Orlando, FL 32826-3224

Approved for public release;distribution is unlimited

FRANK OHAREK, Acting Head H.C. OKRASKI, DirectorAdvanced Simulation Concepts Research and EngineeringDivision Department


GOVERNMENT RIGHTS IN DATA STATEMENTReproduction of this publication in whole or inpart is permitted for any purpose of the UnitedStates Government.

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SECURITY CLASSIFICATION OF THIS PAGE

I REPORT DOCUMENTATION PAGE

!I.REPORT SECURITY CLASSIFICATION lb RESTRICTIVE MARKINGS2a. SECURITY CLASSIFICATION AUTHORITY 3. DISTRIPUTION /AVAILAILITY Of REPORT

______________________________ Approved for public release;Zb. DECLASSIFICATION I DOWNGRADING SCHEDULE distribution is unlimited

)4. PERFORMING ORGANIZATION REPORT NUMBER(S) S. MONITORING ORGANIZATION REPORT NUMBER(S)

Ispecial Report NTSC-SR91-003

6a NAME OF PERFORMING ORGANIZATION 16b. OFFICE SYMBOL 7ia. NAME OF MONITORING ORGANIZATIONiNavra ysCen Ieof "

6C. ADDRESS (City, State, and ZIP Code) 7b. ADDRESS (City. State, and ZWCode)I12350 Research ParkwayOrlando-, FL 32826-3224

SS... NAME OF FUNDING / SPONSORING 8 b. OFFICE SYMBOL 9. PROCUREMENT INSTRUMENT IDENTIFICATION NUMBER*ORGANIZATIObNT (If applicable)

Sc. ADDRESS (City, State, and ZIP Code) 10. SOURCE OF FUNDING NUMBERS

PROGRAM IPROJECT ITASK IWORK UNIT

ELEMENT NO. NO. INO IACCESSION NOI11. TITLE (Include Security CIausication)Technical Advancements In Simulator-based Weapons Team Training

~1.PERSONAL AUTHOR(S)1Aibert H. Marsall., Robert T. McCormack, Ronald S. Wolff, Edward J. Purvis

peca F REPORT '13b. TIAAE COVERED 14,~ RVOWApriT (ftr,1oonth. Day) I i PAGE COUNTLSeia FROM _____TO 114RAJORPT

16. SUPPLEMENTARY NOTATION

117 COSATI CODES 1 8. SUBJECT TERMS (Continue on reverse if necessary and identify bibock number)SFIELD IGROUP SUB-GROUP Weapons Training; Computer Graphis V~ideo Disc

Training

19. ABSTRACT (Continue on reverie if necessary and idmntify' by block number)

The research and development reported here represents one phase of abroader effort to improve the effectiveness and realism of training a weaponfire team in a simulator environment. Currently simulator-based team trainersuse technology which restricts both realism in tactical training situationsand ablility for thorough performance measurements. The overall goal of thisdevelopment effort is to introduce new technology and techniques which canimprove current team training system technology. These new developmentsincude interactive aggressor targets and a high speed weapon tracking system.

TeNaval Training System Center has developed a test-bed ( Weapons TeamEngagement Trainr, WTET ) which allows two trainees to engage aggressor

taretswhih ae pesetedon a large video projection screen.I20 DIST RtBU TION IAVAILABILITY OF ABSTRACT 121. ABSTRACI SECURITY CLASSIFICATION0 UNCLASSIFIEDIUNLIMITED 0 SAME AS RPT. EJ TIC USERS

12a NAME OF RESPONSIBLE INDIVIDUAL 122b. TELEPHONE (Include Area Code) I22c. OFFICE SYMBOL

DO FORM 1473. 54 MAR 83 APR edition may be used until exhausted SECURITY CLASSIFICATION OF THIS PAGEAll other edition% are obsolete

OUL Oo9wmat hm"E~ O10a: 11M-404au

19 (continued)

The new technology and techniques described are demonstrated using this te.bed.

The objectives of the research reported here were: (1) to developmethod to remove aggressor targets which are hit as a training scenar;progresses; (2) to develop a method which allows aggressor targets to engacand disable trainees who do not take appropriate cover; and (3) to designweapon tracking system which continously and accurately provides weapon aipoints for up to 9 trainees.

The Test-bed model constructed at NTSC met the stated objectiveEAggressor targets were instantly removed from a training scenario as they weldisabled by weapon fire from trainees. An array of infrared emitting diodcwas placed above the projection screen and a detector harness was developed tdetect a modulated infrared bpam from this array. This increased tacticErealism in training by requiring trainees to seek appropriate cover whEengaged by the aggressor targets. An innovative weapon tracking system whicgenerates accurate weapon position data at over 300 Hz was designed alconstructed. This device is capable of continuously tracking weapon ajpoints for up to 9 trainees.

Increased realism and effectiveness in simulator-based weapons teEtraining can be realized through implementation of these new techniques artechnology. Continuously tracking weapon aimpoints'for all members of a fiiteam expands performance measurement capabilities. Training effectiveness alrealism are also increased by instantly removing disabled aggressors from tytraining scenario and requiring trainees to take appropriate cover whenaggressor returns fire. This results in an increase in communication arawareness between members of the team. In contrast, previous training systerdid not require trainees to seek appropriate cover. Also, aggressor targetwere not removed from the progressing training scenario when they wersuccessfully engaged and disabled.


ACKNOWLEDGMENTS

The authors wish to thank Mr. Joe Porthouse and the modelmakers of the Laboratory Services Division who performedmechanical design and fabrication for the Weapon Team EngagementTrainer test-bed.

Accession For

NTIS GRA&IDTIC TABUnannounced 0Justification

Distribution/

Availability Codes

Avail and/orDist jSpecial

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THIS PAGE INTENTIONALLY LEFT BLANK.

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EXECUTIVE SUMMARY

PROBLEM

The research and development here represents one phase ofa broader effort to improve the effectiveness and realism oftraining a weapon fire team in a simulator environment.Currently simulator-based team trainers use technology whichrestricts both realism in tactical training situations andability 4or thorough performance measurements. The overall goalof this development effort is to introduce new technology andtechniques which can improve current team training systemtechnology. These new developments include interactive aggres-sor targets and a high speed weapon tracking system. The NavalTraining System Center has developed a test-bci ( Weapons TeamEngagement Trainer, WTET ) which allows two trainees to engageaggressor targets which are presented on a large video projec-tion screen. The new technology and techniques described weredemonstrated using this test-bed.

OBJECTIVES

The objectives of the research reported here were: (1) todevelop a method to remove aggressor targets which are hit as atraining scenario progresses; (2) to develop a method whichallows aggressor targets to engage and disable trainees who donot take appropriate cover; and (3) to design a weapon trackingsystem which continuously and accurately provides weaponaimpoint coordinates for up tc 9 trainees.

FINDINGS

The Test-bed model constructed at NTSC met the statedobjectives. Aggressor targets were instantly removed from atraining scenario as they were disabled by weapon fire fromtrainees. An array of infrared emitting diodes was placed abovethe projection screen and a detector harness was developed todetect a modulated infrared beam from this array. This in-creased tactical realism in training by requiring trainees toseek appropriate cover when engaged by the aggressor targets.An innovative weapon tracking system which generated accurateweapon position data at over 300 Hz was designed and construct-ed. This device is capable of continuously tracking weaponaiming points for up to 9 trainees.

CONCLUSIONS

Increased realism and effectiveness in simulator-basedweapons team training can be realized through implementation ofthese new techniques and technology. Continuously tracking

7


weapon aiming points for all members of a fire team expandsperformance measurement and playback capabilities. Trainingeffectiveness and realism are also increased by instantlyremoving disabled aggressors from the training scenario andrequiring trainees to take appropriate cover when an aggressorreturns fire. This results in an increase in communication andawareness between members of the team. In contrast, previoustraining systems did not require trainees to seek appropriatecover. Also, aggressor targets were not removed from theprogressing training scenario when they were successfullyengaged and disabled by trainees.

RECOMMENDATIONS

The authors recommend development of an advanced prototypewhich would further increase realism in the training environ-ment. An engineering model could be developed for potentialuser tests to determine both training and cost effectiveness.This engineering prototype could enhance both realism andperformance measurements by:

(1) eliminating cords interfacing weapons to computers.(2) allowing up to 9 trainees to rehearse tactical

situations.(3) using multiple screens to increase trainee mobility;(4) tracking each trainees movements within the training

area to both control shoot-back and enhance feedback.(5) presenting results in a split screen display to show

both trainee movement, aggressor actions, and othersresults.

(6) analyzing the performance results using an expertsystem.

(7) using an expert system to generate aggressor actionsbased on team performance.

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TABLE OF CONTENTS

Page

INTRODUCTION ......... ...................... 11

Problem ........... .......................... 11Objectives .. .......................... 12System Overview .......... ..................... 12

SYSTEM DESCRIPTION ........ .................... 19

Scenario and Software Development ..... ............. 19

Scenario Development ...... ................. 19Scenario Processing ...... ................. 20Interactive Targets ....... ................ 20Tracking System Software ..... ............... 20Scenario Presentation ...... ................ 22Scenario Replay ........ .................. 23

Aggressor Shoot-back System ...... ................ 23

Sound System .......... ...................... 25

Weapon Tracking System ........... ........ 27

CONCLUSIONS .......... ........................ 37

RECOMMENDATIONS ............ ................... 39

REFERENCES .......... ........................ 41

LIST OF ILLUSTRATIONS

FiQure Page

1 Weapons Team Engagement TrainerConfiguration ........ .................... 13

2 Photograph of Collimated Infrared Sourceon M-16 Rifle ........ .................... 14

3 Infrared Spot Tracker Imaging Diagram .. ........ 15

4 WTET System Block Diagram ..... .............. 16

5 Timing Sequence for Tracking Weapon Aim points . . . 21

6 Shoot-back IRED Array Mounted HorizontallyAbove Projection Screen ..... ............... 24

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7 Block Diagram of IR Detection Circuitry ......... ... 25

8 Sound System Components andSpeaker Configuration ...... ................ .26

9 Two Dimensional PSD Structure .... ............ .29

10 One Dimensional PSD Structure .... ............ .30

11 Infrared Spot Tracker Block Diagram ... ......... .. 33

12 DC Coupled PSD/TransimpedanceAmplifier Configuration .... ............. ... 34

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INTRODUCTION

The requirement to maintain a high state of readinessduring austere budget times and to simulate close combattraining effectively has placed new requirements on the trainingdevice community. Increased use of small echelon militaryoperations to perform anti-terrorist, anti-drug and law enforce-ment functions have placed some unique and new emphasis onsimulation and training.

The Naval Training Systems Center has developed a WeaponsTeam Engagement Trainer (WTET) test-bed that will allow twotrainees to practice and rehearse close combat training exercis-es such as low intensity conflict, light infantry, SWAT andsecurity operations with an unsurpassed level of realism andfeedback. Typical events might include security operations,hostage rescue, shoot-no-shoot, ambush training situations androutine law enforcement operations in a common team scenarioenvironment.

A typical trainee can expend over 5,000 rounds of ammuni-tion during one week of live fire training. It is expected thatthe average trainee will use $905.00 worth of ammunition eachweek. If fifty trainees use the training device each week apotential cost savings of $45,250.00 would be realized eachweek. These savings do not include the cost of facilities,ranges, fuel, and transportation to and from the live fireranges. As can be seen the potential cost savings in ammunitionalone are very beneficial.

Safety is also a concern during live fire training exercis-es. Since the WTET uses no live ammunition the dangers of aninadvertent weapon discharge or lead poisoning is eliminatedentirely.

PROBLEM

The research and development here represents one phase ofa broader effort to improve the effectiveness and realism oftraining a team in a simulator environment. Currently simula-tor-based team trainers use technology which restricts bothrealism in tactical training situations and ability for thoroughperformance measurements. The overall goal of this developmenteffort is to introduce new technology and techniques which canimprove current team training system technology. These newdevelopments include a high speed weapon tracking system andinteractive aggressor targets. The Naval Training System Centerhas developed a test-bed, Weapons Team Engagement Trainer (WTET)which allows two trainees to engage aggressor targets which arepresented on a large video projection screen. The new technol-

11


ogy and techniques described are demonstrated using this test-bed.

OBJECTIVE

This report highlights new technology that was developedunder the WTET research effort. This new technology will allowfor effective and realistic training of small echelon militaryoperations previously unobtainable through simulation. Theauthors identified what they determined to be three majorweaknesses which limit the effectiveness of existing teamtrainers. These weaknesses are as follows:

1. Aggressors are not removed from the scenario when hitas they are in the real world. Trainees can not adjust theirstrategy based on other team members performance since thisinformation is not readily apparent (i.e., killed targets remainin the scenario).

2. Trainees are not required to seek sensible cover andconcealment. Team trainers currently available permit thetrainees to engage targets while fully exposed to on-screenaggressors since here is no aggressor shoot-back.

3. The tracking system for determining the aiming pointof the trainees' weapon's is limited to collecting data only attrigger-pull. As a result, continuous weapon position data isnot available for replay, analysis, and feedback. There is alsoa substantial delay between trigger-pull and data collectionproportional to the number of trainees in the team trainer.

The testbed model was developed to perform research anddevelopment on the three basic weaknesses previously addressed.Funding constraints and the potential size of a nine member teamtrainer mandated the initial research model to accommodate onlytwo trainees. However, the technology developed from theresearch effort is readily applicable to a full scale WTETcapable of handling up to nine trainees simultaneously.

SYSTEM OVERVIEW

The WTET test-bed accommodates training for two military orlaw enforcement trainees in a common-threat scenario. Thetrainees interact with a 100 inch video projection screen set upin a training exercise room. The video projection screendisplays both live video targets and graphics overlay from avideo projector and a video disk player under computer control.Each trainee has a weapon that is equipped with a collimatedsource of infrared (IR) energy, an infrared emitting diode(IRED). Figure 1 illustrates the configuration of the WTETtest-bed. The IRED is collimated to maximize the IR energytransferred from the weapon to the projection screen while

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minimizing the IR beam divergence. The collimated infraredsource is aligned with the trainee's weapon and places a smallinfrared spot on the video projection screen corresponding tothe location the trainee is pointing his weapon. Figure 2 showsthe collimated infrared source and its location on the M-16rifle. The infrared sources are sequentially modulated in atime multiplexed mode by the system computer to both identifythe active weapon and to improve signal detection.

Collimated Infrared Source(1" diameter, 4" long)

Figure 2. Collimated Infrared Source Mounted on M-16 rifle.

A high-speed, low cost, infrared spot tracker determinesthe continuous X and Y position coordinates of each weapon.The optical system for the infrared spot tracker (IST) views theentire video projection screen from a distance of approximately12 feet. The infrared spot imaged onto the projection screensurface is optically transferred or reimaged to a correspondinglocation on the Position Sensing Detector (PSD) as shown inFigure 3. The PSD and associated electronic circuitry islocated within the IST enclosure. The system computer deter-mines the position coordinates of the infrared spot on the PSDand consequently the video projection screen as well.

The high-speed PSD-based infrared spot tracker, designed aspart of the research model generates the continuous positioncoordinate data of each weapon in less than 3 milliseconds; incontrast, a typical CCD-based tracker would require over 16milliseconds. Due to the high-speed tracking capability of thePSD-based tracker, the WTET allows for accurate tracking and

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VIDEO PROJECTION SCREEN

UNIFORMIR SPOT•FROM

WEAPON

VIE LINE

BACKGROUND

, VISIBLE FILTER

MOUNTED O IMAGING OPTICSIR SPOT- "" PSD

Figure 3. Infrared Spot Tracker Imaging Diagram

trigger-pull synchronization for up to nine trainees.

The system computer synchronizes the time-multiplexedenable signal for each weapon with the 12-bit analog to digitalconversion of the IST position data. Once the system computerknows the position coordinates of a weapon, it can compare thatdata to the stored coordinates of active targets on the projec-tion screen at the time of trigger pull. If the IST positiondata matches the coordinates of a target on the projectionscreen, a hit is recorded for that weapon. A high-speed videographics board utilizing "active windows" enables the targets todisappear when hit without affecting the ongoing scenario. Theability to have targets disappear after they have been hit isvery important in a team trainer. Other team members now knowthat this target has been hit, and they can adjust theirstrategy accordingly.

A block diagram of the WTET testbed components is illus-trated in Figure 4.

The trainees are encouraged to take sensible cover as theywould in the real world while engaging targets displayed on thevideo projection screen. Each trainee wears a Multiple Inte-grated Laser Engagement System (MILES) torso harness containing

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OPTICAL DISC

113232C O41E

VIDEOQRW PROJECTOR

r--SAMPLER

V sIEO ALALO RU ERIL

AD AN.OGI SURROUND

PROCESSOR

/0AL V ¢ L S SOUND SYSTEM

386 PERSONALCOMPUTER A/oCL_ O FOUR TRIUCIER

"C SOARO *CONTROLLER RIFLE 2

CIRCUIT

NTSC SHODOACKSHOOTBACK IREDSCIRCUIT

NTSC IWRAREDSPOT TRACKER

Figure 4. WTET System Block Diagram

infrared detectors and an alarming device to indicate if he hasbeen hit by an on-screen aggressor. The on-screen aggressorshoot-back is simulated by using an array of infrared emittingdiodes (IREDs) located above the video projection screen. EachIRED is pointed in a particular sector within the trainingexercise room so that all exposed areas are within the field offire of the on-screen aggressors. The individual IREDs areturned on and off by the system computer corresponding to wherethe on-screen aggressor is pointing his weapon. If a traineedoes not take cover while in the field of fire of the on-screenaggressors he will be illuminated with infrared energy. Theinfrared detectors positioned on the MILES torso vest willdetect the incident IR energy and activate an alarm to indicatethat the trainee has been shot by the on-screen aggressor. Oncea trainee has been hit he is considered dead and his weapon isdisabled.

After a training session is over, the video scenario isplayed back in slow motion. The system computer shows thecontinuous pointing location of each weapon by graphicallydisplaying color coded icons representing the continuous ISTposition data stored by the system computer during the actualtraining session. Hit and miss shot locations are indicated bychanging the color of the icons.

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A complete sound system has also been developed to simulatethe actual acoustical training environment of each scenario. AnAnalog/Digital sampler digitizes, stores and plays back thebackground sounds as well as the synchronized gun shot soundscorresponding to the trainees and the on-screen aggressors. Thesampler is under the control of a Musical Instrument DigitalInterface (MIDI) port interfaced to the system computer forproper timing and synchronization.

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18


SYSTEM DESCRIPTION

SCENARIO AND SOFTWARE DEVELOPMENT

Several software programs, written in C under the MS-DOSoperating system, control both training scenario development andpresentation for the WTET. Computer software control of theoptical disc player allows automated scenario development andrapid aggressor selection. Control of the weapon trackingsystem hardware provides continuous tracking of each weapon'saimpoint and status. Various functions of the video graphicsadapter allow interactive control of the on-screen aggressors.Commands transmitted by MIDI (Musical Instrument DigitalInterface) provide sound effects as each scenario progresses.Synchronous control of the WTET system hardware based on thescenario content creates the training session.

Scenario Development

Moving video footage from an optical disc player generatesthe WTET aggressor threat. Scenario development begins withformulation of a script for the aggressor force. The scriptdescribes aggressor actions including timing and movement withinthe camera's field of view. Creating interactive aggressors (i.e., aggressors disappear when hit) imposes ,some restrictionson the video recording process. Scenario constraints includemaintaining a stationary camera, restricting overlap of aggres-sor targets, and sustaining consistent lighting. However, theseconstraints enable instant feedback through disappearing targetsand increase flexibility in aggressor selection.

Creating aggressor targets which disappear when hitrequires consistency in background and lighting of the videoimage. These factors are crucial during portions of a scenariowhere aggressor targets are visible and engageable. Eachscenario's moving video can be sectioned into segments in whichan aggressor appears into view, engages the trainee, and thentakes appropriate cover. Dividing a scenario's moving videofootage into sections maximizes optical disc storage by elimi-nating nonessential video. During each section, camera stabili-ty and lighting consistency allow the video graphics adapter toadd or remove aggressor targets as a training session progress-es.

Depending on the type of scenario, movement of the cameramay be necessary to recreate the threat situation. For example,a security force clearing a building would maneuver through thebuilding. Therefore, maneuvering the camera is necessary toproduce this type of scenario. To allow for this type of cameramovement the scenario script specifies locations where aggressor

19


engagements occur. Before aggressors are introduced into thescenario, the camera position is fixed at a designated locationwhich maintains a consistent background. From this location,multiple aggressor actions are recorded. The camera is thenmaneuvered to the next designated area and the process isrepeated. Recording multiple aggressor actions at each locationenables the training session to branch based upon the traineeperformance. These video segments of aggressor engagement andcamera movement are edited and transferred to optical disc.

Scenario Processing

After transferring a scenario's video segments to opticaldisc, a program generates a detailed description or map of eachsegment. This program automates this mapping process by usinga user-friendly menu system, graphical overlays under mousecontrol, and optical disc control functions. The mappingprocess generates a data file specifying each video segment.First, the optical disc is scanned to locate the start frame fora video segment. Once located, the number of aggressor targetsis identified and entered. For each target, a rectangle isdrawn around the area which covers the complete exposure or pathof the aggressor target during the video segment. This rectan-gle defines the live video window used to interactively controleach aggressor. By single stepping the optical disc both hitareas and shootback directions are identified for each frame ofthe video segment. Specifying a unique filename for eachsegment's mapping data creates a data base whith describes everyvideo segment applicable to a specific training scenario.

Interactive Targets

The purpose of this detailed mapping process is to allow avideo graphics adapter to interactively present the aggressorforce during a training scenario. The optical disc playercomposite video output is converted to an analog RGB signal forinput to the video graphics adapter. The video graphics adapteris configured for a 756 x 972 pixel display buffer which iscapable of storing two high resolution video frames, eachcontaining 756 x 486 pixels. The video graphics adapterperforms real-time capture of the video image at 16 bits perpixel. This 16 bit per pixel format allows the display of bothlive video and high resolution graphics. Addition and removalof aggressor targets is accomplished by opening and closing livevideo windows within the captured video image. Closing a livevideo window while using a double buffer drawing techniqueallows instantaneous removal of the aggressor target.

Tracking System Software

Software control of the tracking system hardware allowseach weapon to be continuously monitored during a training

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scenario. The hardware is comprised of a newly developedinfrared spot tracker based on a position sensing detector(PSD), an analog to digital (A/D) conversion board, a highpowered infrared emitting diode (IRED) mounted on each weapon,and control electronics. Each weapon's aimpoint, trigger switchposition, selector switch position, and magazine reload indica-tor are sampled at approximately 60 Hz.

A periodic interrupt procedure controls the weapon trackingprocess. The A/D board is configured to acquire the IST's fouranalog outputs with direct memory (DMA) data transfer, whichrequires minimal CPU overhead. A programmable interval timerprovides timing signals which sequence the process. Theprogrammable interval timer is configured to generate both a 3millisecond periodic interrupt (rate generator) and a 2 milli-second one shot delay. Activated every 3 milliseconds, aninterrupt service procedure controls the weapon trackingprocess.

The timing sequence for a two weapon system is shown inFigure 5. At the start of the first interrupt cycle weaponone's IRED is activated and the programmable oneshot is re-triggered. After 2 milliseconds the infrared spot tracker's

Interrupt Cycle 1 2 3 4

PeriodicInterrupt

Weapon21[ I IRt*E

weapon 2 BRED____ _ _ _

Programmable ~ -~~~One-shot

G - Weapon I A/D conversions ( DM data transfer

@ - Weapon 2 A/D conversions (DMA data transfer

im - Interrupt Period - 3 msec.

- Tracker Settling Time - 2 msec.( one-shot time out delay )

t - Tracker Sampling Time - 640 usec.8 repetitive position samples

Figure 5. Timing Sequence for Tracking Weapon Aim Points

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four analog outputs have settled and reflect the horizontal andvertical position of weapon one's aimpoint. Simultaneously, theprogrammable oneshot output gates the A/D board to acquire thetracker's four outputs. Each output is converted at 50 kHz to12-bit digital values. During approximately 640 microsecondsthe four outputs are sampled eight times and the 12-bit resultsare DMA transferred into a data buffer. Upon entry of thesecond interrupt cycle, weapon one's IRED is turned off and theA/D data buffer is monitored. Comparing data buffer elements toa voltage threshold determines the presence of the weapon one'sinfrared spot. If detected, the tracker's raw data is averaged.Calculations are then used to determine weapon one's non-scaledhorizontal and vertical positions. In addition, weapon one'sswitch positions are updated. Similarly, weapon two's IRED ismodulated during interrupt cycle three and positional data isgenerated during cycle four.

Repetition of this interrupt sequence provides continuousupdate of each weapon's aimpoint and switch status. Twotechniques enable this tracking process to require minimal CPUoverhead. First, multiple conversions of the tracker's fouranalog outputs are performed with DMA data transfer. Second, aperiodic interrupt procedure, essentially a background task,performs both tracking system controls and basic position datacalculations.

Presently, a simple weapon zeroing procedure is used tofind coefficients and offsets for two first order equations.These equations are then used to convert the raw tracking systemdata to x and y screen coordinates. This method, however, doesnot maximize the accuracy and stability of the tracking systemhardware. Several future improvements will increase theaccuracy of the tracking system. First, the weapon alignmentalgorithm will account for the tracker's viewing angle, thetracker's lens distortion, and the video projector's linearity.Second, optimizing the tracker's imaging optics will increaseaccuracy. Furthermore, increasing the A/D conversion rate toacquire more samples and improving data conditioning algorithmswill improve tracking system performance.

Currently, the WTET is configured as a two weapon system.However, the weapon tracking process is expandable. Additionalweapons can be added while achieving sufficient sampling rates,up to 9 weapons at greater than 30 Hz. Also, a larger field ofview can be covered through the use of multiple infrared spottrackers.

Scenario Presentation

The WTET system computer controls the presentation of eachscenario's moving video footage through a RS-232 communicationlink to the optical disc player. Synchronizing the moving video

22


footage to the simulation software provides an event timingmechanism. Each moving video segment is synchronized byinitiating the optical disc playback operation and monitoring avertical sync counter on the video/graphics board. Duringoptical disc playback the current frame number is instantlyaccessible by reading this counter. This provides an accurateand efficient method for synchronizing the simulation software.In comparison, polling the optical disc player through the RS-232 port requires too much time and CPU overhead.

During a training scenario various segments of moving videofootage are presented to the trainees. Target mapping and hitareas are read from a data file located on ramdisk. Thesimulation is controlled by synchronizing scenario mapping datato the interrupt generated rifle tracking data. An aggressortarget is removed from the training scenario when a traineesuccesfully fires his weapon within the hit area defined for thecurrent video frame. Weapon sound effects are generated basedon both rifle tracking data and aggressor target shoot-backdata. Weapon aim points, shot locations, and status arecontinuously stored for each trainee during the trainingsession. After a training session is completed, this informa-tion is provided to the trainees for review.

Scenario Replay

The performance of each trainee is evaluated based on thenumber of rounds expended, the number of aggressor targets hit,and a visual replay of each weapon's movement with shot loca-tions. Upon completion of a training scenario a replay functionperforms a slow-motion display of the scenario with graphicaloverlays. During replay a different colored circle representseach weapon's aim point. Shot locations are indicated bychanging the weapon's aim point color and briefly pausing thevideo playback. An aggressor target hit, a semi-automatic firemiss, or an automatic fire miss is indicated by changing the aimpoint color to red, blue, or green respectively. The ability tocontinuously track each weapon's movement enhances both individ-ual and team performance measurements.

AGGRESSOR SHOOT-BACK SYSTEM

The implementation of the aggressor shoot-back systemconsist of three subsystems: 1) the shoot-back bar, consistingof a horizontal IRED array located just above the video projec-tion screen, 2) the IRED modulator/driver circuitry located inthe proximity of the system computer, and 3) the infrareddetection circuitry located on the back of the MILES torso vest.The system computer turns the IRED modulator/driver on and offin synchronization with the on-screen aggressors action. If theon-screen aggressor is shooting his weapon towards a particular

23


sector then the corresponding IRED is enabled and modulated,forcing the trainee to take cover while in that sector.

The shoot-back bar consist of, but is not limited to, nineIREDs with built in lenses placed horizontally across the top ofthe video projection screen. Figure 6 illustrates the shoot-back IRED array used to simulate aggressor shoot-back. Theindividual IREDs are mounted on a ball and socket swivel mount

IRED1

Swivel Mount "

wiring

harness

IRED MODULATOR

and DRIVER

CIRCUITRY

IR BEAM PATIERN ISystem computer

control lines

Figure 6. Shoot-back IRED Array Mounted Horizontally AboveVideo Projection Screen

for optimum adjustment. The IREDs have a half intensity beamangle of less than six degrees. The small beam angle allows theindividual IREDs output energy to be strategically directedthroughout the training exercise room.

The IREDs are modulated by a 1.6 Khz square wave whenenabled by the system computer. Modulating the IREDs allows thedriver circuit to pulse more current through the IRED for ahigher output power as well as increasing the detectivity of thelow level IR signal by the detection circuitry.

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The modulator circuit consist of a LM555 timer integratedcircuit operating in the astable oscillating mode. The TTLoutput voltage of the LM555 timer supplies the gate voltage foran Enhancement Mode Junction Field-Effect Transistor (EMJFET)which then sources the required current to IRED.

The IR detection circuitry consist of eight infrareddetectors connected in parallel and strategically placed on theMILES torso vest. The original MILES electronics is replacedwith specific electronics to detect the modulated infraredenergy from the IRED array used to simulates shoot-back. Ablock diagram of the IR detection system is shown in Figure 7.

IR ENERGY

-- Z_ MILES TRANSIMPEDANCE BANDPASSDETECTORS AMPLIFIER FILTER

DISABLE KEY

Figure 7. Block Diagram of IR Detection Circuitry

A low noise transimpedance amplifier converts the outputcurrent from the photodetectors into a proportional voltage.The infrared signal voltage is amplified and filtered with afourth order bandpass filter. The output signal from thebandpass filter is rectified and demodulated with a lowpassfilter. The lowpass filtered signal is compared to a referencevoltage to determine if the trainee was hit by an on-screenaggressor. If a sufficient signal is detected to indicate ahit, then an alarm sounds to indicate to the trainee he has beenkilled. The alarm is latched with an SCR; therefore the traineemust disable his weapon to utilize a "key" to turn off the hitindicator alarm.

SOUND SYSTEM

Sound effects are generated during a training scenario.The sound system provides sounds of the various weapons beingfired by both the trainees and their on-screen adversaries.Also, background sounds are generated to increase realism duringa training scenario. The heart of the sound system is a digital

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COMPUTER--

SOLO LEFT RIHT DISK REAR SPEAKERSS! L! RI

L+S t R+ L R

AMPLIIER AMPLIFIER

PROJECTIO" SCREEN

~ FRONT SPEAKERS

COMPONENTS SPEAKER CONFIGURATION

Figure 8. Sound System Components and Speaker Configuration

sampler module. The sampler digitizes, stores and plays backsound effects under the control of a MIDI (Musical InstrumentDigital Interface) port. A MIDI controller card is installed inthe system computer. During a scenario the computer sendsappropriate commands to the sampler via the MIDI interface. Thesampler creates the appropriate sounds and sends to amplifierswhich drive foreground and background sounds. Mixers are usedto control dispersion between the foreground and background.Figure 8 shows the major sound system components and speakerconfiguration.

Using a sampler module with an external storage deviceallows a multitude of sound effects to be available for increas-ing realism in training. The sampler uses both a 3.5 inch 800Kbyte floppy drive and an 80 Mbyte SCSI hard disk to storedigitized sounds. Depending on sample rate, the 80 Mbyte SCSIdisk can hold as much as an hour or more of sampled sounds thatcan be mixed and sequenced by the sampler to generate essential-ly unlimited amounts of audio feedback. The sounds that aredigitized and recreated by the sampler come from a variety ofsources. Some are commercially available sound effects pur-

26


chased on compact disk. Some are recorded in the field usingboth regular and DAT tape recorders. Still others may besynthesized. The Army's HEL provided several recordings ofactual artillery rounds exploding. The sounds have been editedand sometimes normalized before being digitized. Realism andvariation in training scenarios is enhanced by adding computercontrolled sound effects.

WEAPON TRACKING SYSTEM

An infrared spot tracking system is used in the WeaponsTeam Engagement Trainer (WTET) to determine the continuous X andY position coordinates representative of where each trainee ispointing his weapon.

Commercially available infrared spot tracking systemstypically consist of a Charge Coupled Device (CCD) video camerainterfaced to a digital frame grabber operating at standardvideo rates. A suitable lens system images the tracking area(i.e., video projection screen) onto the CCD imaging sensor.The frame grabber digitizes each frame of video data collectedby the CCD camera. This data is further processed with digitalsignal processing hardware as well as proprietary softwarealgorithms to find the position coordinates of the imaged IRspot.

The CCD imaging sensor consists of a two-dimensional matrixof discrete photodiode elements. A 10-bit (1024 horizontalelements x 1024 vertical elements) CCD imaging sensor has overone-million individual photodiode elements that convert theincident illumination into a proportional quantity of electricalcharges. The electrical charges are sequentially transferred toa readout stage. At the readout stage, each electrical chargeis converted into a proportional voltage signal. This voltageis further amplified to give a low impedance output videosignal. The charge transfer image is generated in one videoframe requiring over 30 milliseconds.

For accurate tracking and trigger-pull synchronization theposition coordinates of each weapon should be updated at leastevery 3 milliseconds with a resolution of 10 bits. The CCD-based tracking system discussed above requires over 30 millisec-onds to sequentially sample the weapon position coordinate.This time frame is obviously much too long for the WTET'sapplication of multiple trainees. Another disadvantage of theCCD-based tracking system is the high cost. A complete low-endCCD-based tracking system typically cost over $10,000.

To overcome the disadvantages of the CCD-based trackingsystem, we developed a low-cost, high-speed, IST utilizing atwo-dimensional lateral-effect photodiode, the Position Sensing

27


Detector (PSD). The PSD is not a discrete charge transferdevice such as the CCD, but rather a continuous analog outputdevice. In contrast to other types of position sensing photodevices such as CCD detectors, the PSD offers higher resolution,faster speed, larger dynamic range, and simpler signal process-ing.

The PSD is a photoelectronic device utilizing the lateralphoto-effect [1] to convert an incident light spot into continu-ous position data. The lateral photo-effect occurs because ofthe diffusion properties of separated charge carriers along auniformly or nonuniformly irradiated p-n junction. The currentdiffusion in a fully reversed-biased p-n junction occursprimarily due to the external collection of generated chargecarriers through finite loading impedances [2]. Woltring [3]showed that for the two-dimensional fully reversed-bias PSD withzero loading impedance, there is an analytical linear relation-ship between the output current and the light spot positionalong the pertinent axis.

The basic construction of a two-dimensional lateral-effectPSD consist of p and n doped layers of silicon forming a p-njunction. The front side of the PSD is an implanted p-typeresistive layer with two lateral contacts placed opposite eachother. The back side of the PSD is an implanted n-type resis-tive layer with two lateral contacts placed orthoganol to thecontacts on the front side. The p and n layers are formed byion implantation to ensure uniform resistivity. As an example,high resistivity silicon can be implanted with boron on thefront side and with phosphorus on the back side. The p-njunction is light sensitive; therefore, incident light willgenerate a photoelectric current which flows through the ionimplanted resistive layers. Electrodes are formed at the edgesof the PSD by metalization on the ion-implanted resistivelayers. Transimpedance amplifiers serve as a finite loadimpedance to convert the generated charge carriers to a positiondependent voltage.

The two-dimensional lateral-effect PSD used in the designof the IST is able to detect an incident light spot position onits rectangular surface with a maximum non-linearity of 0.1percent. Figure 9 illustrates the two-dimensional PSD struc-ture.

The photoelectric current generated by the incident lightflows through the device and can be seen as two input currentsand two output currents. The distribution of the outputcurrents to the electrodes determines the light position in theY dimension; the distribution of the input currents determinesthe light position in the X dimension. The current to eachelectrode is inversely proportional to the distance between theincident light position and the actual electrode due to the

28


IIx1~ ~~~ 1..

/ "... x2

Incident Light

Figure 9. Two-Dimensional PSD Structure

Incident Lightoriginf

R1 I R2

lxi I L + X a x2

L L

Figure 20. one-dimensional PSD Position Model

uniform resistivity of the ion implanted resistive layers. Aone-dimensional PSD position model is shown in Figure 10. Thisillustrates how simple algebraic equations determine theincident light spot position. This model assumes a zero ohmload impedance and a theoretically uniform implanted resistivelayer.

Referring to Figure 10, the distance between electrodes 1

and 2 is 2L, and the uniform resistance is R. The distance from

29


electrode 1 to the position of the incident light spot is L - X,and the resistance is R. The distance from electrode 2 to theposition of the incident light spot is L + X, and the resis-tance is R2. The photocurrents produced at electrodes 1 and 2are proportional to the incident input energy and inverselyproportional to the uniform resistant path from the incidentlight to the electrodes. The total photocurrent produced bythe input energy is 10. The sum of the output currents I, and 12is equal to I .

From Figure 10, we can derive the following equations,

11 0 R2(1)Ri + R 2

12 = 0 Ri (2)

R i + R 2

The resistance of R, and R2 is proportional to the lineardistance that R, and R, represent since the resistive layer isuniform. In general, the resistance of a given material isgiven by

R = PL (3)A

where,p = resistivity of the material in ohms-meterL = length of material in metersA = area of material in meters

2

IF we now define R, and R, with respect to p, L, and A we obtainthe following expressions:

R,= p(L-x) (4)A

R2 : p(L + x) (5)

A

Substituting equations (4) and (5) into equations (1) and(2),

30


the output currents I, and I, can now be written as:

I, 2 TO L + (6)2L

1210 L (7)

We can eliminate the dependance of equations (6) and (7) on I, bydividing the difference of 11 and 12 by the sum of I, and 12. Wecan now solve for the X position (X,) of the incident inputenergy relative to the chosen coordinate system shown in Figure10.

111 -2 (8)1ii + 12

Substituting equations (6) and (7) into equation (8) gives

XP - X (9)L

Equation (9) gives the linear position of the incident energysource independent of its intensity. This feature is veryimportant since the intensity of the focused energy source onthe PSD surface is rarely constant in a typical application. Thetwo-dimensional PSD position model operates analogous to theone-dimensional PSD position model except that there are now twouniform resistive layers and four electrodes. The top resistivelayer is used to divide the output currents into I, and I,,. Thebottom resistive layer is used to divide the input currentsinto I,, and 1 2 . The four currents IY1, IY, I.,,, and I., determinethe x and y position coordinates of the incident energy sourceanalogous to the one-dimensional case.The X position coordinate is given by

I, - I,I X+ IX 2 (10)

The Y position coordinate is given by

Y = -Y Iy (11)Ypos Iy + 1yy1 y2

31


Equations (10) and (11) clearly show that we may obtain the Xand Y position coordinates of an incident energy spot focusedonto the PSD surface by a simple manipulation of the outputphotocurrents.

Since it is the magnitude of the photocurrents that we wishto manipulate we can represent the four output currents withfour output voltages as long as we preserve the magnitudeinformation. We now have the following design equations:

=P X 1 2 X 2 (12)

0 V, +V,

= YI Y2 (13)

The design of the analog electronic subsystems for the PSD-based tracker is dependent on the amount of reflected IR energycollected and focused onto the PSD surface. This energy is afunction of the IR energy source mounted on the weapon, theprojection screen reflectivity, the angle of incidence of thecollimated energy source to the projection, screen, and thecollecting optics used to collect and focus the reflected IRenergy onto the PSD surface.

The electronic design of the IST consist of six functionalblocks as shown in Figure 11. The lens system as previouslydiscussed images the video projection screen onto the PSDsurface, thereby imaging the modulated IR spot on the PSDaccordingly. The PSD's photo-voltaic effect converts themodulated IR energy focused on its surface into four separatephotocurrent outputs. The voltage representation of themagnitude of the photocurrent outputs are used to calculate thespot position on the PSD surface according to equations (12) and(13).

The photocurrent outputs from the PSD electrodes areterminated into low noise transimpedance amplifiers. Figure 12illustrates a typical dc coupled transimpedance configurationwith a bias potential for reverse biasing the p-n PSD junction.

32


visible light tronsimpedonce bond-pass precision low-pass

blocking filter amplifiers filters full-wove filters

rectifiers (demodulator)

o .= .. ..... ...... .. .

optical system IR spot

Figure 11. Infrared Spot Tracker Block Diagram

In this configuration, the PSD views a load impedance Z,(s)

defined as

Zs)= Rt(14)SI A(s) [RfC s + 1]

where,A(s) is the amplifier's open-loop transfer functionw is the modulating frequency of the IRED

R! is the feedback resistorC1 is the feedback capacitor

To maximize the lateral photo-effect and the linearity ofthe PSD output currents, the terminating load impedance ZL(S)should be much less than the position sensing sheet resistanceof the PSD [3]. As can be seen from equation (14), this limitsthe magnitude of the feedback resistor and the modulatingfrequency of the IRED for optimum performance.

The transimpedance amplifier converts the generatedcharge carriers from the PSD to a representative voltage.

33


KVos)

POSITIOl CURl1T +

FROM PSD .LevY

DIAS FOR CATHODE

SIDE OF PSD

Rb

Rbb

Figure 12. DC Coupled PSD/Transimpedance AmplifierConfiguration

The output voltage of the transimpedance amplifier is givenby,

V, (S) = I(S) [ + v (s) + Vo (S) (15)Rf Cfs +1

where,Vo(s) is the output voltage of the amplifierI(s) is one of four modulated PSD output currentsV.(s) is the total output noise voltage including

shot noise, thermal noise, and amplifier noiseV"'(s) is the total offset voltage due to the dark

current and amplifier bias currents

The low-level dc coupled output voltage from the trans-impedance amplifier is band-pass filtered with a wide-bandfourth order Butterworth filter. The band-pass filter suppress-es the unwanted background signal (e.g., room lights), thereverse bias voltage, the offset voltage, and the output noisefrom the transimpedance amplifier while amplifying the 10 KHz IRsignal from the trainee's weapon.

34


The band-pass filtered signal is further amplified andconverted back to a modulated dc voltage level by a precisionfull-wave rectifier circuit. The dc restoration enables theoriginal dc modulated 10 KHz photocurrent magnitude informationto be retained as a dc modulated 20 KHz time varying voltagewith a nonzero average.

The full-wave rectified signal is low-pass filtered(demodulated) with a fourth-order Bessel filter to remove the acFourier components of the waveform while retaining the dc magni-tude information. A cutoff frequency of 500 Hz was chosen tominimize the transient response of the low-pass filter whilestill allowing for adequate filtering.

The analog output voltages from the low-pass filters areused to calculate the incident spot position relative to the PSDsurface according to the following equations:For the X position coordinate,

pos X1 X2 (16)

and for the Y position coordinate,

ypos - Y2 (17)YPS VY + VY

where, V.., V.2, V),, and Vy. are the analog output voltages repre-senting the photocurrent magnitude information from the PSD.

A high-speed analog to digital converter board converts theanalog output data from the IST to a 12-bit digital signal. Thesystem computer performs the simple calculations to determinethe X, and Yp. coordinates of the IR spot based on equations (16)and (17). An algorithm based on statistical averaging andposition probablity is performed over a number of samples toincrease the effective resolution to 10 bits.

The objectives of the IST design were to maximize the speedand resolution with which the tracker can determine the X and Yweapon position coordinates for up to nine trainees. The PSD-based tracking system requires less than 3.0 milliseconds togenerate the position coordinates of an imaged IR spot with aresolution of 10 bits; in contrast, a typical CCD-based trackingsystem requires over 30 milliseconds with similar resolution.Due to the simplicity of the PSD operating characteristics and

35


circuit design, a PSD-based tracking system can be built to costseveral orders of magnitude less than a similar CCD-basedtracking system.

36


CONCLUSIONS

Increased realism and effectiveness in simulator-basedweapons team training can be realized through implementation ofinteractive aggressor targets and a high speed weapon trackingsystem. Continuously tracking weapon aiming points for allmembers of a fire team expands performance measurement capabili-ties. Training effectiveness and realism is also increased byinstantly removing disabled aggressors from the trainingscenario and requiring trainees to take appropriate cover whenan aggressor returns fire. This results in an increase incommunication and awareness between members of the trainingteam. In contrast, previous training systems did not requiretrainees to seek appropriate cover. Also, aggressor targetswere not removed from the progressing training scenario whenthey were successfully engaged and disabled by trainees.

Prior to the implementation of the PSD-based trackerdesign, the replay scenario data collection process for two ormore trainees, utilizing a CCD-based tracker, was only capableof generating the aiming point for each trainee at trigger-pull.This limitation, due to the relatively slow data rate of CCD-based trackers, severely diminishes the effectiveness in whichthe trainee performance can be evaluated. The PSD-based trackeroffers a significant advantage over the CCD-based tracker inmeasuring the dynamic performance of multiple,team members in ateam engagement training system.

To overcome the disadvantages of the CCD-based trackingsystem, NTSC developed a low-cost, high-speed, infrared spottracker which utilizes a two-dimensional lateral-effect photodi-ode, or Position Sensing Detector (PSD). The PSD is not adiscrete charge transfer device such as the CCD, but rather acontinuous analog output device. In contrast to other types ofposition sensing photo devices such as CCD detectors, the PSDoffers higher resolution, faster speed, larger dynamic range,and simpler signal processing.

37



38


RECOMMENDATIONS

The authors recommend development of an advanced prototypewhich would further increase realism in the training environ-ment. An engineering model could be developed for potentialuser tests to determine both training and cost effectiveness.This engineering prototype could enhance both realism andperformance measurements by:

(1) eliminating cords interfacing weapons to computers.(2) allowing up to 9 trainees to rehearse tactical

situations.(3) using multiple screens to increase trainee mobility;(4) tracking each trainees movements within the training

area to both control shoot-back and enhance feedback.(5) presenting results in a split screen display to show

both trainee movement, aggressor actions, and othersresults.

(6) analyzing the performance results using an expertsystem.

(7) using an expert system to generate aggressor actionsbased on team performance.

39



40


REFERENCES

G. Lucovsky (1960). Photo-effects in nonuniformly irradiatedpn junctions. Jornal of Applied Physics, 31, 1088-1095.

W.P. Connors (1971). Lateral photodetector operating in thefully reverse-biased mode. IEEE Trans. Electron Devices,18, 591-596.

H.J. Woltring (1975). Single-and Dual-Axis lateral photodetec-tors of rectangular shape, IEEE Trans. Electron Devices,22, 581-586.

41



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