AOC International Exhibition and Symposium 2008

Simultaneous IR and RF modelling and simulation of platforms, threats and countermeasures using CounterSim

This presentation is unclassified and does not contain controlled technology

Richard Ayling, Brian Butters, Nic Millwood, Roy Walmsley

Chemring Countermeasures Ltd, Salisbury, UK

Presented by Brian Butters

brian.butters@chemringcm.com

Presentation order

IntroductionThe joint IR and RF platform model using Modified Open Inventor [1] Format Descriptions

3D model formatIR definitionRF definition

Validation of the IR and RCS definitionsExample scenarioConclusions

[1] Open Inventor open source licence at http://oss.sgi.com/projects/inventor/

Chemring modelling and simulation

Chemring Group companies provide expendable countermeasures for air, naval and land applications.Chemring modelling and simulation aims are:-

Understanding IR/EO and RF threat characteristics Development of expendable countermeasures and deployment tactics

Platform manoeuvreDispensing sequencesLocation and orientation of dispensers and expendables on platformsEnvironment effects – wind - atmosphere

Understanding the use of our expendables with other countermeasures such as

On-board IR and RF – e.g. DIRCM, jammersExpendable active RF countermeasures

Chemring modelling and simulation capability

Needs to coverAir, naval and land platformsIR and RF threatsIR and RF expendable countermeasures

Needs to beDriven by product development and sales and marketing needsCost effectiveVerified, validatedRespected in the wider defence community

Developed since 1986 by a team of software engineers with practical experience of expendable countermeasures development and user trials

Many models and many simulation applications

Many government R&D labs developed their own narrow specialised sets of models and simulation applications e.g. Air IR, Naval IR, Air RF and Naval RFInitiatives such as High Level Architecture (HLA) seek to promote

Coherent development of distributed interoperable and reusable simulation representationsData standardization to provide common, interchangeable representations of data in M&SReuse of information, algorithms, and modelsPotential difficulties include data format, data interchange and timing issues[2]

Composability[3] is “the capability to select and assemble simulation components in various combinations into simulation systems to satisfy specific user requirements”

SISO Base Object Model (BOM) seeks to facilitate interoperability, reuse, and composability in the HLA Federation Development and Execution Process

[3] Petty, Dr. Mikel “Composable M&S Workshop” Virginia Modeling, Analysis, and Simulation Center July 9-10, 2002,

[2] Macal, C., Li, Z., Nevins, M., Sutton, M., “The Implications of Developing an HLA-Compliant Logistics Model -Lessons Learned”

CounterSim design

Uses IR and RF in the same framework or containerNo current requirement to be HLA compliantStructure allows future extension to visible and UVComposability achieved with

A comprehensive set of .ocx model objectsAbility to link via an interface script to any external dll

dll typically compiled from Matlab / Simulink models

External Models

Chemring or other CounterSim users may have other external models (possibly already validated)External models can be used with CounterSim and can consist of

Complete items e.g. Aircraft, Ship, Missile etcParts of items or sub items e.g. Autopilot, MAW, Signal Processing, Warhead etc

Implementation unspecificMatlab/SimulinkProprietary code e.g. FORTRAN, C, C++ etc

Dynamic Link Library (DLL) Interface

External models

External ModelsExternal models

Either side blind of the

otherCounterSim

Item

CounterSim Item

CounterSim Item

CounterSimScenario

CounterSim Item

CounterSimScenario External ModelDLL

Interface

External ModelDLL Interface

3D model strategy

The early CounterSim IR platform modelling used Open Inventor because

The Open Inventor toolkit allows the library of objects to be modified and extended in CounterSim - derived nodes were first used for IR properties.The text files can be easily edited, components can be copied and re-used.3D models of platforms are readily obtained in the public domainin different 3D file formats and easily converted when necessary.

Example IR and RF models and engagement simulations

Models usedAn AMX fighter bomber with unclassified but typical IR and RCS signatures A generic monopulse radar modelA generic Manpad with a rising sun reticle tracker and no counter countermeasures (CCMs)Chaff, ejected in a typical pulsed sequenceConventional MTV flares

The models used are unclassified and generic.No conclusions should be drawn about real life outcomes compared with the example scenario that is used later

Aircraft model preparation

Prior to assigning an IR signature to a platform the Open Inventor file is edited and the number of polygons and sub-objects optimised to have

Sufficient resolution to fit the measured dataNo more objects than necessary

This places an unnecessary burden on the IR calculations and therenderingHence the simulation is slower

The AMX example 3D model originally had a polygon count of 16,093 with 93 sub-objects.In the AMX example there are now 49 sub-objects.

Setting IR properties

An SoIRMaterial node is added to describe temperature and emissivity of a surface as a grey body.

Alternatively a normalised spectral radiance file is used if the emissivity is wavelength dependant.

The SoIRMaterial values are conveniently set using the IR viewer application developed by Chemring.

This provides an image editor mode and false colour views in any user selected IR waveband.Dialog boxes enable the easy entry of temperature, emissivity or spectral radiance definitions.

A more a skilled user can set the values in a text editor.CounterSim uses additional IR viewer nodes in scene-graph to specify waveband, radiance range and other parametersWhen calculating the surface radiance during rendering, the scaled spectrum is integrated over the viewer waveband to determine theradiance.

IR properties edit with the IR viewer

DEF REAR_COCKPIT_CANOPY Separator {

SoIRMaterial {

spectralType TEMPERATURE

ambientColor 0.2 0.2 0.2

diffuseColor 0.2 0.2 0.2

specularColor 0.2 0.2 0.2

emissiveColor 0 0 0

shininess 0.2

transparency 0

temperature 20

emissivity 0.5

}

RF modelling

Methods of modelling RCS in engagement simulations with reasonable fidelity and efficiency were researchedHughes [4] used a decision analysis is used to choose between 4 modelling methods - Real Data, a Scatterer Model, a Statistical Model and a Structural Model

The most practical appears to be the use of scatterer models Scatterers allow the radar cross section to be calculated quickly for any angle and at any frequency.

Correlations between cross section and motion are inherent in the modelComplex cross section patterns may be represented easily with a moderate number of scatterersThe effective resolution of the data can be increased by interpolating between measured sample pointsThe interpolation is non-linear and is related to the arrangement of the scatterers The interpolated data therefore appear as a realistic radar cross section pattern

[4] Hughes, Evan James. “Radar Cross Section Modelling Using Genetic Algorithms” PhD diss., Cranfield University 1998.

Setting RF scatterer prperties

The Open Inventor reflectors file contains cone and sphere nodes that represent the reflectors.The reflectors file is easier to develop if it references the 3D file of the target

Allows the position of the cone and sphere reflectors to be seen against the target body and how they correspond to structural features.The 3D file reference can be left out of the reflectors file used by CounterSim but makes little difference to the file size and no difference to the simulation.

It is separate from the IR definition file because

It is the simplest way to avoid the cones and spheres being seen in the IR imageThe much smaller reflectors file can be more easily edited when separate from the larger IR definition file.

Cone and sphere reflectorsCones are used to represent directional reflection points on the target.

The apex gives the position of the reflection pointThe direction of the cone axis gives the direction of peak reflectionThe cone angle gives the 3dB width of the reflection patternThe height of the cone gives the square root of the RCSPattern is modelled as a single lobeThe reflector’s RCS is reduced by the cosine of the angle between the view direction and the peak direction, raised to a power. The power is chosen to give the specified pattern width

Spheres are used to represent omni-directional reflection points on the target.

The position of the centre gives the position of the reflection pointThe radius of the sphere gives the square root of RCS of the reflector

Phase for cones and spheresThe change in phase on reflection is given by the red value of the diffuse colour.The phase change is given by the red value multiplied by 360°

0.5 ≡ 180° phase change1.0 ≡ 360° phase change.

0

30

60

90

120

150

180

210

240

270

300

330

0

0.25

0.5

0.75

1

LobeCone

Relative Directional Reflection for a 60°cone angle

Inventor V2.1 asciiSeparator {

File {name "AMX-A1.iv"

}DEF Cone0 Separator {

Transform {translation -5.0114899 0.74626905 1.8492652rotation 0.99979001 0.020486446 0.00054504466 3.0884011scaleFactor 0.25614116 0.78523439 0.25614116center 0 0 0

}Material {

diffuseColor 0.51179832 0.70113409 0.69077253}Cone {}

Radar scatterer file description

A section of the reflectors file is shown to the rightThe whole file consists of 302 lines. The file size is 5.1Kbytes.The included IR definitions file AMX-A1.iv is referenced followed by one of the cones - Cone0With the exception of the diffuse red value, the colour channels and Material node fields do not affect the RCS properties of the reflectorThey can be changed for visual effect, to help identify reflectors in the Viewer

184.25° phase change

IR validationValidation of an IR definition is an iterative process involving comparison of the IR model radiant intensity from all aspects and in a least 2 wavebands, e.g. 3 – 5µm and 8 – 12 µm.Method

“Fly” the aircraft model in a circular path in a CounterSim simulation – record azimuth / timeObserve the aircraft with a model of an IR imager – record radiance / time.Combine to give radiance / azimuth Compare with calibrated measurement data of the aircraftAdjust the definition until a good match is achieved.Use any un-calibrated IR images to identify heat sources and adjust relative levels.

Correct adjustment of the IR model definition is based on knowledge of the position and thermal characteristics of real objects corresponding to identified sub-objects in the Open Inventor file.Engines and engine plume set up is always critical

Engine exhaust sub-objects may need to be broken down to several parts to obtain the correct IR responsePlumes are currently modelled as

3 or more concentric cones with the same temperature and emissivityIncreasing transparencies from the inner to the outer cone.

AMX model radiant intensity

Radiant intensity polar diagram at 3 - 5µm

RF validation

Scatterer models first have to be generated from some known radar cross section data either

From real aircraft in a specific RCS measurement trial e.g execution of 540° turns at different bank anglesSynthetic data generated from a CAD surface model

Other measurements of a real aircraft can be obtained from dry runs in a chaff or IR trial where the aircraft may be straight and level or in a high G turn

Measured versus modelled RCS

Measured and modelled scintillation – 4G turn

Example air scenario definition

CounterSim is an object oriented applicationObjects are arranged in a tree of logical collections and hierarchies. Each object has a Properties dialog -enables

Parameters to be setData logging options to be selected

The CM Controller item initiates manoeuvres and fires countermeasures singly, in sequences or in bursts.Branches of the tree can be saved as named collections – e.g. a complete aircraft type with its set of dispensers and countermeasures load.

Allows the easy composition of other scenarios with other pre-defined platforms and threats.

Example air scenario

Chaff is dispensed at 5.4s when the aircraft radial velocity and Doppler return pass through zero.The Manpad is fired 1.5s after the run startsMTV flares are fired from the starboard launcher 2.2s and 2.4s after the missile launch

The fire control radar is at (0, 0) - the Manpad is at (-1650, 2400) The aircraft flies at a constant altitude of 305m and follows the track (x,y) shown below

The aircraft track is a comma separated variable (csv) file of aircraft x, y, z, azimuth angle and bank angle versus time at 0.2s intervalsThe track file therefore defines the aircraft velocity, which in the example, is 100 m/s

Example air scenario recorded from CounterSim

Aircraft and chaff Doppler

The monopulse radar data analysis from the run can be used to produce a Doppler plotThe aircraft track is shown in the left of the plot up to 5.4sThe chaff then shows a broad Doppler at releaseThe chaff Doppler response narrows as it slows down

Conclusions 1The IR extension

Has been in use for more than 10 yearsGood results in a variety of air, naval and land studies for static IR signatureMore recently the Interpolator feature has been used to change engine plumes and hence IR signature during a simulation by using a time varying engine state parameter

RF scatterer definitionDeveloped in the last 2 yearsEarly validation work with the gives good agreement with RCS, Doppler and Power Spectral Density (PSD) - more validation work will be doneA more efficient method will be developed for determination of the optimum number of scatterers and setting their position, RCS andphase on the platform

Conclusions 2Open Inventor provides an efficient means of defining platform models

A complete definition in IR and RF signatures uses 2 files of 565Kbytes and 5.1Kbytes in the aircraft example

Programming advantagesUse of common codeReduced run times

Ongoing work will further increase speed by GPGPU processing of components such as the IR seeker reticule and the monopulse signal processing

Synchronised IR and RF data for object positions and other properties

Countermeasure development advantagesSimulation of separate IR and RF threatsModelling countermeasures with combined IR and RF propertiesRadar target discrimination through PSD and glintModelling of dual mode threats - needs data fusion

Questions