Infrared Signature Studies of Aerospace Vehicles(Aero-Optics)

• Mission Attainment Measure (Offensive)M ss o tta e t Measu e (O e s ve) Survivability of Aircraft / Helicopters (Carriers of Offense): Foremost in Design

• Parallel devpts. in sensitive detection & tracking systemsp g y Dynamic nature of ‘Stealth’o Rao & Mahulikar (2002) Aeronaut. J.

• Passive detection tactically superior / anti-radiation missiles Effectiveness of RADAR is challenged

• Low flying mission (RADAR horizon) IRSS, IRCMs mandatoryh l k lo Mahulikar et al. (2007) Prog. Aerospace Sci.

MANPADS M t i th t t i ti i f t• MANPADS: Most serious threats to aviation in futureo Bolkcom et al. (2005) CRS Report for Congress, RL31741

Sources of IR Signature in Aircrafto Principle: Discriminate ‘Aircraft IR’ with ‘Background IR’o Grey Surface Emission Characteristics

Planck’s Law: ebλ(λ,T) [W/m3]; Wien’s Law: λm·Tpeak = 2897.6 μm-K 1st generation - 1.9-2.9 µm: Tpeak = 934°C (only for rear aspect)

d 2nd generation - 3-5 µm: Tpeak = 450°C (for - hot spots) Latest - 8-12 µm: Tpeak = 17°C (for - higher sensitivity)

Engine

Aerodynamically

Engine exhaust plume (internal source)

heated surfaces, e.g. nose, wing leading edges (internal source)

Hot engine parts, e.g. tail-pipe (internal source)

Rear fuselage skin heated byRear fuselage skin heated by engine / plume (internal source)

Sunshine / Skyshine

EarthshineEarthshine reflection (external source) Mahulikar et al. (2007) Prog. Aerospace Sci.

Directional Dependence of Aircraft IR Signature1 1

nsity 0 02.4 3.2 4.0 4.8 2.4 3.2 4.0 4.8

Rear side

tive

Inte

n

30° 80°Front-side: All-Aspect Missiles

Rear-side

Engine Hot-PartsPlume & airframe

Rela

1 10° 180°

Plume & airframe

002 4 3 2 4 0 4 8 4 84 03 22 42.4 3.2 4.0 4.8 4.84.03.22.4

λ (μm): 1st & 2nd Generation DetectorsFront: All-Aspect Missiles Rear

(μ )

Ball (2003) AIAA Ed. Ser.

IR Signature of Helicoptero Engine Exh. Duct &

Hot Parts (e.g. t bi bl d )

3-5 μm band

turbine blades)

T il B H t d

135° 45°

o Tail-Boom Heated by Plume• > Plume !• > Plume !

o Plume0°180°

o Plume

315°225°

270°Thompson et al. (1999) 7th CASI Propulsion Symp.

IR Detectors & their Constraint on Flight Envelope

o Cooled GaAs / AlGaAs (Aluminum Gallium Arsenide) & HgCdTe (Mercury Cadmium Telluride)(Me cu y Cad u e u de)

o Mid-Wave (3-5 µm) & Long-Wave (8-12 µm) 0.5 μW/m210

Mahulikar et al. (2001) Aeronaut. J.

Long Wave (8 12 µm) o Multi-Colour

Thermal-Imaging Systems

μ

2 μW/m28Thermal Imaging Systems QWIP Technology IR-detection in wider spectrum 2(k

m) 6

IR detection in wider spectrum all aspect spatial map of scene

IRSL = 5 μW/m2

NEI = 50 μW/m2

H(

4

o A/c H ↑• (IR-Det. Sensitivity, M∞) ↑

↑

NEI = 50 μW/m

IR Signal = 200 μW/m2

0

2

• H ↑ w.r.t. Radar-det. 0.4 0.8 1.2 1.6M∞

Comparison of NEIs for TJE & TFE on Flight Envelope

NEI for TJENEI for TJE

6

NEI for TFE

With plume IR (3-5 μm) Plume-IR ↓ at M∞ ↑

4

NEI for TJEWithout plume IR (8-12

) C i IR ↓ M ↓H(k

m)

NEI for TFEμm) Casing-IR ↓ at M∞ ↓2

H

0 4 0 8 1 2 1 60 0.4 0.8 1.2 1.60M∞

Mahulikar et al. (2001) Aeronaut. J.

Atmosphere Role: IR-Transmission & IR-Radiance

o CO2, H2O (vap.), O3, & CH4: p, T, & Conc.

o τλ_(λ+dλ): Spectral Distribution of Source IR Radiation & Intensity LOWTRAN (empirical-based program) Rao & Mahulikar (2006) J AircraftLOW N (e p ca based p og a ) 8-14 μm: widest window 1.0

Rao & Mahulikar (2006) J. AircraftLvert = 5 km

o Spectral Distribution of Atmospheric IR Radiance 0.6

0.8

λ)

Mid-latitude summer

thermal emission by gases & sunlight scatteringB ’ d l

0.4

τ λ_(

λ+dλ

Tropical

Berger’s model:Empirical-basedMeasurement of skies 0 0

0.2

Measurement of skies 0.00 2 4 6 8 10 12 14 16 18 20

λ (μm)

Berger’s Model for Atmospheric Radianceo Input: Surface Temperature & Humidityo ελ & Eλ: f(Ground & Dew Pt. Temperatures)

Berger (1988) Solar Energyo εΔλ = 1 − exp(−kΔλ·w)

kΔλ = C1 + C2·tdew :

m)

10

0°: Horizon (Black-Body)

Berger (1988) Solar Energy

absorption coefficient w: equivalent absorber

w /m2 ⋅S

r⋅μm

15°w1,night = 2.020exp(0.0243tdew) & w1 day = an

ce (W

/5 30°

1,day

1.621exp(0.0193tdew)With O3 in 9.3-9.6 µm

tral R

adia

90°: Zenithw2,night = 4.050exp(−0.0212tdew) & w

Spec

t 90 : Zenith

Spectral clear sky radiance on ground for mid-latitude summer

& w2,day = 3.317exp(−0.0182tdew) λ (μm)

05 10 15 20 25

Path-Lengths of Horizontal & Vertical Beams

HatmVertical path-

Horizontal path-length: Horizon[Hatm·(Hatm+2Re)]0.5

length: Zenith[Hatm (Hatm 2Re)]

Horizontal / Vertical = [1 + 2(Re/Hatm)]0.5

Re Re+Hatm

EARTH

Atmosphere containing IR-radiation participating gasesradiation participating gases

Mahulikar et al. (2007) Prog. Aerospace Sci.

Spectral Contrast between Aircraft & Background

10

m)

Rear-Fuselage Skin / Atm. Radiance

6/m

2 ⋅Sr⋅μ

mMid-Latitude Summer: +ve Contrast ↑

2

trast

(W

/

6

−2

tral C

ont

−6

Spec

t

−10Tropical: −ve Contrast ↑

R & M h lik 0 2 204 6 8 10 12 14 16 18λ (μm)

Rao & Mahulikar (2006) J. Aircraft

o Tail-pipe Invisible, IRSL: 3.24-4.18, 4.50-4.93, 8.20–11.80 μmo Tail-pipe Visible, also: 1.95–2.50, 2.92–3.20 μm

Role of Earthshine in IRSL (Mahulikar et al. 2009 J. Opt. A)o Earthshine ↑ ⇐ εa/c ↓ (w.r.t. temp. based), 8-12 μm band

IR radiance from earth reflected off aircraft & collected by detector

o εearth(soil type & temp. water body, vegetation, humidity) ∼ 0.93 Hipps (1989) Remote Sensing of Environment

o Non-Lambertian: 8

8-12 μm band, with earthshine

m2 )

Vegetation B.R.D.F.

Nicodemus (1965) 4

8-12 μm band, without (W

/Sr-m

Nicodemus (1965)Appl. Optics

earthshine3-5 μm band, with

th hiCon

trast

εfuse

0 0.2 0.4 0.6 0.8 1

earthshine

3-5 μm band, without

IR C

εMahulikar et al

−4

without earthshine

Mahulikar et al. (2006) J. Aircraft

Analysis & Modeling of IR Signature Sourcesh lo Re-entry Vehicle

Sources: Shock heated air, Heated surface, Ablation products, Wake Prediction: Trajectory i e variation of H M ρ α; Shock structure & B L Prediction: Trajectory i.e. variation of H, M∞, ρ, α; Shock structure & B.L. Prediction of surface temps. by multimode thermal model

o Aircraft (A/c) Engine: Exptl. Measurements( ) Static engine testing - Engine is instrumented in outdoor test facility Wind tunnel testing - Scaled a/c model (prob. stray radiation)

o A/c Sources: Power-Plant, Jet-Nozzle, Exhaust Plume, Airframe Plume - visible from all aspects - 2-5 μm, A/c surfaces – 3-5 & 8-12 μmp μ μ Amount & specific wavelength bands ?

o Aircraft Rear Fuselage: Large area at lower temp.i l l l f d i h i Sources - internal power-plant & external free-stream aerodynamic heating

Earthshine & Skyshine reflections: ε↓ & 8-12 μmo Rear Fuselage Temp. Pred. Multimode Thermal Modelo Rear Fuselage Temp. Pred. Multimode Thermal Model Variations in: a) transport & flow properties with temp. b) cross-sectional

area, c) heat transfer (Rayleigh flow), d) skin friction (Fanno flow)

Jet pipe700

800Dry mode

Skin Temp. PredictionT

(K) 600

Mahulikar et al. (2005) J. Thermophys. & Heat Transf.

Radiation shield

R f l ki400

T 500

Rear fuselage skin

3000.0

L (m)0.4 0.8 1.2 1.6 2.0

L (m)

Jet pipe1400Afterburning mode

o Afterburning Mode:

R di ti hi ld

1000

K)

Jet-pipe temp. doubles (Rear-View)

k Radiation shield

Rear fuselage skin600

T( Skin temp. increases

by 70 K (All Aspects)

2000.0 0.4 0.8 1.2 1.6 2.0L (m)

Role of Free-stream in Rear Fuselage Skin’s IRSL

o Free-stream as Heatas Heat Source IRSL from

Sink-to-source transition points

Mahulikar et al. (2005) J. Thermophys. & Heat Transf.

IRSL from rear fuselage skin

1.4 Sink-to-source transition line

<

IRSL from 1.2

∞

Free-stream as heat-source: airframe / wings

1.0

M∞ M∞ ↑ (> M∞,trans) & H ↓ (< H∞,trans)

0 8

Free-stream as heat-sink:

M ↓ (< M t ) & H ↑ (> H t )0.8

0 2 4 6 8 10 12 14 16H (km)

M∞ ↓ (< M∞,trans) & H ↑ (> H∞,trans)

Estimation of ω(φ)-subtended: Parallel Rays Projectiono Engine Layout (Well-Resolved)

turbine exit discjet nozzle

Mahulikar et al. (2007) Applied Optics

jet- nozzle rear fuselage skin

2

3

/m

1

2

)×10

6Sr

/

0

0 060

80(Ω/l)

0.0

1.00.5

1.520

40JP φ°l (m)

Dgt. sect. ω ↑ & ω > 0 ∀ φ∈[0,90°]2.0 0Cgt. sect.

A/c Plume IRSLVisible from φ ↑; Rad H O (vap ) CO CO; TJE (IRSL ↑) > TFEo Visible from φ ↑; Rad. H2O (vap.), CO2, CO; TJE (IRSL ↑) > TFE

o AR ↑ (Pot. Core)↓ IRSL ↓ (Decher 1981 J. Aircraft)

TJE

TFEHudson Jr. (1969) Infrared System Engg. (Wiley NY)

Spectral Plume IRSL Emitted

160m

) • A/c at zenith over SAM site

120

/m⋅S

r⋅μm • Ipl,λ recd. by SAM: 4.15-4.45 μm band

80nsity

(W/

I pl,λ

40nce

Inte

n

40

Rad

ian

D M d Pl IRSL << t il i & f l IRSL

0 4 8 12 16 200

λ (μm)

o Dry Mode: Plume IRSL << tail-pipe & rear fuselage IRSLo 8-12 μm band: No Gaseous Plume IRSL Mahulikar et al. (2005)

J. Thermophys. & Heat Transf.

V hi l N f N l N l S i B DiParameters Affecting IRSL of Rocket Plume

o Vehicle - No. of Nozzles, Nozzle Spacing, Base Dia.o Ambient - Solar Azimuth / Elevation; Flight - M∞, H, α

E i (N l 1987 J S ft & R k t )o Engine (Nelson 1987 J. Spacecraft & Rockets) Mass flow rate, Propellant type, Oxidizer-to-fuel ratio, Area ratio,

Nozzle contour Chamber pressureNozzle contour, Chamber pressure

Standard Models for Prediction of IRSLo Models for IRSL from plume, power-plant, & complete aircraft

SIRUS, SIRRM, NIRATAM, SPIRITS, IRSTORM, MIRSAT, OPTASMS US, S M, N M, S S, S O M, M S , O SM

o Models for atmospheric IR transmission & radiance LOWTRAN, MODTRAN, & HITRAN

o Models for processing & generating spatial scene map, wire model SPIRITS, IRST, IIR, EOSAS

o Models for IRSL prediction from ships & ground vehicles SHIPIR, GTSIG, PRISM

NIRATAM (NATO InfraRed Air Target Model 1991)NIRATAM (NATO InfraRed Air Target Model, 1991)o Based on Field Measurements, Theor. Studies, & Data Analysiso Considers IRSL by Internally & Aerodynamically Heated Surfaceso Considers IRSL by Internally & Aerodynamically Heated Surfaces,

Hot Engine Parts, Combustion Gases, Plume Particleso Skyshine (Radiance) Atmospheric Trans Sunshine Earthshineo Skyshine (Radiance), Atmospheric Trans., Sunshine, Earthshine

SIRUS (Spectral Signature Analysis Code)SIRUS (Spectral Signature Analysis Code)o For: Air Breathing & Rocket Motor Propelled Vehicleso Models (Based on B.R.D.F.):o Mode s ( ased o ) surface temperature, surface reflectance, cavity physics, plume gas

radiative transfer, atmospheric effects (including solar contribution), background & imaging sensor effects (imaging & threshold detection)background & imaging sensor effects (imaging & threshold detection)

o Capability to Assess IR Characteristics of Paints on Airframes

IRST (IR Search & Track) 1989IRST (IR Search & Track) 1989o Simulates Air-to-Air Detection & Tracking Engagements; Integrates:

LOWTRAN; SPIRITS (aircraft IR signatures imaging module)LOWTRAN; SPIRITS (aircraft IR signatures imaging module) CLOUD (sky background imaging module) TRACKER (signal processing & tracking module)

l l d l IPAS (optical sensor & spatial processing module) MISSION (dynamic trajectory module) HIGH LEVEL SCENARIO SPECIFIER (user interface module)( )

Modelso Empirical-Based Models:

IR measurements obtained on operating a/c for multiple aspects & operating diti d t l d t fill di ticonditions, data analyzed to fill prediction-gaps

o Physics-Based Models (I/Ps): a/c geometry surface emissivity temp profile surface reflectionsa/c geometry, surface emissivity, temp. profile, surface reflections

Lock-On vs. Lethal Envelope & Target A/c Susceptibility (PH)( )

o Lock-On (L-O) E l 10

12

90°RLO =12 km Rbo =10 km

Envelope: Locus of pts. around

target a/c where missile’s 5

10RLO

(km)g / w

IR seeker locks-on

o Missiles Constrained by 0°(km)180°

5Rlethal

B-O Range L-O Inadequate for PH

P f[L th l E l

012

( )

Target Aircraft

12180

Lethal envelopeLock-on

o PH = f[Lethal Envelope = φ(L-O, Vac, B-O, ....)]: locus of pts within

5envelope

Isotropic locus of pts. within which, if missile is launched → hitting

b bilit ↑

1012

270°

Isotropic RLO = const.

probability ↑ Rao & Mahulikar (2005) Aerospace Sci. & Tech.

(Vac/Vm) = 0.66(Vac/Vm) = 0.50(V /V ) 0 33

Rbo = 10 km 40020Rbo = 10 km(V /V ) 0 33300 (Vac/Vm) = 0.33

(Vac/Vm) = 0.25(Vac/Vm) = 0.20 30016

Lethal Envelop

(Vac/Vm) = 0.33

200)A

letha

RLO,th

p

Lock-on Rm

)

(V /V )↑thal

(km

2 ) 200

al (km2)

12Range

R LO

(km

100

(Vac/Vm)↑

A let

1008

0IRSLth400 4 8 12 16

RLO (km)

0

IRSL (W/Sr)0 100 200 300

4

Rao & Mahulikar (2005) Aerospace Sci. & Tech.

IR Counter-Measures (IRCMs)Mahulikar et al. (2007) Prog Aerospace Sci

Passive Active

Prog. Aerospace Sci.

IR Suppressors /Optimizers

IR: Flares, Jammers, Pyrotechnic Decoys,Lamp on Sacrificial StructureOptimizers

Obj. to minimize a/c IRSL

Lamp on Sacrificial Structure

Obj. to confuse IR seeker by IRObj. to minimize a/c IRSL Obj. to confuse IR seeker by IR jamming / luring away towards false target / sacrificial structurePassive Countermeasures

o R ∝ (IRSL)½ IRSL ↓o RLO ∝ (IRSL)½ IRSL ↓ Minimise penalties: back-pressure, wt. cost,

complexity, drago Techniques:

Conceal hot engine parts; Peak temp. reduction of exhaust gases

IR-Suppressor for HelicopterM h lik t l (2008) Jreduction of exhaust gases

Camouflage IR by modifying exposed temp. Reducing reflectivity of reflecting surfaces

Mahulikar et al. (2008) J. Propulsion Power

Modification to Exhaust Systemo D.R.E.S. Canada: F.C.T. & C.B.T.o Characteristics of Typical Patented IRSS System: Efficient mixing / pumping of plume with ambient Engine temperature reduction by fuel coolingFuselage IRSSFuselage IRSS:

Aircraft skin heating / cooling, Emissivity optimisation10o Penalties of IR Signature

8

0

8-12 μmo Penalties of IR Signature

Suppressors (IRSS)– Wt.

Mahulikar et al. (2006) J. Aircraft

4

6R L

O(k

m)

– Complexity– Changes to nozzle

geometry

2

4

3-5 μmgeometry

– Power losso Mission Power = Engine Power

0.0 0.2 0.4 0.6 0.8 1.00

εfuse

o g − Power for IRSS Penalties

Active Countermeasureso IR jammers, IR flares as decoyso Smart jammers: non-directional / directional (DIRCM)( )o MAWS: Radar, IR Detectors (scanning & staring), UV detectorso High altitude flight to avoid detectiong g

Counter-Countermeasures (C2M)Counter Countermeasures (C M)o to counter active & passive IRCMs increasingly sensitive IR sensors ; imaging seekers increasingly sensitive IR sensors ; imaging seekers high speed temporal processing (to minimise reaction time) multiple attack multiple attack

Conclusions IR SignaturesConclusions IR Signatures →→ PassivePassiveConclusions: IR Signatures Conclusions: IR Signatures →→ PassivePassive

o Missiles: fire & forget capability portable lethal↑o Missiles: fire-&-forget capability, portable, lethal↑ IR-detection / guidance up to terminal phase (unlike mono-static radar)

o Fuselage: Main Source for 8-12 μm; A/c Plume: for 4.15-4.20 μmg μ ; μo Background IR-Radiance (+ve & -ve contrast)o Earthshine ↑: Rear Fuselage → (ε & H) ↓o Divergent-Nozzle: Imprudent → From Rear Aspecto Nozzle Shape Modification:

↑ notching / corrugating; aspect ratio ↑; retrofit deviceso IRSL ↓ with (Performance Penalties) ↓ e.g. Emissivity Optimization

Next Gen IR Imaging Sys → multi λ spatial detectiono Next Gen. IR Imaging Sys. → multi-λ spatial detection large area, multi-spectral / multi-colour staring arrays / immune to IRCM