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Developing a Phenomenological Model of Infrared Emissions

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Developing a Phenomenological Model of Infrared Emissions from Detonation Fireballs for Explosives IdentificationKevin C. Gross, Glen P. Perram, Ronald F. Tuttle Air Force Institute of TechnologyRiverside Research InstituteNinth Biennial HITRAN ConferenceHarvard-Smithsonian Center for AstrophysicsCambridge MA26 June 20063Introduction•Traditional battle space characterization•Classification of transient, infrared events•Bomb detonations, muzzle flashes, rocket and missile plumes•Classifying explosives is difficult•No simple model exists for describing emissions from detonation fireballs•High-explosive detonations are non-reproducible•Inherent irreproducibility (age, mixture tolerances, casing design, impact angle, etc.)•Environmental interaction (soil type, atmospheric conditions, etc.)•Cost and safety concerns lead to small-scale tests with limited reproducibility•Broadband absolute radiometric signatures not apparently useful for classification•Roughly, variance within explosive class same size as variance between classes4IntroductionFramework for solving the explosives classification problem•Collect data using spectrometers, radiometers, and several banded imagers•Develop a low-dimensional phenomenological model for fireball emissions•Spectrometers: Chemistry•Imagers: Fluid dynamics•Extract key features (fit model to data)•Reproducible within the same explosive class (small within-class scatter)•Distinguishing for different explosive classes (large variance between classes)•Invariant to uncontrollable factors•Constrained by physics•Quantify classification potential of extracted features using pattern-recognition codes5Field Tests•Radiant Brass III: Conventional Bomb•Brilliant Flash II: Enhanced Novel Explosives (ENEs)•Bronze Scorpio: IEDs•ABB/Bomem MR Series FTS•RB3: 16 cm-1 / 21 Hz (InSb: 1800–7100 cm-1, MCT 500-6000 cm-1)•BF2: 4 cm-1 / 8 Hz (InSb: 1800–7100 cm-1, MCT 500-6000 cm-1)•BS: 4 cm-1 / 38 Hz (InSb: 1800–7100 cm-1,InGaAs 6000-11000 cm-1)•Radiometers (4 MWIR bands)•Banded Imagers (Vis, NIR, MWIR)RB3BF2BS56 Events44 Events58 Events3 distinct compositions5 distinct compositions3 distinct compositions4 sizes4 sizes2 sizesHalf delivered by aircraftUncased chargesCased artillerary shellRIVERSIDE RESEARCH INSTITUTETemporal Profile7˜2100 cm1˜ 5500 cm1t (s)Iobs˜, t (W/sr-cm1)0 0.5 1 1.5 2 2.5 305001000150020001.5 N22.5 H2O3.5 CO 3.5 C HDC7H5N3O6Detonation (µs)3.5 CO 3.5 C 5.25 O27 CO2HABAfterburn (s)1.00.00.51.5200030004000500060000.01.02.03.00.5Iobs˜ , tWk/sr cm1˜ cm1t sFast-scanning FTS collects time-resolved spectraTemporal profiles reveal detonation and afterburn timescalesSpectral resolution degraded2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 700000.10.20.30.40.50.60.70.80.912000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000!0.04!0.0200.020.04Uncased Explosive, 4 cm!1, 8 HzIobs"˜Ν, t$[no units]t ! 0.000 sIm!Iobs"˜Ν#cm!1$Typical Spectra8Typical Spectra2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 700000.10.20.30.40.50.60.70.80.912000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000!0.0200.02Uncased Explosive, 4 cm!1, 8 HzIobs"˜Ν, t$[no units]t ! 0.362 sIm!Iobs"˜Ν#cm!1$9Scene-Change Artifacts10At each frequency, assume spectrum’s temporal evolution is quadratic over the scan time of the interferometer2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 700000.20.40.60.811.22000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000!505x 10!32000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000!202x 10!4Re!Iobs"[no units]Simulation - Cooling PlanckianIobsI1/ ΤI2/ ΤI3/ ΤIm!Iobs"I2! Re!Iobs"˜Ν#cm!1$!t " 0.1 s, !˜Ν " 8 cm$1T !!TH" TL"e"k t# TLTH! 2000 K, TL! 300 K, k ! 1 s"1Iobs!˜Ν# $ I2%14Π2L2'2!2I1% 4I2( 2I3"'˜Ν2!i12ΠL#!I3$ I1"#˜ΝI3!ˆIobs"˜Ν, x ! L$I2!ˆIobs"˜Ν, x ! L/ 2$I1!ˆIobs"˜Ν, x ! 0$Y YzpdYzpdYYkT/kIErrorConventional (Cased) Munition12Transmittance00.20.40.60.81H2OCO2O3N2OCOCH4O2˜ (cm1)Iobs˜ , t (W/sr-cm1)200025003000 3500 400045005000 5500 60000500100015002000t 0. 000 st 0. 247 st 0. 493 st 0. 740 st 0. 986 st 1. 233 st 1. 479 sIobs!˜Ν, t# $arb.%t 0 st 0.25 st 0.5 s˜ ( cm1)Iobs˜, t (W/sr-cm1)2500 2550 2600 2650 2700 2750 2800 2850 29001200140016001800200022002400Iobs! Iobs"˜Νi, tj$/Iobs"˜Νi% k &˜Ν, tj$Atmospheric Compensation13Iobs!˜Ν, t# $ Τ!˜Ν# Isrc!˜Ν, t#∆ " c/ coldIobs! Τ∆mΤrIsrcΤ"˜Ν$ % e!i!i"˜Ν$ cilIobs!˜Ν, t# $ Τi!˜Ν#∆Τj'i!˜Ν# Isrc!˜Ν, t#Find single set of absorber concentrations for entire data cubeWeighted linear regression to estimate δAtmospheric Compensationlog!Τm#log!Iobs/ΤrIsrc#!2!1.5!1!0.500.511.52!2!1.5!1!0.500.511.5214Iobs!˜Ν, t# $ Τ!˜Ν# Isrc!˜Ν, t#∆ " c/ coldIobs! Τ∆mΤrIsrclog!IobsΤrIsrc"" ∆ log$Τm%Τ"˜Ν$ % e!i!i"˜Ν$ cilIobs!˜Ν, t# $ Τi!˜Ν#∆Τj'i!˜Ν# Isrc!˜Ν, t#Iteratively recompute τm with new concentration until δ = 1Estimate of log(τm)which varies with timeBeer’s Law not strictly appropriate for moderate resolution spectraFind single set of absorber concentrations for entire data cube!"Τ"˜Ν$ ILS"˜Ν %˜Ν&$ d˜Ν&#∆("Τ"˜Ν$∆ILS"˜Ν %˜Ν&$ d˜Ν&Atmospheric Compensation15Test NumberH2O (ppm)5101525003000350040004500Test NumberCO2(ppm)5 1015360370380Test NumberN2O (ppm)510 150.2950.30.3050.310.3150.32Test NumberCH4(ppm)5 10 151.551.61.65371±9 ppm366 ppm1.59±0.04 ppm1.70 ppm305±7 ppb310 ppbRadiant Brass III Field TestRadiative Transfer17(Over-) Simplified RT for fireballNo sources except fireballNo gradients (uniform T, ρ)Local thermodynamic equilibriumNo scatteringFireball parameters: ρ(H2O, CO2, CO,Tg), TcRough approximation to full RT solutionIgnore geometryInclude continuum emitters additivelyIap! ta!AcB"Tc# $ Ag"1 % tg# B"Tg#$$ "1 % ta# B"Ta#tg! tg!Tg,"H2O#,"CO2#,"CO#$tg! exp"####$%L &!iNiΣi(˜Ν, Tg*+,,,,-H2O & CO: HITEMP (HITRAN) databaseCO2: CDSD !""" !#"" $""" $#"" %""" %#"" #""" ##"" &""" &#"" '"""""()"(!"($"(%"(#"(&"('"(*"(+)!""" !#"" $""" $#"" %""" %#"" #""" ##"" &""" &#"" '"""!"("!""("!Uncased Explosive, 4 cm!1, 8 HzIobs"˜Ν, t$[no units]t ! ".$&! ,Im!Iobs"˜Ν#cm!1$I˜Ν"si# $ I˜Ν"si%1# e%!sisi%1Κ˜Ν"s'# ds'("sisi%1Κ˜Ν"s'# B˜Ν#T"s'#$e%!s'si%1Κ˜Ν"s''# ds''ds'AtmosphereFireball FTSt˜Ν" e#$si#si#1%Κ˜Νt˜ΝI˜Ν"si#1$ % "1 # t˜Ν$ B!Ti"2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 700000.10.20.30.40.50.60.70.80.912000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000!0.1!0.0500.05p = [1.96E-01 2.01E+00


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