Research of detection range of LWIR dispersive imaging spectrometer

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1 Reerch of detecton rnge of LWIR dperve mgng pectrometer Hong Xu*, Xngjun Wng College of Precon Intrument nd Opto-Electronc Engneerng, Tnjn Unverty, Ntonl Lbortory of Precon Meurement Technology nd Intrument, Tnjn, Chn ABSTRACT Among vrou type of long-wve nfrred pectrometer, dperve pectrometer h the mplt tructure nd h hown good ervce behvor n ll knd of mgng pectrocopy pplcton. For the technology of nfrred remote mgng pectrocopy, n excellent degned mgng pectrometer the key fctor. Of ll the degnng fctor, the trdeoff between the detecton performnce nd the tructure ze lwy the mn topc. In th pper, ccordng to the performnce prmeter of the ued nfrred enor, chrctertc of energy trnmon of dperve pectrometer, chrctertc of trget rdton nd the effect of tmopherc trnmon, comprehenve reerch done to contruct perfect recevng rdton model of LWIR dperve pectrometer, provdng theoretcl foundton for ccurtely determnng the reltonhp between ntrumentl tructure prmeter nd the detecton rnge. A degnng model wth n uncooled mcrobolometer t detector clculteded to nlye t potentl n the pplcton of longwve remote mgng pectrocopy. Keyword: LWIR, mgng pectrometer, dperve pectrometer, detecton rnge, hyperpectrl, remote enng. INTRODUCTION Nowdy, LWIR(8~4µm) remote enng mgng pectrometer hve been wdely ued n feld of geogrphcl remote enng, pollutnt remote enng, well detecton nd urvellnce of mltry trget, plyng more nd more mportnt role. Accordng to the dfferent workng mechnm, LWIR pectrometer cn be contructed nto vrou tyle. Of ll knd of uch pectrometer, the dperve pectrometer h ubtntl tructure, hgh pectrl nd pcl reoluton nd good rel-tme qulty, whch epeclly utble for rborne nd tellte-borne pplcton n hrd envronment. Snce object wth norml temperture n nture rdte t low level; dperve pectrometer wth prm or grtng the dperve component, reolve the ncdent rdton nto ere of nrrow bnd, ledng to very low rdton n every nrrow bnd; the enor workng n LWIR hve uully low entvte nd reltvely hgh noe; nd lo the ncdent rdton ttenuted by the tmophere n trnmon, ll the bove fctor mke LWIR dperve pectrometer hve to ncree t perture of telecope objectve to receve enough rdton, whch led to lrge ntrument volume. To ccurtely determne the reltonhp between ntrument tructure prmeter nd the detecton rnge, comprehenve reerch needed to do wth the conderton of performnce of LWIR enor ued, chrctertc of energy trnmon of dperve pectrometer, chrctertc of trget rdton nd the effect of tmopherc trnmttnce. In th pper, ll the mn fctor concerned wth the rdton trnmon re condered n theory, contructng generl nlytcl model, gvng the reltonhp equton between the detecton rnge nd ll the nvolved fctor. *xuhongpot@63.com; phone ; fx MIPPR 007: Automtc Trget Recognton nd Imge Anly; nd Multpectrl Imge Acquton, edted by Tnxu Zhng, Crl Nrdell, Dune Smth, Hngqng Lu, Proc. of SPIE Vol. 6786, , (007) X/07/$8 do: 0.7/ Proc. of SPIE Vol Downloded From: on /3/04 Term of Ue:

2 . RADIATION TRANSMISSION MODEL AND DETECTION RANGE EXPRESSION. Rdnt llumnton ncdent on entrnce lt The rdnt llumnton ncdent on the entrnce lt cn be expreed by the followng equton: E ( f λ ) = πl( D 4 () n whch D the recevng telecope objectve dmeter, f the focu of telecope objectve, L ( the pectrl rdnce of the trget, nd ( the tmopherc trnmttnce. When Cegrn objectve ued n the ntrument, the rdnt llumnton ncdent on the entrnce lt cn be expreed : λ ) = πl( ( D D ) 4 () E ( f where D the dmeter of the mn mrror, nd D the dmeter of econdry mrror.. Chrctertc of energy trnmon of dperve pectrometer The recevng rdnt flux focued on the entrnce lt dpered by the grtng component, nd the pectrl llumnton E ( ncdent on the enor pxel cn be expreed by equton []: o Eo = β m E f f γ (3) where β the dffrcton effcency on the frt order of dffrcton, m the trnmttnce of mrror, f the focu of the collmtng object len, f the focu of the mgng len. γ the trnvere mgnfcton of the grtng dperve component, whch expreed by the equton: γ = co coθ (4) where the ncdent ngle, nd θ the dffrcton ngle. Alke the nly of energy trnmon of grtng dperve pectrometer, n the prm dperve pectrometer, the outgong pectrl llumnton E ) cn be expreed by the followng equton: o (λ Eo = p m E (nε ) f f γ (5) where p ( the pectrl trnmttnce of the prm, whch determned by the ued prm, nd ε the ngle of nclnton between the mgng plne nd the optcl x of the mgng ytem.. γ the trnvere mgnfcton of the prm dperve ytem, whch cn be expreed by the equton: γ = co co co 'co ' (6) n whch the ncdent ngle wth t refrcton ngle of well..3 Effect of tmopherc trnmon ', the ext ngle wth t refrcton ngle of ' Although the LWIR bnd one of the tmopherc wndow, the borpton of wter nd CO the key fctor n determnng the detecton rnge when t too fr wy. Theoretclly, t umed tht the tmopherc compoton t the lttude of h tble. In the dtnce of l, the trnmttnce of th tmopherc lyer cn be clculted by the followng equton: α ( λ, h) l λ, h ( l) = e (7) Proc. of SPIE Vol Downloded From: on /3/04 Term of Ue:

3 α λ the tmopherc ttenuton coeffcent t the lttude of h. where (, h) When n oblque or vertcl remote enng wth the lttude of H nd the enor vewng ngle of θ, the tmopherc trnmttnce from the object to the nfrred pectrl remote enor cn be expreed by the equton: H ( H α ( λ, h) ecθdh 0 (8) λ, θ ) = e In the clculton of the tmopherc trnmttnce, t needed to obtn the ccurte dtrbuton of the tmopherc ttenuton coeffcent α ( λ, h). At preent, n the feld of tmopherc remote enng nd photoelectrc detecton technologe, the tmopherc code LOWTRAN nd MODTRAN hve been ued wdely n the degn of photoelectrc detecton ntrument nd the clbrton of pectrl dt. LOWTRAN the low-reoluton tmopherc code wth the pectrl reoluton of 0cm -, nd MODTRAN the moderte-reoluton tmopherc code wth the pectrl reoluton of cm -, whch how the excellent performnce n pplcton..4 Chrctertc of LWIR rdton from object Snce the olr rdton n the LWIR bnd very low, the effect of the olr rdton cn be dmed. Thu, the compoton of the LWIR rdton from the object re compoed of three prt whch re repectvely the pontneou therml rdton of the object, the reflecton prt of the downwrd tmopherc rdton from the object, well the route ctterng prt nd t rdton prt. Therefore, the pectrl rdnce cn be expreed by the equton []: L L + L + L (9) = t r Knowng the object emvty ε (, the pectrl rdnce from the object to the enor cn be expreed by the followng equton: where ε ( the emvty of object, ( L ε L ( λ, T ) + [ ε ] L L (0) = B + r L the rdnce prt cued by the downwrd tmopherc rdnce L (, L (λ ) the route tmopherc rdnce. L (, T ) r B λ the pectrl rdnce of the blckbody wth t bolute temperture of T, whch expre : where h the Plnck contnt, nd K the Boltzmnn contnt..5 Detecton rnge of the LWIR hyperpectrl remote enng enor L B 5 hc λkt ( λ, T ) = hc λ ( e ) () To obtn ccurte pectrl dt, the SNR between the gnl voltge trnformed by the nfrred enor nd the noe voltge h to be greter thn threhold SNR whch defned ccordng to requred detecton probblty. Accordng to bove nly, the gnl voltge cn be clculted by the followng equton: V th = Ad S( λ ) πl( D 4 f = At S( πl( D 4R () where R the detecton rnge, A d the entve re of the enor, A t the object re, S ( the pectrl repone, nd ( the ytem trnmttnce of the pectrometer. V n the RMS noe voltge of enor whch cn be obtned by the followng equton: V n * = S( λ ) Ad f D (3) where f the ytem bndwdth, nd * D the detectvty of enor. Proc. of SPIE Vol Downloded From: on /3/04 Term of Ue:

4 Conderng the lmt of SNR SNRth, detecton rnge cn be fnlly expreed followng: * πa ( ) ( ) ( ) t D D L λ λ λ R 4 Ad f SNRth (4) 3. SIMULATION AND RESULTS Ung the expreon of detecton rnge, the tructure prmeter of knd of mll remote mgng pectrometer, of whch uncooled mcrobolomerer FPA ued the detector, hve been clculted n th ecton. A known to ll, uncooled mcrobolometer wthout the bulk cryogenertor cn be degned nto mll therml nfrred mgng ytem. But the low detectvty lmt t remote-enng pplcton. However, wth the development of the mcrobolometer technology, the performnce hve been mproved lot nd t potentl n remote enng becomng ncreng. The pplcton feblty of uncooled mcrobolometer FPA n mgng pectrocopy nlyzed n th ecton. Th multon condered the remote enng mgng pectrometer for mll flyng pltform workng t low lttude, uch UMV, to do remote obervton of lnd cene. The workng prmeter ued here n the clculton re et follow: workng lttude>km, flyng peed=0km/h, ground reoluton=m, the rnge of workng pectrum: 7.8~3.4µm, pectrl reoluton=0.µm, the ground urfce temperture=300k. The performnce prmeter of uncooled mcrobolometer FPA refer to document [3, 4]. Here, t thought tht the pectrl repone nd detectvty of mcrobolometer re nvrble. The mn requet of ytem nd the devce prmeter re lted on Tble. Tble.. Requet of mll mgng pectrometer nd performnce prmeter of uncooled-mcrobolometer FPA. Requet of mll dperve mgng pectrometer Alttude km Flyng peed 0 km/h Spectrl reoluton 0.µm Number of wve bnd 56 Ground reoluton m Performnce prmeter of uncooled-mcrobolometer FPA Reponvty V/W Detectvty cmhz / /W Pxel re 39µm 39 µm Frme frequency 30 Hz For the purpoe of prece mgng pectrl detecton for vrou ground object, t needed to obtn relble gnl wth hgh SNR n every nrrow bnd. To relze th objectve, t necery to comprehenvely conder the emvty of ll the object of nteret, ung the mnmum vlue of emvty n degn clculton. The long-wve emvty of everl mterl object re hown n fgure, the dt come from [5]. A hown n the fgure, mot object n nture hve mlr hgh emvty n LWIR bnd. But for the nd, there n obvou borpton pek t ner 9µm. A the dfference of long-wve nfrred emvty between mot object re rther low, n order to dtnguh the pectrum Proc. of SPIE Vol Downloded From: on /3/04 Term of Ue:

5 emvty of dfferent object, t needed to et hgh SNR. Accordng to the reltve document [6, 7], the SNR et 500. At the mentme, for the ke of mplfcton, the trnmttnce of mgng pectrometer ytem et to be 0.5, whch creful nd cutou Emvty (00%) Gr Pvement Snd Alumnum dk Wvelength (µm) Fg.. Spectrl emvty of everl mterl n LWIR bnd. In the multon, nce reflectnce of mot of ground object nd the tmopherc route rdton re both very low n LWIR regon, the effect of tmophere not tken nto conderton, nd the recevng rdton only produced by the pontneou therml rdton. Here, we ue LOWTRAN code to clculte the tmopherc trnmttnce of everl pplcton envronment, nd the mn prmeter re et follow: 976 Amercn Stndrd Atmopherc Model; country extncton coeffcent erool model, wth meteorologcl vul rnge equl to 3km; prng-ummer tropophere/trtophere profle; zenth ngle of 0. The Fgure how the curve of tmopherc rdton trnmttnce t dfferent obervton lttude Trnmttnce (00%) Trnmttnce of km tmophere Trnmttnce of 5km tmophere Trnmttnce of 0km tmophere Trnmttnce of 5km tmophere Wvelength (µm) Fg.. Curve of tmopherc trnmttnce t dfferent obervton lttude. Proc. of SPIE Vol Downloded From: on /3/04 Term of Ue:

6 The perture dmenon of telecope objectve t dfferent detecton heght re clculted through the bove formul, nd the reult re hown on Tble. When the detecton heght km, the objectve perture need to be 9cm. It cn be een tht th dmenon prctclly feble to remote-enng mgng pectrometer ung uncooled mcrobolometer FPA. But when hgher thn 5km, the ytem h to ncree the recevng objectve perture over m. In the ene of engneerng, th h lot t prctcblty, nd the cooled photon FPA wth hgher detectvty mut be needed. It needed to pont out tht the nly bed on ome mplfcton. To obtn prece reult, the ccurte prmeter ued n the clculton hould be known. Tble.. Reltonhp between objectve perture nd lttude. Alttude (km) Objectve perture (m) CONCLUSION Accordng to the performnce prmeter of nfrred enor ued, chrctertc of energy trnmon of dperve pectrometer, chrctertc of trget rdton nd the effect of tmopherc trnmon, comprehenve reerch done to contruct perfect recevng rdton model of LWIR dperve pectrometer, provdng theoretcl foundton for ccurtely determnng the reltonhp between ntrumentl tructure prmeter nd the detecton rnge. The optmzton of hyperpecrtrl remote enor, epeclly LWIR mgng pectrometer, key ue n the degn of uch knd of ophtcted ntrument. A trdeoff h to be condered between the requrement nd the ntrumentl tructure. Accordng to th reerch, the perture of telecope objectve cn be determned to be the bet dvntge. REFERENCES. L Qunchen nd Jng Yuejun, Prncple of Spectrl Intrument, Bejng Inttute of Technology Pre, Bejng, Tn GuoLng, Therml Remote Senng, Publhng Houe of Electronc Indutry, Bejng, Tmothy. D. Pope, Chrtne Aln, nd Aln Bergeron, Mcrobolometer Detector Arry for Stellte-Bed Therml Infrred Imgng, Proceedng of the 004 Interntonl Conference on MEMS, NANO nd Smrt Sytem, pp , Aug D. Murphy, W. Rdford, nd J. Fnch, Mult-pectrl Uncooled Mcrobolometer Senor for the Mr 00 Orbter THEMIS Intrument, Aeropce Conference Proceedng, 000 IEEE, vol. 3, pp. 5-63, Mr MODIS UCSB Emvty Lbrry, 6. Lee W. Schumnn nd Terrence S. Lomhem, Infrred hyperpectrl Imgng Fourer Trnform nd Dperve Spectrometer: Compron of Sgnl-to-noe-bed Performnce, n Imgng Spectrometry VII, Mchel R. Decour, Sylv S. Shen, Ed, vol. 4480, pp. -4, SPIE, Jn J. Coln Mhoney, Hrold R. Sobel, nd Anne B. Khle, Therml Infrred Imgng Spectrometer: An Advnced Optc Technology Intrument, n Imgng Spectrocopy of Terretrl Envronment, Gregg Vne, Edtor, vol. 98, pp. 87-9, SPIE, Sep 990. Proc. of SPIE Vol Downloded From: on /3/04 Term of Ue:

Effect of Wind Speed on Reaction Coefficient of Different Building Height. Chunli Ren1, a, Yun Liu2,b

Effect of Wind Speed on Reaction Coefficient of Different Building Height. Chunli Ren1, a, Yun Liu2,b 4th Interntonl Conference on Senor, Meurement nd Intellgent Mterl (ICSMIM 015) Effect of Wnd Speed on Recton Coeffcent of Dfferent Buldng Heght Chunl Ren1,, Yun Lu,b 1 No.9 Dxuexdo. Tnghn Cty, Hebe Provnce,