Research and Analysis Laser Target Optics Characteristics and Signal Recognition Processing in Detection Screen System

Transcription

1 Snsors & ransducrs, Vol. 64, Issu, Fbruary 04, pp Snsors & ransducrs 04 by IFSA Publishing, S. L. Rsarch and Analysis Lasr argt ptics Charactristics and Signal Rcognition Procssing in Dtction Scrn Systm Hanshan LI, Yanran LI School of Elctronic Information Enginring, Xi an chnological Univrsity, Xi an, 700, China Rcivd: 0 Novmbr 03 /Accptd: 8 January 04 /Publishd: 8 Fbruary 04 Abstract: In ordr to improv th masurmnt accuracy of th lasr masurmnt distanc systm, this papr study th lasr targt optics charactristics basd on th lasr dtction principl in th lasr masurmnt distanc systm. A calculation modl of lasr rflctiv cho signal is put forward by analyzing th influnc factors on th dtctor output valu, and discuss th rlationship btwn th distanc from th dtctor to th targt, th lasr wavlngth, th ransmission powr of lasr and th dtctor output powr, th radiation intnsity, and us th Fishr idntification and modulus maxima mthod basd on wavlt analysis to distinguish and idntify th rcivd cho signals. By th thortical calculation and xprimntation, th rsult shows th lasr targt optics charactristics ar consistnt with th calculation mthod of radiation. h ral rflctiv signal can b idntifid by using wavlt transform, and th numrical valu of th distanc btwn th targt and th dtctor is largr, th numrical valu of cho signal will b smallr. Copyright 04 IFSA Publishing, S. L. Kywords: argt optics charactristics, Dtction distanc, Signal rcognition procssing, Dtction scrn systm.. Introduction With th rapid dvlopmnt of modrn construction, a high prcision masurmnt in masuring th hight, lngth and width of th industrial buildings is mor and mor important, so as gtting th transportation hubs paramtr in transport systms. Currntly, th mthod of obtaining th distanc in th systm oftn adopts lasr masurmnt distanc mthod []. Du to th variability in nvironmnt and divrsity in masurmnt objctivs, th accuracy in lasr masurmnt distanc systm is affctd gratly. Espcially in th fild tsts, thr ar many influntial factors, such as lighting, trrain, rflctiv surfac of targt []. h accuracy in lasr masurmnt distanc systm dpnds on th cho signal charactristics of targt, cho signal of targt may b burid in nois and it is difficult to idntify th ral usful signal whn th nois in xtrnal nvironmnt is big. hrfor, w rsarch cho charactristics of th lasr targt and idntification of th signal by th dtction principl of lasr masurmnt distanc systm. hn, w provid th analysis and rsarch to improv th accuracy of lasr masurmnt distanc systm. For th signal procssing of lasr masurmnt distanc systm, in rfrnc [3-5], thy proposd many factors that affct th prcision Articl numbr P_859 49

2 Snsors & ransducrs, Vol. 64, Issu, Fbruary 04, pp about th short-rang masurmnt distanc systm in impuls-typ lasr masurmnt distanc systm, thy mainly discussd influncing factors about th idntification in momnt and th masuring accuracy of tim intrval in rfrnc [6]. In th manwhil, thy also had studid th rlvant improvmnt masurs. Howvr, ths mthods do not systmatically analyz th cho charactristics in dtction systm. h papr basd on th prspctiv of principl of lasr dtction by using th wavlt signal procssing mthods to study th cho charactristics of th lasr targt and idntification of th signal in ordr to improv th dtction prformanc of dtction systm.. h Principl of ptics Dtction Analysis in Scrn Dtction Systm h impuls-typ lasr masurmnt distanc systm is mainly using th tim diffrnc btwn transmitting lasr puls signal and rciving lasr cho signal of targt to masur th distanc btwn th lasr mission sourc and targt. h principl of impuls-typ lasr dtction systm is shown as follows, s Fig. : signal is snt to th nd-timing modul of tim-digital convrsion chip, th whol masurmnt procss is compltd. Hr, L is th distanc to b masurd. is th doubl tst tim which is usd from th lasr mission point to th objct. C is th lasr spd in air (assuming th masurd nvironmntal paramtrs hav bn st), n is th atmosphric rfractivity, thn w can obtain th formula of th distanc from th lasr mission point to tst targt position, th formula is L = C/n. In th principl of lasr masurmnt distanc systm, whthr w can dtct th usful signal is rlatd to th lasr cho signal strngth of targt. h cho signal of th targt is affctd by xtrnal influncs bcaus of th variability in nvironmnt, thn th lasr masurmnt distanc systm will los fficacy, so th cho signal dtction of this systm is th important parts of th dsign. his papr basd on th principl of lasr masurmnt distanc systm, w stablish th charactristic modl of th rflctiv surfac by th curvatur faturs of surfac on targt, signal procssing is as th cor to idntify th cho signal. 3. Rsarch argt ptics Charactristics in Dtction Systm 3.. h Radiation Charactristics on argt By calculating and analyzing th radiation from surfac lmnt of th targt, w can s th spctral radiant xitanc of surfac lmnt varis with wav lngth valus. W can gain that th surfac spctral radianc xitanc of targt is M by th Plancks law [8, 9]. Fig.. Dtction principl diagram. M a 5 ( a / ), () h high frquncy impuls-typ squnc of lasr bam is transmittd by th mission circuit. h divrgnc angl of lasr bam is comprssd through th lns, thn, th lasr bam startd flying, th diffus rflction b occurrd aftr ncountrd obstacls. h rflctd lasr in ffctiv ara rturnd to th rciving dtctor, w obtain th intgrat cho signal of targt by using th photolctric convrsion circuit and amplifir rctifir filtr circuit [7]. W put th lasr fdback timing modul in th dtction circuit: a lasr bam is rflctd by th plan mirror which is in front of th lns, thn th lasr bam ntr into th lasr fdback timing modul, thn, th lasr bam pass through th photolctric convrsion circuit and amplifying circuit, th lvl signal is snt to th start-timing modul of tim-digital convrsion chip; th rciving lasr cho signal of targt passing through amplifying circuit is changd into a lvl signal, thn th lvr whr is th rflctivity of th surfac lmnt, is th tmpratur of th surfac lmnt, is th lasr radiation wavlngth, a and a ar th radiation constant, -6 a Wm, - a mk. In ordr to mak th dtctor obtaining ffctiv spctral radiant flux from th targt, th spctral radiant flux of th dtctor on th targt for ach surfac lmnt must b calculatd. hn add up all th spctral radiant flux of ach surfac lmnt to th dtctor in a crtain way. W dfin that th ovrlap ara of transmitting and rciving light path of th lasr masurmnt distanc systm is ffctiv ara. h photosnsitiv window of th dtctor rciv radiation flux in any surfac lmnt (, i j ) in th ffctiv ara is M. hn th radiation flux M about this surfac lmnt in th cho of targt fild is 50

3 Snsors & ransducrs, Vol. 64, Issu, Fbruary 04, pp M M, () whr is angular cofficint of surfac lmnt (, i j) about accptanc point of dtctor. cos / R, (3) whr is th angl btwn two lins. n of lins is from th point of rciving ara on th dtctor to th surfac lmnt of targt, anothr lin is normals of objctiv surfac. h rang of th angl is half of th fild of th ffctiv ara. According to cho charactristics, w stablish a calculation modl about cho information, showing as Fig., Qxy (, ) is th position of dtction rcivr. Assuming that th targt is at th origin of th coordinat, its rflction nrgy of th surfac lmnt Ai, j in th coordinat systm is Q (, ) (, i j) x y, according to th calculation principl of th radiation fluxs about cho, th radiation flux of currnt surfac lmnt can b calculatd by M a ( ) A, (4) ( ) Q( i, j) ( x, y) 5 a / t whr t is th tmpratur of th surfac lmnt (, i j ), w put formula (4) into formula (), and gain spctral radiant flux, it can b xprssd by a M ( ) A 5 a / ( () y t ) M ( ) M ( ), (6) i, j Hr, M ( ) is th total spctral radiant flux of a b surfac lmnt of targt. According to abov calculation, L ( t, ) is radiation brightnss of surfac on targt in a momnt at ~ [0], L ( t, ) can b xprssd by L ( t, ) M ( ) d (7) Basd on th targt radiation brightnss, w suppos that th ffctiv radiatd powr rcivd by dtctor is, can b xprssd by A A R L ( t, ) d, (8) whr A is th ara of targt radiation sourc, A is th snsitiv ara of dtction rcivr, R is th distanc btwn th dtctor and targt. 3.. Analysis on argt Rflction Charactristic h illumination of lasr mission sourc whos luminous intnsity is I at th distanc R from th lasr mission sourc to targt is E, E can b xprssd by formula (9). Id IdA cos I E cos, (9) da da da R R A i j Qxy (, ), / o Fig.. h cho charactristic diagram. x whr I is th luminous intnsity, is th angl btwn th radius vctor R from lasr sourc to targt cntr and th normals of th surfac. Luminanc L is constant, th radiator which L is rgardlss of th dirction is known as th cosin radiator, or Lambrtian radiator [-]. h luminous flux that mittd by this kind of radiator in cub angl lmnt d is proportional to th cosin of th angl of inclination on light-mitting surfac. d Lcos dad (0) In (5), th spctral radiant flux contributd to th dtctor from any surfac lmnt of th targt can b got. h radiation of all surfac lmnts projct to th rciving surfac of photolctric dtctor. h total spctral radiant flux is qual to suprposition of all surfac lmnts. For th cosin radiation surfac, its luminanc L has th following rlationship with th radianc M, it can b xprssd by M L () 5

4 Snsors & ransducrs, Vol. 64, Issu, Fbruary 04, pp Whn th cosin radiation surfac is not luminous surfac but illuminatd surfac, thn th rlationship btwn luminanc L and intnsity of illumination is as follows: L E, () whr is th rflctivity of th targt. h luminanc L of th light-mitting surfac lmnt has th following rlationship with luminous intnsity [3]: L I, (3) da cos whr da is th surfac lmnt ara of th lightmitting sourc. Namly, th luminanc of th surfac lmnt is qual to th luminous intnsity on unit ara in th normal dirction. h Intnsity of illumination gnratd from surfac lmnt da to th surfac lmnt da is E, th distanc btwn surfac lmnt da and th surfac lmnt da is R. da cos cos E L R Ld cos, (5) whr is th angl btwn cntr radius vctor of surfac lmnt da and normals of unit surfac, is th angl btwn Cntr radius vctor of surfac lmnt da and normals of unit surfac [, ], d is th cub angl btwn th cntr of da and th cntr of da. d dacos R (5) Combind with th analysis of th lasr targt radiation flux and th targt surfac luminanc in rflction fild, th output voltag signal can b calculatd by using function rlationship btwn th input radiation flux and th output signal strngth of th dtctor aftr gtting th ffctiv radiation flux. 4. h Idntification of th argt Signal h output signal of th dtctor contains high frquncy and low frquncy signals, tc. Usually th low frquncy part in circuit procssing can b liminatd by th filtr circuit, th transint high frquncy componnts can also b appropriat liminatd by using th principl [3] of band-pass filtr circuit. Howvr, th cho signal of targt is also a kind of high frquncy signal, so w nd dtct and xtract a crtain band-pass output signal. hrfor, according to th principl of wavlt transform, w nd to focus on th charactristics of band-pass frquncy in th xtraction procss of th cho signal of targt charactristics. As an xampl of thr layrs of wavlt dcomposition, w xclud mor than half of locking frquncy wavlt cofficints which is h, only xtract th wavlt cofficints which ar h, h 3, h 4. Using frquncy band nrgy as fatur, w construct th fatur vctors: E ( E0, E, E). Aftr dtctor rcivs th cho signal, th rcognition of output analog signal from dtction circuit can b thought of as two kinds of discriminant problm, in ordr to idntify th cho signal of targt quickly, w choos Fishr discriminant mthod. h thought of Fishr discriminant mthod is: wo n-dimnsional sampls b projctd to a crtain dirction, and w us varianc analysis to mak th dats sparatd btwn on projctd dats and th sampls as much as possibl, a linar discriminant function is obtaind from Fishr critrion [4], this function is: f ( x) M X MxMx... Mnxn, (6) whr M ( M, M, M3,..., M ) n, M is th discriminant cofficint vctor, X ( x, x, x3,..., x ) n, X is th charactristic vctor. o dtrmin th cho signal of targt from th output signal of th dtction circuit, w put forward two discriminat modls. Dscription of th thory of th two discriminat modls is: thr ar two sampl populations that ar B and B. B is th sampl population of background signal, B is th sampl population which contains th cho signal of targt, charactristics vctor of th two sampl populations is n-dimnsional vctor X. For a givn nw sampl, w nd to dtrmin that th nw sampl blongs to B or B, namly, w nd to dtrmin th signal is th background signal or cho signal. Assuming th avrag of th two sampl population ar k and k, th corrsponding discriminant function valus ar M k and M k. If M k < M k and M k ( ) f0 x, w dtrmin that th sampl blong to B ; if M k ( ) f0 x, th sampl is B. f ( x ) 0 is th thrshold point, f ( ) 0 x can b th avrag or wightd avrag of M k and M k. W construct th fatur vctor X ( E0, E, E) by using charactristic from th nrgy of th signal band, th charactristic is obtaind by only xtracting wavlt cofficints 5

5 Snsors & ransducrs, Vol. 64, Issu, Fbruary 04, pp which ar h, h 3 and h 4 in thr layr wavlt dcomposition from th principl of wavlt transform. Although th xtractd part of wavlt cofficints can not accuratly rstor th original targt of cho signal, th idntification problm for th cho signal of targt dos not nd to rstor th original signal, w hav only to xtract th signal charactristics of targt accuratly and fficintly for idntification. In ordr to nsur ral-tim of th algorithm, w rduc th numbr of fatur dimnsion undr th ffctiv wavlt dcomposition, so w improv th idntification raltim of th cho signal [5, 6]. W provid that charactristics vctor of n tims obsrvation data of dtction systm background () () () signal is X, X,, Xn, charactristics vctor of n tims obsrvation data of containing th cho () () () signal is X, X,, Xn, w obtain linar discriminant function [6] by Fishr critrion: f( x) M X M E M E M E, (7) 0 0 In (7), M ( M, M, M3,..., M ) n, M is th discriminant cofficint vctor, w can judg whthr th cho signal of targt xist by combind with th discriminant ruls. 5. h Exprimnt and Analysis W mak quantitativ analysis about th output powr, radiation intnsity and othr paramtrs, using diffrnt lasr wavlngth and transmission powr of lasr transmittr in th laboratory on th basis of th abov principl. Assuming is th dtctor rspons rat. = 7 0 V / W, A is th sourc ara of targt radiation, A = 9 3cm, A is th snsitiv lmnt ara of dtction rcivr, A =.4.8 mm, is rflctivity of th targt, =0.75. W slct two kinds lasr transmittr to xprimnt and analysis. h transmission powr of lasr transmittr ar 30 mw and 50 mw rspctivly, th distanc R from th dtctor to th targt changs btwn 0 to 4 m. h rlationship btwn th corrsponding output powr P out and R is shown in Fig. 3; th wavlngth changs btwn 0.4 to. um, th rlationship btwn th corrsponding output powr Pout and is shown in Fig. 4. W still slct two kinds lasr transmittr to xprimnt and analysis. h transmission powr of lasr transmittr ar 30 mw and 50 mw rspctivly, th distanc R from th dtctor to th targt changs btwn 0 to 4 m, thn th diagram btwn th radiation intnsity L and distanc R is shown in Fig. 5; th wavlngth changs btwn 0.4 to.6 um, so th diagram btwn th radiation intnsity L and is shown in Fig P out mv Fig. 3. h output powr varis with th distanc R. 50 Pout mv R m um Fig. 4. h output powr varis with wavlngth L ( mw / sr m ) R ( m) Fig. 5. Radiation brightnss varis with distanc R L ( mw / sr m ) ( um) Fig. 6. Radiation brightnss varis with th wavlngth. 53

6 Snsors & ransducrs, Vol. 64, Issu, Fbruary 04, pp By th abov diagram, w can gt that th output powr P out is invrsly proportional to R. h closr distanc btwn targt and th dtctor, th gratr th output powr; th farthr th distanc, th smallr th output powr. h magnitud of th output powr P out has a maximum valu in th procss of changs by. Using diffrnt transmission powr of lasr transmittr, th magnitud of th output powr P out is also diffrnt, th biggr th transmission powr, th gratr th output powr. h radiation intnsity L and th distanc R from th targt to dtctor both ar invrsly proportional to th wavlngth. h chang rat of invrs proportion by th wavlngth is highr than by th distanc R. h radiation intnsity L accompany with transmission powr incrass. In ordr to obtain th rflctd cho nrgy undr diffrnt distancs, w st a hardwar platform of lasr targt cho dtction systm. It includs th lasr mission systm and th targt cho dtction systm. w gt th rsults by xprimnt on th hardwar platform ar shown in th following diagrams, w still slct two kinds distanc to xprimnt and analysis. h distanc btwn targt and dtctor ar 3 m and 5 m rspctivly. h xprimntal data is consistnt with th thortical analysis. 6. Conclusions W analyz th cho charactristics of lasr targt by th principl of targt dtction basd on lasr masurmnt distanc systm in this papr. W construct th calculation modl by analyzing th factors which will affct th output voltag of dtctor, whn th transmit powr of lasr is constant, th output powr of th dtctor is invrsly proportional to th dtction distanc, th magnitud of th output powr at th chang procss of th wavlngth has a maximum valu; h radiation intnsity and th distanc R from th targt to dtctor both ar invrsly proportional to th wavlngth, but th chang rat of invrs proportion by th wavlngth is highr than by th distanc R. With th incras of th transmit powr of lasr, th output powr and th radiation intnsity of targt cho is also incrasd. W hav vrifid that th xprimntal data is consistnt with th thortical analysis and th xprimnt on th hardwar platform. In viw of th abov analysis, w provids a thortical basis about improving prformanc of dtction part of lasr masurmnt distanc systm, and uss th Fishr discriminant mthod of th Wavlt analysis and wavlt maxima mthod for cho signal to discriminat and distinguish, and improvs th rliability of cho signal. So lasr dtction part can provid bttr srvic for th whol lasr masurmnt distanc systm. Acknowldgmnts Fig. 7. argt rflct cho signal in 5 mtrs. his work has bn supportd by Projct of th Foundation of Dpartmnt Education of Shaanxi Provinc of China (No. 03JK08) and th National Natural Scinc Foundation of China (No ). Rfrncs Fig. 8. argt rflct cho signal in 3 mtrs. It can b sn from th xprimntal pictur, th output voltag of dtctor is corrlatd with th distanc btwn th targt and th dtctor. h distanc R is largr, th output voltag will b smallr. Incrasing th dtction distanc of th dtctor, thn th output voltag will b affctd. []. Xiaofan Wu, Chun Chn, Jia Jun Bu, An intrfrnc-awar transmission powr control schm for vhicular on-board monitoring wirlss snsor ntwork, ELKMNIKA Indonsian Journal of Elctrical Enginring, Vol. 0, No. 5, 0, pp []. X. F. Mao, X. Y. Su, Y. K. Liu, Analysis on optical coordinat masurmnt basd on phas targt, Acta ptica Sinica, Vol. 9, No. 9, Sptmbr 009, pp [3]. Y. H. Yuan, J. J. Zhang, Z. L. Chn, Simulation study on tmpratur and infrard radiation charactristics of flying projctil, Acta Armamntarn, Vol. 3, No. 8, August 00, pp

7 Snsors & ransducrs, Vol. 64, Issu, Fbruary 04, pp [4]. Hanshan Li, Zhiyong Li, Zmin Wang, Junchai Gao, Rsarch on objction information xtraction arithmtic in photo-lctric dtction targt bas on wavlt analysis mthod, Przglad Elktrotchniczny, Vol. 88, No. 9, 0, pp [5]. Chn Guichu, Fan Guanghan, h ffct of spontanous mission on AM nois for quantum cascad lasr, Chins Journal of Luminscnc, Vol. 30, No. 3, 009, pp [6]. W. Yang, J. Q. Zhang, J. S. Liu, hortical calculation of infrard radiation of th projctil in flight, Infrard and Lasr Enginring, Vol. 34, No., January 005, pp [7]. H. P. Wang, H. Xu, Z. K. Sun, hortical calculation of IR radiation charactristics of ballistic targt out of atmosphr, Systms Enginring and Elctronics, Vol. 0, No. 3, March 998, pp. -6. [8]. Song Jiangtao, Shn Xianghng, utdoor simulation systm of infrard radianc of larg ground targts, ptics and Prcision Enginring, Vol. 8, No. 5, 00, pp [9]. Li Yuan, Rong Zhiguo, Zhng Zhaojun, Post launch sit calibration of visibl and nar infrard channls of FY-3A visibl and infrard radiomtrs, ptics and Prcision Enginring, 009, Vol. 7, No., pp [0]. C. Van Nikrk, W. J. Rossouw, A proposd format for firing tabls of a sris of carrir projctils []. []. [3]. [4]. [5]. [6]. possssing ballistic similarity with a HE projctil, in Procdings of th Intrnational Symposium on Ballistics, USA, Sptmbr 00, Vol. 5, No., pp Hanshan Li, Zhiyong Li, Zmin Wang, Rsarch objct photolctric charactristic and fir coordinat distributing probability in across scrn systm, Journal of Nanolctronics and ptolctronics, Vol. 7, No., 0, pp Y. Jon, Y. J. Shn, Z. M. Zhang, B. K. sai, Bidirctional rflctanc distribution function of rough silicon wafrs, Intrnational Journal of hrmophysics, Vol., No. 4, 004, pp Zhang ao, An Wi, Zhou Yiyu, h trajctory locating and tracking algorithm in boost phas, Journal of Ballistics, Vol. 7, No. 4, 005, pp. -6. Zhuxin Zhao, Gongjian Wn, Xing Zhang, Modlbasd stimation for pos, vlocity of projctil from stro linar array imag, Masurmnt Scinc Rviw, Vol., No. 3, 0, pp Hu Jin, Du Li, Zhang Yiqi t al., Nois as a rprsntation for rliability of light mitting diod, Acta Physica Sinica, Vol. 55, No. 3, 006, pp Hanshan Li, Zhiyong Li, Rsarch on idntification and dtction of high vlocity projctil information basd on sky-scrn, Smiconductor ptolctronics, Vol. 3, No. 5, 0, pp Copyright, Intrnational Frquncy Snsor Association (IFSA) Publishing, S. L. All rights rsrvd. ( 55