Theoretical and Experimental Investigation Into the Influence Factors for Range Gated Reconstruction

Transcription

1 PHOTONIC SENSORS / Vol. 6, No. 4, 016: Theorecal and Experenal Invesgaon Ino he Influence Facors for Range Gaed Reconsrucon Sng Yee CHUA 1, Xn WANG 1*, Nngqun GUO 1, and Chng Seong TAN 1 School of Engneerng, Monash Unversy Malaysa, Jalan Lagoon Selanan, Bandar Sunway, Selangor, Malaysa Faculy of Engneerng, Muleda Unversy, Jalan Muleda, Cyberjaya, Selangor, Malaysa * Correspondng auhor: Xn WANG E-al: wang.xn@onash.edu Absrac: Range gaed s a laser rangng echnque ha has been appled n varous felds due o s good applcaon prospecs. In order o prove he effecveness of hs ehod, nfluence facors conrbung o he syse perforance should be well undersood. Thus hs paper perfors heorecal and experenal nvesgaon o coprehend he effecs caused by ulple facors on range gaed reconsrucon. Our sudy focuses on he dsance, arge reflecon, and acquson e sep paraeer where her pacs on he qualy of range reconsrucon are analyzed. The presened experenal resuls show he expeced rends of range error o suppor he valdy of our heorecal odel and dscusson whch can be used n fuure proveen works. Keywords: Laser rangng; reflecon; sensor Caon: Sng Yee CHUA, Xn WANG, Nngqun GUO, and Chng Seong TAN, Theorecal and Experenal Invesgaon Ino he Influence Facors for Range Gaed Reconsrucon, Phoonc Sensors, 016, 6(4): Inroducon Over he pas decades, laser rangng has been a popular approach n opcal erology because of s unque characerscs of non-conac and nondesrucve naure [1]. As of oday, laser rangng has been appled n varous felds such as oceanc and envronenal research, survellance, ndusry, and day-o-day applcaons []. Range gaed s a laser rangng echnque operaes based on e-of-flgh (TOF) prncple o easure he ravel e beween he eed laser pulse and he pulse refleced fro he arge. Pulsed laser and sensor s gae are conrolled sulaneously o capure he refleced pulse where range r s deerned fro he round rp e and he speed of lgh c. c r. (1) Range gaed has been a prosng ehod n applcaons such as arge deecon and recognon [3], ngh vson [4, 5], underwaer [6, 7], and hree-densonal (3) agng [8, 9]. Besdes, connuous developen n laser, sensor, sgnal processng, and copuer echnology furher proves he cos effecveness of hs approach. The good applcaon prospecs ovae he sudy no he nfluence facors for range gaed reconsrucon whch can conrbue o prove he syse perforance. In a range gaed syse, laser pulse neracs wh he arge surface o generae a backscaer sgnal whch conans he key nforaon for range reconsrucon. Hence, he qualy of range Receved: 13 June 016 / Revsed: 17 July 016 The Auhor(s) 016. Ths arcle s publshed wh open access a Sprngerlnk.co OI: /s Arcle ype: Regular

2 360 Phoonc Sensors reconsrucon srongly reles on he refleced laser pulse fro he arge whch undergoes changes along he propagaon. Essenally, he deeced laser pulse s affeced by he laser source, sensor, arge, and aospherc effec [11]. These paraeers could change he characerscs and cause varaons n he refleced laser pulse whch drecly pac he accuracy of range deernaon. The porance of laser nensy profle [11, 1], dsance nerference [10], sensor [13, 14], and scaerng effecs [16] were dscussed n varous leraures. In hs paper, range gaed reconsrucon s analyzed heorecally and experenally o oban a coprehensve undersandng and relaonshp beween he nfluence facors and rangng perforance. In Secon, a bref of range gaed echnque s gven, and heorecal dervaon and analyss of 3 range gaed reconsrucon odel are presened. On he oher hand, he experenal seup for our nvesgaon s descrbed n Secon 3. The pac of ulple nfluence facors s analyzed and dscussed n Secon 4. Fnally, a concluson s gven n Secon 5.. Theorecal dervaon of range gaed reconsrucon odel Range gaed approach operaes based on TOF concep by easurng he round rp e beween he eed laser pulse and he pulse echo resulng fro s reflecance off he arge. The workng prncple of a range gaed agng syse usng e slcng echnque s llusraed n Fg. 1. Pulsed laser s used as he llunaon source, and gaed caera s e delayed o open only for a very shor duraon norally n nanoseconds or pcoseconds o capure he refleced age slce fro he arge over a dsance. Synchronzaon beween he laser and gaed caera s parcularly poran. Caera gae reans closed when he laser pulse s eed owards arge. Caera gae s confgured o open a he desgnaed delayed e o capure he vsble e slce refleced n he for of nensy age. Synchronzaon conrol pxel 1Es laser pulse & caera gae closes 5 Laser Gaed caera 6 n1 n Refleced laser pulse & caera gae opens Iage sequence =1,,, n Vsble e slce Fg. 1 Operang prncple of range gaed agng syse. Based on e slcng echnque [8, 9, 1], he caera gae G() s delayed by e wh a e sep sep o acqure an age sequence =1,, 3,, n. Inensy capured n an age pxel I (x, y) s he ncden energy of refleced laser pulse P r () negraed when he caera gae s opened for a gae e whch can be expressed as r I( xy, ) Pr G ( ) d c. () Typcally, he caera gae G() s assued as consan; hence he pxel nensy reles on he refleced laser energy P r (). Fro laser deecon and rangng (LAAR) range equaon, he receved sgnal P r s defned as [17] sys a AP P r r ( r) (3) R where P r and P are he receved and ransed sgnals across range r, and ɳ sys and ɳ a represen he syse effcency facor and aospherc ranssson loss caused by absorpon and scaerng. s he daeer of recever aperure, and ρ s he arge surface reflecvy. represens he laser ranser bea daeer and angular dvergence, and R s he sold angle over whch radaon s dspersed upon reflecon.

3 Sng Yee CHUA e al.: Theorecal and Experenal Invesgaon Ino he Influence Facors for Range Gaed Reconsrucon 361 Assue he arge surface area A s equal o he projeced area of laser bea [17] A r. (4) 4 Equaon (3) can be splfed as sys a Pr P (5) 4r where R corresponds o he arge reflecon characerscs whch we can represen wh a bdreconal reflecon dsrbuon funcon (BRF) odel [18] where K S and K are he specular and dffuse reflecon consans, s he angle of ncdence and reflecon, s s he surface slope, and s he dffusvy coeffcen. K S an BRF exp K cos. 6 (6) cos s Gaussan for s coonly assued for eporal funcon of he ransed laser pulse P () where P o represens he ransed power and p denoes he sandard devaon of laser pulse [9, 13]: P o P () exp. (7) p p Accordngly, (5) can be wren as P Pr () exp sys a o 4r p p R KS an exp K cos. 6 (8) cos s Usng e slcng echnque, he suaon of radan energy n he age pxel can be seen as he negraon over e slces d / as he e sep sep for age acquson s uch saller han he laser pulse wdh and caera gae [9]: I( x, y) d I( x, y) I ( x, y). (9) sep Based on (), we can furher splfy I(x, y) as Pr () d G( ) d I( x, y). (10) By subsung P r () fro (8) no (10) and assue sep G()=1 when 0 gae, I(x, y) becoes sys a I( x, y) 4r sep KS an exp K cos 6 cos s P gae o exp d d. (11) 0 p p Ths equaon evenually resolved no I( x, y) sys a gae P o 4r sep KS an exp K cos. 6 cos s (1) Sgnal o nose rao (SNR) s an poran paraeer n analyzng he syse perforance [19]. SNR s defned as he rao beween he refleced nensy and he assocaed noses. For our range gaed reconsrucon, SNR can be expressed as follows afer subsue I fro (9) [10]: I Id SNR. ( I ) ( I ) sep (13) Uncerany n he wo-way ravel e s gven by he acquson e sep sep ; hence he expeced range error can be wren as c c Id r sep. (14) SNR ( I ) Average range <r> and wo-way ravel e <> of an age pxel (x, y) can be deerned fro he capured nensy over an age sequence =1,, 3,, n usng weghed average ehod: c c r 1 ( x, y). n n 1 I ( xy, ) I ( xy, ) (15) The calculaed range <r> srongly reles on he refleced nensy whch s nfluenced by varous facors as shown n (1). In addon, range accuracy s paced by SNR whch s proporonal o he

4 36 Phoonc Sensors refleced nensy when he syse nose level reans unchanged. Generally, he decreased SNR resuls n hgher range errors. Based on he range gaed reconsrucon odel derved, he relaonshp beween he refleced nensy I and varous nfluence facors n he syse s shown as well as her pac o he SNR and range error. Experenal sudy nvolves a few facors ncludng he dsance, arge reflecon, and acquson e sep o valdae our heorecal dscusson. 3. Experenal seup In order o nvesgae he effecs nduced by varous nfluence facors, an experenal seup as llusraed n Fg. s used. A pulsed dode puped sold sae Q-swched Nd:YAG laser ha operaes a wavelengh 53 n wh oupu energy up o 1J s used. Slcon hgh speed based non-aplfed phoodeecor wh acve daeer of 400 and <300 ps rse/fall e s used o deec he laser pulses n he eng or reflecng drecon. Phoodeecor ransfors he opcal pulse no he usable sgnal for analyss va osclloscope. o focus on hree facors: dsance, arge reflecon, and acquson e sep where he refleced nensy and range error are analyzed. 4. Analyss of nfluencng facors 4.1 sance The refleced nensy odel derved as (1) shows ha he refleced laser energy underles an nverse range-squared dependency. Usng he experenal seup descrbed n Secon 3, varaon of he refleced nensy across dsance s suded. The analyzed resuls are suarzed n Fg. 3 where clearly shows an nverse range-squared relaonshp of he refleced nensy [10]. Power supply & laser rgger Phoo deecor Fg. 3 Measured refleced laser nensy versus 1/range rendlne [10]. osclloscope Laser Phoo deecor Eed laser pulse Refleced laser pulse Targe Fg. Scheac dagra of experenal seup o capure he eed and refleced laser pulse for nvesgaon. A backscaer sgnal s produced afer he eed laser pulse neracs wh he arge surface and s receved by he deecor n he for of e funcon. Two-way ravel e across he dsance beween arge and he deecor s deerned fro he e dfference beween he eed and refleced laser pulse. Correspondngly, he dsance or range r can be obaned based on he TOF prncple. For our sudy, he experen s desgned Fg. 4 Coparson of range error versus dsance/range under he sae consan seup condon. Because of he reduced nensy over dsance, SNR decreases, and we expec hgher range error as deduced fro (14). Fgure 4 shows he range error calculaed usng weghed average ehod based on

5 Sng Yee CHUA e al.: Theorecal and Experenal Invesgaon Ino he Influence Facors for Range Gaed Reconsrucon easureens capured a dfferen dsances. The daa ses are acqured under he sae seup condon o ensure he range error s no nfluenced by oher paraeers n he syse. The resuls show ha an ncrease n dsance causes a proporonal decrease n he refleced nensy and leads o ncreasng range error as observed whch agrees well wh our heorecal dscusson. 4. Targe reflecon Refleced nensy srongly depends on he characerscs of he arge surface [0]. Alhough Laberan arge (deal dffuse surface) s coonly assued due o s splcy, arge reflecon s n fac far ore coplcaed, and BRF concep s norally used o descrbe ha. Our heorecal odel has adoped a BRF odel gven by (6) whch consss of specular and dffuse reflecon o analyze he characerscs of refleced nensy n hs sudy. Reflecon off a rough surface reurned n any drecons leads o dffuse reflecon whle reflecon fro a sooh surface reans concenraed wh he angle of reflecon whch causes specular reflecon. Any arge surface praccally exhbs xure of specular and dffuse behavor per surface properes such as roughness and absorpon level. Sulaon based on he BRF odel s shown n Fg. 5 where four exaples of arge surface odel are copared. These nclude wo exree cases of pure specular and pure dffuse surface odels, and wo exaples of xed coponens surface wh dfferen raos of surface gln o dffuse behavour gven by specular and dffuse reflecon consans,.e. K S /K. The aplude of he reflecon s axu when angle of ncdence =0 degree and decreases when ncreases, adheres o he BRF odel. As a resul, he decreased nensy causes he reduced SNR whch gves rse o range error. Fg. 5 BRF sulaon as a coparson of dfferen arge surface odels. For our experenal sudy, varous arge surface aerals and roughnesses are esed. Fgure 6 copares he range error for arge surfaces capured a 5, and he resuls are analyzed based on average of 30 easureens. Fro he resuls, we observe ha he range error s hgher for rough and weak reflecve surfaces as copared o sooh and srong reflecve surfaces [1] where hese surfaces can be odeled usng BRF descrbed n our heorecal odel. In addon, he effec of angle varaon s evaluaed for varous arge surfaces where he correspondng range error s shown n Fg. 7. I can be clearly seen ha he range error s nu a zero angle of ncdence =0 degree and ncreases wh he angle of ncdence n general. Ths has deonsraed he angular dependency whch agrees wh he heorecal odel dscussed. Range error (%) Roug h wood Range error coparson for arge surfaces a 5 Sooh wood Rou gh pap er Sooh paper R ough plasc Soo h plasc Ro ugh seel Sooh seel Fg. 6 Coparson of range error for arge surfaces wh dfferen reflecvy and roughness.

6 364 Phoonc Sensors Range error (%) Range error versus angle of ncdence for arge surfaces Sooh seel Sooh wood Angle of ncdence (degree) Fg. 7 Coparson of range error versus angle of ncdence for arge surfaces wh dfferen reflecvy. 4.3 Acquson e sep Sooh plasc Sooh paper Fro (1) and (14), can be seen ha he refleced nensy s nversely proporonal o he e sep used o acqure a seres of age slces and error n he calculaed range r shows drec dependency on he e sep paraeer. Under he sae seup condon where all paraeers are regarded as consans, range error s expeced o ncrease wh e sep value n heory. Fgure 8 shows he range error rend analyzed based on average of 30 easureens. Ths se of experenal resul clearly pons ou ha a saller e sep should be seleced o gan hgher accuracy. However, he choce of he e sep used s a rade-off beween range accuracy and processng cos n ers of e and effor whch should be aken no consderaon. Fg. 8 Coparson of range error for dfferen e seps. 5. Conclusons In suary, hs paper has deonsraed he nfluence of ulple facors on range gaed reconsrucon hrough heorecal and experenal nvesgaon. Based on he operang prncple of e slcng echnque, LAAR, and BRF, heorecal dervaon of range gaed reconsrucon odel s presened. Range accuracy shows dependency on he SNR whch s proporonal o he refleced laser nensy when he syse nose level reans unchanged. Ipac on he accuracy of range reconsrucon s suded fro he perspecve of dsance, arge reflecon, and acquson e sep. Each nfluence facor s analyzed heorecally, and experenal nvesgaon s perfored o valdae he heorecal dscusson. I s concluded ha our experenal resuls agree well wh he heorecal analyss where he expeced range error rends are shown. The presened fndngs esablsh a coprehensve undersandng of ulple nfluence facors whch ay benef varous applcaons and serve as references o perfor correcon or copensaon. In fuure, follow-up proveen of range reconsrucon can be proposed and addonal effecs caused by llunaon, sensor, and nose can be ncluded. Acknowledgen The auhors graefully acknowledge he suppor of fundng fro Mnsry of Hgher Educaon, Malaysa under he Gran No: FRGS/1/016/STG0/ MUSM/0/1. Open Access Ths arcle s dsrbued under he ers of he Creave Coons Arbuon 4.0 Inernaonal Lcense (hp://creavecoons.org/lcenses/by/4.0/), whch pers unresrced use, dsrbuon, and reproducon n any edu, provded you gve approprae cred o he orgnal auhor(s) and he source, provde a lnk o he Creave Coons lcense, and ndcae f changes were ade.

7 Sng Yee CHUA e al.: Theorecal and Experenal Invesgaon Ino he Influence Facors for Range Gaed Reconsrucon 365 References [1] P. Huke, R. Klaenhoff, and C. V. Kopylow, Novel rends n opcal non-desrucve esng ehods, Journal of he European Opcal Socey Rapd Publcaons, 013, 8(13): 1 7. [] M. C. Aann, T. Bosch, M. Lescure, R. Myllylä, and M. Roux, Laser rangng: a crcal revew of usual echnques for dsance easureen, Opcal Engneerng, 001, 40(1): [3] Y. Lu, W. Zhang, T. Xu, J. He, F. Zhang, and F. L, Fber laser sensng syse and s applcaons, Phoonc Sensors, 011, 1(1): [4] A. Velen, T. Wllwacher, O. Gupa, A. Veeraraghavan, M. G. Bawend, and R. Raskar, Recoverng hree-densonal shape around a corner usng ulrafas e-of-flgh agng, Naure Councaons, 01, 3(745): 1 8. [5]. Monnn, A. L. Schneder, F. Chrsnacher, and Y. Luz, A 3 oudoor scene scanner based on a ngh-vson range-gaed acve agng syse, n Thrd Inernaonal Syposu on 3 aa Processng, Vsualzaon, and Transsson, Chapel Hll, NC, pp , 006. [6] X. W. Wang, Y. Zhou, S. T. Fan, J. He, and Y. L. Lu, Range-gaed laser sroboscopc agng for ngh reoe survellance, Chnese Physcs Leers, 010, 7(9): [7] J. Busck, Underwaer 3- opcal agng wh a gaed vewng laser radar, Opcal Engneerng, 005, 44(11): [8] C. Tan, G. See, A. Sluzek, and. He, A novel applcaon of range-gaed underwaer laser agng syse (ULIS) n near-arge urbd edu, Opcal and Lasers Engneerng, 005, 43(9): [9] J. Busck and H. Heselberg, Gaed vewng and hgh-accuracy hree-densonal laser radar, Appled Opcs, 004, 43(4): [10] S. Y. Chua, X. Wang, N. Guo, and C. S. Tan, Range copensaon for accurae 3 agng syse, Appled Opcs, 016, 55(1): [11] B. Höfle and N. Pfefer, Correcon of laser scannng nensy daa: aa and odel-drven approaches, ISPRS Journal of Phoograery and Reoe Sensng, 007, 6(6): [1] X. W. Wang, Y. F. Lu, and Y. Zhou, Trangularrange-nensy profle spaal-correlaon ehod for 3 super-resoluon range-gaed agng, Appled Opcs, 013, 5(30): [13] S. Y. Chua, X. Wang, N. Guo, C. S. Tan, T. Y. Cha, and G. G. L. See, Iprovng hree-densonal (3) range gaed reconsrucon hrough e-of-flgh (TOF) agng analyss, Journal of European Opcal Socey Rapd Publcaons, 016, 11: [14] B. Fu, K. Yang, J. Rao, and M. Xa, Analyss of MCP gan selecon for underwaer range-gaed agng applcaons based on ICC, Journal of Modern Opcs, 010, 57(5): [15] X. Wang, L. Hu, Q. Zh, Z. Chen, and W. Jn, Influence of range-gaed nensfers on underwaer agng syse SNR, Proc. SPIE, 013, 891: 8910E. [16] M. Laurenzs, F. Chrsnacher,. Monnn, and T. Scholz, Invesgaon of range-gaed agng n scaerng envronens, Opcal Engneerng, 01, 51(6): [17] R.. Rchond and S. C. Can, rec-deecon LAAR syses. U. S. A.: SPIE Press, 010: 1 6. [18] O. Senvall, Effecs of arge shape and reflecon on laser radar cross secons, Appled Opcs, 000, 39(4): [19]. Kong, J. Chang, P. Gong, Y. Lu, B. Sun, X. Lu, e al., Analyss and proveen of SNR n FBG sensng syse, Phoonc Sensors, 01, (): [0] S. S. Pal and A.. Shalgra, On-lne defec deecon of alunu coang usng fber opc sensor, Phoonc Sensors, 015, 5(1): [1] S. Y. Chua, X. Wang, N. Guo, C. S. Tan, and T. Y. Cha, Effecs of arge reflecvy on he refleced laser pulse for range esaon, n Progress In Elecroagnecs Research Syposu Proceedngs, Prague, Czech Republc, pp , 015.