PRINCIPLES OF USING GROUND PENETRATING RADAR AND GPS TECHNOLOGY FOR DETECTION OF UNDERGROUND UTILITIES

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1 PRINCIPLS OF USING GROUND PNTRATING RADAR AND GPS TCHNOLOGY FOR DTCTION OF UNDRGROUND UTILITIS PTROVAČKI Dušan RISTIĆ Aleksanda UNIVRSITY OF NOVI SAD FACULTY OF TCHNICAL SCINCS DPARTMNT OF AUTOMATIC CONTROL ABSTRACT This pape descibes moden non-invasive daa acquisiion mehods in undegound uiliy deecion. The wok pesens he possibiliies of connecing daa acquied wih a Gound Peneaing Rada wih GPS daa. Also he basic paamees mehods and hei influence on he acquisiion speed and daa qualiy ae defined.. INTRODUCTION No dig uiliy mapping echnology is impoan in daa acquisiion fo compuaion modelling and conol of undegound infasucue sysems. Today he developmen and ealisaion of new pipelines and cables in uban envionmen ae significanly fase han convenional mehods of uiliy mapping. Classic echnology based on ecavaion 30 yea old maps wih moe o less pecise pipeline oues and incoec measuemens causes incoec infomaion and majo poblems wih undegound uiliy mapping. A diec consequence of his appoach is an epensive uncoodinaed pocess of esablishing new pipelines accompanied wih damage o eising uiliies. Low qualiy infomaion abou condiion and opeaion of fo eample ciy wae supply sysem implicily affecs he fleibiliy of ha sysem. This can be seen on he diffenece beween he amoun of pocessed and disibued wae.. PHYSICAL AND THORTICAL CONCPTS OF GPR WORK The Gound Peneaing Rada GPR is a device used fo non-invasive scanning and pecise deecion of undegound uiliies. GPR is composed of a eceive and ansmie anenna a conol uni wih Win C OS baey supply and a suvey ca. Suvey ca is a icycle equipped wih incemenal encode. The incemenal encode is used fo pecise posiioning of he cene of he anenna above a pipeline oue. The GPR also has a make which is useful fo making ineesing deails on a ada scan. The GPR can be equipped wih a GPS Global Posiioning Sysem ove which is used fo measuing spaial coodinaes of he pojecion of he pipeline oue on he sie suface. The GPS ove can measue coodinaes eihe independenly o synchonied wih he GPR

2 ANNALS OF TH FACULTY OF NGINRING HUNDOARA 005 TOM III. Fascicole scan. In he second case he GPS ove measues all poins on he scanned ajecoy o jus he sa and end coodinaes. Synchonied wok imply diec communicaion beween GPS ove and he GPR device. Measuemen of pipeline paamees wih GPR and GPS measuemen coodinaes on he sie suface ae wih cenimee accuancy. This measuemen accuancy saisfies geodehic mapping laws []. Figue shows he schemaic picue of he GPR equipmen is funcional pas and he connecions beween hem. When he suvey ca moves on he sie suface he ansmiing anenna sends polaised high fequency elecomagneic M waves in he gound. Because of diffeen eising inhomogeneies in he gound e.g. soil layes undegound uiliies sones gavel caviies and ohe anomalies pa of he M waves is efleced fom he dielecic bounday beween diffeen maeials and he ohe pa is efaced and goes o he deepe layes. The decibed pocess is epeaed unil he M waves become oo weak. Reflecion of M waves fom he dielecic bounday is he consequence of diffeences in he elecic and magneic popeies of maeials of infasucual objecs and soil layes. Figue. Funcional pas of GPR The pinciple of funcioning GPR is he analyses of he popagaion of M waves in mae of measuemen of he elecic and magneic field sengh vecos wih espec o ime and spaial coodinaes. M field vecos in linea homogeneous envionmens saisfy Mawell's equaions and hey can be wien as wave equaions e.g. Helmhol equaions []: Δ σ 0 H H Δ H σ 0 whee: - elecic field sengh veco [V/m] H - magneic field sengh veco [A/m] - dielecic pemiiviy [F/m] 0 R σ conduciviy [S/m] [F/m] dielecic pemiiviy of fee space - magneic pemeabiliy [H/m] 0 R 0 4π 0-7 [H/m] magneic pemeabiliy of fee space If we conside he case when he M wave passes hough a pefec dielecic σ0 and wih espec o he naue of plane unifom wave equaions i can be shown wih a one dimensional wave equaion of polaised M wave popagaion along ais [3]: 6

3 ANNALS OF TH FACULTY OF NGINRING HUNDOARA 005 TOM III. Fascicole y H whee: [Ω] medium impedance i.e.measue of influence elecic and magneic popeies of medium y H - M wave veco componens pependicula fo each ohe and pependicula on M popagaion oue. The geneal soluion of equaion is he following: [ ] [ ] cos cos m y H m c f C β β 3 whee: m elecic field componen ampliude - elecic field componen fequency 0 0 c - speed of ligh: c [m/s] 4 / c β - phase aio WAV v The geneal soluion 3 descibes he popagaion of M waves moving wih speed c along he ais. Funcion f is a plain peiodic funcion. The geneal soluion shows he changes of speed of he M wave and magniude of elecic and magneic field sengh vecos when he wave passes ough a medium. Tha is caused by he influence of elecic and magneic popeies of a medium. In eal poblems he medium hough which M waves pass is no a pefec dielecic medium. The geneal soluion of equaion is he following [3]: cos cos e y H e θ θ β α θ β α effecive value of elecic field componen θ elecic field sa phase θ medium impedance agumen α - aenuaion consan of medium [Np/m] - field componen fequency / c β - phase aio c [m/s] - speed of ligh σ j [Ω] comple medium impedance in case of impefec medium. 7

4 ANNALS OF TH FACULTY OF NGINRING HUNDOARA 005 TOM III. Fascicole quaions 5 show eponenial aenuaion of he veco field ampliude along he ais. The ae of speed change is popoional o he aenuaion consan of he medium - α. In geneal i σ ae comple values so eac calculaion of paamees α i β is no simple. quaion 6 shows he speed of he M wave popagaion wih a clealy visible influence of conduciviy. Soil conduciviy causes wave dispesion. Based on hese facs we conclude ha media wih high conduciviy ae impeneable fo M waves [4]. 8 σ c β 8 vwav [m/s] 6 Pacical use of Mawell's equaions fo he deeminaion of field popeies duing GPR scanning is difficul. Because of his ceain assumpions should be acceped. Fo he majoiy of media R meaning ha he influence of he magneic popeies of he medium can be ignoed. This assumpion inoduces a small eo in he majoiy of he cases. Also he influence of he specific conduciviy can be ignoed. Medium ypes ae chaaceied by looking up hei paamee values fom ables. Reseach is conduced in ode o find a moe pecise mehod of deemining he value of hese paamees. Based on hese assumpions he speed of M wave popagaion is defined as: c ν [m/s] 7 wave R Time necessay fo he popagaion of M waves fom ansmi anenna o he bounday suface and is eflecion back o he eceive anenna is defined as a wo way avel R [ns] ime. The GPR measues R and finally calculaes he elaive deph of he undegound objec: c v R R R [m] 8 Because each locaion has is specific soil sucue R has o be ecalculaed fo each sie. Usually he GPR ecalibaion mehod is used on sie. This mehod is based on a GPR scan of an undegound objec wih known deph [3]. Mehodology of ada scan geneaion is shown in Figue. A ada scan is a spaial secion of he woking aea. The anenna's linea X N X 0 X N ajecoy is shown on X ais X N X 0 X N and Y ais shows he wo way N 0 N undegound objec. N 0 N avel ime R i.e. he elaive deph fom he suface o he OBJCT HYPRBOLA ANTNNA MOVMNT DISTANC PROJCTION RADAR SCAN Figue. Rada scan geneaion The disance beween ansmi and eceive anenna is vey small. Because of his he disance fom ansmi anenna o bounday suface is appoimaely equal o he disance fom bounday suface o he eceive anenna. The disance fom anenna o he undegound objec coninuously changes. Disances 0... N ae pojeced oogonally on he

ANNALS OF TH FACULTY OF NGINRING HUNDOARA 005 TOM III. Fascicole movemen ais see poins -N... 0... N see middle secion of Figue.

5 ANNALS OF TH FACULTY OF NGINRING HUNDOARA 005 TOM III. Fascicole movemen ais see poins -N N see middle secion of Figue.. By sequenially connecing he ends of hese segmens a geomeical hypebola is fomed. All poins on he scan include efleced wave ampliude daa. Poins on op of he segmens have peak ampliude value. The peak on he shoes segmen 0 anenna cene is on he pipe ais is highes posiive o negaive. This value is cieia fo scan seaching and deeminaion of locaion and deph of undegound uiliy. Negaive peaks indicae empy pipes while posiive peaks indicae full pipes o cable. Pipe and cable eflecion have diffeen posiive peaks. Cables eflec moe and have highe posiive peaks. Tansmi anenna adiaes a conical M wave beam wih a bandwidh β Based on hese facs i is no necessay fo he cene of he anenna o be above he undegound objec o deec i. Figue shows an ideal one pipe ada scan in a homogenous soil laye. Anenna moved oogonally o he pipeline ais. In eal condiions scan is wih diffeen noises and hypebolical eflecions caused by ohe infasucual objecs. This can be eliminaed by pospocessing. Figue 3. shows a eal scan fom he GPR wih maked ajecoies on he X ais and deph on he Y ais. The oscilloscope shows posiive peaks indicaing a full pipe. If i was a cable he hypebola wouldn' have been as open bu would have had a lage ampliude. l.40m v0.m/ns.54m R 7.45ns Amp. ma. 59 hypebola R GPR TRANSFR FUNCTION Figue 3. Real GPR scan Basic GPR paamees ae maimum peneaion deph M and spaial veical δ i hoional δ X δ Y esoluion δ R. GPR's ansfe funcion is he aio of signal powes a ansmi and eceive anenna especively. GPR ansfe funcion is used o calculae M Figue 4: GT σ obj S R α + PR PT e 9 4π G T ansmi anenna gain 9

6 ANNALS OF TH FACULTY OF NGINRING HUNDOARA 005 TOM III. Fascicole S R ada coss secion [m ] λ c s R 4 π 4 π f - fo spheical objecs whose cicumfeence is appoimaely Oπ λ; f M wave fequency [MH] disance beween he ansmi anenna and he undegound objec [m] disance beween he undegound objec and he eceive anenna [m] M αf f A aenuaion as a funcion of fequency [db/m] A 0.5 fo fequencies beween 00 and 300 MH A fo fequencies above 000 MH [5] Figue 4 shows impoan vaiables fo ime space ansfe funcion definiion. Maimum peneaion deph in pipeline deecion is usually 3.5 o 7m 400MH and 00MH anenna especively. Figue 4. The pinciple of funcioning GPR Spaial esoluion δ R is a funcion of he fequency band and of he comple dielecic pemiiviy [5]. The GPR's veical esoluion along ais δ is: c δ 0 ' Δf f Veical esoluion in pipeline deecion is usually 3 o 7cm 400MH and 00MH anenna especively. 4. PARAMTRS ACQUISITION MTHODS Paamees ae deeced by D and/o 3D scans of he sie. Compleiy ype of pipeline newok and amoun of daa deemine which mehod is used fo scaning. D scanning is useful fo quick undegound uiliies locaion. The fis sep is he ecalculaion of R based on a scan of an undegound objec wih known deph. Oogonal scanning is used o deemine pipeline deph and diecion. To deemine pipeline diecion a leas wo scans ae needed. A egula hypebola shows up on he scan when oogonally cossing above he pipeline ais. In ha case ules eplained in figue ae saisfied and he efleced wave ampliude is maimal because of maimum ada coss secion. When anenna cosses a a shap angle above he pipeline ais he hypebola has a oally diffeen shape which is no longe hypebolic. In an eeme case when he anenna ajecoy is along he pipeline ais he hypebola is disoed ino a saigh line [67]. 0

7 ANNALS OF TH FACULTY OF NGINRING HUNDOARA 005 TOM III. Fascicole plained popeies of M waves show he possibiliy o deec pipes of diffeen maeials. Diffeences beween efleced waves would be only in ampliude values eflecion sengh [67]. Huge wae supply newoks have abou 0% of losses caused by pipe leakage. Beside seveal anohe moden mehods GPRs have a significan ole in he pocess of quick and efficien deecion of pipe leakage especially in pipes wih small diamee. Idenificaion of pipe leakage is possible by deecing of caviies ceaed by leaking fluids o analysing changes in soil sucue caused by moisue change of dielecic pemiiviy R [8]. Taking his ino accoun D scanning is useful in deemining deph diecions in he hoional and veical planes pipe inclinaion pipe lengh fluid/void aio changes of pipe diamee pipe maeial deecion of pipe leakage pipe adius esimaion ec. Pipe adius esimaion equies addiional sofwae pocessing because i depends on hypebolic eflecion geomey. In 3D scanning he sofwae connecs a numbe of D scans in a pedefined sequence hence ceaing a 3D model of he sie. I ovecomes he obvious limiaions of he common fom of GPR daa display which is a D veical coss-secion. Voids beween he D scans ae filled wih sofwae inepolaion mehods. The 3D display has he advanage of looking a he enie suvey sie a once. Technology of 3D scanning is useful fo comple pocessing. This is especially impoan in aeas wih muliple inesecing dipping o layeed ages pipes eba ec. ha may be had o idenify on single ada pofiles. Pospocessing sofwae RADAN is used fo fileing nomaliaion and ansfomaion of aw signals. RADAN has special funcions fo applicaions ha equie linea feaue ecogniion [7]. Spaial coodinaes of all chaaceisic poins on he suface wee measued wih vaious GPS equipmen: high pecision ~cm GPS equipmen ove Timble 5800 using RTK Real Time Kinemaic o wih a GPS ove in decimee pecision Geoploe XT. The measued coodinaes have o be coeced o achieve even highe pecision. Coecions come fom a newok of pemanen base saions wih fied posiions and can be acquied in eal ime o offline [9]. Real ime coecions RTK- Real Time Kinemaic can be eceived hough GPRS Geneal Packe Radio Sevice o fom a GSM modem. Offline PPK Pos Pocessing Kinemaic coecions can be downloaded fom he Inene [0]. A newok of base saions coves he egion Vojvodina enabling he measuemen of GPS coodinaes wih a pecision of cm [0]. The newok is fully opeaional longe han a yea now. I is in he phase of final eension afe which i will cove he eioy of Sebia. 5. CONCLUSIONS This pape pesens he physical-heoeical pinciples of funcioning of a gound peneaing ada GPR. Special emphasis was pu on

8 ANNALS OF TH FACULTY OF NGINRING HUNDOARA 005 TOM III. Fascicole analysing he capabiliies of GPR in he acquisiion of daa equied fo he ceaion of complee model of wae supply newoks. The GPR can deemine he lenghs of saigh pipeline segmens pipeline diecion diecions in he hoional and veical planes pipe inclinaion pipe lengh fluid/void aio changes of pipe diamee pipe maeial deecion of pipe leakage pipe adius esimaion ec. The limiaions of his mehod include pooe esuls in highly conducive media. Anohe limiaions is ha i is usually difficul o esimae he pipe diamee on sie o even using pos-pocessing algoihms. These poblems ae sill subjecs of scienific eseach. The pesened of D/3D sie scannings allow 3D epesenaion and comple analyses. The pesened pinciples and echniques allow he deecion of pipes and cables of diffeen maeials goundwae level deecion he anlysis of oad sae soil conaminaion levels ec. This pape pesens he basic pinciples and echniques of efficien mapping using a newok of pemanen base saions and high pecision equipmen. Fuhe eseach is aimed a develop pocedues fo even bee paamee esimaion and finding new aeas of use. ACKNOWLDGMNT The discussed GPR elaed eseach was done as pa of he naional pojec Auomaic conol in indusy Naional enegeic efficiency pogam founded by he Depamen of science and echnology Republic of Sebia NP 305-0A. The discussed GPR elaed eseach was done as pa of he naional pojec Sebian naional pogam fo wae egulaion poecion and usage founded by he Depamen of science and echnology Republic of Sebia NPV-9B. LITRATUR/RFRNCS [.] Republika Sbija Republički Geodeski avod Pavilnik o kaasu vodova Beogad 999. [.] Jan van de Kuk 3D imaging of muli-komponen GPR daa PhD hesis TU Delf The Nehelands 00. [3.] D.J. Daniels Suface peneaing ada The Insiuion of lecical nginees London GBR 996. [4.] Anja Pälli Polyhemal Glacie Sudies In Svalbad Deemined By Gound- Peneaing Rada Academic Disseaion Univesiy of Oulu Finland 003. [5.] Nikolay Chubinsky Real mehod fo descipion of he GPR pefomances 0-h Inenaional Confeence on GPR -4 June Delf The Nehelands 004. [6.] W. Al-Nuaimy S. Shihab and A. iksen Daa fusion fo accuae chaaceisaion of buied cylindical objecs using GPR 0-h Inenaional Confeence on GPR - 4 June Delf The Nehelands 004. [7.] GSSI Radan 6 Use Manual Noh Salem USA 004. [8.] Osama Hunaidi GPR fo deecion of leaks in buied plasic wae disibuion pipes 7-h Inenaional Confeence on GPR 7-30 May Lawence Cansas USA 998. [9.] B. Hofmann a all "Global Posiioning Sysem Theoy and Pacice" fifh ediion NewYok USA 00. [0.] hp://gpsweb.ns.ac.yu

Computer Propagation Analysis Tools

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