COMPARISONOFGROUNDPENETRATINGRADARACQUISITION TECHNIQUESINVALIDATIONOFBUILDINGSPACEDIMENSIONS ATTHEFINALSEWAREPIPELINEOFEMBUNGB,UNIVERSITY OFLAMPUNG

SultanAlGhifari1*,AmbrosiusHernawanWibisono1,RestuWildanuAhadi1,IGedeBoyDarmawan1, Rustadi1

1ProgramStudiTeknikGeofisika,FakultasTeknik,UniversitasLampung (Jln. Prof. Dr. Sumantri Brojonegoro No. 1, Bandar Lampung 35145 Indonesia)

*Corresponding author’s email: sultan.algi12@gmail.com

Abstract.Thisstudyaimstodeterminethedifferencesinspatialdimensionsusingtwogroundpenetrating radar (GPR) acquisition techniques and correlate them with the actual dimensions. The research was conducted on April 19, 2022 at the final disposal pipe of Embung B, University of Lampung. Ground PenetratingRadar(GPR)isageophysicalmethodusedtodetectsubsurfacestructureswithshallowdepth, usinganelectromagneticwavesourceintheformofradar,usuallyinthe10MHzto1GHzrange.Thetool used is a Multichannel GPR with a support instrument for sea (water level) acquisition, with the aim of makingitmoremobileinmeasurement.ThemeasurementdataisthenprocessedusingReflexwsoftware. Data processing (filtering) carried out in this study includes static correction, dewow, bandpass filter, background removal, gain function, fk-filter and then horizon picking is carried out to determine the boundariesofthespatialstructureontheacquisitiontarget.Theresultsobtainedfromthetwofinalsewers, thetypeofanomalyfromtheradargramdepictsasquareandhyperbolicslabthatshowsacuboid(line1)and cylindricaltarget(line2).Geometrically,theantennaacquisitiontechniqueperpendiculartopath1getsa widthof1.12metersandalengthof0.995meters.Whiletheacquisitiontechniqueoftheantennaalonewith line 1 gets a width of 0.991 meters and a length of 0.996 meters. Then for the acquisition technique perpendicular to line 2, it gets a diagonal (length and width) of 0.8 meters and the acquisition technique paralleltoline2getsadiagonallengthof0.89metersandalengthof0.78meters.Basedontheresultsofthe error calculation, it was found that the perpendicular acquisition technique on lanes 1 and 2 obtained a relativelysmallererrorvaluecomparedtotheparallelacquisitiontechniqueonbothpaths(closetooriginal value).

Keywords:GPR,pipeline,acquisition

1.Introduction

In this modern era, to drain clean water, waste, and naturalgas,werelyonsubsurfacepipes.Subsurface utility networks sometimes require maintenance, repairs,andtheadditionofnewpipes.However,the utilitynetworkissometimesnotwellmapped,soits position and dimensions are often not known with certainty This will increase the risk of damage to existing utilities [2]. In such a scenario, only detecting the pipe at a specific location may not be sufficientinformation.Oneofthesolutionsusedfor this problem can use the GPR method GPR resolution is not only to determine the presence of pipes, but can also be used to determine pipe diameters, pipe materials, or pipe filling materials (egair,water)[3].

Identificationofthepresence of water pipes, gas pipes, electricity cables and underground telecommunication cables to find out the utility network can use the Ground Penetrating Radar (GPR) method or better known as the Georadar method. This method is one of the active geophysical methods, which is a method that uses artificial sources to observe the anomalous response of subsurface objects with results that can be directly observed. The GPR method basically utilizes the propagation and radiation properties of electromagneticwavesthatshowreflectionsfroma material.The type of wave used is radio waves at a frequencyof1MHz-1000MHz[1].Theamountof penetration or depth that can be achieved by radar wavesisverydependentonthesizeofthefrequency used. The smaller the frequency of the transmitter antennaused,thegreaterthepenetrationachievedby theradarwaveandviceversa.Whenradarwavesare emitted from the transmitter, they will produce reflection waves with different amplitudes The amplitude of the reflected wave recorded at the receiver depends on the electromagnetic properties oftheobjectbeneaththesurfacethattheradarwave passes through. The electromagnetic properties of various materials that exist below the surface are closelyrelatedtothecompositionofmineralsbelow thesurface[5].

The velocity factor of electromagnetic waves in variousmediumsisbasedonthespeedoflightinair, the relative dielectric constant, and magnetic permeability.Theotherfactoristhetypeofmaterial and is a function of the relative permittivity of the material.

2.DataandMethodology

2.1.Researchprocedure

ThedatausedareprimarydatatakenonJuly5,2022. The data acquisition was carried out at Embung B, University of Lampung using theAkula 9000 GPR with a frequency of 100 Mhz. There are two paths (A1andA2)passingthroughtheobjectintheformof a 1 x 1 meter concrete pipe. The acquisition techniqueonthetrajectoryiscarriedoutparalleland perpendiculartothe5-meter-longline.

areasothattheradargramweseeisclosetotheactual situation.

• Subtract Mean (Dewow) is a processing step performed to eliminate very low frequencies recordedintheradargram.

• The Butterworth bandpass is determined by the setting of two frequency values. The first point determines the low-frequency cut, the second determinesthehigh-frequencycut.

•BackgroundRemovalaimstoeliminatenoisethat always appears consistently throughout the profile so that it covers the actual signal in the horizontal direction

• Gain aims to re-strengthen the lost amplitude in suchawaythatitseemsasifeachpointhasthesame energy

•Velocityanalysisisthedeterminationofthespeed of propagation of electromagnetic waves on the subsurfacematerial,thenconvertingthetraveltime tothedepthofpenetration

• Horizon Picking is done by determining the location of the boundary layer and concrete pipe as shownintheGPRdata.

• Dimension Difference Comparison isconducted to compare the dimensions between the radargram data generated by GPR and the physical measurement data so that the difference and error valuebetweenthetwodatacanbeknown.

2.3.DataInterpretation

Based on the results of the processing, the data is analyzed and interpreted to obtain some important information related to the characteristics of the mediumandobjectunderstudy.Thefrequencyused at the time of data collection is very helpful in the interpretation process. High frequency will provide excellent resolution so that the recorded image will beseenclearly,especiallyiftheobjectbeingtargeted is conductive. In addition, a comparison of the physical dimensions of the concrete pipe data with theGPRdatadimensionsisalsocarriedout.

3.ResultsandDiscussion

GPR measurement in this study uses a monostatic mode radar reflection profiling configuration where the transmitter and receiver antennas move simultaneously (combined in one antenna) and the display on the radargram is a collection of each observationpoint

2.2.

Dataprocessing

GPR data processing aims to produce a good GPR cross-section profile so that based on the GPR crosssection the state and shape of rock layers (reflectors)andutilitiescanbeinterpretedaccording tothedesiredtarget.

•StaticCorrectionStaticCorrectionaimstomake theradargrammatchthetopographyofthesurvey

3.1.PickingResult

In the field survey, the results of measuring the dimensionsoftheacquisitiontargetspacehavebeen obtained,whereonline1withthedimensionsofthe cube, the length and width are 1 meter, and there is concreteonthepipewithalengthof1meter Online 2 with cylindrical dimensions, the diameter is 1 meter, and there is concrete above the pipe with a length of 1 meter. Based on the picking results, the upper, lower, left, and right limits of each track are obtained. This is used to determine the length and widthofthedimensionsofthetargetspace,whichis then calculated to determine the dimensions of the building.

Basedontheresultsofprocessingdata,online1after horizonpicking,theresultsobtainedarelength0,995 m and width 1,12 m with parallel acquisition technique. As for the perpendicular acquisition technique, the results are obtained with a length of 0,996 m and a width of 0,991 m. On line 2, with a cylindrical dimension pipe target, the results obtained with the acquisition technique perpendiculartothelength0,8mandwidth0,8m.As for the parallel acquisition technique, the results obtainedwithlength0,78mandwidth0,89m.

3.2.

ComparisonResults

From the results of the calculation of the measured andcalculatedspatialareaerror,theresultsonpaths 1and2withtheperpendicularacquisitiontechnique showarelativelyverysmallerrorvalueof1.29and 0.76%. While for paths 1 and 2 with parallel acquisition techniques, the results obtained with relatively larger error values, namely 11.44 and 7.09%.Thisisthoughttobeduetotheexistingnoise. This is because the data collection location has a relatively narrow access path, while the tools used havelargerdimensionsthanthelinebody.Sothatthe GPR tool and antenna are affected by noise on the surfacesuchasanironpillarnearline1.

4.Conclusions

Basedontheresultsofdataprocessing,theresultsof the radargram do not show a parabolic reflection in thecylindricalshape,thisisbecauseitusesamedium frequency device (100 Mhz), so the satellite dish is not very visible on the radargram. Based on the comparisonresults, it was found that the perpendicular acquisition technique on paths 1 and 2 obtained a relatively smaller error value compared to the parallel acquisitiontechniqueonbothpaths.Itcannotbesaid thattheacquisitiontechniqueusedismoreeffective thanotheracquisitiontechniques.Furtherresearchis needed using the GPR method with a higher frequencytoobtainapenetrationdepththatmatches thetarget(pipe).Thenitisnecessarytopayattention to field conditions, so as to minimize noise on the surfaceandmaximizetheresultsoftheradargramfor thenextresearch.

Acknowledgments

Thank you to all lecturers and employees of the Department of Geophysics Engineering, University of Lampung who have motivated us in completing this paper and for allowing us to borrow GPR tools andaplacetocarryoutthisresearch.

References

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