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Ground Penetrating Radar (GPR) Data Processing

Ground Penetrating Radar (GPR) is now used extensively for a variety of applications in

many differing fields. Ground penetrating radar (GPR) has gained popularity as a shallow

subsurface, geophysical imaging tool due to its ease of use and portability for recording high

resolution sections. GPR has a range of applications in archaeology, engineering, and the earthsciences such as delineating the water table depth, fro!en"unfro!en interfaces, mapping soil

stratigraphy, subsurface bedroc# topography, peat deposits, geological structure, and locating

buried pipes, cables$. GPR is a techni%ue that transmits pulsed electromagnetic waves (&' "

&''' !) which can be refracted and*or reflected off subsurface features, received, and

recorded digitally in a manner similar to seismic surveying techni%ues. owever, many of the

problems affecting seismic signals also affect GPR. +herefore, assuming electromagnetic

waves propagate analogously to elastic energy, seismic data processing techni%ues are for 

GPR. +his is a reasonable assumption for propagating radar wave traveltimesere are steps of 

GPR data processing

&. Data -diting (Raw Data)

nce data are recorded, the first step in processing is data editing. Data editing

encompasses issues such as data organi!ation, data file merging, data header or bac#ground

information updates, repositioning and inclusion of elevation information with the data.

/. 0ignal 0aturation

1ecause of the large energy input from the airwave, groundwave, and near surface

reflectors, the GPR receiver becomes signal saturated and unable to ad2ust fast enough to the

large variations between vertical stac#s. +his induces a low fre%uency, slowly decaying wow

on the higher fre%uencies of the signal trace arrivals, ma#ing arrivals on the shaded wiggle

traces tough to distinguish. D3 signal saturation is constant across each trace and can becorrected for by a bul# D3 offset shift in amplitude towards !ero. +he final correction is an

optimal low " cut filter.

4. Gain Recovery

Due to geometrical spreading of transmitted wavefields, later arrivals on a signal trace

show noticeably lower amplitudes than earlier arrivals. +o recover relative amplitude information,

a time " variant, trace e%uali!ation function such as spherical divergence or automatic gain

control (5G3) is applied.

6. 0pi#ing Deconvolution

0pi#ing wavelet deconvolution (6' ns operator window and &7prewhitening) vs !ero"

phase deconvolution was found, by trial and error, to best enhance the resolution of the data

when followed by a bandpass filter. Predictive deconvolution was also attempted but failed to

remove the primary multiple at "89'ns.

9. 1andpass :ilter 

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 5mplitude spectra were plotted by for each trace and summed to determine the signal

fre%uency bands of the 9' ! (;illiam9 ! was observed. +he fre%uency bands chosen for 

filtering were /'*4' " >'*&'' and /'*4' " &''*&/9 ! for the 9' and &'' ! transmitter bandpass filters respectively.

?. @elocity 5nalysis

 5 common midpoint (3P) gather was a%uired by Aol and 0mith (&==&) at ;illiam. Dielectric 3onstants

 5nalogous to acoustic impedance in seismic, dielectric constants (B) determine the

reflection coefficients for GPR signal reflections. +hus, assuming a low"loss geological

environment, the dielectric is related to electromagnetic velocity (@).

8. -levation 3orrection

:lattening a GPR profile based on the airwave does not account for near surface

elevation and velocity static effects. +herefore, elevation and velocity static corrections shouldbe performed to obtain more realistic subsurface images. GPR systems measure the travel time

of radar waves off subsurface reflectors relative to their position. 5ssuming a constant radar 

velocity of '.'> m*ns, the elevation correction for a topographic low.

=. 0tatic 3orrection

@elocity static shifts occur when the near surface has significantly different radar 

velocities than underlying units. +he velocity push down effect appears to be greater further 

down in the section for each static. 0ince no elevation surveys were made for this profile, the

statics were water " table flattened as an attempt to correct the statics. +his is attributed to a

significant velocity conu

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+herefore, this appears to be a case of a velocity static caused by a high velocity surface layer.

+hese velocity static corrections should be performed before normal moveout () because it

is mathematically simpler. +he earlier attempt to resolve the static was done by flattening the

water table reflection.

&'. ormal oveoutPerformed to account for the /m transmitter * receiver separation using the semblance

velocities pic#ed earlier, so traces approximate !ero"offset rays.

&&. igration

Relocates reflections to their true spatial position based on the velocity spectrum to

produce a real structure map of subsurface features. +he ;illiam