Geoscience Reference
In-Depth Information
the transmitting antenna, partially reflects off a buried feature, and is eventually returned to the
surface, where it is picked up by a receiving antenna. Reflections from different depths produce
a signal trace, which is a function of returning radar wave amplitude (and hence, energy) versus
two-way travel time. Differences in the dielectric constant across a discontinuity govern the amount
of reflected radar energy returning to the surface. In this study, these discontinuities include the
boundaries between soil layers along with those interfaces between the soil material surrounding
the drainage pipe, the drainage pipe, and the air and water inside the drainage pipe.
It was previously stated that due to its greater overall design complexity compared to a Califor-
nia Method green, the analysis approach employed in this investigation, in order to be more rigor-
ous, focused efforts only on a USGA Method green. The data used for analysis in this investigation
was therefore obtained on the seventeenth hole USGA Method green at the Muirfield Village Golf
Club in Dublin, Ohio. The GPR system used to collect the data was a Sensors & Software Inc. Nog-
gin plus (Mississauga, Ontario, Canada) with 1000 MHz center frequency transmitter and receiver
antennas that were separated by 0.076 m. For data collection, the distance between measurement
points along a transect was 0.05 m, eight signal traces were averaged at each point location, and for
each signal trace, a 0.1 nanosecond (ns) sampling interval was employed. GPR measurements were
collected along two sets of parallel transects oriented perpendicular to one another and forming
a rectangular grid covering the green. The spacing distance between adjacent GPR measurement
lines was 1 m. These transect measurements were then used to produce GPR images of the soil
profile and time-slice amplitude maps.
As discussed in Chapter 7, GPR profiles are constructed by plotting side by side the sequential
signal traces collected along a line of measurement. GPR profiles represent the amount of reflected
radar energy returning to the surface from different depths beneath the line along which data were
collected. The golf course green GPR profiles will be most useful for determining thicknesses and
depths of constructed soil layers and horizontal and vertical positions of individual drainage pipes.
Information from all of the measurement transects is employed to generate the GPR time-slice
amplitude maps, which represent the amount of reflected radar energy returning to the surface over
an area from a specified interval of two-way travel time (or depth). The golf course green GPR time-
slice amplitude maps have their greatest potential for use in determining the pattern of the drainage
pipe network that is present.
Two Sensors & Software Inc. computer software packages were employed to process the GPR
data: EKKO View Deluxe for the profiles and EKKO Mapper for the time-slice amplitude maps.
The computer-processing procedures evaluated in this study, with respect to producing GPR profiles
and time-slice amplitude maps, are listed as follows with corresponding abbreviations to be used
throughout the remainder of this case history and a short description of what each procedure does:
1. Signal Saturation Correction Filter (SSCF) —This filter removes slowly decaying low-fre-
quency noise introduced by factors related to transmitting and receiving antenna proximity
and electrical properties of the ground.
2. Signal Gain Functions —Gain functions amplify the radar signal strength.
a.
Constant Gain Function (CGF) —For this gain function, the signal trace amplitudes
are multiplied by a constant factor, thereby enhancing the signal while preserving rela-
tive amplitude variations.
b.
Automatic Gain Control Function (AGCF) —This gain function equalizes amplitudes
along the radar signal trace.
3. Signal Trace Enveloping (STE) —The purpose of this process is to convert the wavelets
composing a radar signal trace from ones having positive and negative components to ones
that are mono-pulse and all positive. The overall process tends to simplify the data, in turn
making interpretation easier in some instances.
4. Spatial Background Subtraction Filter (SBSF) —For this filter, a set number of sequential
signal traces (which are a subset of all the signal traces collected along a particular line)
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