Geoscience Reference
In-Depth Information
are averaged, and the resultant is then subtracted from the signal trace in the center of the
sequence. Next, using the same number of sequential signal traces, the process is moved
over along the line by one signal trace and then repeated. The overall effect of the filter is
to remove the radar signal response from flat-lying features.
5.
2-D Migration (2DM)
—A synthetic aperture image reconstruction process is applied to
the GPR data set. The process tends to focus scattered signals, in particular, collapsing
hyperbolic responses into localized point responses. (Note that hyperbolic GPR responses
have an upside-down U-shaped pattern, are often referred to as “reflection hyperbolas,”
and for this study, are typically associated with buried drainage pipes.)
Issues related to setting up a GPR golf course green survey need to be addressed before data
collection efforts can begin, in order to obtain the best-quality time-slice amplitude maps. Particu-
larly important are decisions regarding whether a unidirectional or bidirectional survey is to be con-
ducted and the spacing distance to use between lines along which GPR measurements are obtained.
Because GPR data at the Muirfield Village seventeenth hole green were collected bidirectionally
(two sets of parallel measurement transects oriented perpendicular to one another) with a spacing
distance of 1 m between adjacent measurement lines, subsets of the total data set can be utilized to
simulate the impact of different field survey setups. The different field survey setups to be evalu-
ated include (1) a bidirectional survey with a 1 m spacing distance between adjacent measurement
lines, (2) a bidirectional survey with a 2 m spacing distance between adjacent measurement lines,
(3) a bidirectional survey with a 3 m spacing distance between adjacent measurement lines, (4) a
unidirectional survey based on one set of parallel northwest-southeast transects with a 1 m spacing
distance between adjacent measurement lines, and finally, (5) a second unidirectional survey based
on the other set of parallel transects, in this case southwest-northeast, with a 1 m spacing distance
between adjacent measurement lines.
28.3 ReSUltS And dISCUSSIon
Constructed soil layers and drainage pipes within a golf course green will reflect radar energy, and
with proper computer processing, have a response that can be clearly exhibited on GPR profiles.
Figure 28.2 provides some typical examples for the computer processing of golf course green GPR
profiles generated with EKKO View Deluxe. The Figure 28.2 profiles represent the application of
different computer-processing procedures to the same set of raw 1000 MHz GPR data collected
along a line oriented southwest to northeast on the Muirfield Village Golf Club seventeenth hole
USGA Method green. For each Figure 28.2 GPR profile, the left vertical axis represents the two-
way radar signal travel time, the right vertical axis represents depth in meters, and the bottom axis
is distance in meters along the line of measurement. The raw data are presented in Figure 28.2a.
The Figure 28.2a GPR responses to the bottoms of the constructed sand and gravel layers are
barely visible, and reflection hyperbolas representing buried drainage pipes cannot be detected.
The Figure 28.2b GPR profile processing sequence began with a signal saturation correction filter
(SSCF) followed by a constant gain function (CGF) with a factor of 25. The bottom of the con-
structed sand layer (indicated by the downward pointing arrows), the bottom of the constructed
gravel layer (indicated by the upward pointing arrows), and three upside-down U-shaped drainage
pipe reflection hyperbolas (one is highlighted by an oval-shaped gray line) are all clearly visible.
The actual position for the top of a drainage pipe coincides with the apex position of its reflection
fIGURe 28.2
(
see facing page
) Ground-penetrating radar (GPR) profile computer-processing results, (a) raw
data, (b) signal saturation correction filter (SSCF) and constant gain function (CGF), (c) SSCF and automatic
gain control function (AGCF), (d) SSCF, CGF, signal trace enveloping (STE), and 2-D migration (2DM), and
(e) SSCF, CGF, and spatial background subtraction filter (SBSF).
