27.2.1 Description of the Selected Golf Greens
The GPR was used to locate drainage tile on two different greens. These two golf greens were constructed by different styles. Figure 27.1 shows golf green No. 3, with an area of about 500 m2, at the Stone Creek golf course (SCGC), Makanda, IL. This green was constructed following the U.S. Golf Association (USGA) recommendations. The USGA green consisted of a 30 cm thick layer of sand mix overlying a 10 cm layer of gravel. The drainage tile, surrounded with gravel, was installed beneath the gravel layer. Figure 27.2 shows green No. 2, approximately 200 m2, at the Hickory Ridge golf course (HRGC), Carbondale, IL. The green was constructed following the California-style recommendations. The California green is similar to the USGA green but without the 10 cm layer of gravel. Even though the drainage tile was surrounded with gravel, the sand mix was placed immediately on top of the native soil. The drain tile often used in golf greens is a 10 cm diameter corrugated plastic pipe. The layout of the drainage tile was often installed either with a herringbone or gridiron
pattern. Spacing between the lateral lines was about 3 to 5 m (USGA Green Section Record, 1993). The blueprints of the drainage system of both greens were available for comparison.
In mapping the golf green drainage system, a Subsurface Interface Radar Model SIR 2000 (manufactured by Geophysical Survey Systems Inc., Salem, NH) was used. Both 400 and 900 MHz antenna were tested (Boniak et al., 2003). The 400 MHz antenna was good for a deeper soil but provided less resolution. The 900 MHz antenna had a higher resolution for a shallow soil that would seem ideal for the golf green. Prior to measurement, the GPR was calibrated and standardized to select the best viewing parameter settings. The adjustment included maximum depth range, position of ground surface reflection, and proper signal amplification. In the calibration, the depth of the image was set to a subsurface truth object such as the gravel layer. It is best not to apply frequency filters in the field because it may remove critical data that may be needed later.
A two-person team worked together in conducting the experiment. Prior to scanning, a 1 x 1 m grid pattern was overlaid on the entire green. In the establishment of the grid pattern, the sprinkler heads around the green were used as reference points. The sprinkler heads were selected because they are stationary and easily located. If sprinkler heads are not readily available, stakes may put into the ground for permanent reference points. The grids were flagged at every meter on both sides of the green (Figure 27.3). Due to the irregular shape of each green, marking the green boundary is critical for identifying the location of the drainage tile.
Initially, a 900 MHz antenna was used because of its ability to examine shallow subsurface features with high resolution. However, a large amount of unexpected noise appeared in the image. This might be attributed to the granular fertilizer applied to the green earlier. High salt index in the
FIGURE 27.3 Grid layout.
fertilizer may possibly cause some distortion as well. The 400 MHz antenna was used in the same area, but very little noise was found. In order to prevent the interference by the applied chemicals, the 400 MHz antenna was used for the entire study. Data were collected at each flagged line and marked at every meter point. The speed of pulling the antenna would be best if the scanning speed can be maintained constant.
At the Stone Creek Golf Course (SCGC) site, the team took about 45 minutes to complete the entire measurement, including flagging and scanning. For the green at Hickory Ridge Golf Course (HRGC), the experiment was finished within 30 minutes. On both greens, it took longer to overlay and flag the sampling pattern than to scan the site.
In the analysis, the software RADAN (Geophysical Survey Systems, Inc.. Salem, NH) was used for analyzing the image data. The first step in processing was to correct the horizontal scale by normalizing the data. After removing all pauses or speed changes between markers, the data were filtered to remove any unnecessary noise or clutter and keep the needed reflection signal. The last major step was to migrate the data to display the hyperbola image of the drain tile. The processed two-dimensional image provided the location of the drain tile. The data could be expressed as a two- or three-dimensional image.
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