GSSI 200 HS, Руководство пользователя

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Geophysical Survey Systems, Inc. GS Series
200 HS Antenna
MN27-151 Rev A 10
• Distance:
For collection with a survey wheel encoder. The important variable here is scan density
(scans/unit). Scan density controls the number of scans per ft/m that you collect as you move the
antenna. The speed which you move the antenna is not a factor. Generally, you will want dense data
collection because you can always stack or remove data in RADAN post-processing.
• Point:
For collecting single scans with a stationary antenna. This mode is best for very uneven terrain
or for situations where you want to maximize depth penetration by collecting multiple scans and
averaging (stacking) them at a single location. You will notice that the data display view changes
from Linescan profiles to Wiggle trace where the waveform of each individual scan is shown. The
important variable is scans/point. This controls the number of averaged scans at each given location
to create a single recorded scan. The higher the value here, the more averaging and the greater
potential for increased depth penetration since the signal to noise ratio may improve. The only
tradeoff is that it may take the GPR longer to collect the data.
Scan menu showing different options by Collection mode
Vertical Scale:
Toggles the option from Time to Depth. When set to time, the vertical scale is displayed
in nanoseconds (ns). This represents the two-way travel time from antenna transmission to recording of
the reflected energy. When set to depth, the vertical scale is displayed in the desired depth units and the
GPR software will perform a conversion calculation from time to depth by assuming a dielectric value.
The accuracy of this calculation depends on your inputting the correct dielectric.
Time Range:
This option is only visible if the vertical scale is set to time. This parameter is expressed in
nanoseconds (ns) and controls the time the GPR will listen for reflections from the subsurface. This
represents two-way travel time (TWTT). Increasing this value allows for deeper penetration. Tapping on
the value allows you to change in steps from 50 to 1000 ns.
Dielectric:
This value represents the ratio of GPR energy speed in a material when compared to a
vacuum. The lower the value the faster GPR energy will move. This setting is only used for the time to
depth calculation. Although the vertical scale (when set to depth) will appear to change when you change
this value, GPR energy is still penetrating to the same depth regardless of what value you enter here.
Changing this to match the assumed dielectric of the actual ground will result in a more accurate time to
depth calculation. This value can be modified when playing back data or in the RADAN post-processing
software. Please see Appendix D for a detailed discussion of dielectric.