SPX SPIDAR NIC-500s Operation Manual page 43

4.3.3 GPR
The GPR tab allows the user to setup parameters specific to the connected antennas (Figure
4-19). This section describes the settings common to all NIC-500s.
Note: When using a single NIC-500 with multiple GPR units, there are some settings that
must be same for the GPR units (such as step size, points per trace and stacks); these are
detailed in the paragraphs below. In particular, the step size required for the highest
frequency GPR is what determines the spatial sampling for both GPR systems. This results
in spatial over-sampling of any lower frequency GPR units connected.
Time Window
The Time Window setting determines how long (and therefore how deep) the GPR will collect
data. It is important that it is set to a value appropriate for the depth of the survey target. An
entire survey could fail if the window is not sufficiently long enough to sample to the depth of the
target. Conversely, too long a time window increases the data volume, can make data hard to
interpret and increases collection time.
For users that are more comfortable working with depth, rather than time, the following equation
relates time to depth
Assuming a velocity of 0.1 m/ns, if the targeted depth is 2m deep, then set the time window to
approximately 40 ns. Remember that Time Window also includes time before time-zero.
Figure 4-19: Setting parameters under the GPR tab
Time = (Depth x 2) / Velocity
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