3-System Setup Parameters
pulseEKKO PRO
36
The wave velocity depends on the properties of the material. The Noggin software allows the user to input
different velocities, which changes the total depth range displayed on the screen. A value of 0.1 m/ns (or 0.
33 ft/ns) is a good average value for geologic materials; a table of the velocities of common geologic
materials is listed below (Section 3.2.6: P39).
3.2.3 Temporal Sampling Interval
The pulseEKKO PRO system samples the GPR signals returning to the receiver. The resulting GPR data
is a series of numbers that represent signal amplitude at equally spaced time intervals. The time interval
between points on the trace is called the Temporal Sampling Interval.
The sampling interval is dependent on the frequency of the antennas being used. Higher frequencies
need to be sampled at a finer time sampling interval than lower frequencies.
This parameter is set under System Setup - GPR Parameters - Sampling Interval.
The Sampling Interval value will be set to a default value based on the antenna frequency selected
(Section 3.2.1: P34) as shown in the table below. It can, however, be changed.
In general, the default
Sampling Interval should NOT be changed by the user.
The recommended temporal sampling interval versus antenna frequency is reproduced below:
It is important not to choose a sampling interval that is too large for a particular frequency otherwise the
data may be aliased (undersampled and thus not very representative of the real signal). Choosing a
sampling interval too small will increase the data volume unnecessarily and may slow down the data
collection process.
3.2.3.1
Determining the Number of Points per Trace
The number of points per trace is displayed in the View Setup screen (See Figure 3-2 on page 31). Points
are calculated based on the time window length and the sampling interval. For example, using a time
window of 300 ns and a sampling interval of 0.8 ns, the number of points is calculated as follows:
points = time window/sampling interval
= 300 ns / 0.8 ns
= 375
Center Frequency
(MHz)
Recommended Sampling
Interval (ns)
12.5
6.4
25
3.2
50
1.6
100
0.8
200
0.4
250
0.4
500
0.2
1000
0.1
