User's Manual

pulseEKKO PRO 3-System Setup Parameters
35
3.2.2 Time Window
The Time Window setting determines how long (and therefore how deep) the radar system will probe the
subsurface. 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 and decreases productivity.
This parameter is set under System Setup - GPR Parameters - Time Window.
The Time Window 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.
Note: The default Time Window value may not be appropriate for the survey at hand. If not, the value can
be changed by the user.
Since the radar system really measures time, and survey targets are at a specific depth, an estimate of
velocity can be used to relate depth to time to obtain a good time window value. The DVL automatically
calculates and displays a depth value based on the Time Window value and the current Radar Velocity
value (Section 3.2.6: P39).
3.2.2.1 How Depth is Determined
Ground penetrating radar systems record the time for a radio wave to travel to a target and back. The
depth to that target is calculated based on the velocity at which the wave travels to the target. In ideal
reflection operation, depth is calculated as:
D = V x T/2
Where D is Depth (m)
V is Velocity (m/ns)
T is Two-way travel time (ns)
Frequency (MHz)
Default Time
Window (ns)
Approximate
Depth (m) with
V=0.1m/ns
Approximate
Depth (ft) with
V=0.328ft/ns
12.5 1600 80 262
25 800 40 131
50 400 20 66
100 200 10 33
200 100 5 16
250 100 5 16
500 50 2.5 8
1000 25 1.25 4