User's Manual

Geophysical Survey Systems, Inc. Model 4105 Antenna
System Settings and User’s Notes
MN34-559 Rev C
5
Position: Signal position should be adjusted so that the latest arriving wavelet of the direct-
coupling is near the top of the scan. This wavelet should always be visible in the data. GSSI’s
RADAN post-processing software requires the presence of this wavelet in the data. Figure 2
shows a typical scan of data with the signal properly positioned. The largest amplitude reflection
will be the pavement surface. The next largest reflection will be desired direct-coupling
waveform. This will occur several nanoseconds before the pavement surface reflection and
appear in the Position window (below) as the next significant waveform to the left of that
pavement surface. Unlike ground-coupled antennas, the desired direct-coupling waveform is not
the first significant return in the trace. You may see another waveform that looks similar to the
direct-coupling higher in the trace. You do not want this waveform, but the second one. Since the
antenna and the pavement are separated by nothing but air, the trace between the pavement
reflector and the desired waveform should be fairly flat (as below). If you accidentally set the
position to the incorrect waveform, the post-processing will not work correctly.
Figure 2: Typical data scan obtained with Model 4105 and recommended software settings.
Direct-coupling waveform
Pavement surface reflection