Field procedure
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Inform yourself about the area, where you are searching. Does it make sense to detect here? Are
there historical references which confirms your speculation? What type of soil is on this area? Are
there good conditions for data recording? Is it allowed to search at this place (e.g. private property)?
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Your first measurement in an unknown area has to be large enough to get representative values. All
further control measurements should be adjusted individually.
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What is the shape and the dimensions of the object that you search? When looking for a long pipe,
you should measure across the object to better “see” it in your scan.
•
To get better values concerning depth measurements, the object has to be in the center of the
graphic, which means it has to be framed by normal reference values (normal ground). If the object
is on the side of the graphic and not totally visible an estimated depth measurement is not possible
and also measurement of size and form are limited. In this case, repeat the scan and change the
position of your scan area, to receive an optimal position of the anomaly inside of the graphic.
•
You should do at least two control scans to be more sure about your results.
6.3.1 Orientation of the antennas
During one measurement the antennas should have always the same distance to the ground. Generally we
recommend a height of about 10 cm (0.4 inches) from the surface of the ground if possible.
In the event that you are going to go over stones, wood or high grass that is higher, start your scan with the
antennas higher right from the beginning. In circumstances like these, then perhaps you will need to start
the scan with the antennas at a height of 30 cm (1 ft) and keep it at that level for the entire scan. It is
important to maintain the height, this will eradicate many errors. As a rule, do not change the height during a
scan for it may create unnecessary errors.
6.3.2 Parallel or Zig-Zag?
For skilled users of the Gepard GPR both scan modes are suitable. According to experience the best graphics
has been received in the "Parallel" mode, because you are starting at the same point and traveling in the
same direction. It is also easier to control your walking speed.
Especially in uneven territories like mountain sides, acclivities or other inclined layers the parallel mode is
preferred. When it comes to speed, the experienced user will very often use the Zig-Zag mode for the initial
scan to determine if there are anomalies in the area worth further research.
OKM GmbH
