Recollecting Lines In The Grid Scan; Depth Slice Interpretation; Conquest Resolution; Orientation - Sensors & Software CONQUEST 100 User Manual

Conquest 100 SliceView

8.2 Recollecting Lines in the Grid Scan

After looking at the grid data in SliceView you may discover that one or more grid lines need to
be re-collected (maybe the starting position was off or rebar appear to "bend" in the depth slices
when they shouldn't). If so, you will need to enter the Grid Scan menu again and select the grid
(the grid number will be in red, since data exists).
Select the grid line that needs to be re-collected. When you press Start, it will display a prompt
confirming if you want to overwrite the line, as shown in Figure 7-10.
After recollecting the grid lines, go back into SliceView and reprocess the grid data.

8.3 Depth Slice Interpretation

8.3.1 Conquest Resolution

One of the first things to note when looking at depth slices is the resolution of Conquest.
Features will show up with a minimum size of about 1.5 inches (40 mm). This is a fundamental
limit of the antenna response characteristics. You should not interpret a Conquest feature to be
fully representative of the dimension in the Depth Slice image. The object may be 1 inch in
diameter or 1/8 of an inch in diameter but it still will result in a 1.5 inch wide event on the depth
slice image. Be careful about interpreting sizes of features.

8.3.2 Orientation

Scroll through the depth slices and look for patterns. Normally regular patterns of rebar will
appear at different depths. Sometimes when a bar or conduit has a dip or a tilt, it will show up
partially at one depth and then show up at another depth more clearly as the bar or conduit cuts
down through the selected depth range.

8.3.3 PCD Image

Notice that, similar to GPR responses from rebar and other objects described above, the PCD
response is broad compared to the actual size of the cable. The width of the PCD response has
no relation to the size of the cable. In fact, sometimes the PCD response from a cable can
appear so broad in width that a 2' x 2' (600 x 600 mm) grid may not show the edges of the
response and the whole image appears as one strong color. In this case it may be necessary to
collect a larger grid to see the edges of the PCD response.

8.4 Marking the site

It is necessary to view the depth slices through the total depth range in order to mark the site.
The normal process is to step down through each depth and look for linear features which may
indicate rebar, post-tension cables, pipes and conduits. At each depth, mark the location of the
feature on the surface using the grid as a guide.
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