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Noggin 13-Survey & Map Mode
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13.3.4.4 Survey Format
The Survey Format specifies how the lines will be collected.
Forward Only
The lines shown in Figure 13-10 , Figure 13-11 , and Figure 13-12 are all collected in the
Forward direction only. This means that each line starts at the X or Y baseline.
Forward and Reverse
When the length of the survey lines are more than about 20 meters, data acquisition speed may
be increased by collecting every second line in the reverse direction (
Figure 13-13 ). This is
called a Forward and Reverse survey format.
Using forward and reverse format can speed acquisition but can lead to mapping artifacts called
“herringbone” if there are positional errors. It is important that the odometer is calibrated (
13.5.2:
p.120 ), the Grid Dimensions are correct ( 13.3.4.2: p.109 ) and that lines are always collected
starting on a baseline.
Using the Forward and Reverse survey format, X line data are collected in the pattern shown in
Figure 13-13 .
Figure: 13-13 For collecting GPR data consisting of long data lines it makes more sense to follow a forward and
reverse surveying pattern. For the final data to be spatially correct with a minimum of editing, data collected in this pat-
tern should be on lines that extend completely from one baseline to the other.
When data are collected like this, it is important that lines start and end on established baselines,
otherwise, when lines are reversed to the correct orientation for the display, they may be offset
from one another.