GSSI SIR 20, User Manual

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Geophysical Survey Systems, Inc. SIR® 20
Manual
MN92-078 Rev F 15
Data Collection Methods
There are three ways that you can collect GPR data: In Survey Wheel mode, i.e. scans per unit distance,
Free Run mode, i.e. scans per second, and Point Mode, i.e. one scan per each discrete antenna position.
Survey wheel
data collection means that you have a survey wheel distance encoder, DMI, or a
StructureScan minicart. These devices allow you to collect data at a specific even scan spacing so that
your data is collected with a linear horizontal scale, no matter what speed you are collecting data at. This
is the easiest, most accurate way to collect data and is recommended for most users. This mode of data
collection is required for the RADAN Migration routine and other signal processing functions to operate
correctly.
Free run
data is collected without the benefit of a survey wheel. Your data does not have position
information unless you are also using a GPS. The SIR 20 will collect a certain number of scans per
second and it is up to you to move your antenna over your survey surface at a constant rate. If you collect
free run data you should lay out a tape measure along your survey line and click your marker button
whenever you antenna passes a measured grid point (e.g. every 5 feet). This will allow you to determine
the approximate location of reflectors in your data. You can perform distance normalization in RADAN
on this type of data later to convert the horizontal scale to an approximate linear scale. See the RADAN
User’s Manual for details on distance normalization.
Point mode
data is collected one scan at a time with the antenna placed at a discrete location along a
profile line. After a scan is collected, the antenna is picked up and moved to a new location for the next
scan. This is commonly done with large, low frequency antennas, in areas with rough surface conditions
or rugged terrain, or when collecting a common mid-point stack with two antennas.
Now let’s look at how to set up for each of these modes.
Survey Wheel Controlled Collection
1
Create a new collection project by going to File > New or clicking the New Project button on the
collection controls bar. This will open a window with the heading Create New Data Collection
Project (Figure 10).
Figure 10: Project File Name box.