GSSI SIR 4000, Manual

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Geophysical Survey Systems, Inc. SIR® 4000
Manual
MN72-433 Rev F 142
C.3: Data Collection Methods: 2D vs. 3D
Time is money. Whether you are a university-based researcher working off a grant or performing NDT
work for pay, the faster you can get the survey done the better off you will be. Those charging by the hour
understand the fine balance between a price that reflects a realistic estimate of how long it will take to get
the job done, and padding the cost with unnecessary work. The point of this discussion is to get you to
think about how much information you really need to make a decision.
2D
Two-dimensional data collection means that you will be collecting and interpreting single profiles of data.
This is useful for quickly following a pipe by scanning over an area, noting the location of the pipe
hyperbola on the ground, then moving some distance away and scanning again for the pipe. The real
benefit of 2D data collection is speed and ease of use. Processing is certainly possible on 2D data to clean
up the image, but most clients will only use it for visually noting the presence/absence of targets in the
field. 2D data collection is also useful for geologic applications such as bedrock and water table mapping.
3D
Collecting data for 3D imaging obviously takes more time than 2D collection. While the SIR(R) 4000
makes it faster and easier than it has ever been before, it can still add significant time (and cost) to a job.
It also requires some software processing to produce an interpretable image. These two issues may
frighten some users away from 3D data collection, but like GPR in general, it only requires some practice
to gain confidence.
Three-dimensional data can be a great aid in interpretation. The question many people ask is “When do I
use 3D?” Aside from producing a 3D map for its own sake, there are really only three main reasons: a
complicated area, prospecting, or dangerous targets in the subsurface. A complicated area might be a city
street with many different types of pipes running in different directions. In a situation like that, the best
option is usually to do 3D data collection so that you are able to visually track targets as they twist and
turn around other targets. Prospecting is mainly what those doing Archaeology will face. In this case, you
don’t have any concrete information about the subsurface so you will need to do 3D over the area and
look for human-made patterns that could be targets. An example of the final reason would be coring or
cutting into an area that has live high-voltage in the floor. When the safety of your crew is at stake, the
more information, the better.