Trends & Insights from an Industry Pioneer
About Subsurface Reflections:
The goal of this blog is to share interesting and inspiring articles related to subsurface imaging and geophysics. Written by experts in the field of geophysics, ground penetrating radar, software development and data analysis, this is a source for insights about the practical application of technology in the field of subsurface imaging and a place to shed light on common misconceptions in the industry.
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Ground Penetrating Radar (GPR)
Dr. Peter Annan
Founder & CEO
Peter is the CEO of Sensors & Software. His scientific research has been recognized worldwide with numerous awards for his pioneering work in ground penetrating radar (GPR) instruments and data analysis methods. He has authored multiple scientific publications, patents, and technical reports and served on various government and professional committees.
GPR is now a complementary tool to EM when locating buried utilities. Unlike active EM methods where an individual utility is excited, GPR sees any buried feature that differs from its surroundings which can result in many targets being observed. This article focuses on getting the most out of your utility data in two common but challenging situations:
Challenge #1: Too Many Targets
When there are many buried targets present, sorting out the identity of responses from at different depths, oriented in different directions, and separating utilities from other targets (such as rocks, tree roots, etc) – can be challenging. Figure 1 shows an example of a complex multi-target GPR cross section.
Challenge #2: Weak Targets
Targets of differing composition, at varying depths in differing soil conditions, result in highly variable varied GPR reflection responses amplitudes. As a result, the sought after buried utility may not be the strongest most prominent response in the GPR cross section. Non-metallic pipes and conduits utilities often produce weak responses since their composition represents a small contrast to the host material properties. In many instances a desired targets may be overlooked if the response is weak as illustrated in Figure 2.
Let’s look at some strategies to help to get the most from your data in these situations or a combination of these situations.
Interpretations & MapView
When locating utilities, existing plan map records often provide initial guidance as to what to expect on site. Further, standard practice requires creation of site sketch maps of observed features and targets prior to leaving the locate area. MapView is an integrated display feature that enables GPR data to be viewed in a similar manner on site. During data collection, the operator simply adds color-coded dots (interpretations) on all responses (normally each hyperbola) by touching the screen at the top of the hyperbola (Figure 3). Little discrimination is needed in this first step, every potential target can be marked. Attention should be given to the pattern, direction and spacing of the GPR data collection path to ensure that the area is properly covered.