Unit 3: Case Studies and Limitations of GPR

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Students gathering around the Noggin GPR SmartCart sensor prior to a GPR survey.

Provenance: Photo by John McDaris for the IGUaNA-GETSI Workshop
Reuse: This item is offered under a Creative Commons Attribution-NonCommercial-ShareAlike license http://creativecommons.org/licenses/by-nc-sa/3.0/ You may reuse this item for non-commercial purposes as long as you provide attribution and offer any derivative works under a similar license.

Students will be able to:

1. Describe wave attenuation in terms of ground properties, both in words and graphically
2. Explain how a tree root might look similar to/different from a grave
3. Recognize a GPR depth slice versus a GPR profile.
4. Describe how GPR data could be misinterpreted
5. Describe environments where GPR will likely not work.

This unit is intended for undergraduate students with no previous exposure to geophysics. There is no math or science prerequisite.

The instructor can expect to spend 1–2 class periods with this material depending on class length and size. Student materials are contained in the PowerPoint. The instructor also has the option to use the other examples of GPR in engineering and forensic application for class discussions. Assessment activities may be done in groups or as individuals.

Part 1: Data analysis—Data collected by others

The teaching material includes a PowerPoint presentation with links to an external website and an interactive app that provides additional instructional content. The videos embedded in the PowerPoint are animations of GPR wave propagation in different settings and the resulting radargrams. The interactive app allows students to "see" how much the GPR signal attenuates as a function of depth.

• Presentation: What are the limitations of GPR (PowerPoint 2007 (.pptx) 12MB Sep6 24)

Student materials include a worksheet, think-pair-share questions, and synthesis questions. The worksheet is designed to be completed as students follow along with the slide presentation or outside of class and refer to the slides. This worksheet may also serve as a quiz or test questions if desired. Think-pair-share questions are best implemented during class time. These may also serve as short-essay questions to be answered individually.

• Worksheet and case study, limitations of GPR (Microsoft Word 2007 (.docx) 2.1MB Sep15 24)

There is an opportunity in this module to assign a writing exercise. Students may be asked to address the last part of the worksheet in an essay. They can write from the perspective of a GPR expert who was asked why GPR was used at the same site twice but was successful only the first time.

[optional] Part 2: Collecting and analyzing your own data

This part will guide you through the steps of collecting your own dataset, particularly using instrumentation resources available at the EarthScope Primary Instrument Center (EPIC). Instructions for requesting instruments for educational use are on the Geophysics Field Education page. Guidelines are provided for defining a research question, doing background research and interpreting your results. A review of acquisition and analysis is provided, with links to the primary materials on these topics covered elsewhere in the IGUaNA teaching materials.

Materials provided:

• Collecting and analyzing your own GPR dataset (PowerPoint 2007 (.pptx) 9.9MB Sep18 24)
• Instrument guides for Sensors & Software Noggin GPR
  • Noggin GPR unpacking and assembly guide (also repacking) (Microsoft Word 2007 (.docx) 12.8MB Sep15 24)—If you use a GPR loaned from EPIC, it will come in a box in several pieces that need to be assembled on site. Note: the box is fairly large and a bit heavy (~150 lbs). You will need to think about how to transport it from the campus delivery location to your teaching site.
  • Noggin survey guide for instrument setup and data acquisition (Microsoft Word 2007 (.docx) 4.9MB Sep8 24)
• Software guides for EKKO Project software—GPR data analysis
  • EKKO Project GPR software download and install instructions (Microsoft Word 2007 (.docx) 963kB Sep15 24)
  • EKKO Project GPR software guide (Microsoft Word 2007 (.docx) 3.3MB Sep8 24)

Key concepts in this unit

1. Multiple profiles are necessary to properly image a 3D feature.
2. Identify areas/environments in their local region where GPR would likely be successful or unsuccessful.
3. Explain conductivity and permittivity.
4. GPR signal is both waves and rays.

Contextualizing the use of GPR to locate unmarked graves

One of the case studies in this module involves the use of GPR to evaluate a site for the presence of unmarked graves. Unmarked grave sites in the United States include cemeteries for enslaved people, where slaveholders typically made no effort to mark or protect burial sites, and cemeteries on the grounds of "Indian boarding schools" run by U.S. government agencies, where Native American students were buried without their families' knowledge or consent. The module overview page has contextual information about using GPR to locate unmarked graves and incorporating this content into your teaching, and a list of references you can explore to learn more.

The Unit 3 handout includes fill-in-the-blank questions to confirm that students read through the PowerPoint and links, and open-ended questions that can be used in a think-pair-share format. The assessment is designed to be completed as students follow along with the slide presentation or outside of class and referring to the slides. This worksheet may also serve as a source of quiz or test questions if desired. Think-pair-share questions are best implemented during class time. These may also serve as short-essay questions to be answered individually.

• Worksheet and case study, limitations of GPR (Microsoft Word 2007 (.docx) 2.1MB Sep15 24)
  • Note: This is the same file as is linked above, in the Teaching Materials section of this page.

Solutions for instructors

• Answer key, What are the limitations of GPR? -- private instructor-only file
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Resources

• Interactive app that illustrates wave attenuation in a user-selected ground material.
• Geosci.xyz is an open-source educational resource for the geosciences. The site provides a comprehensive explanation of GPR theory that the instructor may refer to as needed to expand on this unit.
• Suggestions for supporting students (Microsoft Word 2007 (.docx) 16kB Sep6 24)

References

Explore references about African-American slave cemeteries and Native American boarding schools on the module overview page.