Unit 5: Integrated Geophysical Interpretation and Comparison with Ground Truthing

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Example of a sample of the marsh sediments acquired with a Russian peat corer in Harrier Meadow

Provenance: Lee Slater, Rutgers University-Newark
Reuse: This item is in the public domain and maybe reused freely without restriction.

• Interpret the image of electrical conductivity acquired in Unit 4 along with the images of conductivity structure from a provided 3D EM conductivity mapping dataset in terms of variations in salinity and soil physical properties (porosity, grain size) across the study site
• Summarize the evidence for a relationship between soil electrical conductivity and pickleweed intensity based on a hypothesis introduced in Unit 1, Exploring Harrier Meadow
• Refine their interpretations of geophysical datasets based on results of direct sampling observations at the study site
• Integrate geophysical and direct sampling datasets to evaluate the extent to which the findings support the hypothesis introduced in Unit 1: "Salinity-tolerant plants are thriving in regions of locally elevated salinity. As salinity exerts a strong control on electrical conductivity, we expect to map out increases in salinity in regions where pickleweed is thriving."

This unit is designed as a guided-learning project that is foremost to be used as part of a series for an introductory geophysics lab. It is the fifth of a sequence of five units and designed to take approximately 1.5–2.0 hours, with students doing independent exploration in using a geophysical data visualization tool embedded in a GIS story map. The target audience is first year or sophomore earth and environmental science students with little prior experience with near-surface geophysics. However, the materials could easily be adapted and expanded by faculty teaching an upper-level undergraduate course in geophysics. The materials needed to use this unit are all provided as handouts and embedded links. This unit could adapted to be used as an independent (of the remaining units) module to teach electrical resistivity inversion concepts, although the instructor would need to pull some content from earlier units.

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Sampling the salinity of a lysimeter installation in Harrier Meadow

Provenance: Lee Slater, Rutgers University-Newark
Reuse: This item is in the public domain and maybe reused freely without restriction.

Materials provided:

1. Geophysical Interpretation and Comparison with Vegetation Patterning (PowerPoint Slideshow (.ppsx) 28.3MB Jul26 20): Narrated slideshow that introduces students to the exercises that explore the relationship between the geophysical measurements and the vegetation patterning. Please see the note about colorblindness in the "Teaching notes and tips" section of this page.
2. ArcGIS story map for visualizing the correlation between electrical conductivity structure from EM geophysical datasets and vegetation patterning
3. Geophysical Interpretation and Comparison with Ground Truthing (PowerPoint Slideshow (.ppsx) 33.8MB Jul26 20): Narrated slideshow that introduces students to the exercises that explore the relationship between the geophysical measurements and the direct coring datasets
4. Unit 5 Student Exercise (Microsoft Word 2007 (.docx) 81kB Sep23 24): Student handout describing unit activities to the student
5. Unit 5 Student Worksheet (Microsoft Word 2007 (.docx) 4.1MB Sep23 24): Student worksheet that can be used to assess student comprehension of the unit and achievement of learning objectives. The answer key is available for instructors. See the "Assessment" section of this page, below.

• Students should first watch the narrated slideshow focused on the comparison of the geophysical inversions and the vegetation patterning [Note that the PPSX file can be opened as a regular PowerPoint file if Powerpoint is running]. This sets them up to use the slider tool in the ArcGIS story map for the project to explore in detail the relationship between electrical conductivity of the soils/sediments and the vegetation patterning.
• Note: approximately one in twelve males and one in two hundred females are red-green colorblind; for these people, there is no visual difference between the pickleweed and other vegetation in the imagery, and the red and green portions of the resistivity datasets are indistinguishable from each other as well. (If you have "normal" color vision, you can use this color blindness simulator to see what the images look like to people with many different kinds of color vision deficiencies.) One way to accommodate students with colorblindness is to have students work in pairs or small groups as they interpret the imagery. Alternatively, you could provide annotated images of the pickleweed distribution and conductivity datasets to all students, so that they are all working with the same data.
• After they have completed these exercises (Tasks 5.2.1 and 5.2.2) students are ready to explore the relationships between the geophysical inversions and the results of direct coring/sampling. Students should watch the narrated slideshow focused on the comparison of the geophysical inversions and the vegetation patterning. Subsequently, they should tackle the final task (Task 5.2.3) of the unit and the module.

The student exercise (along with the associated worksheet) is the summative assessment for the unit. It includes a suggested rubric for assessment.

Solutions for instructors

Unit 5 Student Worksheet KEY -- private instructor-only file

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All references and resources relevant to this unit can be found in the associated section of the earlier units in this module.