Unit 5: Integrated Geophysical Interpretation and Comparison with Ground Truthing

Compiled by Lee Slater, Rutgers University Newark (lslater@newark.rutgers.edu)


Summary

In this unit, students explore spatial associations between the three-dimensional electromagnetic (EM) conductivity inversions and the visible patterns of Salicornia (Pickleweed) introduced in Unit 1, Exploring Harrier Meadow. The Arcview Storymap started in Unit 1 allows students to overlay inverted electrical conductivity patterns for different depths on aerial photographs of Harrier Meadow that highlight the patches of Pickleweed. Students analyze how conductivity patterns vary with depth and explore for evidence for a relationship between electrical conductivity and Pickleweed patches based on the hypothesis introduced in Unit 1. Students then perform an integrated interpretation of both the EM and electrical imaging inversions along with the results of direct sampling (coring, pore water sampling, soil characterization) conducted at locations selected using the electrical conductivity patterns observed in the EM dataset. Students perform basic qualitative assessments of the correlation between physical and chemical properties of the sampled soils and soil electrical conductivity from the EM inversions. Students finish the module by evaluating the extent to which the geophysical dataset and supporting direct measurements support the hypothesis pertaining to the cause of the Salicornia clusters introduced in Unit 1.

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Learning Goals

Students will be able to:

  • 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."

Context for Use

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.

Description and Teaching Materials

Students evaluate the extent to which the geophysical dataset and supporting direct measurements support the hypothesis pertaining to the cause of the Salicornia clusters introduced in Unit 1.

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. Student handout, Wetlands unit 5 (Microsoft Word 2007 (.docx) PRIVATE FILE 80kB Oct22 21): Student handout describing unit activities to the student
  5. Student worksheet, Wetlands unit 5 (Microsoft Word 2007 (.docx) PRIVATE FILE 4.1MB Oct22 21): 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.

Teaching Notes and Tips

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 12 males and one in 200 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.

Assessment

The Student worksheet, Wetlands unit 5 (Microsoft Word 2007 (.docx) PRIVATE FILE 4.1MB Oct22 21) is designed to help evaluate whether students have grasped the main concepts in this assignment. Note: This file is also linked above, in the Teaching Materials section of this page.

Solutions for instructors

References and Resources

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