Unit 2: Environmental Magnetism

Students will be able to:

• Describe the fundamental principles of magnetism and how they may be applicable to environmental concerns (e.g., abandoned oil and gas wells)
• Explain how magnetometers and gradiometers leverage magnetic force to collect data
• Explain how the physical properties of soils and rocks can influence magnetism
• Produce and analyze a 2D magnetic intensity plot with Python using raw measurements from a real magnetics survey
• Conduct a magnetics survey with a smartphone app, then produce and analyze a 2D magnetic intensity plot with Python
• Evaluate the advantages and limitations of using magnetism to detect objects in the subsurface

This unit is designed as a guided learning project that is best used as an introductory lab. The target audience is first-year or second-year earth and environmental science students with little prior experience with near-surface geophysics and data processing. However, the materials could be adapted and used by faculty teaching an upper-level undergraduate course in geophysics. The materials needed to use this unit include access to smartphones, as well as materials available from embedded links. The material in this unit complements the third unit of this module, which focuses on the application of magnetic (and gravity) datasets.

Performing a magnetometer survey at the historic site used in this unit

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

Environmental Magnetism Student Worksheet (Microsoft Word 2007 (.docx) 4.3MB Jul15 26)

Environmental Magnetism Overview Handout (Microsoft Word 2007 (.docx) 2.7MB Jul15 26)

Part 1: Environmental concerns and the fundamentals of magnetism

• Student worksheet (Part 1)
• Narrated environmental magnetism video (start to 2:38)

Part 2: Simulating a magnetic field and exploring uses of magnetism

• Student worksheet (Part 2) with external links
• Narrated environmental magnetism video (2:38 to end)

Part 3: Creating a 2D magnetic survey plot using real magnetic survey data

• Student worksheet (Part 3)
• Online Python script (Using existing data from a real magnetics survey)

Part 4: How you can run a magnetics survey with your smartphone!

• Student worksheet (Part 4) with external links, including a downloadable smartphone app
• Printable data recording sheet (Microsoft Word 2007 (.docx) 2.8MB Jul15 26)
• Online Python script (Using the students' data from their smartphone magnetics survey)

This module is designed to be flexible and suitable for an introductory-level science class and requires no software or specialized instrumentation. Given the intended audience, the mathematical content in this module is kept to a minimum. Use of the online Python script has been simplified to the fullest extent possible, with students required to make only a few, carefully guided, changes to the provided code. However, it should still give students an appreciation of how computer programming is used to process geoscience datasets.

Smartphone magnetometer survey:

The smartphone magnetometer survey portion of this module is intended to be customized according to the instructor's preference and can be expanded or minimized to accommodate any size. The following notes outline a suggested example setup; however, they can be adjusted to any extent as needed.

• The smartphone magnetometer app "phyphox" is freely downloadable for iOS or Google Play.
  • After downloading and opening the app, select "Magnetometer" from the list of Raw Sensors.
  • The magnetometer in a smartphone is typically located near the camera.
  • To calibrate the cellphone magnetometer, the user should rotate the phone above their head in the shape of a circle for a few seconds.
  • Select the "Absolute" option from the toolbar at the top of the magnetometer screen. This will allow the user to view the absolute magnetic induction value in real-time, as well as a live time-series. Press the triangle (play button) to start collecting data.
  • A selfie stick is a convenient tool to make measuring easier; however, it is not necessary.
• The instructor will need to create a grid with their preferred dimensions, adding hidden magnetic anomalies along any coordinates of their choice.
  • The grid size and measurement increments can be adjusted according to preference. Opting for larger grids (e.g., 20 x 20 meters) is advisable for replicating realistic magnetic surveys and will also extend the time required for completion.
  • If you wish to modify the grid dimensions, alter the grid details under "🧲 Survey Details" in your instructor copy of the phone magnetics survey Python script. Ensure that the instructor's Google Sheets copy (accessible from the script) and the Printable data recording sheet (Microsoft Word 2007 (.docx) 2.8MB Jul15 26) are updated to accommodate for changes in the X and Y dimensions.
• Create two sets of marker flags that will act as a reference marker on the grid for students to measure using their cellphone magnetometer:
  

  Demonstration of how to create magnetic or non-magnetic marker flags using a wooden dowel/stake, red tape, and a magnet.

  Provenance: Klaudio Peshtani, Rutgers University-Newark
  Reuse: If you wish to use this item outside this site in ways that exceed fair use (see http://fairuse.stanford.edu/) you must seek permission from its creator.
  1. Nonmagnetic marker flags: Wrap a wooden dowel or plastic stake with colored duct tape (preferably red/light colors), creating a flag (see figure). Six-inch dowels are recommended so the marker flag is as close to the ground as possible.
  2. Magnetic marker flags: Place a small magnet next to the wooden dowel or stake and encase it by wrapping colored duct tape around it (see figure). The magnetic marker flags will look identical to the nonmagnetic marker flags. You can place these magnetic anomalies at any preferred point along the grid. It is recommended that you vary the amount of magnetic material hidden in each magnetic marker flag to create a more diverse contour plot.

• The illustration to the right presents an example of a 5 x 5 meter grid, with measurements taken at 0.5 meter intervals and marker flags positioned every meter (for student convenience, marker flags can also be placed at each measurement point).

Example of 5 x 5 meter grid setup for the cellphone magnetics survey.

Provenance: Klaudio Peshtani, Rutgers University-Newark
Reuse: If you wish to use this item outside this site in ways that exceed fair use (see http://fairuse.stanford.edu/) you must seek permission from its creator.

• Students will work in teams of two to ensure all students are actively participating in the survey. Student one will be measuring data with their smartphone magnetometer and relaying it to the recorder (student two), who will be recording the magnetic data at the corresponding grid coordinate on the printable datasheet provided. Using this datasheet, students will then generate individualized 2D magnetic contour plots using the provided Python script.
  • Recommend students to download the smartphone magnetometer app prior to relocating/beginning the survey to avoid troubleshooting during the survey.
  • Direct students to form a line at point 0 (X) 0 (Y) on the grid with their paired partner. After the first pair completes at least two meters of measurements, direct the next pair to start to avoid clustering.
  • It is recommended that students alternate between roles as the measurer and recorder in their paired groups.

Formative assessments can be conducted via class or small group discussions after each part of the narrated video, in between each part of the worksheet, and during the smartphone magnetics survey.

The Environmental Magnetism Student Worksheet assesses the learning goals above and is intended to be the summative assessment for this unit. The instructor copy of this worksheet, with solutions, can be found below. An instructor solution to the real magnetics survey Python script is also linked in the document. 

• Environmental Magnetism Worksheet KEY -- private instructor-only file
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  Environmental Magnetism Worksheet KEY

  
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