Unit 3: Getting started with GPS data
This unit provides essential background information on GPS (global positioning system) and reference frames. Students learn how to access GPS location and velocity data from the Network of the Americas (NOTA). They calculate total horizontal motion graphically and mathematically and tie the observed motions to local strain.
Unit 3 Learning Outcomes
- Students are able to locate Plate Boundary Observatory (PBO) GPS stations and download precise location and velocity data.
- Students are able to calculate the total horizontal GPS velocities both graphically and mathematically.
- Students are able to predict the type/s of strain and/or deformation resulting from different velocities at neighboring GPS stations
Unit 3 Teaching Objectives
- Cognitive: Facilitate student ability to solve infinitesimal strain calculations using multiple quantitative methods and to qualitatively describe the connection between GPS velocities and strain.
- Behavioral: Provide an opportunity for students to access and download GPS data.
Context for Use
This module was designed for structural geology courses but can also be successfully used in geophysics, tectonics, or geohazards courses or possibly even a physics or engineering course seeking practical applications. It can be done at most any point during the term. The module assumes that students have had a basic physical geology introduction to plate tectonics, faults, and earthquakes. Students gain the strongest intuitive understanding of strain (Unit 2: Mashing it up: Physical models of deformation and strain) and the human impacts of earthquakes (Unit 1: Earthquake!) if these prior units are used. However, Unit 3 can be done without these preceding units if students are familiar with the terminology related to strain, strain ellipses, translation, rotation, etc. Unit 3 is intended as the precursor to Units 4–6, teaching the students essential skills in GPS data access.
Description and Teaching Materials
Start out the class with the presentation "Introduction to GPS." This gives an overview of GPS from applications students are familiar with (phones, cameras, etc.) and then introduces high-precision scientific GPS instruments and data. The students then do an exercise in which they access the Plate Boundary Observatory data to locate stations and find the precise coordinates and velocity. After the introduction, the exercise can be done in class or at home. The exercise does require Internet, so for classes without easy access to computers, it maybe easier to do as a homework assignment. If the exercise is done in class, students can work in groups of three—each finding the data for one of the stations and then compiling the data. After the exercise is complete, another short presentation is provided for the instructor to go over the findings from the exercise and come to a better understanding of the ongoing strain in the coastal Oregon. Although no graded reflections are included in the exercise, the wrap-up presentation can be a good time to pose reflection questions to the class, such as "Did anything about this exercise particularly surprise or confuse you?" "What other areas interest you to explore in this way and why?"
- Introduction to GPS presentation (PowerPoint 2007 (.pptx) 30.5MB Oct23 20)
- Unit 3 Finding GPS data student exercise (Oregon Cascades) (Microsoft Word 2007 (.docx) 4.8MB Nov6 19)
Unit 3 Finding GPS data student exercise (Oregon Cascades) PDF (Acrobat (PDF) 3.5MB Nov6 19)
- Unlike most student exercises, we do not provide an answer key because the exact numbers will vary slightly as the station velocities are updated. However, the following presentation shows the sense of strain that will be observed and gives the instructor necessary images to walk students through a wrap up after they have completed the exercise.
Teaching Notes and Tips
- We also provide supporting math materials in Unit 2 for instructors interested in having students take the quantitative analysis to a deeper level. These include vector, matrices, and infinitesimal strain analysis background.
- Before turning the students loose to do the exercise in class or for homework, it may help to pick some other station in the western United States to walk them through the process. Have them watch while you go to the PBO website and find a station of interest. Show them how to find the velocity measurements by clicking through to the "detrended" time series (also described in their exercise, but seeing it in advance does seem to help). You can also show them how to view pictures of the GPS station. That seems to make it more real for them.
- If you are ever interested in having students generate vector maps for other GPS stations besides the ones featured in this module, you can use this Adobe Illustrator file as a starting point. GPS Triangle Vector Map (Adobe Illustrator) (Zip Archive 2.2MB Nov18 16)
- The concepts of translation, rotation, and strain ellipses are covered more completely in Unit 4: GPS and infinitesimal strain analysis, but in the Unit 3 exercise students are asked to make conceptual estimates for these characteristics for the three example stations in Oregon. They may need some guidance on applying what they saw in Unit 2: Mashing it up: Physical models of deformation and strain with the vectors they are now looking at. Instructors may wish to remind themselves of these concepts before teaching. Explanation of GPS Strain Calculator output PDF (Acrobat (PDF) 1.1MB Dec28 17) may be helpful to review.
Observation of student activity and conversations, individual questioning, and group discussion are excellent ways to conduct formative assessment as the students complete this exercise.
The student exercise is the summative assessment for this unit. Most of the questions have definite right or wrong answers. To receive full credit, students must show their work, where appropriate. Where an open-ended answer is required, students are assessed based on a simple 2-point system.
2 points = correct answer with thorough supporting evidence and/or complete description
1 point = answer not completely correct or lacking thorough supporting evidence or description
0 points = incorrect answer
References and Resources
- Information and data from the EarthScope Plate Boundary Observatory (PBO)
- Another way to access PBO data and to see velocity vectors is via the UNAVCO Velocity Viewer
- Information about geodetic reference frames
- Information about UNAVCO, the university-run consortium that run's NSF's geodetic facility.
- The full public GPS/GNSS data holdings of UNAVCO are available via their Data Archive Interface Version 2.