Bruce Douglas: Using Analyzing High Resolution Topography with TLS and SfM in G429: Field Geology in the Rocky Mountains at Indiana University
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Provenance: Bruce Douglas (Indiana University)
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About this Course
This is an upper division summer field camp program for later-stage geoscience majors. Although Indiana University (IU) is a PhD-granting university, students come from many different types of schools around the USA. In a typical summer 30-40 different schools are represented.
~12
students (max 22)
~4 days of intense field time and evenings
spent working on field instrument deployment and data collection; data processing; and analysis of the geological problem that has been the focus for that day.
Summer field camp
Syllabus (Acrobat (PDF) 540kB Nov2 16)
GEOL G429 is a 7.5-week 6 credit summer field course for later-stage geoscience majors offered by the Department of Geological Sciences at Indiana University, Bloomington. The course is taught from the IU Geological Field Station located in the Tobacco Root Mountains in SW Montana. Students learn fundamental field observation and mapping skills. This module (using the TLS method) is offered as an elective near the midpoint of the program for students particularly interested in geophysics.
Our department requires the completion of G429 for all students pursuing the BS degree option in order for them to gain essential field skills. Students in the BA degree option are encouraged to enroll in G429, but it is not required. The course is open to any individual from a university or college that needs to satisfy a degree requirement for a field course with a significant time duration. Topics include sedimentology and stratigraphy, structural evolution and tectonic history, analysis of metamorphic and igneous complexes, neotectonics and seismic risk, and mining and mine reclamation. Two regional trips include stops in the Teton National Park, Yellowstone National Park, Sun River Canyon, and Glacier National Park.
I first integrated TLS into Indiana University field camp in 2010. It was an experiment as we were not aware of any other undergraduate programs, including both instrument courses or summer field courses, teaching TLS at the time. As always with teaching new topics, there were some challenges in figuring out how to best engage the students and keep them actively involved in the field and how to get data and software to individuals' computers. However their overall enthusiasm for the geophysics learning and their clear progress over just a few days – moving from basic survey design to applying it to different geologic research questions – has been truly satisfying. Since then we have gradually expanded the teaching materials to include more geologic applications and have added a computer cluster to our facilities which has addressed the problems of data uploading via a server and software already loaded and available. TLS has become a mainstay elective for students at the field camp – repeated every year since its start.
It can be a challenge to keep a dozen students involved and occupied when there is only one scanner, which only a few students can be operating at a time. These teaching materials fold in many years of experience in making sure that students experience all the different observations and activities needed to really understand how TLS works and the supporting data that needs to be collected. In addition to scanner operation students set up other equipment such as targets and GPS antennae, complete scan parameter worksheets to optimize the scan for the available time and research needs, and make traditional field observations and sketches. Thus TLS scanning becomes a tool that extends how they can observe Earth processes but is clearly still tied to fundamental field skills and math.
The annual student evaluations are uniformly positive with comments about how pleased the students were to have learned about this new and powerful geodetic tool. I have even had a student report back that learning TLS method and applications while at field camp influenced her ultimate path in graduate school.
My Experience Teaching with GETSI Materials
I have used all the units in the module except Unit 4: Change detection. The versions of Units 2 and 3 assignments were somewhat modified to fit the specific problems chosen in a given year and the associated field sites near the Indiana University Geologic Field Station.
Relationship of GETSI Materials to my Course
The summer field program, G429: Field Geology in the Rocky Mountains, is 7.5 weeks long. At the outset students learn fundamental field observation and mapping skills in a more supported environment with more faculty interaction. As the summer goes on students work increasingly independently from instructors and fellow students. Around the fifth week, they have the option to choose from four electives, including geophysics (TLS surveying).
I have always worked with a UNAVCO field engineer for the technical side of running the Riegl scanner and managing the data. UNAVCO has a process for requesting field geodesy education support. One of the particular challenges for using TLS in the intense IU field camp setting is the short turn around time between data collection (daytime) and analysis (evening). Students write up all their work individually even though they work in teams for data collection.
Unit 1
- This unit is an absolutely essential starting point for introducing students to the methods of TLS surveying. It starts with a lecture (usually the night before) on the applications and workflow for TLS surveying.
- Before we go into the field, we gather the students around the considerable amount of TLS equipment and have a discussion about the purposes of the various elements.
- I have used a variety of simple field sites including the field station building and a gravel borrow pit. It is nice if the site can have a small geologic application (ex. distance a fault has been offset), but really the most important element is that it is a small field area that can easily be captured in a couple scan positions.
- The next discussion we have as a group is about the scan design itself (i.e. where the scan and target positions should be).
- Then the group is split into teams of 3-4 students who rotate through the various tasks over the course of the day so everyone gets at least some time with the scanner.
- The students are also tasked with creating an equipment checklist and a document that provides a step-by-step description of the field and analytical components: instrument packing, scanner set up, parameter selection, etc.
Unit 2
- Unit 2 applies high-resolution topographic data to analysis of a stratigraphic section. This is usually the second full day of TLS work. One stratigraphic section that I have used for this is Milligan Canyon, MT, which has a set of carbonate parasequnces within the Mississippian Lodgepole formation. The other is located in Sandy Hollow, MT where interbedded sandstone and shale units are nicely exposed in the Cretaceous Kootenai formation.
- The ultimate goal is to have students look at varying bed and parasequence thicknesses or sandstone shale ratios and estimate feasible sedimentation durations or fluvial settings and transport directions.
- With just one day of TLS surveying behind them, the students are vastly more comfortable with the elements of the survey design. We are able to do the design discussion more efficiently, despite the fact that it is notably more complicated than Day 1. At least three scan positions are needed and there are more complicated sub-scans and target placement.
- After a day of data collection, we return to the field station. After dinner the students further exploring the range of data analysis tools in the TLS RiScan software and become familiar with how to best analyze the data collected that day. This might involve learning how to clean up the data by removing extraneous portions such as vegetation or working to enhance the reflectance amplitude contrast. These steps aid in analysis for the particular question/s being addressed.
- The students complete a digital report for each project that includes responses to specific questions posed as well as summaries of procedures they have used. Typically this involves the use of additional software such as Adobe Illustrator to enhance the relatively simple graphics produced by the TLS RiScan software.
Unit 3
- The students enjoy this unit a lot because of the excitement of working on a recent fault. Most years we have visited Hebgen Lake fault scarp at Cabin Creek, which formed in 1959. Thus I modify the Unit 3 exercise a bit to specifically include mention of our field site and its geologic setting.
- On this third day, the survey design discussion proceeds more quickly, even though the additional complication of a forested field area does make the scan positioning challenging.
- The Cabin Creek fault scarp is a transport-limited situation, so the fault shape can be potentially modeled using 1-D diffusion.
- I have not used the Unit 3.5 Matlab extension, but have instead used the Unit 3 Part B by N. Pinter. Students use the small Excel spreadsheet developed by R. Arrowsmith to experiment with the influence of the 1-D diffusion equation components.
- Evening time is spent in a similar fashion to that which took place on Day 2/Unit 2 with the incorporation of additional features within the TLS RiScan software such as scan parameter summaries, accuracy determinations, and scanner-target geometries.
Unit 4
- I have not actually taught Unit 4 change detection as currently written. We designed the module to have more applications than most courses would likely be able to use. Our hope is that at least one of the 3 suggested scientific applications for high-resolution topographic data (Units 2-4) is available for a given course.
- I have experimented with change detection on two occasions. The first was after a fire, but the vegetation growth was so rapid that it obscured many of the features which had been the focus of the original scan. Another year I tried to return to a cut bank that we had surveyed the year before. I had hoped to determine bank erosion and transport rates, but found that the area was entirely filled with >2 meters of tumble weeds. Definitely a change but not the one I was hoping to capture.
- I know from colleagues that change detection can be used successfully in undergraduate field courses, but I have not pursued it further as the areas around the IU Field Station have field sites better suited for Units 2 and 3.
Assessments
Unit 5 is the summative assessment for the module. On the fourth day of TLS surveying, students are introduced to a new field site with a geologic research question and asked to work in their teams to design an appropriate survey. Each team then makes a presentation presenting their primary scientific objective/s, their plan, and their rationale for what they are proposing. As there is only one scanner, the different teams then need to negotiate between themselves the best elements of the different suggestions to reach a final plan. With very little instructor support, the students divide up the survey tasks and execute the survey. The groups are expected to be able to run all aspects of the surveys completely independently. The sites used for the summative assessment have varied over the years ranging from portions of the IU Field Station to other sites with the potential for several problems to be identified. Students turn in the write-ups individually, which are due later that evening. This includes the scanning procedure documentation and equipment check list.
Outcomes
My original goal for introducing TLS was for students to learn a valuable field method for obtaining high-resolution topographic data. As time has gone on, I have increased the emphasis on the geologic research questions that can be addressed with the data. I have found that the majority of students accomplish the learning goals and gain significant confidence on using a method that initially appears daunting and complicated.
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