OpenTopography Data Sources and Topographic Differencing

Sharon Bywater-Reyes, University of Northern Colorado
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Initial Publication Date: June 28, 2021 | Reviewed: August 4, 2022


In spring 2020, the world was hit by a pandemic that spread globally by March, causing universities and most of the world to move to remote means. Summer field camps, long hailed as a rite of passage in the geosciences, were cancelled throughout the US. The community moved quickly, with NAGT developing remote learning tools and arranging for sharing and collaboration between instructors and institutions. As such, a summer field course "Geoscience Field Issues Using High-Resolution Topography to Understand Earth Surface Processes" – originally slated for in-person teaching, was adapted for remote instruction. This assignment uses existing high-resolution datasets housed within OpenTopography (OT), expanding upon data sources and skills practiced in the beginning sections of this course (i.e., structure from motion, and terrestrial laser scanning). First, student practice downloading and viewing data from OT; second students conduct a topographic differencing exercise, complementing the point cloud and raster differencing students conduct in Day 8 of the course.

Day 9 - This activity is part of the 2-week remote field course Geoscience Field Issues Using High-Resolution Topography to Understand Earth Surface Processes

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This exercise is intended for majors-level geoscience courses that have field or remote (online) field components.

Skills and concepts that students must have mastered

Familiarity with point cloud data, geospatial data, raster data and a background in geomorphology and/or physical geography concepts is helpful.

How the activity is situated in the course

This is situated after the first week of SfM activities and the TLS activity, as outlined in the Sheep Draw Vignette and the course page, and after a point-cloud and raster differencing assignment Day 9 of the course. As such, students have been introduced to point cloud data and associated post-processing techniques, and raster data. This assignment could easily be used as a stand-alone exercise on high-resolution topography and topographic differencing. This could be used in conjunction with the OT Topographic Differencing Webinar recorded Dec 17, 2020.

Activity Length

The instructor gives a lecture (~45 mins) on Airborne Laser Swath (ALSM) mapping (e.g. airborne light detecting and ranging; airborne lidar) and ALSM data sources, including OT. The students then work on Workflow 1 (OT Data Download and Viewing) and Workflow 2 (OT Geomorphic Change Detection). Students can work on data download and workflows synchronously (with communication and screen sharing via Zoom or similar; ~2 hours) or work independently and reconvene for office hours and group share. An office hours with trouble shooting and help with interpretation (~1 hour) would be helpful as well. All in all, the lecture and activity is ~4 hours, including time for students to finish their associated deliverables.


Content/concepts goals for this activity

ALSM datasources, with a focus on OT resources and OT Geomorphic Change Detection

Higher order thinking skills goals for this activity

Interpret geomorphic change in the context of an existing dataset; compare and contrast to SfM and TLS used in previous assignments of course

Other skills goals for this activity

Web-based computing

Description and Teaching Materials

This exercise follows SfM and TLS units of the course. Students have already conducted point cloud and raster differencing, but are here introduced to ALSM and web-based data sources and computing. After the instructor gives the lectures on "Airborne Laser Swath (ALSM) Mapping and Data Sources", students download data from OT for an area of interest in Workflow 1, generating a number of available products they will explore in a browser, Google Earth, and ArcGIS. In Workflow 2, students conduct a geomorphic change analysis by using the OT Topographic Differencing tool. Students are asked to interpret the change detection and ponder the pros and cons of ALSM OT differencing compared to the other methods used in the course.
Sheep Draw Vignette (Microsoft Word 2007 (.docx) 2MB Jan14 21)
OpenTopography Exercise for Students (Microsoft Word 2007 (.docx) 873kB Jan14 21)
Airborne Laser Swath (ALSM) Mapping and Data Sources (PowerPoint 2007 (.pptx) 28.7MB Jan14 21)

Technology Needs

Web browser
Google Earth Pro
ArcGIS Map or Pro (as preferred)

Teaching Notes and Tips

●You will need to help students navigate the OT browser download and help them interpret the results
●You may need to help with Google Earth .kmz data viewing and ArcGIS data viewing, depending on students' previous experience with these interfaces


As the summative assessment, students answer questions about the differencing methods used. Formative assessment should be done through discussion with students as a whole group or individually.

References and Resources

"Airborne Laser Swath (ALSM) Mapping and Data Sources" Presentation, compiled with permission, from
J Ramón Arrowsmith (School of Earth and Space Exploration Arizona State University), Ed Nissen (Colorado School of Mines), and Christopher J. Crosby (UNAVCO)


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