GETSI Teaching Materials >High Precision Positioning with Static and Kinematic GPS > Unit 2: Kinematic GPS/GNSS Methods > Unit 2.2: Change Detection with Kinematic GPS/GNSS
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Unit 2.2: Change Detection with Kinematic GPS/GNSS

Benjamin Crosby, Idaho State University (crosby@isu.edu)
Ian Lauer, Idaho State University (laueian@isu.edu)

This material was developed and reviewed through the GETSI curricular materials development process. This rigorous, structured process includes:

  • team-based development to ensure materials are appropriate across multiple educational settings.
  • multiple iterative reviews and feedback cycles through the course of material development with input to the authoring team from both project editors and an external assessment team.
  • real in-class or field camp/course testing of materials in multiple courses with external review of student assessment data.
  • multiple reviews to ensure the materials meet the GETSI materials rubric which codifies best practices in curricular development, student assessment and pedagogic techniques.
  • created or reviewed by content experts for accuracy of the science content.


This page first made public: Apr 24, 2018

Summary

Though it may be difficult to perceive, landscapes are constantly changing form and position. High-precision GNSS is one of a handful of techniques capable of quantifying these changes and is a key component of many modern geologic, biologic, and engineering studies. In this unit, students will learn how to approach a study in change detection in the context of a geomorphic or structural problem, then design and implement a GNSS survey that effectively explores the problem. Through field-based application of kinematic GNSS techniques, students will design, execute, and analyze data from a survey to detect change. Students design the survey based on a question of scientific or societal impetus and are asked to defend their design and implementation. This is the final unit focused on kinematic GNSS and is aimed at solidifying students knowledge and technical skill in this technique.

Note: Although the term GPS (Global Positioning System) is more commonly used in everyday language, it officially refers only to the USA's constellation of satellites. GNSS (Global Navigation Satellite System) is a universal term that refers to all satellite navigation systems including those from the USA (GPS), Russia (GLONASS), European Union (Galileo), China (BeiDou), and others. In this module, we use the term GNSS to refer generically to the use of one or more satellite constellations to determine position.

Learning Goals

  • Students can design, conduct, and analyze a GNSS survey of changes in monumented objects.
  • Students can analyze and interpret changes in monumented objects.
  • Students can analyze and interpret changes in both two and three dimensions and know which is appropriate for a given question.

Unit 2.2 Teaching Objectives

  • Cognitive: Students are taught how to calculate and interpret three-dimensional change between objects. They are shown how to decide whether change detection is possible in a given setting.
  • Behavioral: Students are directed to use kinematic GNSS techniques (field-based and post-processing) to accurately measure the positions of moving objects.
  • Affective: Students are shown examples of how change detection can be used to assess hazards (e.g. mass movements in transportation corridors) and/ or to study the dynamics of hazard producing processes.

Context for Use

This introductory unit is appropriate for upper-division geoscience, earth science, geography, or civil/environmental engineering students who have already been introduced to basic concepts such as plate tectonics, mass movements, and hydrology. Students should also have a first-order familiarity with uncertainty, precision, and accuracy. Appropriate for academic year courses with field components or a summer field camp.

This is the last unit of the field-based kinematic GNSS series and assumes completion of Unit 1: GPS/GNSS Fundamentals and Unit 2: Kinematic GPS/GNSS Methods. Unit 2.1: Measuring Topography with Kinematic GPS/GNSS, including instruction on surface interpolation; if your Unit 2.2 project will include surface difference maps, you will want to include some elements of Unit 2.1. Otherwise, instructors can choose to do one or both of the application units: Unit 2.1 and/or Unit 2.2. The unit should require ~6 hours to complete the lecture, design, implementation, processing, and analysis steps. Changes should be greater than 3 cm to be confidently detected. Tracked objects should be numerous and varied rather than singular. Singular objects are best tracked using static GNSS techniques discussed in Unit 3: Static GPS/GNSS Methods. Students will be trained to use these techniques for a variety of change-detection applications in earth sciences, engineering, and geography.

Description and Teaching Materials

1) Lecture and Exercise

Students are introduced to various change-detection applications and shown under which circumstances kinematic GNSS is best applied. Students practice calculating change in a monument's position between two points in time and are asked to consider the continuity of that change over the interval.

2) Design

This unit begins by presenting students with a field area and posing questions to them on how they might apply a kinematic GNSS survey to ask a question of scientific or social importance. Will the measured changes be greater than the uncertainty of the method? Will our traffic in the field site affect the rate of movement? How do we assure that the techniques we use now are similar to those used in the previous survey (method consistency)? Etc. Students will work first individually, then seek a group consensus for the design of a kinematic GNSS survey to detect change.

3) Implementation

Students work together to implement their survey design in a field environment. Students are in charge of all aspects of the deployment from packing, to setup, surveying, and data collection. Students are asked to keep individual field book entries with appropriate metadata and logs that will be turned in and assessed. Any change in the monumented objects caused by student activity must be noted.

4) Processing and Analysis

After students have implemented their survey, they will post-process it with guidance from Unit 2's methods manual. Students are expected to provide individual analyses of the change detected using a variety of methods. A write-up is then formulated answering posed questions and using their total experience and knowledge on kinematic GNSS system and its appropriateness for the study.

Teaching Materials

Teaching Notes and Tips

General

This unit requires kinematic GNSS hardware. We suggest one base station for the group and at least one rover per 5 students. All hardware should come from the same manufacturer for ease of instruction and data processing. Always have your hardware fully charged, professionally serviced and recently field tested before handing it over to students. In-class hardware malfunctions are distracting and frustrating. If your school does not have kinematic GNSS equipment, you may be able to find colleagues who do or consider requesting support from UNAVCO, which runs NSF's Geodetic Facility.

This unit is intended to be field based and student driven. Students should demonstrate their ability to run a survey with minimal help beyond the guide materials provided. Student will likely need some direction in asking questions relevant to available sites and their characteristics, but the final decision should be made by the students. If revisiting a previous site with repeat observations, ask the students more complex questions as to why the survey is designed the way it is and to justify whether kinematic GNSS is the appropriate method.

Survey and site considerations

It is most effective for instructors to have coordinated the locations prior to teaching. Students should be given a site that provides them an opportunity to answer a scientific question with some societal relevance and that challenges them to think about various elements of survey design. This should include a few challenges such as line of sight, multi-path errors, limited sky and satellite geometry, etc. Students will likely need some assistance, but this should moderated. Students should be encouraged to work out problems as a group and make decisions. Work with students to make certain that their design is appropriate for the time you have allotted.

With large groups or multiple pieces of equipment, two survey designs may be implemented or a single design can be repeated by multiple teams. This gives students an additional data set with which they can assess their ability.

We have provided some ideas for field sites with preexisting benchmarks or campaign data sets to help you get started with change detection ideas.

Be sure to get landowner permissions.

Field notes

Students should be aware that GNSS surveys are about precision, which includes detailed notes on metadata about the setup. Students must take personal notes about the equipment, survey design, and its execution to be successful. Students are encouraged to notate when they encounter issues and how they resolve them.

An example of a field book setup may be provided to students and is available in the educational resources, but it is only a guide and may be modified or substituted based on instructor preference. The spreadsheet-style format can also be distributed to the students if they do not have field books or if the full-page format is preferred.

Keeping students occupied

One of the challenges of integrating GNSS surveys into a course with more than a few students is making sure that students stay engaged and mentally challenged even while they are waiting for their chance to participate in the data collection process. Students should also be encouraged to notate or map features of the survey area to ensure they can complete the data exploration portion of their assignment. Breaking students into small groups and conducting multiple surveys if multiple rovers are available is great. Most systems allow multiple rovers to operate with a single base station.

An example field log is provided, and students are encouraged to fill this out or create their own. Metadata such as equipment type, manufacturer, and important settings should be recorded. Additionally, an equipment log is provided, and this can be used to engage students while they are not taking points.

Adapting based on available computers

The data processing section of this unit requires proprietary software from the manufacturer of the GNSS system you are using, often meaning licenses are limited. This section of the unit can be modified based on resources available. If no student computers are available, we encourage the instructor to project their screen and walk through the data processing with students. The OPUS portion of the processing (processing base station position) is freely accessible on the web for students to practice.

Once processing is complete, students should be individually responsible for completing the mapping assignment and interpretation of results. Group discussion is great, but students turn in individual work.

Ideas for societal challenges addressed by kinematic GNSS

  • Delineating or measuring migration of a river channel with proximity to a valuable resource or infrastructure
  • Measuring movement on a natural hazard such as a landslide, earthflow, or slump
  • Delineate or measure motion of monuments on a glacier, glacial retreat or snowpack change
  • Measuring a scarp surface or profile to determine potential hazard to infrastructure with earthquakes
  • Creating topographic models of flood plains to calculate flood volume and determine potential for flood hazard at various stage levels
  • Create digital elevation models to determine slope stability with addition of roadcuts or other infrastructure

Assessment

Formative

Much of the formative assessment can be done through observations of and discussions with students individually, in pairs, or periodically in the whole group. This should be done periodically throughout the process and helps gauge student understanding and weaknesses. Students should be encouraged to answer their own questions through deductive reasoning. A large portion of the grading should be attributed to students' individual participation and contribution to the group effort. Students will turn in their Unit 2.2 Calculating Change student exercise. Questions should be graded for completeness.

Summative

The students will turn in their survey design, sketches, and final write-up. The final write-up needs to display the student's cumulative understanding of kinematic GNSS systems, their application, and techniques. A large portion of the grade should focus on the student's understanding of why the specific technique and design they used was appropriate for the questions posed and how kinematic GNSS improved the quality of the study over other methods.

Student Examples:

  • Unit 2.2 Summative Assignment: Field Survey and Analysis of Change

References and Resources

Papers that have discussed similar applications of this technique


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This module is part of a growing collection of classroom-tested materials developed by GETSI. The materials engage students in understanding the earth system as it intertwines with key societal issues. The collection is freely available and ready to be adapted by undergraduate educators across a range of courses including: general education or majors courses in Earth-focused disciplines such as geoscience or environmental science, social science, engineering, and other sciences, as well as courses for interdisciplinary programs.
Explore the Collection »