Global Positioning System Instruction in Higher Education
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Although students can gain a conceptual understanding of Earth coordinate systems through instruction involving diagrams and globes, there is no substitute for an outdoor experience in teaching field mapping and navigation. Such training is essential for students interested in careers involving data collection in the field, such as forestry, oil exploration, land-use planning or farm management.
Until recently, the principal tools available for instruction involving field mapping and navigation have been the topographic map and magnetic compass. Although useful for coarse navigation or positioning when landmarks are easily seen, a map and compass are not suitable for precision mapping and can be difficult to use when landmarks are not identifiable. Surveying equipment provides better accuracy but less portability and requires specialized training and considerable set-up time. Trends in the need for information, especially spatial information, have also fueled the demand for a fast and reliable method to determine Earth coordinates in the field.
The recent completion of the global positioning system (GPS) and increased availability and affordability of GPS receivers have introduced exciting tools for instructional programs that emphasize field data collection. Unfortunately, many educators may not be aware of the potential benefits that GPS can provide in improving methods for field data collection.
Our purpose here is to provide educators with a brief overview of GPS technology and includes some illustrations of how we have GPS introduced in classroom exercises.
GPS, The Global Positioning System
GPS is a satellite-based system developed by the U.S. Department of Defense (DoD) to simplify and improve military and civilian navigation and positioning anywhere on earth.[1] Testing of the first GPS satellite began in the 1970s, with the system becoming fully operational in the early 1990s.
As Figure 1 shows, GPS is composed of three parts. The Space component is made up of 24 satellites circling the Earth at a distance of approximately 10,900 nautical miles.[2] Each satellite travels along one of six orbital planes and makes a complete orbit in slightly less than 12 hours. GPS satellites send a continuous stream of radio signals to Earth containing information about orbit, equipment status and the exact time. The Control component includes five monitoring stations located throughout the world and a Master Control Station (MCS) at Falcon Air Force Base in Colorado. Information processed at the MCS is sent to monitoring stations, where satellite clock and orbital corrections can be made via ground antennas. The User component is comprised of a hand-held receiver that processes satellite information to determine a user's position and velocity. Equipped with a GPS receiver, it is possible to navigate or collect positions while stationary or moving and while located on the ground, in the air or over water.
How GPS Works
The basic principle used by GPS to determine Earth positions is relatively simple. Extremely precise clocks and the principle of triangulation are applied to measuring distances between a user and a combination of three or more satellites based on the time needed for the radio signal from each satellite to reach the hand-held receiver.
Several factors affect the accuracy obtainable with civilian GPS receivers. U.S. military concerns over the risks of GPS being used by hostile forces prompted the DoD to reduce the accuracy of positions that can be obtained by civilian receivers. This intentional error, known as "selective availability" or SA, degrades positions reported by civilian receivers, causing the positions reported to deviate up to 100 meters from the receiver's location. Recently, however, the DoD announced plans to eliminate SA within the next five to ten years. Without SA in effect, GPS receivers can obtain accuracies of about 30 meters.
GPS receivers are also becoming more affordable. In the mid-1980s, a typical civilian receiver cost between $20,000 and $120,000.[3] But in just the last few years, the price of GPS receivers has fallen dramatically. Personal GPS receivers today can be purchased for as little as $200, depending on precision and features needed. Receiver size is also shrinking, with some measuring only slightly larger than a pack of cigarettes.
A Way to Improve Accuracy
For many applications, especially those involving high-precision mapping and surveying, 100 or even 30 meter accuracy is unacceptable. To combat SA and other factors causing errors, a processing technique called "differential correction" can be carried out. Differential GPS (DGPS) is accomplished by using two GPS receivers simultaneously.
One unit, called the Base, is placed over a precisely known location such as a surveyor's monument and set to collect a continuous stream of positions. The second receiver, called the Rover, is used in the field to collect position data for the area of interest. When data collection with the Rover has been completed, errors in positions can be removed because the location of the Base unit is already known and errors reported by the Base and Rover receivers will be identical for any given moment in time. In most cases DGPS improves horizontal position accuracy to between two and five meters of the receiver's actual location. Sophisticated and expensive survey-grade receivers can yield even better accuracies of up to one centimeter; however, these units are generally beyond the budget of most educational institutions.
The Real-World Utility of GPS
In addition to its military uses, GPS has become a tool for civilian applications ranging from land surveying to ocean and aircraft navigation. The range of potential applications for GPS is limited only by a user's imagination. For example, trucking companies and overnight package-delivery services have discovered the advantages of using GPS to locate and track trucks to improve their deliveries. Civil authorities responding to natural disasters now use GPS to locate flammable liquid or gas in underground pipelines and storage tanks. In an application to which everyone can relate, once expensive and time-consuming highway maintenance surveys are made more efficient. A van equipped with a roadsensor and GPS receiver can log the positions of potholes, cracks or other irregularities in a road's surface. This data can later be displayed in a mapped form to assist highway crews.
GPS has seemingly endless applications: seismologists and geologists use it for mapping the movement of the Earth's crustal plates or fault lines; surveyors are using high-precision GPS equipment to establish survey monuments in less time and with smaller crews; and foresters map tree stands and identify the location of endangered species habitat with it. Despite GPS' utility to improve the efficiency of field-data collection, instruction in the use of GPS is not widely available at the college level. Instructors in the Geography and Forestry Departments are now working to address this issue for students at Oklahoma State University.
The GPS Program at OSU
The Geography/Forestry GPS Program at Oklahoma State University (OSU) was funded in 1994 through a grant from the National Science Foundation with matching funds from OSU. The project involves fall and spring semester courses taught within the Department of Geography and a summer course taught by the Department of Forestry. Equipment purchased for the project included three Trimble 6-channel Ge'Explorer receivers, two Trimble Pathfinder Plus receivers with external antennas, and a 12-channel Trimble Pathfinder Community Basestation. The basestation, used to improve the accuracy of positions collected in the field through differential correction, is located in a room within the Geography Building. GPS positions collected by the basestation receiver are logged continuously to a computer and basestation data can be accessed directly from this computer or remotely via a bulletin board system.
Geography Courses
GPS has been integrated into the curricula of several courses offered by the Department of Geography including Introductory Physical Geography, Field Techniques, Computer Mapping, and Geographic Information Systems.[4] Exercises designed for each course are presented as stand-alone modules so that students taking only one geography course are provided with necessary theory and other background material. Lectures provide an opportunity for instructors to explain GPS theory and to discuss applications; labs provide students with "hands-on" field experiences. Instructors coordinate the content of exercises so that activities have minimal overlap with other courses. This enables a student who might have gained exposure to GPS in another course to learn something new. The following provides a brief illustration concerning the "hands on" GPS activity associated with each course.
GPS Hands-on Activity: Groups of students in Introductory Physical Geography are provided with a brief demonstration of a GPS receiver and are then given a team assignment to determine longitude/latitude coordinates for several campus locations. The emphasis is on helping students to visualize latitude and longitude as forming an invisible grid on the landscape that can be used to record any object's location. Students take turns operating the receiver while completing a series of tasks to determine the coordinates for manhole covers, light poles and street corners on campus. In addition, they must plot the sky location (height, azimuth) of the satellites used to determine positions.
GPS Hands-on Activity: Teams of three to four students in the Field Techniques course use GPS receivers to record the location of commercial establishments during a walking survey of a small town. In addition to providing latitude/longitude coordinates, the Ge'Explorer receivers permit students to code information about features of interest. For example, the type of commercial establishment and its street address can be tied to each location by entering it on the receiver's keypad. Students are also taught to use the Ge'Explorer in navigation mode. Receivers are set in advance with coordinates that students must find. The unit provides students with commands to turn left or right as they walk and updates their speed of movement and distance from the target location.
GPS Hands-on Activity: The emphasis for students in Computer Mapping is to use GPS for precision spatial data collection. Therefore, student teams learn how to use "mission planning" software that enables them to determine optimal times for data collection in the field. Mission planning software facilitates creation of diagrams showing when satellite availability and geometry will yield the lowest horizontal or vertical error in positions reported. Following fieldwork, student teams then integrate GPS data with existing digital data from a U.S. Geological Survey digital map containing, among other things, streets, roads, highways, parks and hydrologic features.
GPS Hands-on Activity: Students enrolled in Geographic Information Systems (GIS) collect GPS data to create a "layer" of geographic information for their term project. GPS gathers geographic information not available through other sources. As an example, one student in GIS used a GPS receiver to identify the location of bank cash machines within the city of Stillwater. Using GIS mapping, the student was then able to combine this information with population data to create a map showing areas with large populations that are currently under-served by automatic teller machines.
Forestry Courses
The profession of forestry has always required a strong foundation in surveying because an integral part of natural resources management is being able to accurately describe the land. For generations, foresters have relied upon compasses to determine direction and either chaining or pacing to determine distance. However, new technologies such as GPS have begun to replace less efficient procedures for the measurement of forest resources.
Academic Summer Camp: The OSU Forestry Summer Camp is a field-oriented academic program offered annually to students between their sophomore and junior years in the Forestry curriculum. The experience combines theory, field instruction and practical application by emphasizing hands-on exercises and projects.
GPS equipment is used in Forest Mensuration II, a course that emphasizes the use of measurement equipment, statistical and physical design of forest sampling methods, and special topics in individual tree and stand-level mensuration. Teams of three students are expected to complete field exercises that involve mapping, measuring and analyzing characteristics of forest resources. Each team is assigned a study area of 50 to 164 acres. The overall assignment is to design, conduct, analyze and summarize an inventory of the forest resources contained on the tract.
In past years, the initial activity was a survey of the tract perimeter using a staff compass and surveyor's chain. Field data were then entered by hand back in the office and computer software was used to output maps and associated information such as calculations of area and error of closure. However, with GPS receivers, students simply walk the boundary of the study area while collecting positions. Back at camp, they differentially correct the data and transfer it to surveying software for map generation.
Re-visitation Activity: Another important aspect of many forest inventories is the periodic re-visitation of previously identified locations. Permanent study plots are often established and remeasured at specified time intervals for the purpose of estimating change in forest growth over a given time frame. While permanent markers are often placed on or near these plots, these easily become lost or stolen. This problem is eliminated by using a GPS receiver in navigation mode.
Student crews are given GPS receivers pre-programmed with the known latitude and longitude of each marker. They then follow direction and distance instructions to get to the location of that specific marker's point. Students then repeat the process using compass and pacing methods in an exercise to demonstrate how traditional survey methods are enhanced with GPS technology. In addition to forest measurement techniques, students are also shown how GPS methods can be used to collect non-commodity data about watershed boundaries, wildlife, recreation and aesthetic values.[5]
Measures of Program Success
Success of the GPS program implemented by the Geography and Forestry Departments has been demonstrated by a measurable improvement in students' understanding of field data-collection methods as suggested by performance on exercises and exams. In addition, a significant number of students and faculty from disciplines across campus have expressed interest in courses that contain a GPS module, while others ask for informal training on GPS equipment. Students themselves have developed among the most innovative uses for GPS data for independent research projects such as mapping human impacts in wilderness areas. Most important to Geography and Forestry majors has been the edge GPS training has provided them in their search for employment in an increasingly competitive job market.
GPS in Other Disciplines: While it is not possible to describe all potential ways in which GPS could improve instruction in other disciplines, a few examples help illustrate the breadth of possibilities.
Archeology: Of considerable concern to archaeologists are the architectural features of sites, and the precise and relative location of artifacts and other cultural remains. GPS can be used to map these features within archaeological sites and can help document the location of newly encountered small occupation sites in isolated areas.
Geology: GPS benefits geology because of the inherently spatial nature of the science. Surface mapping of rock types, structural features and geomorphological phenomena can proceed rapidly when geologists use GPS. This technology can also be dove-tailed to other methodologies in watershed studies.
Wildlife Science: This discipline can benefit from GPS in several ways. With faculty guidance, students can use GPS to document the location of wildlife features such as habitats, ranges, breeding and feeding sites, dens and nests, and animal trails. Rapid mapping of such features facilitates responsive wildlife protection and can be used to create regional databases for large-scale management activities.
Conclusion
GPS potentially benefits instructional programs in a wide range of disciplines and at many educational levels. Already, GPS equipment is within the budget range of most college and university programs; especially if departments pool resources and cooperate in acquisitions and maintenance of this surprisingly useful educational tool. Further, the declining cost of GPS will eventually place equipment within range of many secondary educational budgets.
In addition to those disciplines in which GPS instruction has already taken firm hold-- surveying, geography and forestry -- we suggest that the relatively quick and accurate positioning capabilities of GPS could improve field instruction in other disciplines: agronomy, hydrology, range management, transportation planning, urban and regional planning, resource management, landscape design and industrial arts. As GPS is increasingly utilized in real-world industries and careers, so it is an appropriate and valuable tool for students to learn how to use.
Thomas Wikle is Head of the Dept. of Geography at OSU and an Assistant Professor, teaching computer mapping and physical geography. His research interests focus on dialect geography and recreation management. E-mail: [email protected]
Lawrence Gering is an Associate Professor in the Dept. of Forestry and an Adjunct Associate Professor in Geography at Oklahoma State University. He also teaches courses in Dept. of Forestry's Summer Camp.
Dean Lambert is an Assistant Professor in the Dept. of Geography and teaches biogeography and field methods. With a doctoral degree from the University of Texas, his research interests are in cultural ecology.
The authors would like to acknowledge grant support from the National Science Foundation (USE-9452441) and Oklahoma State University.
References:
- Trimble Navigation (1989), A Guide to the Next Utility, Sunnyvale, CA: Trimble Navigation
- Leick, A. (1995), GPS Satellite Surveying, New York, NY: John Wiley & Sons
- Bossler, J. & Challstrom, C. (1995), GPS Instrumentation and Federal Policy Proceedings: First Symposium on Precision Positioning with the Global Positioning System, Rockville, MD. April 15-19.
- Wikle, T. & Lambert, D. (in press), "The Global Positioning System and its Integration into College Geography Curricula," Journal of Geography
- Boucher, B. & Oderwald, R. (1994), Global Positioning and Forest Inventory, The Compiler, 12(2), pp.23-26.
Products Mentioned:
Ge'Explorer, Pathfinder Plus, 12-channel Trimble Pathfinder; Community Basestation; Trimble Navigation, Sunnyvale, Calif., (408) 481-8000