Global Positioning System Instruction in Higher Education
Wikle, Thomas A., Gering, Lawrence R., Lambert, Dean P., T H E Journal (Technological Horizons In Education)
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 m@ 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.
* Purpose of this Article
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. 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. 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. …