How the Advent of GPS Has Permanently Altered World Travel
By Dr. Gary Deel
Faculty Director, School of Business, American Public University
Imagine what it must have been like to try to navigate before satellites and computers, before even compasses were invented. For thousands of years the primary means of positioning and navigation was to track the stars and compare their positions in the sky to determine where you were and where you were going. Consequently, accuracy was limited.
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For example, if you followed the star Polaris (aka the North Star), you’d know that you’re tracking north. (Escaping slaves used the North Star to guide them to freedom in the North.) But you wouldn’t have much of an idea about your latitude or longitude from this simple assessment. Obtaining that information required tracking other stars and constellations, which complicated the task even more.
Over time, human ingenuity developed tools to improve the accuracy and usefulness of navigation by the stars. Compasses, quadrants, sextants, and astrolabes allowed sea captains to calculate their positions and directions of travel with impressive accuracy. And yet, even those tools rendered data with limited precision. They could tell sailors where they were within an error margin of a degree or two. But this margin could result in a standard deviation of tens or even hundreds of miles.
Today’s Global Positioning System Tracking Is Reliably Accurate between 10 and 26 Feet
Compare that with today’s global positioning system (GPS) tracking, which is reliably accurate between 10 and 26 feet (three and eight meters). In addition, anyone can use a GPS without any specific training, specialized equipment, or knowledge of the stars and celestial bodies. It is easy, therefore, to see just how far we’ve come in the past few centuries, and how far superior today’s methods are to those of yesteryear.
Today’s positioning and navigation systems are ubiquitous; they’re found on cars, buses, trains, planes, ships, and even on pedestrians and hikers.
GPS Relies on Two Distinct but Closely Partnered Remote Sensing Satellite Functions
GPS relies upon two distinct but closely partnered remote sensing satellite functions: high-resolution imaging and mapping of the Earth’s surface, and global positioning through real-time signal trilateration.
The first function, high-resolution imaging and mapping, is straightforward. Orbiting satellites collect image data using carefully plotted orbits and meticulously timed intervals to map surfaces, monitor weather, and perform other critical functions. However, in order to produce imaging and mapping data that is optimally useful, the images must be obtained with a clear and unobstructed view.
This means that imaging schedules must take into consideration weather patterns and cloud cover, and avoid any conditions that would render images that are less than ideal.
Engineers must also consider the types of film used and the wavelengths of light captured in the process. Earth’s atmosphere can scatter various light bands and distort images taken from space. So light filters are also used to capture only the light needed for the imaging.
The Time of Day that the Images Are Taken Is Extremely Important
Finally, the time of day that the images are taken is extremely important. Shadows created by the angle of the Sun will vary throughout the daylight hours. So it is equally important that photographs be taken at a consistent time and angle on each pass by the imaging satellite; that requires precise timing and orientation.
Obviously, high-resolution imaging and mapping serve different functions for different types of conveyances. For example, mapping applications can use high-resolution images of roadways to assist buses, vehicles, and even pedestrians and joggers find their way around.
Special Remote Sensing Satellites Map the Depths of Rivers and Oceans
By contrast, ships at sea are not limited to such confined paths. They do, however, need to consider the depths of shipping channels to avoid running aground, so special remote sensing satellites map the depths of rivers and oceans. Maritime professionals also need to monitor the weather at sea to avoid potentially dangerous conditions ahead. Remote sensing, by imaging and providing real-time updates on storms and swells, comes in handy for this task as well.
Air travel has some of the same concerns. Aircraft need not worry about roads or sea depths; once they reach cruising altitude they are relatively safe for point-to-point travel. But like ships, aircraft pilots must be mindful of weather conditions to decide whether to fly through, above or around storms along the flight path.
When visibility is extremely poor due to weather conditions, ground mapping and global positioning are also critical for ensuring that planes touch down in the right places and at the right times, every time.
In addition to ensuring that the Earth’s surface is comprehensively imaged and mapped, GPS must also be able to pinpoint the location of vehicles and individuals in real-time. GPS measures the time that it takes for a radio signal to travel between a transponder on a satellite in orbit and a receiving device on the surface of the Earth. Because electromagnetic radiation (including radio waves) travels at a known, constant speed, when the GPS system measures the time it takes for a signal to travel between two points, it also determines the distance between those two points.
But this just tells the GPS network the distance between the satellite and the device being pinged. It doesn’t tell the system which direction the measurement is taken from. So how does our GPS network know exactly where we are?
In the next part of this article, we’ll discuss exactly how GPS pinpoints the location of each individual user, precisely and reliably.
About the Author
Dr. Gary Deel is a Faculty Director with the School of Business at American Public University. He holds a JD in Law and a Ph.D. in Hospitality/Business Management. He teaches human resources and employment law classes for American Military University, the University of Central Florida, Colorado State University and others.