It’s like a scene from a Hollywood movie: on a summer evening at sunset in 1982, a scientist and his colleague pull up in a station wagon to the summit of Mount Watchusett, Massachusetts and lift a bulky, 100-pound piece of electronic equipment from the back, along with some cables and a strange-looking antenna.
In the diminishing evening light, the two struggle for a while to get the thing set up, carefully positioning the square-bladed antenna towards the sky, and soon find themselves fielding questions from a growing group of bystanders. It’s a prototype GPS receiver designed by M.I.T., the scientist explains, as he momentarily shifts his gaze from the instrument panel, designed to pick up signals from a handful of satellites in the sky. We are testing its accuracy by measuring a baseline between the summit here and another receiver located in nearby Woburn.
The test was a success, and 25 years later the scientist, Dr. Alfred Leick, remains at the forefront of the GPS revolution as a professor of Geodesy at the University of Maine’s Dept. of Spatial Information Science and Engineering. As someone who has seen the science of Geodesy grow by leaps and bounds using the amazingly precise GPS tools available today, Leick has a new mission: to deliver high quality, graduate-level courses in GPS-based Geodesy and satellite surveying over the internet, something he has been doing since 2005 (Leick has been teaching the subject of Geodesy traditionally for nearly 30 years.)
Geodesy, the science concerned with the exact positioning of geographical coordinates and the shape of the world has been with us since ancient times. Homer postulated the earth as a flat disc, while Pythagoras imagined a spherical body. In his treatise Aryabhatiya, the fifth century Indian mathematician Aryabhata made amazingly accurate estimates of the earth. But it wasn’t until the widespread use of the telescope and the invention in the 1500’s of the theodolite – an instrument used to measure angles and used in triangulation – that things really started to take off. Still, none of these developments hold a candle to the changes that began after the first GPS satellite was launched by the United States in 1978.
An Ongoing Development
In 1982 terms, the prototype Macrometer GPS device developed at M.I.T. was state-of-the-art, able to define points within a centimeter of accuracy on a single frequency platform. The smaller and much more affordable GPS devices used in 2007 by consumers, military, aerospace and industry have yet to exceed the accuracy of that earlier device, though usability has come a long way in 25 years. “Manufacturers have been working since that time,” Leick explains, “and they’re still improving the receivers. It’s an ongoing development.”
GPS devices took a parallel course with computers, benefiting in the same way from ever-shrinking circuitry and more efficient engineering and growing more powerful and smaller as a result. About 10 years ago, scientists began throwing the phrase “GPS modernization” around, with an eye on the year 2015 as a completion date. One might wonder how the technology could get any better --engineers, surveyors, and mapmakers are now able to push a few buttons and get highly accurate data in just microseconds. Yet with the backing of space and military agencies, the drive for modernization is sure to yield even greater accuracy, with more features and better security.
Called GPS 3, the modernization efforts include adding a third frequency from the current two, changing the codes, and changing the messages the satellites are transmitting. “First of all, it will make it more secure to separate civilian and military users,” Leick explained. “Plus, when you have these modern codes, and a third frequency, their positions become faster, more accurate, and more reliable.” That’s not too surprising, when you consider that developments in satellite and GPS technology are funded by military-sized budgets and pioneered by scientists in labs at JPL and NASA, along with government labs.
At the time of Leick’s test at Mount Watchusett, there were 5 or 6 GPS satellites in the sky; there are now dozens more in medium earth orbit, with an estimated 24 in the NAVSTAR GPS system, 24 belonging in the Soviet GLONASS system, and a comparable number proposed for the European Union’s developing Galileo system. Affordable handheld GPS devices have replaced bulky units like the M.I.T. cube, and countries everywhere are seeing the advantages of developing GPS technology not only for industry and consumer use, but also as a boost to their economies and infrastructure.
“People are waking up to GPS,” Dr. Leick told me. “They are realizing that this is essentially a national asset, (with) real importance for the national economy.” Accordingly, in addition to the systems built by the United States, Russia, and the EU, China is working to develop their own satellite constellation.
It should come as no surprise that the world’s fastest-growing economy would want to harvest the amazing properties of GPS technology – a science that is making headway into every area of our lives. In addition to the highly publicized consumer uses ranging from GPS devices embedded in tennis shoes to those used in automobiles, GPS technology has become an important part of surveying and civil engineering, navigation of aircraft from rockets to jet liners, as well providing breakthroughs for scientists studying weather patterns, predicting earthquakes, and analyzing the changing shape of the earth’s crust.
“When you think about the (benefits of) precise positioning, it’s mind boggling,” Dr. Leick said. “It goes into everything.” At the highest levels of engineering and science, GPS technology can achieve accuracy within about a centimeter. Consumer GPS devices available for cars, boats, and motorcycles offer acceptable yet lower margins of accuracy suitable for their purposes.
The Ever-Changing World
The precision of high-level GPS devices has become so accurate that small movements of the earth are considered when analyzing the position of GPS devices used at the highest levels. “If you accept the fact that you can determine position within a couple of centimeters,” Dr. Leick said, “ then your receiver location is not fixed anymore, because we have plate tectonic motion, plus we have earth tides, the crust moves up and down just like we have ocean tides. And there’s a thing called ocean loading; at the centimeter level, the earth all of a sudden is not a solid body. Everything moves.”
To compensate for such movements, precision GPS devices attach a time stamp to their surveying activities, providing amazing accuracy in spite of the earth’s subtle movements. Surveyors using airplanes take digital photos using GPS-equipped cameras from miles above the earth, with each photo receiving precise coordinate data.
And though the many types of GPS-related tools used today have revolutionized such tasks, more can be done at the user level to improve the accuracy and quality of data. Leick is a believer in the power of his GPS-GAP distance learning program at the University of Maine to provide educational tools that will benefit professional users of GPS equipment worldwide, who can take his classes using a high-speed internet connection, the affordable MathCAD live software, and an equally affordable textbook (Leick’s GPS Satellite Surveying – now in its 3rd edition.)
“I hope to get a lot of those engineers using high positioning survey to take the courses,” he explains, “so they really understand what the limitations of the instruments are, and what they can do with it, rather than just pushing buttons.”
In addition to authoring the textbook GPS Satellite Surveying, Dr. Leick is Editor-In-Chief of the peer-reviewed journal GPS Solutions.
Dr. Leick has done research at M.I.T., the Air Force Geophysics Laboratory, The University of Stuttgart, and the 3S Navigation and Jet Propulsion Laboratory. His research has been funded by NASA, The European Space Research Organization (ESRO), the National Research Council, The Alexander von Humboldt Foundation of Germany, Fulbright, The World Bank, The Corp of Engineers, The Department of the Interior, The National Imagery And Mapping Agency (NIMA), the National Science Foundation, and private industry. He has lectured around the globe on the topic of GPS.
For more information, please visit Dr. Leick’s homepage at: gnss.umaine.edu