The art and science of navigation has been around for thousands of years. The earliest navigators used the earth's magnetic field and the positions of the sun, moon and stars in the sky to guide them on their journeys. In fact, many sailors today still use the celestial navigation methods of centuries ago. Using charts of the positions of various celestial objects at different times of the year, directions can be accurately determined. In addition, knowledge of the time of day (or night) can reveal the navigator's location on earth.
Dr. Don Drost, physicist in the Division of Science and Mathematics, has taught a very popular celestial navigation course in the past at UVI, as well as at the University of Charleston. (If sufficient interest is shown, he could certainly be persuaded to teach it again!)
But another system, incredibly precise, convenient, and increasingly economical, has transformed navigation. It is presently being used by such diverse interests as commercial airlines to land surveyors. Work is in progress to produce an affordable version for your car. It is the Global Positioning System.
Global Positioning System (GPS) is an international system of global location using satellites in orbit about the earth in conjunction with ground based stations. The user of the GPS system must have a GPS receiver. This device (economical hand held models are available today) communicates with the satellites which in turn are in contact with the ground stations. The GPS receiver uses the signals of three or more satellites to pinpoint its location on earth. By knowing the precise position of the satellites (the ground stations help monitor position) and the time required for the signal to travel from the satellite to the receiver (typically < 1/10 of a second), the receiver can determine its position. Most receivers are accurate to within several meters, but the new differential receivers are capable of accuracy within centimeters!
Trimble is a company that makes GPS electronic equipment. They have a great
GPS tutorial that will lead you through the basics. There you'll find the answers to all the questions below. Check out their homepage if you're interested in buying a receiver...you'll never be lost. Happy navigation!
Questions:
Who "owns" the satellites used for GPS?
How many GPS satellites are there in orbit about the earth?
Three satellites should be enough to pinpoint your location on earth. But four are used. Briefly explain what problem the fourth measurement eliminates?
Be sure to enter your full name. Enter your email address ONLY if you want the number of points awarded e-mailed to you. Responses should be brief but complete. You must click the SUBMIT button to submit your entry. Entries are due by noon on Monday of next week.
Global Positioning System (GPS) is an international system of global location using satellites in orbit about the earth in conjunction with ground based stations. The user of the GPS system must have a GPS receiver. This device (economical hand held models are available today) communicates with the satellites which in turn are in contact with the ground stations. The GPS receiver uses the signals of three or more satellites to pinpoint its location on earth. By knowing the precise position of the satellites (the ground stations help monitor position) and the time required for the signal to travel from the satellite to the receiver (typically < 1/10 of a second), the receiver can determine its position. Most receivers are accurate to within several meters, but the new differential receivers are capable of accuracy within centimeters!