How To Understand Global Positioning System (GPS)

As children watching action movies such as those based on the legendary character of "Bond...James Bond," my friends and I have marveled on the amazing technology and gadgetry used in these movies, which enabled mind-blowing stunts being done with the similar ease and élan as cozying up to a very beautiful lady. One of these gadgets guided him from place to place and sometimes even pointed out the location of the enemy. The good news is that this gadget is easily available for you and me as well; it is called a Global Positioning System. Here's how to understand a bit more about GPS.

A Global Positioning System or GPS is a navigation system that functions based on information beamed or transmitted to it from satellites placed about 12,000 miles in the space orbit above us.  These comprise of 24 (twenty four) satellites that are constantly moving [at speeds of 7,000 miles per hour] round the clock, rotating in tandem with the earth's movement. Like many other technologies such as the internet, GPS technology was also invented by the Department of Defense, U.S.A and was initially meant for use in defense purposes only. It is widely believed that sometime in the 1980s, when the Russians shot down a Korean airliner for straying into their air space, the then U.S. President, Ronald Reagan, passed a law making GPS available for civilian uses as well.

For starters, you will need a GPS Receiver (loaded with some maps) that can receive signals transmitted by the GPS satellites; this works on the triangulation system where basically the GPS receiver compares the time when signal is transmitted by the satellite, with time of signal reaching the receiver. By calculating the difference in time, the receiver can accurately predict its location and display it on a map appearing on its screen. Now, you may know that the earth is divided into latitudes and longitudes. The Receiver needs to be get signals from at least three satellites to enable the display of a 2D position and further to track its movement. When the Receiver connects to four satellites or more, it enables the display of a 3D image comprising of latitude, longitude and altitude where the Receiver is positioned. If you are holding the Receiver in your hand, this will then be where you are located. This is the basic information required by the Receiver, which then enables display of much other information such as position of sun, time of day, distance from and route maps to other locations in the world. Essentially three types of information is contained in the signal transmitted by the satellite to the receiver viz. - a pseudo-random code or in simple words information identifying the satellite from where information is being received; ephemeris data or information on position of the satellite; almanac data that includes health status of the satellite, time and date.

The satellites in orbit are powered by solar energy and carry batteries for backup supply in case of a solar eclipse. Lasting 10 years on an average, these satellites are replaced by new ones periodically.  Signals transmitted by the satellites come in two low power radio signals of ultra high frequency band and travel by line of sight through clouds, plastic, glass, foliage and tree cover (not too thick), but cannot pass buildings or rock formations like mountains and other solid objects. 

Constant improvements in technology ensure GPS data is accurate and useful to an explorer or traveler.  This is an overview of the Global Positioning System, which will help you decide whether you should invest in a GPS instrument.