The Global Positioning System (GPS) is straight out of science fiction. Thanks to reference satellites you can now find where you are on the earth with pinpoint accuracy. For many, their first introduction to GPS was through Hertz Rental Cars’ Never Lost System, a handy option when visiting an unfamiliar city. Since I read maps well my favorite use of a GPS is on the water. It’s particularly useful when trying to find my way back home in heavy ocean fog. Their operation depends on the very accurate atomic clocks on board each satellite. Each transmission indicates a satellite’s location and local time. Because the signals arrive in your hand at the speed of light, they arrive at slightly different times. Your GPS receiver will lock on to the transmissions of at least four satellites. By analyzing the time differences it will place you on the earth in three dimensions. It will tell you in which direction you are heading and how fast you are traveling. It’s particularly useful for ocean travel, because it looks at your absolute position on the globe adjusted for the effects of current and wind, errors that are not readily apparent when using a compass, a map, a watch and dead reckoning. Writer Bio
