The Simple Science Behind GPS Tracking Systems

Anyone who has used a smartphone or a navigation unit in their car knows the benefit of being able to find themselves easily on a map. Since its development in the 1970s and first use in the 1990s, positioning technology has become widespread and affordable. Many do not stop to think about the magic behind the devices and may be surprised to find that the way they work is based on some simple mathematical principles.

GPS tracking systems make use of satellite technology provided by the United States government. Currently there are 24 satellites that orbit the Earth in a specific pattern. The patterns are designed so that at least four of them are visible from any point on the Earth's surface at any time of day. The satellites are carefully monitored and controlled by U.S. government stations around the world. Sensitive antennas ensure the satellites stay on course and transmit data correctly. Without this, positioning would not work accurately.

All 24 satellites are constantly transmitting data at a constant rate back to Earth. They are all synchronized to send out messages at the exact same time. Each message states the satellite's position above the Earth as well as what time the message is sent. A device that uses a GPS tracking system listens for signals from these satellites and uses them to calculate its location using trigonometry.

GPS tracking systems work on the same principles that bats use to "see" at night. Bats are blind, but can tell how far away they are from an object by chirping and listening for the echo. It takes time for sound to travel across the air, bounce off of an object, and return to the bat's ears. If the sound returns quickly, the bat knows that there is an object very close to him. If the sound takes awhile to return to his ears, he knows that it object it bounced off of is far away.

Smartphones and navigation systems use the same idea. When a receiver "hears" a message from a satellite, it compares the time that the message was sent with the time that the message was received. The messages always travel at the same speed, so the device is able to calculate exactly how far away it is from the satellite, much like a bat.

You could be at a few different locations on the Earth's surface and be the same distance from a satellite, so the response from one satellite is not enough to determine the device's location. However, as more signals are detected it is possible to pinpoint a location more accurately. GPS tracking systems only need 4 satellite signals to get an accurate lock on a location, which is why the satellites are positioned so that four at a time can be seen anywhere on Earth.

By "looking" at a map and the position of the satellites in the sky, a computer can determine where it is on that map. Furthermore, if the computer constantly checks to see where it is, the speed that the device is moving can be calculated. From this data, all kinds of useful information can be displayed on navigation devices and smartphones.