In the ancient past, people drafted detailed maps, erected monumental landmarks, and read stars in the skies to keep them from getting lost during travels and explorations. Ancient sailors depended on constellations in the night sky to find out their specific location and where they were headed to. In the 21st century however, things have changed for the better. People no longer have to use landmarks or constellations to figure out their specific locations. All that is needed is a simple and easy to use handheld Global Positioning System (GPS) receiver to figure out the location anywhere in the world.
All this has been made possible by the over 30 navigation satellites circling the Earth’s atmosphere.
What is GPS?
Well GPS is basically a system made up of three parts; a constellation of between 24 and 32 solar-powered satellites circling (orbiting) the earth orbits at an altitude of approximately 20, 000 km, a main control station and four control and monitoring stations based in Hawaii, Diego Garcia, Ascension Islands, and Kawajale, as well as GPS receivers. A good example of a GPS receiver is the one found in your car.
Initially, the GPS system was developed by the U.S government for military use but later on made accessible for civilian use. Anyone with a GPS device, including a phone or a handheld receiver, can receive radio signals broadcasted by the satellites.
How Does GPS Work?
The GPS solar-powered satellites circle the earth at approximately 12,000 miles, which translates into 19,300km. They make two complete rotations every day. They are arranged on precise orbits such that they are visible in the sky.
The satellites transmit signal information to earth. Upon receiving the signals, the receiver uses them to work out your exact distance from each one of the four satellites. It then triangulates your exact position on earth to the nearest few meters based on the calculated distances.
Practically, the GPS receiver compares the exact time a signal was transmitted by a satellite with the time it was received. This time difference informs the GPS how far away the satellite is in the skies. Distance measurements from other 3 satellites help the receiver determine your position and display it on the receiver’s electronic map.
Essentially, the signals from three satellites are needed to carry out the Trilateration process. Trilateration is the process involved in determining absolute or relative locations of points by the measurement of distances, using the geometry of circles, triangles, and spheres. The signals from the fourth satellite are only used to confirm if the initial calculations are accurate.
The GPS receiver must be positioned or rather locked on to the signal of about 3 satellites in order to accurately calculate a 2-D position, which is the Latitude and Longitude, and also track movement. If four or more satellites are in view, the receiver can determine your 3-D position, which is the Latitude, Longitude, and Altitude.
Once the exact position has been determined, the receiver can then calculate other essential information such as track, bearing, trip distance, distance to a destination, sunrise, sunset, including others.
This basically means that from all the way in space, you can determine your location on the ground within just a few yards from your actual location. Amazingly, there are some incredible high-tech GPS receivers that can determine your location within just a few inches.
You can no longer get lost; whether on foot or while driving, thanks to the GPS technology.
GPS and Relativity
All GPS satellites have atomic clocks whose work is to keep accurate time. General Relativity predicts that will appear to run a bit slower under strong gravitational pull. As a result, the atomic clocks on board the satellites will therefore seem to run much faster than clocks on Earth. However, the entire GPS system is designed to make allowances for these effects.
How Accurate is GPS?
Thanks to their parallel multi-channel design, the current GPS receivers are extremely accurate. These receivers quickly lock into the satellites when turned on and even maintain strong locks in urban settings (tall buildings) as well as dense foliage. On average, most GPS receivers are accurate within 15 meters.
There are certain types of receivers that use a method known as Differential GPS so as to obtain a higher accuracy. These advanced receivers require and additional receiver that is fixed at a known location nearby.
It’s amazing how recent technologies such as the GPS system have made our lives much easier. Whether you’re lost in the woods, asking ‘where am i?’, or are simply looking for a certain store, a GPS receiver can help you accomplish just that.