How does the Gps work? |
Answer:
Complex operations + Trilateration. |
The GPS's ultimate goal is to be able to find our location and get us to where we want to be. It accomplishes this through expensive equipment and years of science that has created the circumstances for many complex math equations to work.
how does the gps know where i am?
In order to track your location, the GPS uses a method called trilateration. The satellites above you release signals all around it in a sphere. Where all the spheres of the three/four satellites above you intersect, that's where your location would be.
It is better explained in 2D.
It is better explained in 2D.
Satellite-red, satellite-green, and satellite-blue are the 3 satellites closest to you above your head.
If satellite-blue knows that you're R1 km away from it, then you could be anywhere on the circle's circumpherence.
If satellite-blue knows that you're R1 km away from it, then you could be anywhere on the circle's circumpherence.
If satellite-red knows that you're R2 km away from it however, that narrows it down to two possibilities of where you could be, as the red circle and the blue circle intersect at two points.
If satellite-green knows that you're R3 km away from it, then all the circles intersect at a common point; this means that it is only possible that you are there.
This is a simple version of how satellites find your location. But imagine this with spheres.
With spheres it is a little different, since it's 3D instead of 2D. If you only had signal from 3 satellites, there would be two intersecting points, two possibilites of where you could be. But one point is on Earth and one point is in space. The GPS automatically assumes that you are on Earth.
Since trilateration needs at least 3 satellites to calculate your location, there is always at least 24 satellites in the sky; 24 is the minimum amount of satellites needed to cover the entire earth with their electromagnetic radiation, to be able to sense a receiver from anywhere on Earth. The satellites are positioned so that there will always be at least 4 satellites in the sky within your vicinity.
Why 4 satellites? The more satellites, the more accuracy! Also, 4 satellites will let the GPS not only calculate your longitude and latitude, but also your altitude!
With spheres it is a little different, since it's 3D instead of 2D. If you only had signal from 3 satellites, there would be two intersecting points, two possibilites of where you could be. But one point is on Earth and one point is in space. The GPS automatically assumes that you are on Earth.
Since trilateration needs at least 3 satellites to calculate your location, there is always at least 24 satellites in the sky; 24 is the minimum amount of satellites needed to cover the entire earth with their electromagnetic radiation, to be able to sense a receiver from anywhere on Earth. The satellites are positioned so that there will always be at least 4 satellites in the sky within your vicinity.
Why 4 satellites? The more satellites, the more accuracy! Also, 4 satellites will let the GPS not only calculate your longitude and latitude, but also your altitude!
How do satellites know how far away they are from us?
To make things extremely simple, satellites are able to measure and calculate their distance from your GPS receiver by using the following equation:
distance = speed * time
Distance would equal the distance between the satellite and receiver.
Speed would equal the speed of the signals that travel through space between satellite and receiver.
Time would equal the amount of time it took for the signal to travel from satellite to receiver.
The answers to these variables seem simple.
PS satellites consistantly release radio signals (ranging from 1.1 to 1.5 GHz) that travel at the speed of light to GPS receivers.
The speed of the signals would be travelling around 300,000,000 meters per second (the speed of light).
Time is calculated by extremely accurate atomic clocks embedded within satellites and used by GPS receivers. The satellite sends a signal containing the current time. When the GPS receiver receives the information, it can compare the signal's departure time to the arrival time and calculate the difference.
The distance can be calculated using the distance = speed * time equation. This is how satellites know how far away you are.
Of course, it isn't really that easy. As you move, the time lag from the satellite to your device changes. The GPS needs to constantly updated in order to maintain your accurate location. Also, there is more math going on behind the scenes than it seems, as seen in the next section.
Speed would equal the speed of the signals that travel through space between satellite and receiver.
Time would equal the amount of time it took for the signal to travel from satellite to receiver.
The answers to these variables seem simple.
PS satellites consistantly release radio signals (ranging from 1.1 to 1.5 GHz) that travel at the speed of light to GPS receivers.
The speed of the signals would be travelling around 300,000,000 meters per second (the speed of light).
Time is calculated by extremely accurate atomic clocks embedded within satellites and used by GPS receivers. The satellite sends a signal containing the current time. When the GPS receiver receives the information, it can compare the signal's departure time to the arrival time and calculate the difference.
The distance can be calculated using the distance = speed * time equation. This is how satellites know how far away you are.
Of course, it isn't really that easy. As you move, the time lag from the satellite to your device changes. The GPS needs to constantly updated in order to maintain your accurate location. Also, there is more math going on behind the scenes than it seems, as seen in the next section.
how do satellites keep time?
All satellites synchronize operations, so signals are transmitted at same time. If even one of the satellites are offtime, the GPS may think you’re moving and calculations will be way off. There's no way anyone's location can be predicted.
It's not only satellites that must be on time. The receiver also needs to be synchronized, so the time lag of the signal being sent to being received can be calculated.
What the GPS operation needs is a very accurate time reference.
What the GPS operation has is the atomic clock.
The most constant and predictable thing humanity knows is the vibrations of an atom; the Cesium-133 atom in particular, which vibrates 9 192 631 770 times per second. It is one of the most commonly chosen atoms when it comes to creating atomic clocks.
Thanks to these atoms, the atomic clock is accurate to nanoseconds, which it needs to be in order to have optimal accuracy.
Atomic clocks are found on board of every satellite, but not necessarily on each receiver. Many GPS receivers like cellphones simply receive regular updates from places that do have atomic clocks. For example, the US Naval Observatory Master Clock. This is how many modern receivers without atomic clocks keep their time on track.
Even with super accurate clocks, General and Special Relativity predicts that differences will appear between these clocks and the same clocks on Earth
General Relativity predicts that time appear to run slower under stronger gravitational pull. Therefore, clocks on board satellites seem to run faster than clocks on Earth
Extra calculations and complex sciences are incorporated into the GPS network to make allowances for these effects.
It's not only satellites that must be on time. The receiver also needs to be synchronized, so the time lag of the signal being sent to being received can be calculated.
What the GPS operation needs is a very accurate time reference.
What the GPS operation has is the atomic clock.
The most constant and predictable thing humanity knows is the vibrations of an atom; the Cesium-133 atom in particular, which vibrates 9 192 631 770 times per second. It is one of the most commonly chosen atoms when it comes to creating atomic clocks.
Thanks to these atoms, the atomic clock is accurate to nanoseconds, which it needs to be in order to have optimal accuracy.
Atomic clocks are found on board of every satellite, but not necessarily on each receiver. Many GPS receivers like cellphones simply receive regular updates from places that do have atomic clocks. For example, the US Naval Observatory Master Clock. This is how many modern receivers without atomic clocks keep their time on track.
Even with super accurate clocks, General and Special Relativity predicts that differences will appear between these clocks and the same clocks on Earth
General Relativity predicts that time appear to run slower under stronger gravitational pull. Therefore, clocks on board satellites seem to run faster than clocks on Earth
Extra calculations and complex sciences are incorporated into the GPS network to make allowances for these effects.