A properly designed GPS receiver can achieve horizontal accuracy of 3 meters or better and vertical accuracy of 5 meters or better 95% of the time.
Augmented GPS systems can provide submeter accuracy.
However, it is not yet perfect, and it is sometimes buggy. So, what factors affect the accuracy of the GPS?
GDOP (Geometric Dilution of Precision) or PDOP (Dilution of Precision in Position) describes the error generated by the specific position of the GPS satellites.
The point is that the more signals a receiver can “see”, the more accurate they can be.
But, if these satellites are physically close, then you have poor GDOP.
The latter tends to reduce the quality of your GPS positioning most likely in meters.
Based on this information we will then continue to discover the top 5 reasons that can affect a GPS signal and cause errors.
What Factors Affect the Accuracy of the GPS?
GPS Accuracy Factor #1 – Atmospheric Refraction
The troposphere and ionosphere can change the speed of propagation of a GPS signal.
Due to atmospheric conditions, the atmosphere refracts signals from satellites as they pass through them on their way to Earth’s surface.
To get around this, a GPS can use two separate frequencies to minimize the velocity of propagation errors.
Depending on the conditions, these type of errors in the system could compensate the position anywhere starting from 5 meters.
GPS Accuracy Factor #2 – Multipath Effects
One possible source of error in GPS systems is the multipath effect.
This is generated due to the signal from the GPS satellite bouncing off nearby structures such as buildings and mountains.
In effect, the GPS receiver detects the same signal twice at different levels.
However, this error is a little minor serious and could generate a position error of 1 meter.
GPS Accuracy Factor #3 – Satellite Time and Place
The accuracy of the atomic clock of a GPS satellite is 1 nanosecond for each tick of the clock.
That is very impressive!
Using trilateration of time signals in orbit, GPS receivers on the ground can obtain precise positions.
But, due to the inaccuracy of the satellite’s atomic clock being synchronized, this can offset a position measurement by 2 meters or so.
GPS Accuracy Factor #4 – Selective Availability
Before May 2000, the US government added a time-varying code to the Global Positioning System.
Except for privileged groups like the US military and its allies, this degrades the accuracy of GPS.
This whole process of degradation of a GPS signal is called selective availability. When enabled, the signals added 50 meters of error horizontally and 100 meters vertically.
All things considered; this significantly reduced the accuracy of the GPS.
By then differential GPS was capable of correcting.
But after 2000, this source of GPS error was no longer of great concern, since the selective availability switch was turned off.
GPS Accuracy Factor #5 – GPS Differential Correction
GPS receivers improve accuracy by using two receivers because terrestrial receivers can take precise measurements of the error.
As long as the stationary GPS receiver detects the same satellite signals as your GPS receiver, it can send you correction data based on your exactly surveyed location.
Significant improvements in GPS accuracy have been made with the selective availability switch turned off to prevent poor GPS signals.
But with Differential GPS line techniques and a Satellite-Based Augmentation System, positions can improve sub-meter accuracy.