Whether you are hiking through the wilderness or driving down a busy city street, GNSS is a reliable companion that guides you with the utmost accuracy. Global Navigation Satellite System (GNSS) refers to a constellation of satellites that provide signals from space that transmit positioning and timing data to GNSS receivers. Agriculture, mapping, transportation, navigation- GNSS technology has a wide range of applications across industries and everyday life. This article provides an in-depth discussion of satellite navigation systems with a focus on understanding atmospheric GNSS errors.
Some of the most prominent GNSS systems in operation are:
Global Positioning System or GPS, developed by the US Department of Defense, is a network of satellites orbiting around the Earth. There are currently 30 operational GPS satellites. These satellites continuously transmit signals that contain information about their precise location and time.
Global Navigation Satellite Systems or GLONASS is a satellite-based navigation system developed by Russia. The system had an initial constellation of 24 satellites.
Galileo is the European Union’s Global Navigation Satellite System. It aims to provide an independent positioning system for Europe and other regions.
BeiDou Navigation Satellite System or BDS is China’s GNSS. It initially provided regional coverage, but with the completion of the BeiDou-3 constellation, it now provides global navigation services.
Atmospheric errors
One of the most significant sources of errors in GNSS positioning can be attributed to the atmosphere. Since the satellites and the GNSS signal receivers are located far away, the GNSS signal travels thousands of kilometers between the satellite and the receiver. During this journey, the signal passes through atmospheric layers.
The ionosphere is the layer of the atmosphere between 50 and 1000km above the Earth. This outer layer of Earth contains electrically charged particles called ions. They significantly affect the transmission of the GNSS signal causing its distortion and delay.
Since atmospheric errors are challenging to predict due to their changing nature, it’s difficult to determine their precise impact on calculated positions.
The delays caused by the ionosphere can vary based on:
The time of the day
The season of the year
Geographical location
The solar activity
Baselines
Atmospheric errors also depend on the distance between the reference base station and the rover receiver. The distance between the base station and the rover is known as the baseline. If the baseline errors are not taken into account, they cause significant positioning errors specifically in long baseline applications.
The base station is installed at a precisely known location. It estimates GNSS errors and continually sends corrections to the rover receiver. The rover receiver then uses this data to correct all errors and calculate the exact position. This works well when the base station and the rover are close.
We know that when several receivers are placed side by side in an open area, they tend to have similar errors. Both the base station and the rover receivers experience the same delay due to ionosphere and therefore have identical errors. This is known as a standard GNSS error. Thanks to this unique characteristic, we can calculate the relative distance between the receivers more accurately. This makes it easier for systems to correct atmospheric errors.
For the complete article on understanding atmospheric GNSS errors CLICK HERE.
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