For many years, Global Navigation Satellite Systems (GNSS) have been the key tool for determining position and/or time. Data from satellites are globally accessible and, in most cases, free to use. The American GPS is the most widely known, but today, there are several GNSS constellations. The Russian GLONASS, the Chinese BeiDou and the European Galileo are alternatives to GPS, but they can also be used together. Using several different GNSS constellations increases applicability, as the more satellites the user receives signals from, the better the data access and the smaller the margin of error.

GNSS constellations orbit the earth at around 20,000 kilometres’ height. The satellites are equipped with very accurate atomic clocks, and a user’s GNSS receiver calculates the distance to the satellite by measuring the time difference between the satellite and the receiver. To obtain a position, the user needs a GNSS receiver and has to receive data from at least 4 GNSS satellites. Three satellites are needed to determine the user’s position in each dimension, and one satellite to determine the user’s time. Satellite signals can be disturbed on their way through the ionosphere and the troposphere, or by various elements on earth, such as buildings, mountains, etc. The more satellites the user can track, the more you can reduce the margin of error generated by the more redundant measurements and thereby achieve a higher accuracy.

Image courtesy of Taranu Leflot, Sabina-Luiza
23 APRIL 2021