What is the purpose of a mask in relation to GNSS satellites?

In the context of GNSS (Global Navigation Satellite System) satellites, a mask, often referred to as a "mask angle," serves the specific purpose of limiting the reception of signals from satellites that are low on the horizon. This is because satellites that are closer to the horizon typically have to pass through more of the Earth's atmosphere, which can introduce errors and reduce the quality of the signals received.

By applying a mask angle, a GNSS receiver ignores signals from satellites that are below a certain elevation, which helps in mitigating errors caused by atmospheric interference and multipath effects—where signals reflect off buildings or other structures before reaching the receiver. This selection process aids in ensuring that only the most reliable and highest quality signals from the satellites are utilized for accurate positioning and navigation calculations.

The other options, while related to GNSS functionality, do not specifically pertain to the role of a mask in satellite signal processing. For instance, the reduction of interference from terrestrial signals (mentioned in one of the other choices) pertains more to filtering techniques in receiver design rather than the mask function. Enhancing the accuracy of a signal and increasing satellite visibility range do not directly correlate with the specific function of a mask angle, making the chosen response accurate in its context.