In GNSS, what is ephemeris data used for?

• A. Satellite orbit information used to compute precise satellite positions
• B. User weather data
• C. Signal strength indicator
• D. Receiver firmware version

Answer: (A)

Ephemeris data provides the precise orbital parameters and satellite clock corrections broadcast by each GNSS satellite. With this information, the receiver can compute the exact position of every satellite in its orbit at the transmission time, which is essential for turning measured ranges into the user’s position. This data is updated regularly and yields high accuracy for a few hours. Other items like weather data, signal strength indicators, or the receiver’s firmware version don’t describe satellite positions or enable precise navigation calculations.