Ephemeris refers to the orbital and clock data of GNSS satellites, which are essential for positioning and aiding INS systems. The ephemeris data allows a GNSS receiver to determine the precise location of satellites at any given time, enabling accurate navigation when combined with INS measurements.
How Ephemeris Works in INS/GNSS Navigation
GNSS Satellites Transmit Ephemeris Data – Contains satellite position, velocity, and clock corrections.
INS Uses GNSS Ephemeris for Position Updates – Helps correct drift errors in inertial navigation systems.
Real-Time or Pre-Downloaded Ephemeris –
• Real-time ephemeris is received directly from satellites.
• Assisted GNSS (A-GNSS) can use pre-downloaded ephemeris for faster satellite acquisition.
Why is Ephemeris Important for INS?
✔ Improves Position Accuracy – Helps INS maintain precise positioning when GNSS signals are available.
✔ Reduces INS Drift – Corrects accumulated errors in INS-only navigation.
✔ Supports High-Dynamic Applications – Essential for aerospace, military, and autonomous systems that require continuous precision.
Challenges with Ephemeris in INS Navigation
✔ GNSS Signal Loss – In tunnels, underwater, or jamming environments, INS must rely on dead reckoning without ephemeris updates.
✔ Ephemeris Aging – If GNSS updates are delayed, outdated ephemeris can reduce positioning accuracy.
