What is a loosely coupled GNSS/INS integration approach?

• A. Uses INS measurements to update GNSS satellites.
• B. Integrates raw GNSS measurements into the INS state.
• C. Uses GNSS only for clock corrections.
• D. Uses GNSS position/velocity measurements as updates to the INS-based filter; less sensitive to partial GNSS outages.

Answer: (D)

In a loosely coupled GNSS/INS system, the INS does the high-rate motion propagation using accelerometer and gyro data, and the GNSS navigation solution—its position, velocity, and time—is used as a regular update to correct the INS drift. The GNSS solution comes from a standalone receiver and is fed into the INS filter as measurements, not the raw satellite observables. This makes the setup simpler to implement while still leveraging GNSS accuracy to keep the INS orientation and position on track over time. Because updates depend on a valid GNSS fix, the approach is relatively robust to partial GNSS outages: as long as enough satellites allow a usable fix, you can apply the GNSS update; if GNSS is completely unavailable for a period, the system continues to rely on inertial propagation until signals return. The other descriptions describe different architectures: using INS measurements to update GNSS, or integrating raw GNSS measurements directly into the INS (tight coupling), or relying only on GNSS for timing, none of which capture the loose-coupling idea.