How does GNSS Doppler velocity measurement complement INS integration?

• A. Doppler provides velocity along line of sight to satellites; when fused with the INS, it constrains velocity and reduces drift.
• B. Doppler gives acceleration information; fused with INS to correct position.
• C. Doppler measures code phase; used to calibrate clock.
• D. Doppler gives altitude estimates; fused for vertical corrections.

Answer: (A)

The main idea is that GNSS Doppler gives a direct measurement of velocity, specifically the component of the receiver’s velocity along each satellite’s line of sight, and this comes from the rate at which the range to the satellite changes. When you fuse that velocity information with an inertial navigation system, you get a powerful cross-check: the INS computes velocity by integrating accelerations, but small biases and noise cause it to drift over time. The Doppler observations provide an independent, high-rate velocity update that anchors the INS solution, limiting drift and improving accuracy.

With multiple satellites, you can combine several line-of-sight velocity components to resolve the receiver’s 3D velocity, further strengthening the velocity estimate used in the navigation filter. Doppler is not giving acceleration data, code phase, or altitude; its strength is the precise velocity information along satellite lines of sight, which complements the INS by constraining velocity during normal operation and helping recover from drift.