Pitot-Aided Attitude and Air Velocity Estimation with Almost Global Asymptotic Stability Guarantees

This paper investigates the problem of attitude and air velocity estimation for fixed-wing unmanned aerial vehicles (UAVs) using IMU measurements and at least one Pitot tube measurement, with almost global asymptotic stability (AGAS) guarantees. A cascade observer architecture is developed, in which a Riccati/Kalman-type filter estimates the body-fixed frame air velocity and the vehicle’s tilt using IMU data as inputs and Pitot measurements as outputs. Under mild excitation conditions, the resulting air velocity and tilt estimation error dynamics are shown to be uniformly observable. The estimated tilt is then combined with magnetometer measurements in a nonlinear observer on SO(3) to recover the full attitude. Rigorous analysis establishes AGAS of the overall cascade structure under the uniform observability (UO) condition. The effectiveness of the proposed approach is demonstrated through validation on real flight data.

💡 Research Summary

The paper addresses the challenging problem of simultaneously estimating the attitude and air‑velocity of a fixed‑wing unmanned aerial vehicle (UAV) using only inertial‑measurement‑unit (IMU) data and at least one Pitot‑tube measurement. The authors propose a two‑stage cascade observer architecture that provides almost‑global asymptotic stability (AGAS) guarantees under mild excitation conditions.

System model.
The vehicle dynamics are expressed in a North‑East‑Down (NED) inertial frame I and a body‑fixed frame B. The rotation matrix (R\in SO(3)) maps body to inertial coordinates, while the body‑fixed angular velocity (\omega) and specific acceleration (a) are measured by the IMU. The air‑velocity in the body frame, (V_a), obeys (\dot V_a = -\omega\times V_a + g,z + a) where (z = R^\top e_3) is the gravity direction expressed in the body frame (the “tilt”). A Pitot probe measures the scalar projection of (V_a) onto a known body direction (b_i); with a single forward‑axis probe the measurement reduces to the first component of (V_a). A magnetometer provides a known inertial magnetic direction (m_I) expressed in the body frame as (m_B = R^\top m_I).

Stage 1 – Tilt and air‑velocity observer.
The authors stack the unknowns into a six‑dimensional state (x =