Article Figures & Data
Figures
- FIGURE 1
State errors of an EKF-based GNSS/IMU navigation system when an IMU step fault (0.5 m/s2 on each axis of the accelerometer) is injected
- FIGURE 2
Illustration of the integrity and continuity architecture of a KF-based GNSS/IMU navigation system with an emphasis on the IMU fault hypothesis
- FIGURE 3
GNSS/IMU navigation system integrity and continuity requirements
- FIGURE 4
Illustration of KF innovation-based IMU fault monitoring concept
PDF: Probability density function
- FIGURE 5
Example result of the KF innovation-based IMU fault monitor
Two KF innovations exceed their thresholds, and the system declares an IMU fault.
- FIGURE 6
Two types of PLKF,IMU: Real-time and predictive PLKF,IMU
- FIGURE 7
Simulation results for the real-time VPLKF, IMU
- FIGURE 8
Simulation results for the predictive VPLKF,IMU
- FIGURE 9
Simulation results for the predictive VPLKF,IMU under an accelerometer ramp fault
- FIGURE 10
Simulation results for the predictive VPLKF,IMU under a gyroscope step fault
- FIGURE 11
Simulation results for the predictive VPLKF,IMU under a gyroscope ramp fault
Tables
Navigation requirements Integrity requirements allocated to the IMU fault hypothesis, IIMU 3.3 × 10−8 /hour = IGNSS/IMU /3 = (10−7/hour)/3 (IGNSS/IMU is equally allocated among the three hypotheses, as defined in Figure 3) Continuity requirements allocated to the false alert event under the IMU fault hypothesis, CIMU (= Pfa,IMU*)
*Only the continuity requirement due to a false alert is considered
0.5 × 10−6 / hour = *CGNSS/IMU /2 = (10−6/hour)/2 (*CGNSS/IMU is equally allocated among the two fault monitors, as defined in Figure 3) GNSS constellation 31 GPS constellations GNSS GNSS error model -Satellite clock/ephemeris error: 2.4 m (1σ)
-Ionospheric error: 0 m (removed using dual-frequency measurements)
-Tropospheric error: WAAS tropospheric model (RTCA, 2001)
-Multipath error: *2.6 × WAAS airborne multipath model (RTCA, 2001)
*2.6 is the multipath inflation factor caused by using L1/L5 dual-frequency measurements (Walter et al., 2010)
GNSS measurement update rate 2 Hz Prior probability of GNSS faults 10−5 IMU IMU error model -Tactical-grade IMU noise level (Groves, 2007)
-Gyroscope noise (power spectral density [PSD]): 3.4 × 10−11 rad2/s
-Accelerometer noise PSD: 3.8 × 10−6 m2/s3
-Gyroscope bias PSD: 2 × 10−12 rad2/s3
-Accelerometer bias PSD: 1 × 10−7 m2/s5
IMU measurement update rate 100 Hz Prior probability of IMU sensor faults 10−5 Flight trajectory Hovering scenario (static) Note: WAAS: Wide area augmentation system.
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