225 research outputs found
Guidance, Navigation, and Separation Assurance for Local-Area UAV Networks: Putting the Pieces Together
No full textSam and his son at the Pullen house in Skagway, Alaska
No full textImage information taken from the North Olympic Library System's Kellogg Master Index, including the following note:
Sam was cook at the Pullen house for 12 years
Vertical Position Error Bounding for Integrated Sensors to Support Unmanned Aerial Vehicles (UAV)
No full textEnhancements of Long Term Ionospheric Anomaly Monitoring for the Ground-Based Augmentation System
No full textExtremely large ionospheric gradients can pose a potential integrity threat to the users of ground-based augmentation systems (GBAS). A better understanding of the ionospheric behavior (not limited to that during extreme ionospheric activity) is important in the design and operation of GBAS to meet its integrity and availability requirements. A tool for long-term ionosphere monitoring was developed to build an ionosphere threat model, evaluate its validity over the system operation, monitor ionospheric behavior continuously, and update it when necessary. This paper presents the enhanced algorithms of long-term ionospheric anomaly monitoring and evaluates its performance using data from a ionospheric storm day, 20 November 2003, and a nominal day, 9 November 2004. The automation of data processing enables us to more accurately categorize ionospheric behavior under both nominal and anomalous conditions. This paper also demonstrates that the automated procedure of enhanced long-term ionosphere monitoring not only identifies gradients large enough to threaten GBAS users but periodically generates reliable statistics of ionospheric gradients under all conditions
Sigma Overbounding using a Position Domain Method for the Local Area Augmentaion of GPS
No full textThe local area augmentation system (LAAS) is a differential GPS navigation system being developed to support aircraft precision approach and landing navigation with guaranteed integrity and availability. While the system promises to support Category I operations, significant technical challenges are encountered in supporting Category 11 and III operations. The primary concern has been the need to guarantee compliance with stringent requirements for navigation availability. This paper describes how a position domain method (PDM) may be used to improve system availability by reducing the inflation factor for standard deviations of pseudo-range correction errors. Used in combination with the current range domain method (RDM), a 30% reduction in the inflation factor is achieved with the same safety standard. LAAS prototype testing verifies the utility of the PDM to enhance Category IVIII user availability.
Assessment and mitigation of equatorial plasma bubble impacts on category I GBAS operations in the Brazilian region
No full textPrior to initiating GBAS service in equatorial regions, it is vital to evaluate potential integrity threats posed by equatorial plasma bubble (EPB)-induced ionospheric gradients and assess availability when implementing ionospheric threat mitigation methods. Earlier work developed a preliminary EPB model with a gradient bound larger than twice that for mid-latitude ionospheric storms. Position-domain geometry screening (PDGS) with this higher gradient bound decreases availability to 58.3% at the Galeao International Airport, Brazil, during nighttime. A new mitigation method using Monte Carlo simulation randomizes ionospheric scenarios using randomly generated parameter combinations within the threat model and assesses the ensemble impacts. By taking credit for a prior probability of an extreme EPB, this algorithm determines the inflated integrity parameters to meet the safety requirement in the probabilistic definition. This paper shows that with this method, the system availability for category I precision approaches dramatically improved to 89.6% when a data-driven prior probability of 10-5 was applied.
High-Integrity Local-Area Differential GNSS Architectures Optimized to Support Unmanned Aerial Vehicles (UAVs)
No full textSigma-mean monitoring for the local area augmentation of GPS
No full textThe local area augmentation system (LAAS) is a ground-based differential GPS system being developed to support aircraft precision approach and landing navigation with guaranteed integrity. To quantitatively appraise navigation integrity.. an aircraft computes vertical and lateral protection levels using the standard deviation of pseudo-range correction errors. sigma(pr_gnd), broadcast by the LAAS ground facility (LGF). Thus, one significant integrity risk is that the true standard deviation (sigma) of the pseudo-range correction error distribution may grow to exceed the broadcast correction error sigma or that the true mean of the correction error distribution becomes excessive during LAAS operation. This event may occur due to unexpected anomalies of GPS measurements. To insure that the true error distribution is bounded by a zero-mean Gaussian distribution with the broadcast sigma value, real-time sigma and mean monitoring is necessary. Both direct estimation and cumulative sum (CUSUM) methods are useful to detect violations with acceptable residual integrity. risk. For sigma monitoring, the estimation method more rapidly detects small violations of sigma(pr_gnd), but the fast initial response (FIR) CUSUM variant more promptly detects significant violations that would pose a larger threat to user integrity. For the purposes of mean monitoring. the FIR CUSUM variant is superior to the estimation method in detecting any mean violations. The results demonstrate that real-time protection is achievable against all sizes of sigma/mean failures that can threaten navigation integrity.The constructive comments and advice regarding this work provided by many other people in the Stanford GPS research group are greatly appreciated
Monte Carlo Simulation for Impact of Anomalous Ionospheric Gradient on GAST-D GBAS
No full textIn this paper, a tool based on Monte Carlo simulation is developed for probabilistic analysis of the effects of anomalous ionospheric gradients on GAST-D GBAS approach and landing operations. While parameters associated with ionospheric gradients and satellite geometry are assumed to be at their worst-case values in the traditional certification approach, Monte Carlo simulation takes advantage of the random characteristics of these parameters. In the Monte-Carlo approach, simulation parameters are randomly chosen from the probabilistic distributions chosen for to represent the ionospheric threat model. More than 10(9) sampled events are combined into a probability of Hazardously Misleading Information (P-HMI), defined as the sum of the probabilities of missed detections (P(md)s) weighted by the probability of occurrence of the anomalous ionospheric event leading to each Pmd value.
The results are represented in terms of a cumulative distribution function showing the overall probability of exceeding a given differential range error size. The maximum allowable range error due to ionospheric gradients to support GAST-D is 2.75 m according to the reformulated requirements of the Standards and Recommended Practices (SARPs). The simulation results showed that the PH-AK for differential range errors exceeding 2.75 m was well below 10-9. Furthermore, individual ionospheric events were investigated to ensure that integrity requirements were met in the traditional interpretation. The maximum differential range error in the simulation results was 2.74 m. Most of the largest differential range errors are generated from the specific geometry where the baseline direction (between the GBAS ground facility and the landing threshold point, or LTP) is closely aligned with the propagation direction of the ionospheric front
Integrity assurance of Kalman-filter based GNSS/IMU integrated systems against IMU faults for UAV applications
No full textThis study proposes an integrity architecture for an Extended Kalman filter (EKF) based Global Navigation Satellite System (GNSS)/Inertial Measurement Unit (IMU) integrated system to assure integrity of unmanned aerial vehicle (UAV) navigation systems. An integrity risk allocation tree is developed for each sensor fault hypothesis including the nominal hypothesis, a GNSS fault hypothesis, and an IMU sensor fault hypothesis. This paper then proposes a real-time EKF vertical protection level (VPL) against IMU sensor faultsto assure navigation integrity based on the relationship between EKF innovations and EKF state errors resulting from potential IMU faults and measurement noise. Simulations for the derived EKF VPLs are conducted under a specific IMU-fault condition and under no-IMU-fault condition to investigate typical performance. This study will be extended to assure the navigation integrity of different types of multi-sensor systems for UAV applications
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