Aircraft Navigation Mitigating Ionospheric Gradient Threats
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Solution Overview
Problem
Existing navigation systems for aerial platforms face challenges in mitigating ionospheric gradient threats, particularly for variable-speed aircraft, as current methods are not effective in maintaining navigation integrity and availability during severe ionospheric conditions, leading to erroneous range estimates and loss of navigation integrity.
Innovation Solution
The system employs a three-stage approach: iono-free processing at a threshold distance, divergence-free processing during close approach with high velocity, and calculation of floor values for Differential Ionospheric Correction (DIC) sigma when velocity falls below a threshold, to address ionospheric threats and ensure navigation safety and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If iono-free processing is used during navigation, then ionospheric delay errors are reduced, but navigation integrity is lost under extreme ionospheric conditions
Solution Approach 1:
The system dynamically switches between iono-free processing and divergence-free processing based on the aircraft's velocity relative to a threshold. When velocity exceeds the threshold, iono-free processing is used for precision; when velocity falls below the threshold, divergence-free processing is activated to maintain integrity, thus adapting the processing mode to current flight conditions
Solution Approach 2:
The system changes the processing parameter (from iono-free to divergence-free) based on velocity conditions. This parameter change allows the system to optimize for precision during high-speed phases while ensuring integrity during low-speed phases where ionospheric gradients have greater impact
2Reliability
If divergence-free processing is used to address ionospheric threats, then navigation integrity is maintained, but measurement precision is reduced
Solution Approach 1:
The system dynamically selects processing modes based on velocity thresholds. Divergence-free processing is applied only when velocity is below the threshold, while iono-free processing is used when velocity exceeds the threshold, creating a dynamic balance between integrity and precision requirements
Solution Approach 2:
The navigation process is segmented into different phases based on velocity conditions. The system divides the approach into high-velocity phases (using iono-free processing) and low-velocity phases (using divergence-free processing), allowing each segment to use the most appropriate processing method for its specific conditions
3Reliability
If conservative assumptions of ionospheric conditions are made, then navigation integrity is protected, but availability is reduced
Solution Approach 1:
The system dynamically adjusts its conservatism based on real-time velocity measurements. Instead of always assuming extreme ionospheric conditions, the system only applies conservative divergence-free processing when velocity is below the threshold, thereby maintaining integrity when needed while improving availability during high-velocity phases
Solution Approach 2:
The system changes the ionospheric mitigation parameter based on velocity conditions, transitioning from conservative divergence-free processing to less conservative iono-free processing as velocity increases. This parameter change optimizes the balance between integrity protection and navigation availability
Data Source
AI summary
A method includes repeatedly determining a distance of an aircraft from a landing location. The method also includes, during a first stage in which the aircraft is at least a threshold distance from the landing location, performing iono-free processing during navigation of the aircraft. The method further includes, during a second stage in which the aircraft is less than the threshold distance from the landing location and a velocity of the aircraft is greater than a velocity threshold, performing divergence-free processing during navigation of the aircraft to address possible ionospheric threats. In addition, the method includes, during a third stage in which the aircraft is less than the threshold distance from the landing location and the velocity of the aircraft is less than the velocity threshold, calculating one or more floor values for a Differential Ionospheric Correction (DIC) sigma, and determining a navigation solution to protect against nominal ionospheric conditions.