GBAS Multi-Frequency Ionosphere Correction
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Solution Overview
Problem
Conventional Ground Based Augmentation Systems (GBAS) face challenges in mitigating spatial decorrelation errors caused by ionosphere delays, particularly during anomalous ionospheric storms, which can lead to unacceptably large position errors and impact the continuity and availability of navigation systems during precision approach operations.
Innovation Solution
The implementation of a GBAS system that utilizes multi-frequency satellite measurements to determine the true electron count (TEC) and Vertical Ionosphere Gradient standard deviation (σvig) to define valid iono regions, allowing for accurate correction terms to be communicated to aircraft GNSS receivers, thereby mitigating spatial decorrelation errors and ensuring navigation accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional GBAS systems assume worst case ionospheric gradient and use geometric screening to mitigate errors, then position accuracy is improved, but system continuity and availability deteriorate
Solution Approach 1:
The system dynamically adjusts the ionospheric gradient mitigation approach based on real-time conditions. When multi-frequency satellites are available and ionospheric conditions are acceptable, the system uses TEC-based corrections with valid iono regions. When conditions deteriorate or multi-frequency satellites are unavailable, it transitions to geometric screening. This dynamic adaptation resolves the contradiction by adjusting the mitigation strategy to maintain both accuracy and continuity.
Solution Approach 2:
The system changes the operational parameters of ionospheric correction based on satellite availability and ionospheric conditions. It uses TEC values from multi-frequency satellites to define valid iono regions and determines overbounded Vertical Ionosphere Gradient standard deviation (σvig) dynamically. This parameter-based adaptation allows the system to maintain position accuracy while preserving continuity by adjusting correction parameters rather than applying fixed geometric screening.
2Area of stationary object
If GBAS station uses pseudorange corrections from non-uniform ionosphere, then signal coverage is maintained, but position error increases
Solution Approach 1:
The system applies local quality control by defining valid iono regions based on TEC measurements from multi-frequency satellites. Instead of uniformly applying corrections across all satellites, it identifies specific satellites with pierce points in valid regions and applies corrections selectively. This local approach maintains signal coverage from available satellites while preventing position errors by excluding satellites affected by non-uniform ionospheric conditions.
3Measurement precision
If multi-frequency satellite measurements are used to define valid iono regions, then ionospheric correction accuracy is improved, but system complexity increases
Solution Approach 1:
The system uses multi-frequency GNSS satellites that serve multiple functions: navigation positioning and ionospheric monitoring. The same satellites used for positioning also provide TEC measurements for defining valid iono regions. This multi-functionality reduces system complexity by utilizing existing satellite resources rather than requiring separate monitoring infrastructure, while still achieving improved ionospheric correction accuracy.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces position errors to within 10 meters with high probability, maintaining system continuity and availability by accurately accounting for ionospheric delays and gradients, ensuring safe precision approach operations even under anomalous ionospheric conditions.
Implementation Method 1
One major source of error in a GNSS receiver can occur when a GNSS signal experiences delay as it passes through the ionosphere
Implementation Method 2
when ionospheric disturbances produce a non-uniform ionosphere that results in differences in the delay observed by the GBAS station as opposed to the delay observed by the aircraft's GNSS receiver
Data Source
AI summary
Systems and methods for using multi frequency satellite measurements to mitigate spatial decorrelation errors caused by ionosphere delays are provided. In one embodiment, a GBAS comprises: a plurality of GNSS reference receivers that receive signals from GNSS satellites; at least one processing module; at least one aircraft communication device; wherein the processing module determines a TEC along a line of sight of a first observable multi-frequency GNSS satellite to determine a current quality metric of the ionosphere; determines at least one overbounded Vertical Ionosphere Gradient standard deviation sigma-vig (σvig) when the current quality metric of the ionosphere meets a threshold; defines one or more valid iono regions at a given finite period in time where at least one σvig is applicable; and causes the communication device to communicate to an aircraft the σvig and a list of GNSS single and multi-frequency satellites having pierce points in the valid iono regions.