In-Flight Azimuth Calculation Using IMU and Magnetic Field Correction
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Solution Overview
Problem
Existing methods for determining the azimuth of a moving platform, such as gyrocompassing and GNSS, are unreliable or costly, and magnetometers are prone to distortions, making it difficult to accurately determine azimuth without external alignment devices.
Innovation Solution
A method and system that calculates azimuth using IMU measurements without GNSS data, gyrocompassing, or magnetometers, by transforming IMU data to a navigation frame using a transformation matrix derived from IMU acceleration and magnetic field measurements, correcting for distortions through multiple measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If gyrocompassing is used for pre-flight azimuth determination, then accurate azimuth can be obtained, but the cost increases due to requiring accurate and costly IMU
Solution Approach 1:
The patent uses a low-cost IMU configuration that does not require the high precision needed for gyrocompassing. The system accepts that the IMU will drift over time during flight but uses magnetometer measurements to periodically correct the azimuth, effectively using a cheaper, less precise sensor system that is maintained through periodic calibration rather than requiring expensive high-precision hardware throughout.
Solution Approach 2:
The patent introduces magnetometer measurements as an intermediary tool to correct IMU drift. Rather than relying solely on the expensive accurate IMU for continuous azimuth determination, the system uses magnetometer data as a mediator to periodically recalibrate and correct the IMU's azimuth measurements, enabling the use of cheaper IMU hardware.
2Reliability
If GNSS is used for in-flight azimuth determination, then azimuth can be obtained during flight, but the system becomes vulnerable to signal jamming and interference
Solution Approach 1:
The patent extracts the azimuth determination capability from dependence on external GNSS signals. By using the onboard magnetometer to measure the magnetic field and calculate azimuth independently, the system removes its vulnerability to GNSS jamming and interference while maintaining continuous in-flight azimuth determination capability.
3Measurement precision
If magnetometers are used on the ground for azimuth determination, then azimuth measurements can be obtained, but the measurements are distorted by ground environmental influences
Solution Approach 1:
The patent uses the platform's motion during flight to dynamically change the orientation of the magnetometer relative to the magnetic field. By maneuvering the platform through different attitudes and headings, the system collects magnetometer measurements from multiple orientations, which allows computational correction of distortion effects and enables accurate azimuth determination despite the presence of distortions.
Solution Approach 2:
The patent collects more magnetometer measurements than the minimum required by having the platform perform maneuvers that expose the magnetometer to the magnetic field from multiple angles. This excessive collection of data from varied orientations provides redundancy that enables computational correction of distortion effects and improves measurement 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
Enables accurate azimuth determination during flight, reducing costs and avoiding alignment errors, while maintaining reliability and precision.
Implementation Method 1
Some IMUs also include magnetometers (likewise, one per each axis) which are used for determining a magnetic field in each axis
Implementation Method 2
The IMU detects linear acceleration in each axis using the accelerometers
Implementation Method 3
The IMU detects linear acceleration in each axis using the accelerometers and rotation rate in each axis using the gyroscopes
Data Source
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AI summary
The presently disclosed subject matter includes a method and system directed for calculating azimuth of an airborne platform during flight based on IMU measurements, without using GNSS data, gyrocompassing or magnetometers operating on the ground for determining the azimuth.