Radar Velocity Determination via Direction of Arrival
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Solution Overview
Problem
In high-performance synthetic aperture radar systems, the absence of GPS-aiding leads to instrument noise-induced drifts in inertial navigation systems, resulting in inaccurate position, velocity, and angular orientation estimates, causing azimuth scaling errors, mis-focus, and blurring in SAR images, especially at non-broadside squint angles.
Innovation Solution
The system determines radar and aircraft velocities by analyzing Doppler frequencies and squint angles from radar images using interferometric techniques, allowing for independent measurement and correction of navigation data without additional velocity-measuring instrumentation, thereby maintaining alignment of the navigator and improving radar image formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If GPS-aiding is used to correct IMU errors, then navigation accuracy is improved, but system complexity and dependency on external systems increases
Solution Approach 1:
The radar system uses its own operational data (Doppler frequency measurements from multiple apertures) to self-correct navigation errors without requiring external GPS systems. The system performs autonomous velocity determination by analyzing phase differences in radar returns from different antenna positions, enabling it to maintain navigation accuracy through self-measurement and self-correction.
Solution Approach 2:
The radar system performs dual functions: it simultaneously conducts its primary imaging mission and determines velocity for navigation correction. The same radar hardware and signal processing infrastructure used for imaging are leveraged to extract velocity information, eliminating the need for separate velocity measurement instruments and reducing overall system complexity.
2Measurement precision
If additional velocity-measuring instrumentation is added, then velocity measurement accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The radar system performs dual functions: it simultaneously conducts its primary imaging mission and determines velocity for navigation correction. The same radar hardware and signal processing infrastructure used for imaging are leveraged to extract velocity information, eliminating the need for separate velocity measurement instruments and reducing overall system complexity.
Solution Approach 2:
The radar system uses its own operational data (Doppler frequency measurements from multiple apertures) to self-correct navigation errors without requiring external GPS systems. The system performs autonomous velocity determination by analyzing phase differences in radar returns from different antenna positions, enabling it to maintain navigation accuracy through self-measurement and self-correction.
3Device complexity
If INS drifts without GPS correction, then system simplicity is maintained, but position and velocity accuracy deteriorates
Solution Approach 1:
The system implements a feedback mechanism where velocity determined from radar measurements is used to correct INS drift. The process continuously monitors navigation accuracy by comparing radar-derived velocity with INS velocity, and applies corrections to maintain alignment. This closed-loop feedback ensures long-term velocity and position accuracy without requiring complex GPS-dependent systems.
Solution Approach 2:
The radar system uses its own operational data (Doppler frequency measurements from multiple apertures) to self-correct navigation errors without requiring external GPS systems. The system performs autonomous velocity determination by analyzing phase differences in radar returns from different antenna positions, enabling it to maintain navigation accuracy through self-measurement and self-correction.
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 method enables precise determination of radar and aircraft velocities, correcting navigation data and maintaining alignment even with large velocity errors, thus enhancing the accuracy of SAR image formation and radar cross-section estimation without relying on GPS.
Implementation Method 1
radar velocity and direction of arrival (DOA) can combine to yield a measurable Doppler frequency for any particular pixel in the radar image
Implementation Method 2
Multi-aperture techniques such as monopulse radar enable derivation of an independent measure of DOA to each pixel in the radar image based on interferometric analysis
Data Source
AI summary
The various technologies presented herein relate to utilizing direction of arrival (DOA) data to determine various flight parameters for an aircraft A plurality of radar images (e.g., SAR images) can be analyzed to identify a plurality of pixels in the radar images relating to one or more ground targets. In an embodiment, the plurality of pixels can be selected based upon the pixels exceeding a SNR threshold. The DOA data in conjunction with a measurable Doppler frequency for each pixel can be obtained. Multi-aperture technology enables derivation of an independent measure of DOA to each pixel based on interferometric analysis. This independent measure of DOA enables decoupling of the aircraft velocity from the DOA in a range-Doppler map, thereby enabling determination of a radar velocity. The determined aircraft velocity can be utilized to update an onboard INS, and to keep it aligned, without the need for additional velocity-measuring instrumentation.