Phase Center Alignment in Synthetic Aperture Sonar
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Solution Overview
Problem
In synthetic aperture sonar systems, maintaining accurate phase center alignment is challenging due to limitations in physical receiver size and the lack of precise navigation data, especially underwater where GPS is unavailable, leading to impaired correlation quality and the need for variable ping repetition rates.
Innovation Solution
A vehicle-mounted synthetic aperture system that includes a sonar ping transmitter, receiving elements, acquisition circuits, and a processing unit capable of forming stave sums based on real-time navigation state data to align phase centers between pings, allowing for fixed repetition rates and minimizing interference between sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If displaced phase center antenna processing is used to provide high accuracy navigation, then phase center alignment is improved, but the ping repetition rate must be variable which constrains sensor synchronization
Solution Approach 1:
The receiving array is divided into multiple staves (contiguous subsets of receiving elements), where each stave processes signals from a specific spatial segment. This segmentation allows independent phase center calculation for each stave, enabling flexible selection of phase centers that can be aligned between pings without requiring variable repetition rates.
Solution Approach 2:
The system dynamically changes the selection of receiving elements grouped into staves based on real-time navigation state data. By adjusting which elements are grouped together and calculating corresponding phase centers, the system maintains accurate phase center alignment while operating at fixed repetition rates, resolving the contradiction between alignment accuracy and operational flexibility.
2Measurement precision
If GPS information is used for navigation, then position accuracy is improved, but GPS is not available underwater
Solution Approach 1:
The system uses its own receiving elements to self-determine phase center positions based on received acoustic signals and inertial navigation data. Instead of relying on external GPS infrastructure, the sonar system processes its received signals to calculate phase centers, making it self-sufficient and environmentally adaptable to underwater conditions where GPS is unavailable.
Solution Approach 2:
Inertial navigation system data serves as an intermediary between the physical motion of the vehicle and the phase center calculation process. Since INS provides continuous position and orientation data without requiring external signals, it bridges the gap between vehicle motion and the acoustic processing needed for phase center alignment in GPS-denied underwater environments.
3Ease of operation
If inertial navigation data is used, then navigation solution is obtained, but the precision is not sufficient for sub wavelength navigation
Solution Approach 1:
The system uses feedback from the acoustic signal processing itself to refine phase center positions. By analyzing the coherence and correlation of signals received by different elements, the system can determine optimal phase center locations that compensate for inertial navigation errors, achieving sub-wavelength precision through iterative refinement based on acoustic feedback.
Solution Approach 2:
The system performs preliminary grouping of receiving elements into staves and calculates expected phase centers before signal processing. This preliminary organization allows the system to prepare phase alignment configurations in advance based on predicted vehicle position, enabling coherent combination even when real-time navigation precision is limited.
Data Source
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AI summary
A system for adjusting phase centers of a receiving array in real time. In one embodiment, a transmitter transmits a sequence of pings. Receiving elements are grouped into staves and summed prior to subsequent processing, and the groups are selected so that the phase center on a ping is substantially in the same location as another phase center on a previous ping.