Interferometric Sonar for Naval Speed Measurement
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Solution Overview
Problem
Current acoustic logs for naval vehicles face precision and range limitations in determining speed relative to the sea bed, especially when speed vectors are not collinear with the antenna axis, leading to measurement errors and biases due to lack of angular echo location techniques.
Innovation Solution
A sonar device with an interferometric antenna system that uses two phase centers to determine the relative trim angle and angle of sight, allowing precise computation of the naval vehicle's speed by combining correlation techniques with angular location methods, reducing projection errors without requiring excessively fine beams.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If spatial correlation acoustic logs are used to determine speed by comparing echoes from two consecutive transmitted pulses, then speed measurement is possible, but measurement precision deteriorates when the speed vector has components perpendicular to the antenna axis due to projection errors
Solution Approach 1:
The patent introduces angular location measurements in the azimuth dimension to complement the existing range measurements. By adding this new dimensional information (angle of arrival), the system can resolve the ambiguity caused by projection errors when speed vectors are not collinear with the antenna axis, thereby improving speed measurement precision for non-collinear motion
Solution Approach 2:
The patent introduces phase centers as intermediary reference points between the transmitter and receivers. By defining phase centers at intermediate geometric locations and tracking their movement, the system creates a reference framework that enables accurate speed measurement even when the vehicle's motion is not aligned with the antenna axis, mitigating projection errors
2Measurement precision
If Doppler-effect acoustic logs with wideband transmissions are used to estimate speed through frequency shift measurement, then speed estimation is possible, but measurement precision deteriorates due to spread in the Doppler spectrum causing uncertainty in the Doppler shift measurement
Solution Approach 1:
The patent performs preliminary correlation of echoes from multiple receivers to identify the phase center that maximizes correlation before Doppler measurement. This preliminary action of optimizing the phase center selection concentrates the Doppler spectrum, reducing spread and improving the precision of Doppler shift measurement without requiring excessively fine beams
Solution Approach 2:
The patent replaces the mechanical approach of using physically fine beams (which would require high frequency or large dimensions) with a signal processing approach using temporal correlation and phase center optimization. This substitution achieves spectral concentration through computational methods rather than physical beam narrowing
3Measurement precision
If very fine beams are used in Doppler logs to reduce biases in speed determination, then measurement precision improves, but device dimensions become excessive or operating frequency must be increased which limits range
Solution Approach 1:
The patent changes the parameter being optimized from physical beam width to temporal correlation properties. By optimizing the correlation window and phase center selection in the temporal domain rather than narrowing physical beams in space, the system achieves precision improvement without increasing antenna dimensions or operating frequency, thus preserving range capability
Data Source
AI summary
Sonar intended to be carried by a naval vehicle including at least one element for transmitting an acoustic signal, at least one element for receiving the acoustic signal transmitted and reflected on the sea bed and at least two phase centers (PC1, PC2) that are disposed along a first and a second axis (v1, v2), respectively, forming an interferometric antenna. The sonar includes elements for determining the speed of movement of the vehicle as a function of the computed value of the relative trim angle (β) formed between a straight line (d1) that is perpendicular to the axes (v1, v2) of the phase centers and a straight line (d2) that is perpendicular to the sea bed (F) and of the value determined for the angle of sight.