Doppler Sonar Extended Range Tracking via Adaptive Filtering
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Solution Overview
Problem
Conventional Doppler sonars face limitations in achieving extended bottom-tracking range without sacrificing standard deviation and bottom detection fidelity, primarily due to constraints in signal-to-noise ratio (SNR) and noise power, especially in low-SNR environments.
Innovation Solution
The development employs a transmit sequence composed of repeated binary phase shift keying codes, specifically a length-two code, which allows for a longer symbol duration and narrow bandwidth, combined with adaptive narrowband filtering to iteratively decrease bandwidth and reduce noise power, while using phased-array transducers to enhance signal processing and detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If broadband Doppler sonar uses conventional transmit sequences, then bottom detection capability is achieved, but standard deviation increases and detection fidelity decreases
Solution Approach 1:
The patent changes the parameter of transmit sequence from conventional broadband codes to repeated binary phase shift keying codes with length two, which creates a very narrow bandwidth signal. This parameter change resolves the contradiction by achieving low standard deviation (improved measurement precision) while maintaining broadband capability through the iterative filtering process.
Solution Approach 2:
The patent applies dynamic iterative narrowband filtering where the bandwidth is successively decreased over multiple iterations. This dynamic approach allows the system to adaptively refine the signal bandwidth, achieving reduced standard deviation and improved detection fidelity without sacrificing bottom detection capability.
2Reliability
If transmit power is increased to extend maximum tracking range, then signal-to-noise ratio improves, but power consumption increases and cavitation limits are reached
Solution Approach 1:
The patent changes the signal bandwidth parameter to be very narrow (through repeated length-two codes and iterative filtering), which concentrates the signal energy into a smaller frequency range. This improves signal-to-noise ratio and extends maximum tracking range without requiring increased transmit power, thus avoiding cavitation and excessive power consumption.
Solution Approach 2:
The patent replaces the mechanical approach of increasing transmit power with a signal processing approach using repeated binary phase shift keying codes and iterative narrowband filtering. This substitution achieves extended range through signal concentration rather than power increase, avoiding the physical limitations of cavitation and power consumption.
3Reliability
If narrowband Doppler sonar is used to extend range, then maximum tracking range increases, but standard deviation increases and bottom detection fidelity decreases
Solution Approach 1:
The patent uses dynamic iterative filtering where the bandwidth is progressively reduced over multiple iterations. This dynamic refinement allows the system to achieve the narrow bandwidth needed for extended range while maintaining signal quality and bottom detection fidelity that static narrowband systems cannot achieve.
Solution Approach 2:
The patent employs continuous iterative filtering processes that progressively refine the signal over multiple passes. This continuous action maintains signal integrity and detection fidelity while achieving the bandwidth reduction necessary for extended maximum tracking range, overcoming the limitations of single-stage narrowband systems.
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 enables extended range tracking similar to narrowband DVLs with reduced standard deviation and improved detection fidelity, reducing noise power and amplitude variation, and is more resilient to amplitude fades, thereby improving detection probability and estimation accuracy.
Implementation Method 1
Doppler sonars, including Doppler velocity logs (DVL) and acoustic Doppler current profilers (ADCP), measure the relative velocity between the instrument and a group of scatterers by transmitting acoustic pulses along multiple beams that point in different directions and measure the Doppler shift of the acoustic signal that is scattered back towards the instrument in each beam.
Data Source
AI summary
An underwater active sonar system and method for measuring instrument velocity with respect to a boundary surface is disclosed. The system includes an acoustic transducer configured to transmit and receive a plurality of acoustic beams in different directions. The system also includes a processor configured to detect a boundary surface within each beam; iteratively filter received acoustic signals backscattered from the transmitted beams with an adaptive filter and associated bandwidth that is successively decreased for each iteration; and measure instrument velocity with respect to the boundary surface.