Acoustic Mud Layer Depth Mapping With Dual-Frequency Scattering
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Solution Overview
Problem
Existing methods for measuring the thickness of underwater mud layers are inaccurate, particularly when the layer is more than half a meter deep, and do not reliably distinguish between mud and underlying denser layers, which affects dredging operations.
Innovation Solution
A method using sound frequencies above 100 kHz and below 20 kHz, combined with time shifts between scattering received at different heights, to map the depth of the top and bottom surfaces of the underwater mud layer, allowing for the computation of its thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Difficulty of detecting and measuring
If sub-bottom profiling is used to detect the boundary between under water mud layer and denser underlying layer, then the detection capability is improved, but the measurement precision deteriorates with systematically too low values where mud layer is more than half a meter deep
Solution Approach 1:
The patent changes the frequency parameter of acoustic waves from single frequency to multiple frequencies (low frequency 1-10 kHz and high frequency 100-200 kHz). This parameter change enables different frequency components to penetrate and reflect from different depths, allowing accurate measurement of mud layer thickness regardless of depth variations. The dual-frequency approach resolves the systematic underestimation error that occurs with single-frequency sub-bottom profiling when mud layer exceeds half a meter.
2Device complexity
If single beam echo sounding is used to measure distance from vessel to water floor, then the measurement process is simple, but the ability to distinguish between mud layer and underlying layers is insufficient
Solution Approach 1:
The patent segments the acoustic measurement process into two independent parts: low frequency measurement for deep penetration to detect mud layer bottom boundary, and high frequency measurement for precise detection of mud layer top boundary. This segmentation allows each frequency component to specialize in detecting specific interfaces, enabling accurate distinction between mud layer and underlying layers while maintaining operational simplicity.
Solution Approach 2:
The patent adds a frequency dimension to the traditional single-frequency echo sounding approach. By measuring at multiple frequencies simultaneously, the system gains an additional dimension of information that enables differentiation between layers based on their distinct acoustic properties at different frequencies, thereby improving layer distinction capability without significantly increasing operational complexity.
3Area of stationary object
If multiple beam echo sounding is used to map water floor height, then the coverage area is improved, but the accuracy in determining mud layer thickness deteriorates
Solution Approach 1:
The patent makes the acoustic measurement system multi-functional by enabling it to simultaneously perform wide area coverage mapping and precise mud layer thickness measurement. The dual-frequency acoustic waves serve multiple purposes: low frequency waves provide deep penetration for broad area coverage, while high frequency waves provide precise layer boundary detection. This multi-functionality allows the system to achieve both wide coverage and high precision without compromising either aspect.
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
Provides a reliable and accurate mapping of the underwater mud layer thickness, enabling precise dredging techniques by distinguishing between mud and underlying layers.
Implementation Method 1
detecting a plurality of lower frequency signals received at respective different heights in the body of water, due to scattering of the sound in the lower frequency range from scatter positions along the selected horizontal direction
Implementation Method 2
determining time shifts between the plurality of lower frequency signals received at the respective different height from the same scatter positions on the bottom surface of the under water mud layer; and computing a second depth of a bottom surface of the under water mud layer based on the time shifts
Data Source
Figure 1~2
Figure 3
AI summary
Depth of a top (24) and bottom (28) of an under water mud layer (26) are measured as a function of position from acoustical scattering measurement. The measurement involves transmitting sound from a transmitter (12) in a body of water (22) above the mud layer (26), using a higher and lower frequency range, above 100 kHz and below 20 kHz respectively. A higher frequency signal due to scattering of the sound in the higher frequency range from scatter positions along a selected horizontal direction is detected as a function of time from said transmitting, and a first depth, of a top surface (24) of the under water mud layer (26), is computed using this signal. A plurality of received lower frequency signals due to scattering of the sound in the lower frequency range is detected at different height in the body of water (22). A time shift as a function of time between temporal parts of the plurality of received lower frequency signals is determined in the plurality of received lower frequency signals, and a second depth of a bottom surface (28) of the under water mud layer is computed based on the time shifts.