Rigid and elastic acoustic scattering signal separation for underwater target

Review of ultrasonic measurement methods for two-phase flow

Two-phase flow is commonly used in many aspects of industrial production, such as the mixed transport of oil and gas in petroleum exploitation and the feeding of coal powder or coal water slurry to coal-fired boilers. In these situations, it is necessary to measure the two-phase flow in real time and then adjust various parameters in order to achieve high efficiency, energy-saving, and safe production. The ultrasonic method is widely used to measure two-phase flow because of its various measurement approaches, wide range of measurable parameters, insignificant effect on the flow field, and its capacity for continuous online measurement. In this Review, the principles, characteristics, application scope, and research examples of different ultrasonic methods used in two-phase flow measurement are summarized, their advantages and disadvantages are compared, and the future development trends are forecast, which will play a positive role in the development of two-phase flow measurement.

Sparse estimation of backscattered echoes from underwater object using integrated dictionaries

The problem of time-delays estimation of backscattered echoes from underwater targets is presented using a sparse reconstruction framework employing an integrated dictionary. To achieve high resolution, the used dictionary is usually defined over a finely spaced grid over the region of interest. Such a procedure may result in problems of being computational cumbersome or suffering from basis mismatch. In addition, the shape of the backscattered echoes may differ significantly from the expected waveforms used to form the dictionary, causing further mismatch problems. To alleviate such problems, the use of an integrated dictionary framework is introduced. Unlike traditional dictionaries that are defined over a set of grid points, the elements in an integrated dictionary are formed by integrating the expected waveform over bands of the parameter space. The resulting dictionary may be used to find initial regions of the parameters of interest using a smaller dictionary than otherwise required, without suffering a loss of performance. The elements can also better match with the backscattered echoes, even if these differ from their expected shape. Simulated results of the backscattered echoes from a cylindrical shell, as well as results from experimental measurements, illustrate the performance of the proposed method.

An Improved Velocity Estimation Method for Wideband Multi-Highlight Target Echoes in Active Sonar Systems

In active sonar systems, the target echoes are usually equivalent to a superposition of the Doppler-scaled reflections from multiple highlights. The reflections overlap with each other both in the time and frequency domain, which results in a decreased velocity estimation performance. Recently, the hyperbolic-frequency modulated signal has been widely employed in sonar systems for moving targets due to its Doppler tolerance, while the precise velocity estimation becomes a great challenge under such conditions. In this paper, the echo c is modeled onsidering a target with a constant velocity and multi-highlights. The velocity estimation performance is analyzed though the signal’s matched filter and the wideband ambiguity function. An improved method based on the sliding window matching algorithm is proposed to improve the performance. The method controls the energy of environmental noise and interference by focusing on the dominant target highlight, and applying a designed window which utilizes the Doppler characteristics of hyperbolic-frequency modulated signals. Simulations and lake experiment allow us to compare between the improved method and the conventional matched filter method. The results verify the influence of the multi-highlights in velocity estimation and indicate that the improved method has more effective performance.