Evaluation of a high-resolution real-time capable 3D sonar camera for deep sea operation

Abstract

In this work we present the evaluation results of our 3D sonar camera system. The system consists of a matrix antenna array with 1024 single transducer elements and our in house developed DiPhAS sonar beamformer - a 128 channel FPGA-based beamforming system with a 1:8 multiplexing device for each channel. The system is designed to be applicable to ROV and AUV systems for real-time volumetric imaging in a deep sea environment. Defocused excitation of the transducer array is used to achieve a sound field opening angle of up to 40° in lateral and elevational direction. The antenna's sound field can be adjusted electronically in order to increase either the imaged area or the image contrast in a specific area of interest. Different filter algorithms working on a raw data basis have been implemented in order to suppress image artifacts which occur during the reconstruction process. Measurements on different phantoms have been performed in order to prove the real-time imaging as well as spatial resolution capabilities of the camera system

Development of a 2-D Array Ultrasonic Transducer for 3-D Imaging of Objects Immersed in Water

“…A 2-D array ultrasonic transducer can be used to generate 3-D images of underwater objects up to several meters away, even if they are immersed in water with low or no visibility conditions, which is not possible with underwater optical cameras [ 1 , 2 , 3 , 4 ]. This capability makes it attractive for underwater purposes, such as gas and mineral extraction, finding archaeological artifacts and shipwrecks, mine hunting, navigation of divers, and autonomous underwater vehicles (AUVs).…”

“…Also called a planar array [ 2 ], a 2-D array ultrasonic transducer consists of a grid of individual piezoelectric elements, which are controlled to emit and receive signals. If the elements are driven at different instants of time, with previously calculated delays, a focused or defocused [ 1 ] wavefront is emitted.…”

“…On the other hand, the frame rate can be increased if the 2-D array transducer emits a defocused beam to the region with a single emission. The defocused emission is performed by driving the central elements before the peripherals, with delays previously calculated [ 1 ], so the backscattered echoes are sampled in parallel and coherently summed to form post-processed beams (delay-and-sum beamforming) [ 2 , 3 , 5 ]. Since a single emission is necessary to sample an entire region, imaging the same VOI is expected to be 1680 times faster.…”

“…Since a single emission is necessary to sample an entire region, imaging the same VOI is expected to be 1680 times faster. Furthermore, one can improve the images contrast by adjusting electronically the defocusing with delays, opening or closing the field of view [ 1 ]. Alternatively, a simpler 3-D sonar system can be developed by using a single omnidirectional transducer to irradiate the medium, such as a projector, and a 2-D array transducer, such as a bistatic sonar [ 2 , 3 ].…”

Desenvolvimento de um transdutor ultrassônico matricial bidimensional para aplicações submarinas.

“…. Como exemplos, podem ser citados os sonares bidimensionais para imagens tridimensionais desenvolvidos porEhrhardt et al (2016), com passo dos elementos de 2λ e frequência de 1MHz, e por Trucco, Palmese e Repetto (2008),. com passo dos elementos de λ e 2λ para frequências de 600kHz e 1,2MHz, respectivamente.…”