Design and Implementation of a Real-Time Multi-Beam Sonar System Based on FPGA and DSP

Abstract

Aiming at addressing the contradiction between the high-speed real-time positioning and multi-channel signal processing in multi-beam sonar systems, in this work we present a real-time multi-beam sonar system based on a Field Programmable Gate Array (FPGA) and Digital Signal Processing (DSP) from two perspectives, i.e., hardware implementation and software optimization. In terms of hardware, an efficient high-voltage pulse transmitting module and a multi-channel data acquisition module with time versus gain (TVG) compensation with characteristics such as low noise and high phase amplitude consistency, are proposed. In terms of algorithms, we study three beamforming methods, namely delay-and-sum (D&S), direct-method (DM) and Chirp Zeta Transform (CZT). We compare the computational efficiency of DM and CZT in the digital domain. In terms of software, according to the transmission bandwidth of the Gigabit Ethernet and a serial rapid IO (SRIO) interface, the data transmission paths of the acquired data and the beam pattern between the FPGA, the DSP, and a personal computer (PC) are planned. A master-slave multi-core pipelined signal processing architecture is designed based on DSP, which enhances the data throughput of the signal processor by seven times as compared with that of the single-core operation. The experimental results reveal that the sound source level of the transmitting module is around 190.25 dB, the transmitting beam width is 64° × 64°, the background noise of the acquisition module is less than 4 μVrms, the amplitude consistency error of each channel is less than −6.55 dB, and the phase consistency error is less than 0.2°. It is noteworthy that the beam number of the sonar system is 90 × 90, the scanning angle interval is 0.33°, the working distance ranges from 5 m to 40 m, and the maximum distance resolution is 0.384 m. In the positioning experiment performed in this work; the 3-D real-time position of the baffle placed in the detection sector is realized. Please note that the maximum deviation of azimuth is 2°, the maximum deviation of elevation is 2.3°, and the maximum distance deviation is 0.379 m.

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

“…Perhaps this explains the relatively low operating frequencies of 3-D sonar compared to other areas of application of 3-D ultrasound imaging, such as NDE and medical. The most common operating frequencies found in the literature for 3-D sonars are 100 kHz in [ 5 ], 300 kHz in [ 3 , 4 , 14 , 17 ], 600 kHz in [ 2 ], and 1 MHz in [ 1 ]. Based on the literature, the central frequency chosen for the 2-D array was 500 kHz.…”

“…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.…”

“…A multi-beam sonar system consisting of a continuous wave emitter (emitting a 200 μs signal at 100 kHz) and a 2-D uniform planar array is presented in [ 5 ]. The center-to-center distance between the elements is equal to 2 λ (undersampled array) in order to increase the aperture of the array without changing the number of elements.…”

Design and Experiments of a Portable Seabed Integrated Detection Sonar

“…However, no sonar equipment can simultaneously obtain the above three types of feature information, and traditionally, the measurement of the different seabed feature information requires different acoustic detection equipment [11][12][13]. For example, multibeam sounding sonar (MBSS) and side-scan sonar (SSS) can realize the detection of seabed topography and sediment geomorphology, respectively, while sedimentary profile information is generally achieved by sub-bottom profiler (SBP) [14][15][16]. Since the above three sonar devices use independent sound sources, work asynchronous and in different ways, we cannot achieve multiple seabed feature information of the same point at the same time, so it is difficult to realize data fusion and application effectively, many disadvantages are exposed when conducting seabed characteristic detection in this way.…”

“…MBSSS is measured in strips, and the coverage width of each strip can reach several times the depth of the water. On one hand, it can form hundreds or even thousands of sounding points and corresponding backscattering intensity data in the measurement section, which can ensure ultra-wide sweep and high-density of measurement points [16]. Wide coverage measurement has the characteristics of high-precision and high-efficiency, which is especially suitable for large-area and high-efficiency sweeping surveys.…”