Design And Implementation Of The Distributed Synthetic Aperture Sonar Imaging System In Shallow Water

With the exploitation of rivers and lakes and marine resources in China,it is urgent to need high-resolution sonar in the area of waterway safety and underwater detection.Detecting sonar used for large reservoirs,rivers and lakes or marine ports are usually from foreign countries,and the price is more than one million.Once damage caused by improper use,the maintenance and technical costs would be considerable.Since these equipment are imported,it is not conducive to the autonomous detection of water area in our country.Therefore,it is badly in need of a lower cost,higher resolution,stable and reliable sonar imaging detection system.Based on the synthetic aperture imaging principle and synthetic aperture radar altimeter theory,combined with modern acoustics theory and intelligent method,the echo model of the synthetic aperture sonar imaging system in shallow water area is established,and the hardware platform is realized.Conducting data simulation and software processing to verify the feasibility of the imaging system,which brings hope to break the monopoly of foreign technology.The main contents of this paper are as follows:1.Based on the theoretical research,by using the knowledge of synthetic aperture radar(SAR)altimeter and SAR imaging technology,combined with the modern acoustics theory and intelligent method,the distributed synthetic aperture sonar echo model of shallow water is deduced and established in this paper.A signal processing system is realized based on this echo model through the embedded system design.The prototype of the first domestic distributed synthetic aperture sonar imaging system in shallow water is completed.It has achieved a satisfactory result by using computer software to process the echo data and the basic imaging test.2.The hardware architecture of distributed synthetic aperture sonar imaging system in shallow water area is designed with the idea of modularization,including circuit design of every module and interface design of inter-modules.The system is divided into the core control module based on STM32,the signal transmitting module based on DDS technology,the receiving module,the analog signal conditioning module,the A/D conversion module,the data storage module and the integrated water surface positioning module.3.Using the top-down design method,the realization process of the system hardware platform is discussed in detail from the top-level architecture to the bottom in this paper.Among them,the signal receiving part is mainly used for the 32 analog signal amplification,gain control,smoothing,the A/D conversion.Transferring the echo into digital signals and then storing them in the SD card,last submitting the data to the computer to get underwater images.Moreover,in order to verify the correctness of the echo model and the established SAS embedded system,the paper first conducts the output simulation of the echo processing,including band-pass filtering,multi-level amplification,TVG compensation,antialiasing filtering and A/D conversion using MATLAB.Then conducts the joint test and the field test in the anechoic tank.Finally,the image processing is performed by using VS2010 software,and the imaging of 4°angular resolution and 5 cm distance resolution is obtained.The results show good.