Research On Detection And Processing Technology Of Underwater Weak Echo Signal

With the development of science and technology,in the field of underwater detection,the speed?precision and maneuverability of underwater detection was put forward higher requirements.Compared with sonar technology,laser technology with good directionality and high positioning accuracy has gradually entered into the public view.But in the actual underwater detection system,the echo signal reflected from the target is submerged under the strong noise,so how to improve the signal-to-noise ratio of the echo signal is the primary problem.In addition,when the laser irradiates different targets,the reflected echo signal is affected by the characteristics of different material targets,and it will produce polarization decided by the nature of its own characteristics,which is of great significance for the underwater detection.At first,this paper studies the transmission characteristic of laser underwater,to determine the pulse laser of 532 nm as the system emitter.Then it analyzes the mathematical model of the transmission and the receiving signal as well as the noise type of system,and a digital average algorithm is put forward to detect the weak signal.After understanding the polarization characteristics and polarization measurement principle,the optical structure of the front end of the system is designed,and then an echo detection system based on FPGA is set up,it can measure the polarization parameters at the same time improve the signal-to-noise ratio of the echo signal.Finally,in the upper computer,the polarization measurement theory is converted into a computer algorithm,the resolved polarization degree?the polarization angle and the collected echo data are classified and displayed.The results of the experiment show that the lower limit of the echo detection system can reach pJ level,which can effectively detect the weak echo signal,and moreover,the theoretical value and the measured value are in the same order of magnitude.On this basis,the polarization characteristics of target echo signals of different materials are compared.The results show that the degree of polarization of different material objects is different and the degree of polarization of the artificial target is generally higher than the degree of polarization of the natural target.In other words,it is feasible to distinguish the underwater target by using the polarization characteristic of the laser echo.