The Research Of Broadband Echoing Characteristic Of Understand Target

The research of broadband echoing characteristic of underwter target has an important value in theory and application,and it is a basic of exploration,orientation,and sonar and identification for sonar and underwater weapon. The echoing characteristic of underwter target is not only relational with the physics of the target,just as the structure and the material of the target,but also with the character of time-frequency.With the development of the signal processing technology, the analysing method is more and more for the echoing signal of the target.In the truth, we mostly use the CW signals to do the experiment for the research of echoing signal, because its theory is simple. But the broadband signals is little used.In the research of the target echoing character, compared with the narrow brand of the CW signal, the broadband signals have the extent band,so they have the more information about the target. So the research of the broadband signals is attached importance.Based on the reason, the paper do a study about the target echoing signal structure and the character of the time-frequency. Based on the defination of channel transmission net, the indirect frequency-domain algorithm for simulation of broadband echoes is founded.Using elastic scattering theory and the Planar Elements Method, the transfer-function of the elstic spherical shell in water and the transfer-function of underwater complex target are obtanined. Based on the LFM(line frequency modulation) and the Ricker impulse, the simulations of broadband echoes of them in the time-domain are obtained. By signal processing method, the modulus of time-frequency of back scattered signals are obtained. We also do a experiment to get a new exploded pulse,and measure the target strengths of animal lung tissue at the sonar frequency.Lastly,we test the echoing characteristic of the elastic sphere shell and elastic tube. The results show that the broadband signal has the clear structure in time-domain and the broad range in frequency-domain, they are useful in the characteristic extracting and the classification of the target.