주파수영역 합성 소나 처리 기법의 성능향상에 관한 연구

Abstract

Uniform Liner Arrays (ULA) are widely used in underwater to measure the spatial field of propagating acoustic waves. Employing conventional beamforming techniques, the angular resolution and the signal gain are proportional to the ratio of aperture length to signal wavelength. In many ocean environments, however, the signal coherence may exceed the length of a long array, the resolution being limited then by its physical size and stability. In sonar systems, high bearing resolution become more important and more difficult to achieve as the frequency regime is made lower performance of arrays in order to increase the detection range. Because increased low-frequency bearing resolution means longer arrays, it is not practical to increase the physical length of line arrays in order to match the coherence length of signals. An approach in these cases is to employ coherent synthesis of subaperture, so-called Synthetic Aperture Sonar (SAS) technique.

This thesis presents the method of noise suppression to improve performance of SAS technique by using frequency averaging of several short time data. In the result, the array gain is suppressed range from 1.7dB to 9.5 dB when the proposed method is adopted.

The organization of this thesis are as follows. Chapter II introduces the principle of beamforming between Uniform Liner Arrays and Synthetic Aperture Sonar technique. Chapter III explains Synthetic Aperture Sonar technique detailed. In chapter IV, the method of Synthetic Aperture Sonar technique and proposed method are compared in aspect to noise suppression. Finally, chapter V concludes this thesis.