INTERFERENCE OF UNDERWATER NOISE EMITTED BY DRIFTING VESSEL

Transmission ray of underwater noise emitted by drifting vessel have t wo direction i.e. direct and reflected rays. Interference occurs to re ceive the mixed sound wave from both rays at a hydrophone. The present research compares a theoretical interference with the basis of actual measurements of interference. We observed vertically underwater noise emitted by drifting vessel with intervals one meter on 26 m depth and 93 m depth sea area. Also spectrogram by spectrum data was made in ea ch depth. The results, at both stations the same striped patterns appe ared on a range of about 13 m and 16 m from sea bottom, and on the fre quency range of over 50 Hz. By theoretical pattern, this spectrum leve l changed with their phase differences, and the interference relate to the depth of a hydrophone from the sea bottom rather than the depth o f sea area. Ii the frequency increased, the term pattern decreases. Th at observed patterns coincided with a theoretical interference pattern s by both waves at the frequency range of over 100 Hz. A great term pa ttern appeared at the shallow sea area rather than the deep sea.