Comparison of vertical line array data taken at two depths in the deep ocean

Vertical line array data were acquired in the Northeast Pacific using a 31-element vertical line array placed with the center of the array first at the sound channel axis and second at a depth approximately equal to the conjugate depth of a cw source, which was towed at a nominal depth of 100 m for ranges up to 600 km from the array. These time series data have been transformed to the frequency domain and beamformed for frequencies near the cw source frequency to determine the signal arrival structure at each array depth. Preliminary results show that there is a strong persistent multipath arrival structure at both depths even at these long ranges. Although this vertical arrival structure exhibits fluctuations with range, three or four strong arrivals are present during most of the data. Qualitative agreement was found between the measured vertical arrival structure and that computed using range-independent acoustic models. Values of array signal gain computed for both depths were very similar, showing an approximate 3.5-dB degradation from that predicted theoretically. [Work supported by Naval Electronic Systems Command, Code 612.]