Propagation in the underwater sound channel of the Sea of Okhotsk

Experimental results obtained by studying long-range propagation of explosion-generated sound signals under the conditions of a fully developed underwater sound channel in the region of the Kuril Hollow are analyzed. Significant spatial variability of hydrographic parameters is observed throughout the entire 650-km-long propagation path. The variability causes a significant departure of the sound level decay from the cylindrical law of the geometric spread. The departure reaches 4-6 dB per 500 km and is nearly independent of frequency within the frequency band 100-1250 Hz. Sharp changes in the decay curves are observed at a distance about 400 km west of the reception point. Sharp changes in the hydrographic parameters measured a day before the experiment correspond to a distance 450 km from the reception point. Changes in the time structure of the sound field are revealed at the western and eastern regions of the Kuril Hollow by comparing the data of the main experiment with the data of another experiment carried out in the western region of the hollow a few days before. Experimental data on low-frequency sound attenuation in the deep-water region of the Sea of Okhotsk are presented. The sound field time structure measured in the underwater sound channel of the Sea of Okhotsk is compared with the sound field structure recorded in other ocean regions.