Long-term stability of the sound field structure in the central part of the eastern Atlantic

Results of studying the angular and energy structures of the sound field formed in the first convergence zone as a result of the transmission of a continuous pseudonoise signal in the frequency range 0.8–1.5 kHz are presented for the case of the corresponding points lying in the upper ocean layer at depths between 150 and 500 m. The sound field characteristics were studied with the use of omnidirectional and narrow-beam (～2°) reception in the vertical plane. The variability of the basic experimental parameters of the field structure is analyzed using the data of three experiments carried out in the eastern part of the Atlantic Ocean, near the Canary Islands, over a period of 11 years. The experimental results are compared with ray calculations. It is shown that, in the region under investigation, the experimental characteristics of the field structure are relatively stable and the extent to which they agree with the calculated parameters is also stable. In addition, some data are presented to illustrate the effect of a small lens of Mediterranean water, which manifests itself in sound velocity variations at the channel axis, on certain field characteristics.