Effect of stability and mixing of sea water column on the changes of sound channel and Acoustical properties in the Southern part of the Caspian Sea

The southern regions of the Caspian Sea are of great importance as one of the main transportation, military and fishing areas. Therefore, investigating the effects of environmental parameters on sea water characteristics and vice versa plays a significant role in decision-making in the exploitation of this water area. In this research, the results of the evaluation of sound speed changes in water in the southern part of the Caspian Sea and based on the data collected between 2008 and 2016 have been analyzed. This study was conducted based on the analysis of experimental and instrumental measurements along the transverse sections in the western, middle and eastern parts of the deep bank of the South Sea. The analysis and findings showed that the range of velocity variability in the deep water layer is 1450-1454 m/s. The maximum speed in the water in the deep area was about 1454 m/s. The temporal changes of the observed data show that the influence of the thermal structure and stability of the water column in the warm months on the speed of sound is greater than the influence of the salinity parameter. Due to the high correlation between sound speed and temperature in Caspian Sea water, their vertical structure from the sea surface to the sea floor is almost similar. The analysis of underwater sound speed showed that the vertical slope of changes in surface and middle water areas is more than the monthly and seasonal changes in the deep area. The range of measured sound speed data in February was about 1451-1463 m/s. While the values recorded in June were between 1501-1451 m/s. The results indicated the formation of a deep sound channel in the middle and deep areas of the sea water column (150-300m).