Comparison of Acoustic Channel Characteristics for Direct and Multipath Models in Shallow and Deep Water

The primary objective of this study is to compare the acoustic channel characteristics between direct and multipath models in shallow and deep-water environments. Moreover, the study delves into the influence of temperature and salinity on sound speed propagation and absorption. These factors are affected by various chemical compositions present in the underwater medium. The assessment of these effects is conducted for both shallow and deep-water scenarios. Lastly, comprehensive scrutiny and comparison of transmission losses have been conducted for both the direct and multipath models. The simulation results clearly demonstrate that the transmission losses in deep water for the multipath model are significantly higher than those in shallow water. This difference can be attributed to the increased pressure and sound reflections experienced in the deep-water environment. Each 1 ℃ decrease in temperature results in a 3.5 m/s increase in acoustic velocity when sound travels from the water's surface to the bottom. In contrast, deep water maintains a constant acoustic velocity of 1545 m/s regardless of changes in salinity. However, in shallow water, there are significant variations in acoustic velocity due to salinity changes. Comparing deep water to shallow water, there is a considerable attenuation reduction of 20 dB in deep water. Specifically, at lower frequencies (0–100 kHz), the transmission losses for direct paths in deep water are almost negligible. In contrast, for multipath transmission, there is an increase of 93%. In shallow water, the transmission loss increases by 66% for direct path models and as much as 97% for multipath models.