Observing the fluctuations of arrival time and amplitude with short-range experimental data

• We model the fluctuations of the multipath arrivals after short-range propagation.
• Complete source–receiver configurations were observed in the experiments.
• The fluctuation due to the source swing was observed in the experiments.
• Layered microstructures, surface duct and etc. could strengthen the fluctuation.

The arrival time and amplitude fluctuations of about 230-m propagation were analyzed for various source–receiver configurations using experimental data of Shallow Water’06. The minutes-scale and seconds-scale fluctuations of the arrival time were observed on both the direct (D), surface reflected (SR) and bottom reflected (BR) arrivals. Correlation analysis and simulations based on the ray theory demonstrated that the minutes-scale fluctuation was due to the horizontal range variation between the source and receivers while the seconds-scale fluctuation was caused by the source swing in both the vertical and horizontal directions. A noteworthy phenomenon was that the minutes-scale fluctuation of the amplitude was only observed in the D arrivals while it was absent in the SR and BR arrivals. Furthermore, rather strong fluctuation of the D arrival amplitude could not be explained when the environment was modeled using a smoothed sound speed profile. Simulations showed that the layered microstructures, interference of the multiple eigenrays and the surface duct can strengthen the fluctuation of the direct arrival. The variability of the ocean structures combined with the above three factors resulted in the minutes-scale fluctuations of the D arrival amplitude while the source swing combined with the three factors resulted in the seconds-scale fluctuations.