Analysis of Underwater Optical Transfer of Radio-Frequency Signal in Turbulence Water Environment

Water flow and temperature drift are the main sources of underwater turbulence. In laser based underwater frequency transfer, underwater turbulence will introduce timing fluctuations, leading to deterioration of frequency transfer. In order to reveal the relationship between the timing fluctuation of transferred frequency signal and the drift of velocity and temperature, this paper establishes a mathematical model to analyze the timing fluctuation caused by water flow and temperature under different gradients. To validate our model, we transmitted a 100 MHz RF signal on a 3.5-meter underwater transmission link, with different artificial flow velocity and temperature drift set during the transmission process. The measured timing fluctuations are consistent with our analysis. The experimental results show that within 5000s, the root mean square (RMS) timing fluctuations of RF signals with velocity gradient, temperature gradient, and no gradient are approximately 37 ps, 123 ps, and 23 ps, respectively. This indicates that the timing fluctuation caused by temperature gradient is higher than that caused by velocity gradient.