## 4 Analysis of the Experiment Data
### Coefficient of Variation of the Cluster Amplitudes  
The coefficient of variation, which is closely related to the statistical characteristics of the channel amplitude, can quantify the randomness of different path clusters. It provides a basis for subsequent channel statistical modeling [11] and guidance for equalizer designs in deep-sea communication. This subsection analyzes the amplitudes of different path clusters in the channel. A stable path cluster in a channel should have a narrow amplitude distribution. A wide distribution implies that the cluster is influenced by random factors that enlarge its fluctuations and enhance its randomness. The path clusters contributing non-negligibly to the channel at six typical depths were selected and separated for analysis. Figure 10 shows the amplitude distributions of the individual path clusters. The coefficients of variation of the different path clusters at different depths are listed in Table 2. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Rd (m)** & **D** & **S** & **B** & **SB** & **BS** & **SBS** \\ \hline
605 & & 0.186 & 1 & 0.521 & 0.350 & 0.303 \\
1405 & & 0.219 & 1 & 0.574 & 0.241 & 0.246 \\
2405 & & 0.549 & 0.858 & 1 & 0.168 & 0.162 \\
2605 & & 0.804 & 1 & 0.880 & 0.054 & 0.039 \\
3505 & 1 & 0.460 & 0.118 & 0.084 & 0.008 & 0.007 \\
3605 & 1 & 0.561 & 0.222 & 0.100 & 0.009 & 0.008 \\ \hline \end{tabular}
\end{table} 
Table 2: The ratio of the amplitude of different path clusters to the maximum energy path cluster at different receiving depths. Figure 9: Three-dimensional plot of CIR at 226 m (inset is a partial enlargement of the results of S before 32 s). As shown in Table 3, in both zones, the path clusters related to the sea surface presented high coefficients of variation, indicating a high degree of randomness. The fluctuation of the sea surface led to variations in grazing angle and ultimately changed the energy loss of the path clusters interacting with the sea surface. Meanwhile, the bubbles generated by wind and waves introduced many scattering paths to the path clusters. The coefficient of variation of B was very low in both zones, indicating that B was stable. During the experiment, the movement of the transducer and the receiver was small and the sea bottom was approximately flat, so the grazing angles between the rays in B and the sea bottom were almost constant. Therefore, the energy loss of B was consistent over a certain period of time and the amplitudes were very stable. In the direct-arrival zone, the amplitude distribution width and coefficient of variation of D were between those of the sea surface-related clusters and B. The amplitude of D was very sensitive to phase changes, leading to a wide amplitude distribution and high coefficient of variation. In this subsection, the coefficient of variation was used to quantify the randomness of the amplitude of a single-arrival cluster. In both the shadow and direct-arrival zones, a single channel comprised a set of stable path clusters and a series of random path clusters. The path clusters related to the sea surface were affected by random fluctuations and scattering from the sea surface, which introduced amplitude and phase fluctuations and numerous micro-paths that increased the randomness of the clusters. In contrast, the sea bottom interface was not notably changed within a few minutes of the experiment, which led to B being stable. Figure 10: Amplitude distributions of individual clusters at (**a**) 605 m, (**b**) 1405 m, (**c**) 2405 m, (**d**) 2605 m, (**e**) 3505 m, and (**f**) 3605 m (Rd: receiving depth). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Rd (m)** & **D** & **S** & **B** & **SB** & **BS** & **SBS** \\ \hline
605 & & 0.328 & 0.047 & 0.258 & 0.284 & 0.202 \\
1405 & & 0.270 & 0.029 & 0.278 & 0.160 & 0.121 \\
2405 & & 0.492 & 0.063 & 0.256 & 0.156 & 0.137 \\
3105 & & 0.434 & 0.060 & 0.334 & & \\
3505 & 0.193 & 0.274 & 0.061 & 0.330 & & \\
3605 & 0.132 & 0.333 & 0.034 & 0.314 & & \\ \hline \hline \end{tabular}
\end{table}