## 4 Experimental Results
### Sea Trial  
In November 2020, the sea trial was conducted in the East Sea of Korea. The sea trial parameters are presented in Table 4, and the experimental configuration was constructed as shown in Figure 10. The transmitter was composed of a projector that was moored, and the depth of the projector was approximately 175 m. The transmitter was moved at a speed of 3 knots for approximately 20 km, and the transmitter moved away from the receiver. The receiver was composed of 16 vertical line arrays (VLAs) with a hydrophone interval of 2.8 m, which was located at the center of the array at a depth of 250 m. The receiver was moored on a buoy, and the water depth was approximately 1500 m at the receiver side. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Sampling frequency & 16,384 Hz \\ Carrier frequency & 2750 Hz \\ Data rate & 128 bps \\ Bandwidth & 2500 Hz \\ Range between projector and hydrophone & Approximately 20 km \\ Projector depth & Approximately 175 m \\ Hydrophone depth & 228–270 m (2.8 m interval) \\ Water depth at projector side & 1500 m \\ Projector & Neptune Sonar T-161 \\ Hydrophones & 16-VLA \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Parameters for the sea trial. Figure 10: Configuration for sea trial. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**No.** & **Doppler (Hz)** & \
\begin{tabular}{c} **Proposed Method** \\ **(GSFM)** \\ \end{tabular} &
\begin{tabular}{c} **Conventional Method** \\ **(CSS)** \\ \end{tabular} \\ \hline
1. & \(-2.15\sim-1.32\) & 0 & \(3.10\times 10^{-1}\) \\
2. & \(-1.33\sim-1.3\) & \(1.19\times 10^{-2}\) & \(4.61\times 10^{-1}\) \\
3. & \(-4.29\sim-4.59\) & \(1.07\times 10^{-1}\) & \(3.69\times 10^{-1}\) \\
4. & \(1.33\sim 4.91\) & \(2.08\times 10^{-2}\) & \(3.87\times 10^{-1}\) \\
5. & \(-1.05\sim-3.94\) & \(4.17\times 10^{-2}\) & \(3.93\times 10^{-1}\) \\
6. & \(-4.99\sim-0.38\) & \(2.98\times 10^{-2}\) & \(1.91\times 10^{-1}\) \\ \hline \hline \multicolumn{3}{c}{Average} & \(3.52\times 10^{-2}\) & \(3.52\times 10^{-1}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Uncoded BER in the lake trial. Figure 11a represents the measured sound speed profile (SSP) at the experimental site, and Figure 11b represents the transmission loss by Bellhop modeling. The SSP was measured by using expendable bathy thermography (XBT). The XBT measures the temperature profile and computed sound velocity data. The measurable extent of the XBT used was a water depth of 750 m, and a greater depth was generated by extrapolation. Using the SSP in Figure 11a, the transmission loss is calculated in Figure 11b. Figure 11b shows that the transmission loss at the depth where the receivers are located is relatively low at a distance of approximately 20 km. Therefore, a relatively high SNR was predicted. Before receiving signals, we measured the channel impulse response. For the measure of the channel, the signal had a length of 500 ms data composed of a 31 ms LFM pulse train with a 1500 Hz bandwidth, and it was repeated 300 times. Figures 12 and 13 show the UWA channel characteristics estimated at the 7 th and 16 th receivers, respectively. The channel has diverse multipaths and a slight sloping shape when the transmitter moves away from the receiver. Figures 12 and 13b,d show that the Doppler shift was approximately \  
Figure 14 represents the spectrogram of the signals in the sea trial. Figure 14a,b represents the part of the transmitted CSS signal and the received CSS signal, and Figure 14c,d represents the part of the transmitted GSFM signal and the received GSFM signal, respectively. The channel coding technique was not applied. As a result of the experiment, the conventional CSS method is error free for all channels. The uncoded BER of the proposed GSFM method is \(0.3\times 10^{-2}\) for one channel, and the other is error free. However, this is within the range that can be completely decoded if the channel coding method is applied.