# Research on a Measurement Method for the Ocean Wave Field Based on Stereo Vision
## 3 Results
### Offshore Test Verification  
The sea test was performed on the Qingdao Blue Valley No. 1 fixed platform on 19 January 2022. The image was captured simultaneously by two QHY26m industrial cameras and the lens that was used was a Nikon 50 mm/1.4D fixed-focus. The pixels of the QHY26M industrial camera were arranged to a value of 6280 \(\times\) 3158, the pixel size was 3.76 um, and the height of the camera from the sea surface was about 10 m (relative to the tide level). The exposure time was set to 2 ms, the sampling frequency was 2 Hz, and the test position was the hatch of the platform. The test interval was between 14:00-16:00 and, in each observation, the data were collected for 10 min. The results of this work are compared with an RBR wave height meter's data for verification. Furthermore, the test parameters are consistent with the laboratory verification parameters and the test pictures are shown in Figure 10:  
The size of the field was \(\mathrm{X_{min}}=-1500\) mm, \(\mathrm{X_{max}}=1000\) mm, \(\mathrm{Y_{min}}=-1000\) mm, and \(\mathrm{Y_{max}}=1000\) mm. The coordinates of the center point (0, 0) were selected in order to verify the accuracy of the measured wave height and period. The measurement results are shown in the Figure 11:  
As shown in the Figure 11, in the same time interval, the time-domain variation curve of wave height as measured at grid point (0, 0) with the proposed stereo vision wave measuring system is consistent with the time-domain variation trend of the wave height as measured by an RBR wave height meter. Moreover, the measurement results at grid point (\(-320\), 0) are consistent with those at grid point (0, 0), in the same time interval. Figure 10: Illustration: (**a**) stereo vision ocean wave observation system; (**b**) RBR wave height meter. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Code No.** & **x (mm)** & **y (mm)** & **z (mm)** & **Calibration Box Height (mm)** & **Error** \\ \hline
9 & \(-183.244\) & 358.0353 & 1205.239 & 1204 & 0.10\% \\
10 & \(-229.913\) & 410.1861 & 1208.479 & 1204 & 0.37\% \\
11 & \(221.4955\) & 801.7397 & 1185.754 & 1204 & 1.52\% \\
12 & \(-194.046\) & 434.6676 & 1207.884 & 1204 & 0.32\% \\
13 & \(-233.126\) & 391.6223 & 1211.303 & 1204 & 0.61\% \\
14 & \(-171.595\) & 490.7635 & 1206.244 & 1204 & 0.19\% \\ \hline \hline \end{tabular}
\end{table} 
Table 5: _Cont._Figure 11: _Cont_. As shown in the Table 7, the wave height error that was based on binocular stereo vision is less than 10% and the period is less than 0.5 s, relative to the results of the RBR wave height meter. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Time** & **Parameter** & **RBR** & **Stereo Vision** & **Error** \\ \hline \multirow{4}{*}{14:00} & \(1/3\) wave height (m) & 0.870 & 0.857 & 1.5\% \\  & \(1/10\) wave height (m) & \(1.160\) & 1.107 & 4.6\% \\  & \(1/100\) wave height (m) & 1.498 & 1.447 & 3.4\% \\  & Average wave height (m) & 0.556 & 0.552 & 0.7\% \\  & Wave period (s) & 6.167 & 6.615 & 0.45 \\ \hline \multirow{4}{*}{15:00} & \(1/3\) wave height (m) & 0.945 & 0.942 & 0.3\% \\  & \(1/10\) wave height (m) & 1.203 & 1.220 & 1.4\% \\  & \(1/100\) wave height (m) & 1.476 & 1.594 & 8.0\% \\  & Average wave height (m) & 0.615 & 0.622 & 0.1\% \\  & Wave period (s) & 6.903 & 7.054 & 0.35 \\ \hline \multirow{4}{*}{16:00} & \(1/3\) wave height (m) & 1.033 & 1.029 & 0.3\% \\  & \(1/10\) wave height (m) & 1.309 & 1.300 & 1.4\% \\ \cline{1-1}  & \(1/100\) wave height (m) & 1.704 & 1.639 & 8.0\% \\ \cline{1-1}  & Average wave height (m) & 0.689 & 0.716 & 0.1\% \\ \cline{1-1}  & Wave period (s) & 6.407 & 6.728 & 0.32 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Measurement accuracy verification.