Coastal survey by video-image
Measurement and analyses
- Analyses of the Flow-Direction and the Flow-Velocity (Vectors)
The measurements of the flow-directions and the flow-velocities do not cause problem if the positions between the float and the reference points are clear like those n the photograph. However, since the resolution of video pictures is inferior to that of phonographs, a hard copy of he video pictures enhanced by a special device was used for measuring.
The pictures for obtaining the position of the float were taken every 10 seconds and then they were expressed in one minute units. The results of the analysis are shown in fig. 2.
Fig. 2 Vector Chart of the Periphery of Man-made Reefs
- Wave-peak-line Analyses
We analyzed how the wave-peak-lines linking the peaks of the waves change at the periphery of man-made reefs from the continuous video pictures. We used the enhanced hard copies made by the special device in he same way as in the analyses of the flow-directions and flow-velocities. The positions of the wave-peaks were obtained at one-second intervals and then they were expressed in 3-second units. Fig. 3 shows the results of the analysis.
Fig. 3 The Change Chart of the Wave-peak-lines
- Mesh Vector Charts
In a conventional vector chart the positions of floats are linked at equal time intervals as mentioned in Item 4-1. Since such a chart only shows he positions the float passed, it was difficult to now the conditions of the entire survey area. These charts are not realistic because a number of floats must be air dropped to cover this defect.
Therefore, we divided the areas to be enhanced into mesh of 30 m x 30 m and made a mesh vector chart in which each mesh is represented by one vector. As for a mesh for which no observed data is available, vector direction and size are estimated using data of adjacent mesh. The results of the analyses are shown in Fig. 4.
Fig.4 Mesh vector chart
Conclusion
As described above, we fond that the waves and states of flow can be surveyed by the video pictures instead of by photographs. It was also recognized that this survey could be performed even during high waves. In addition, the survey confirmed the following advantageous; the use of the video pictures can not only obtain detailed information of several seconds, but also continuous information of around two hours (flying-possible time of a helicopter).
Finally, because of the remarkable improvement of video instruments, the same analyses, described in 4-1 and 4-2, can now be performed on the video pictures of cathode ray tubes instead of an hard copies.
The personal computer used in the system is shown in Fig. 5
Fig.5 Personal Computer System
