Np LEVEL IN FUKURA P. 
TIDE LEVEL IN ANAKA 1 | 
| 
A lL 
| 1.4 416 
   
HARIMA SEA 
  
  
  
1 
s 
  
TIDAL VELOCITY (knot) 
  
«x 
2^ 
4 
e 
> 
L 
e 
o 
  
  
  
  
  
  
  
  
  
; 0 0.14 0.1 
KIl CHANNEL (southward flow) 
| (m) 
  
12 6 0 6 12 
TIME (hour) 
Fig. 3. Relationship of tidal current and tidal levels. 
‘the Kii Channel is under the lowest. As a result, a gradient of the sea surface 
through the strait is effectively produced and its direction turns from side to 
side every 6 hours, that accompanies a shuttling tidal current through the 
Naruto Strait. 
2. AIRPLANE REMOTE SENSING OF THE SMALL SCALE TIDAL VORTICES 
Airplane remote sensing was applied to reveal the characteristics of 
the " Vortex of Naruto". A pair of airplanes equipped with an aerial camera 
made a flight in parallel each other at the altitude of 1,200 meter. the flight 
course and the shooting points are shown in Fig. 4. The sea surface was synch- 
ronously photographed with 80% overlap to get a series of synchronized airphotos. 
Time lag of the shootings was 3 seconds and the accuracy of the synchronization 
was 1/100 sec. Fig. 5 is an example of the airphotos, that represents two 
series of "Vortex of Naruto". The tidal current is flowing down southward from 
the Harima Sea to the Kii Channel at the center of the water course, with a 
speed of 9.1 knots. Each pair of the synchronized airphotos was analyzed with 
the A-7 autograph and a contour map of the sea surface was produced. Fig. 6 is 
an example of the obtained contourmaps, in which one can estimate the scales of 
the tidal vortices. A series of airphotos were also obtained by an airplane 
flying along the water course to gain the time series of the displacement of the 
tidal vortices. Overlap and time lag between each of the airphotos were 80% and 
3 seconds, respectively. Thermal imageries were obtained from 600 meter flight 
height to gain the details of the temperature distribution of the sea surface. 
  
  
‚ion 
  
  
  
The airphotos and thermal imageries were interpreted hydrodynamically 
from a view point of the coherent structure theory. The theory has been initi- 
ated recently in the age of 1970’s, and was reviewed for example by Davies and 
Yule ((1), 1975). Fig. 7 is a hydrodynamical image of the small scale flow 
field around the strait. Tidal current flowing at the center of the water 
course is considered to be the potential flow with no vorticity. Stagnant water 
behind the cape is considered to be the dead water also with no vorticity. A 
wall turbulent boundary layer is formed along the upstream shore line of the 
cape, and exfoliates at the top end of the cape to form a free turbulent bound- 
ary layer. The free boundary layer is composed of the potential flow region 
without any vorticity and a series of discrete vortices with locally concentrat- 
ed vorticity. The "Vortex of Naruto" is explained to be this kind of coherent 
vorticies. The vortices shift downstream maintaining periodicity in space and 
time, the diameter of each of which corresponds to the local width of the 
737 
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