Full text: Real-time imaging and dynamic analysis

tted by ships is 
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mining the three- 
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hool distribution 
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teristics of fish 
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the school (Weill 
and Simmonds, 
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or to test the 
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-Crosswise ratio 
nsion, and fish 
. characteristic 
matrix of three 
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Forwarding direction 
  
  
Figure 6 Perspective image of plate type fish 
school by surface rendering. 
Viewpoint, lighting angle, shading, cropping, cutout 
can all be controlled to produce the best expression. 
Fish schools, observed and analyzed by three- 
dimensional shape analysis were classified into three 
types: plate type. stick type. and mixture type. 
The plate type fish schools were thin vertically, but 
covered large areas (Figure 6). The scale of the fish 
schools in the horizontal plane was 139m x 152m. 
Such fish schools were abundant at 10-30 m depth. 
The mixture type fish schools (Figure 7) were 
composed of several small schools. The shape of 
perspective image changed drastically with changing 
viewpoint. The mixture type fish schools frequently 
occurred between 30-m depth and the sea bottom. 
The stick type fish schools were long and narrow, and 
parallel to the sea surface (Figure 8). The shape of the 
perspective image also changed deepening on the 
viewpoint angle. These fish schools measured 556 m 
long and 30 m long in diameter, and occurred at all 
depths. 
4. DISCUSSION 
4.1 Three-Dimensional Distribution of Fish School 
and Avoidance Behavior to the Ship 
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Starboard 
  
«pee dam ———»! 
Figure 7 Perspective image of mixture type fish 
school by surface rendering. 
     
  
i ue 
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1 
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Starboard 
  
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Figure 8 Perspective image of stick type fish 
school by surface rendering. 
In general acoustic fish resource surveys, fish school 
echoes are sampled with a vertical echo-sounder that 
has about a 10-degree beam width. However, as 
shown in Figure 5, the echogram only scans a vertical 
cross section under the ship's course. So when 
 
	        
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