It is quite difficult to make a research on the state of substance diffusion in the ocean. The best way to reveal the diffusion, the authors believe, is the use of air photography on dye diffusion.
Hence, we took the air photography of dye patch distribution at Hiroshima-bay and Sagami-bay, regarding it as a nearly circle and calculated the eddy diffusivity, using the following forffula :
K=(r_i²-r²_i-1)/4(t_i-t_i-1)
ti=time (second), ri=radius of dye patch (cm)
As a result, the following points are made clear.
1. The area of dye patch increases in accordance with the time progress to a cirtain limit.
2. The increasing rate of the area relates with the scale of diffusion.
3. The individual eddy diffusivity in a short time varies greatly, however, the mean eddy diffusivity in a long time seem to be connected with the velocity of the current. The latter diffusivity is approximately 7×10²-17×10²cm²⋅sec^-1.
After this research, some of the important problems are raised. It is necessary to recognize the boundary between the dye patch and the circulated sea on the air photography, as well as its vertical diffusion, moreover, the relation of the dye patch density on the air photography and the dye patch density in the ocean is left unsolved.

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Photographs were taken with two amateur cameras, epuipped with a synchroneus motive mechanism, for the purpose of measuring of the speed and direction of the water current.
Inner orientation elements of the cameras have not been determined, but photographs taken from the side of a river, are oriented by the use of a few control points on the other side.
It aims to gain the adequate data with a low cost, getting rid of many difficult conditions in practice.

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