魚群探知機による定置網の網成測定の一つの試み(予報)

概要

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A fish finder can be used not only for detecting fish schools but also for estimating the deformation of fishing gears under water. But a distant to the reflected object directly mesured from the fish finder has to be corrected because of beam angle and inclination of the object. Only the shortest distant Z between the transducer O and the net A or N is measurable from the records of the fish finder but it may not always represent a vertical distance to the net (Fig. 1. ). When the angle of declination of net bottom φ is smaller than θ, one half of beam angle of ultrasonic wave (Fig. 1-i), the deformation of net bottom can be traced as in Fig. 2. But we are not sure which is larger, φ or θ. If φ is larger than θ, it is possible to trace the deformation of net bottom (Fig. 3.). But φ may not be larger than θ, so we can not avoid some error to occur when φ is smaller than θ. This error σ is denoted as follow: σ=cos(θ-φ)-1/ 1-sinθsinφ Then, the relation between σ and φ may be indicated in Fig. 5. Through our experiment conducted on the basis of the above treatment at Kokabe, Iwate Prefecture in November 1954, we have estimated the deformation of set net (Fig. 8) from the records shown in Fig. 7.
公益社団法人日本水産学会の論文