定置漁具のレーダー映像について-I : シイラづけのレーダー映像と探知距離(日本航海学会第31回講演会)

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書誌事項

タイトル別名
  • Radar Echoing Characteristics from the Floating Parts of Fishing Gears-I : Radar pictures of the dolphin bamboo shelter and maximum detectable range of the target
  • 定置漁具のレーダー映像について-1-
  • テイチ ギョグ ノ レーダー エイゾウ ニ ツイテ 1

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A number of fishing gears are customarily set in the coastal waters of Japan. For the safe navigation, accordingly, the Maritime Safety Board of Japan checked up the settled locations of the large-sized fishing gears, and announced the results in "Chart showing the position of set net fisheries". But, in order to pass well clear the fishing gears especially at night, the navigators are obliged to use some subsidiary instruments such as radar because the fishing gears have no light. The dolphin bamboo shelter (SHIIRAZUKE) settled in off-shore is typical fishing gear of probable obstacle to navigation. Many bamboo shelters are settled in the Japan Sea, mainly in summer and autumn, for gathering the scattered individuals of dolphin through their negative phototaxis; and it is very hard to find out these shelters by naked eye at night, although it is rather easy in the daytime. Basing on a series of the observations on the target of the shelter on the radar scope, the author gave some descriptions of the characteristics of the radar picture from the navigator's point of view and discussed statistically the maximum detectable range. The results obtained are summarized as follows: (1) The dolphin bamboo shelter can be detected by radar, although it is small in size and poor in reflective efficiency. (2) The target appears obscure and very small, when the gain control has been adjusted to normal value and range scale to medium one for normal navigation in open waters. And a somewhat higher setting of the gain control on lower range is suitable for making the targets stand out clearly. (3) The frequency distribution of log(2.0-R) follows normal one when "R" represents the maximum detectable range. (4) The average of the maximum detectable range is found to be 1.1 miles with considerable variation. (5) On the scope, the range of finding out the target is 0.2 miles (about 20%) shorter than that of losing sight of it.

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