Frror in Estimated Distance of C.P.A. by Radar Plotting

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  • レーダ・プロッティングによる他船の航過距離の誤差について(日本航海学会第22回講演会)
  • レーダ・プロッティングによる他船の航過距離の誤差について
  • レーダ プロッティング ニ ヨル タ セン ノ コウカキョリ ノ ゴサ ニ ツイテ

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The problem of errors in the Radar plotting was published by Capt. F.J. Wylie (J.I.N. 12, 198) and Capt. H. Topley (J.I.N. 11, 167), and it has been shown that the error in estimated distance of the C.P.A. depends on mean range and range change in plotting interval. The writer wants to introduce the rate of error to the estimated distance of C.P.A., like Topley showed the percentage error in the estimated speed. The formula (6) is the error rate of estimated distance and it gives fairly good result though it is very simple. It shows that a rate of error is inversely proportional to a bearing change, not being concerned with others. In fig.2 drawn from formula (6), the error rate is about 60% when the bearing change is 3°. If a bearing change is 1°, ΔD=1.72D It is ambiguous on which side the ship will pass, as the error is larger than the estimated distance of C.P.A. It can be said from above that it is necessary to have at least 3° bearing change between two observations, so that a maximum error rate is about 60% and probable error rate is about 20%. Further, it is desirable that an estimated distance of C.P.A. is 3 miles in fog, and then maximum error will be 1.8 miles and the remain distance 1.2 miles.

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