山頂仰角距離法の誤差について
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概要
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This experiment was made in the winter season, 1950, at Suruga-wan Iapan, comparing computed vertical angles of Hakachi-zaki (Izu peninsula ; lat. 34°41.'20 N long 138°44.'78E, 260m above M.S.L., true distance 21.'25 sea miles bearing 148°) and observed sextant angles from the known position (Observatory of the University of merchantile marine), lat.34°59.'12N long. 138°31.'12E, height of eye 13.37m above M.S.L., by the following formula under the normal condition of terrestrial refractive co-efficient 1/13, at 10 C, 760mm, (See fig 1.) or [numerical formula]…(1) α_c=α+d…(2) α_c-α_0=Δα…(3) where, H=hh'=246.63m h…height of object h…height of observer D=21.'25…true distance (sea miles) α=12.'92…vertical angle of object above level d√<h'>=6.'50…dip of horizon α_c=19.'42…computed angle of object above visible hozizon. α_0…observed sextant angle of object above visible horizon Δα…difference of angle Now, presume that Δα varies linearly with the changes of following factrs, ΔT=10℃-T T…air temperature (℃) Δt=T-tω tω…water temperature (℃) ΔP=760mm-P P…Barometric height (m.m) Δh=50%-h h…humidity (%) We can make following simple equations of this observation, with co-efficients x, y, z and w. [numerical formula…(4) Solving the equations by Least Square, the results of coefficient in refractive changes and errars are as follows ; [numerical formula]…(5) Probable error (r) =0.'343…(6) (See table 1. and fig 2) From the above results, we can see, (a) The most infulence owing to the difference between air and water temperature. (b) And also a quite effect by the change of air temperature. (c) Slight infulences by barometric pressure and humidity, canceling nearly each other. (d) Probable error of observed distance in this navigational method is given as, [numerical formula] (in sea miles)…(7) differentiating the fromula (1) and by (6) (e) But, not seperated slight local refractive infulences in this experiment. In the coastal area of Japan, +1.'2 of mean re-fractive deflexion (Δα) in Feburuary and +0.'6 in August, will occur to this method, according to Fig 3 and 4, which showed average distributions of ΔT and lines of isothermal difference (Δt). They occasion considerable errors in measuring of distances, especially when by a small angle of an object at a far distance ; for instance, we have to pay attention to that a position by visible distance of a powerful light, will be unexpectedly away from the light under certain atmospheric conditions.
- 社団法人日本航海学会の論文
- 1952-05-05
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