After the shot barge is in place the Observers will measure angles,
by means of a Wild T-2 phototheodolite on the barge, between a number
of identifiable islands.
Furthermore an aerial photograph will be taken,
including the barge and a grid of buoys, and also some of the easily iden-
tifiable islands in the vicinity.
|
From the measured angles, and with the help of the aerial photograph,
the Observers will spot the barge on two charts of the atoll, and will simply
scale the distance to the'Parry photo tower from the charts.
Two published charts are available:
the first was published by the
Japanese Government in 1943, and the second by the United States Navy in
1944 (Hydrographic Office, Chart No. 6033),
Although these charts differ
by about one-half mile as to the absolute geographic latitude and longitude
of the Eniwetok Atoll, and although some of the islands have changed shape
markedly from erosion and deposition, distances between given points
scaled from the two charts generally agree to better than 0.5 percent.
Scaled measurements from the USN Hydrographic Chart, and from a
photostatic copy of the Japanese map, show very good agreement between
the two.
Three pieces of info.mation are available to establish the scales
of each chart:
a) scale of distances (nautical miles in the U.S. chart and
kilometers in the Japanese), b) distance between parallels of latitude 10minutes apart; and c) distance between parallels of longitude 10-minutes
apart.
We know from the standard navigational literature 7,8 that 10 min-
utes of latitude, centered at latitude 11°-30', is 60,483 feet, and of longi-
tude 59,657 feet.
Scaling from the charts gives scale factors in feet per
inch for the three methods:
Method
U.S.
Japanese
8,340
8,370
10-Minute Latitude
8,330
8, 530
10-Minute Longitude
8, 340
8, 460
8,337
8,453
Scale (nautical miles
or kilometers)
Average....
U.S. Department of Commerce, Coast and Geodetic Survey, Special
Publications Nos. 8 and 241.
U.S. Government Printing Office (1949).
Bn. Bowditch, American Practical Navigator.
Office (1943).
-18-
U.S. Hydrographic