cording to a logari....ic Scale.
of logarithmic scales.
The contours are then constructed through the ~ sultant field
The first isodose contours to be constructed are the final contours,
since all information for a given shot can be used.
After this map is completed, the contours
for earlier times are constructed from the final map with the aid of photographic information
on base Surge Shape andposition.
All isodose contours presented suffer from the fact that the point density is too low to permit
reliable construction. Maximum reliance is placed in the final isodose contours (Figures 3.103
and 3.109) in which 21 data points have been used for the Wahoo construction and 79 for Umbrella.
Since no film pack information and only a portion of the total GITR array may be used in the construction of the early time contours, these contours are no better than estimates based on the
limited data available and complete familiarity with conditions in the field at the time of the shot.
On the basis of reVability, only the final contours should be presented, and even this presentation in the case of Wahoo may be questioned; however, since it is realized that a Series of isodose contours at various times Shortly after zero time are needed and will probably be constructed by persons making an operational analysis of ships maneuvering in the vicinity of an
underwater detonation, the estimated isodose contours at these earlier times are also reproduced (Figures 3.98 through 3.102 and 3.104 through 3.107). These contours are, therefore,
presented under the assumption that estimates made by persons completely familiar with all
currently available information and with the situation in the field at the time the measurements
were made are preferable to no information whatsoever. All contours, especially those for
early times, must, however, be used with caution.
The protrusions shown in some early time contours and in the final contour for Wahoo may
be questioned; however, those for Umbrella appear to be supported by sufficient data to be
accepted. Such protrusions might have been caused by discrete bodies of radioactive aerosol
moving only along specific radii. Alternatively, discrete masses of radioactive aerosol might
have been propelled ahead of the rapidly advancing plumes and thus might have arrived at times
substantially ahead of the main body of activity along a given radius. There is some evidence
for this latter hypothesis in plots of base surge radius versus time (Section 3.3.4). Although
the data is insufficient to substantiate either hypothesis, the requirement in both cases fora
relatively small, discrete body of radioactive aerosol] should be noted, since this notion is
contrary to the usual concept of massive toroidal expansion.
Plots of GITR cumulative dose at various times versus distance from surface zero may be
more useful than contours for the operational analysis of situations involving moving ships,
Since the direction of the surface wind and the approximate location of surface zero are the
two factors having the highest probability of being known. The basic cumulative dose informa-
tion has been discussed in Section 3.3.2 (Table 3.9), andthe plots for 1, 2, 3, and 5 minutes
and 6 hours after zero time are presented in Figures 3.110 through 3.119. The points are
somewhat scattered, particularly for cumulative periods less than 5 minutes, a fact that is
probably a result of the variable nature of the contaminating event at close distances. The
plots for Umbrella also exhibit a hump or plateau extending to approximately 7,500 + 1,500
feet, a distance that corresponds to the point at which the radial expansion of the base surge
essentially ceases and the principal transport mechanism becomes the surface wind (Section
3.3.4). It is possible that this change in transport mechanism is reflected in the cumulative
dose.
Further information useful in a study of cloud dynamics 1s obtained by plotting the dose rate
versus distance from the moving cloud center, a presentation that should correct for the effects
of surface wind. Although conaiderable latitude exists in the choice of surface wind, the plot is
reasonably insensitive to changes of the same order of magnitude as those listed in Section A.4.
Consequently, the surface winds reported by the Task Force (15 knots from 090° T for Wahoo
and 20 knots from 050° T for Umbrella) were used to compute the location of a hypothetical
surge center H at various times. The distance of al) stations from this moving hypothetical
center were determined graphically and are summarized together with dose rate {nfermation
in Table 3.13. Only the data for the first 5 minutes has been plotted in Figures 3.120 through
204
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deleted.
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