projection of the path of a particle falling from some level in the s
bi-
lized cloud at a constant fall rate.
ace
The associated points on the su
represent the locations where the particles would land if they origin
over ground zero at the given altitude.
ed
For the CASTLE Series, vecto
were drawn for 5,000-foot (1,524-meter) increments of altitude, showi
wind direction, and with lengths proportional to the time that 100-mi
on
Particles would travel while falling through the layer.
tor
These wind-v
diagrams graphically illustrated the favorable or unfavorable wind pa
@rns
at the two shot atolls.
as-
Using a hodograph, direct time and distance
urements could be calculated (or "normalized") in terms of 100-micron
ar-
ticles, and the behavior of any smaller sized particles could be esti
ted
by taking multiples of the distances.
Before BRAVO it was thought th
Particle sizes down to 70 microns were significant (which amounted to
ou-
bling the distances taken directly from the normalized hodograph).
er
A
BRAVO, however, particle sizes down to 50 microns were considered sig
icant, and appropriate adjustments were made in the predicted fallout
pattern.
PARTICLE TRAJECTORY FORECASTS.
Maps of the path that a particle a
constant altitude would take due to the winds were known as particle t
jectory forecasts.
These forecasts of trajectories from the shot site
covered the period from H-hour to H+72 in 10,000-foot (3.05-km)
ranging from 10,000 to 60,000 feet (3.05 to 18.30 km).
increm
The initial fo
cast was for H-hour and revised trajectories for the same 72-hour peri
were issued at H+6 and H+15.
Radsafe personnel used the forecasts to
sist in analysis of the long-range fallout aspects and to alert sampli
units of probable locations and altitudes of areas with airborne radio}
active particles.
Data from past exercises used in fallout prediction consisted of
Particle-size measurements
tudes)
(which gave the rate of fall from various a
and observations of downwind and crosswind variation of radiati
intensity with distance from ground zero.
Additional considerations i
Cluded initial size of the radiation source (that is, the areal extent
110