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