HIGH-ALTITUDE BURST

A high-altitude burst is an airburst where the point of detonation is above 100,000 feet. The high-altitude burst produces air blast, thermal radiation, an electromagnetic pulse, initial nuclear radiation, and atmospheric ionization. At such high altitudes, the proportion of energy appearing as blast decreases considerably, and at the same time the proportion of radiation energy increases. Due to the low density of the atmosphere above

100,000 feet, the range of the initial nuclear radiation increases. In contrast to explosions below 50,000 feet, the attendant atmospheric ionization from a burst above 100,000 feet will last from minutes to hours. The important effects of high-altitude bursts cause damage to weapons systems or satellites operating in the upper atmosphere or in space. There will also be interference with electromagnetic waves (communications and radar) that pass through or near the region of the burst.

SURFACE BURST

A surface burst (fig. 8-3) is a burst where the point of detonation is on, or above, the surface of the earth and the fireball touches the surface of the earth. The surface burst produces air blast,

Figure 8-4.-Deep underwater burst.

thermal radiation, and an electromagnetic pulse It procudes initial nuclear radition around surface zero (SZ), and residual (transit and deposit) nuclear radiations around SZ and downwind from SZ. Transit radiation is airborne radioactive material (base surge/fallout). Deposit radiation is radioactive material (base surge/fallout) that settles on exposed surfaces. Surface bursts over water will also produce underwater shock and surface water waves, but these effects will be of less importance except to submarines. Overland, earth shock will be produced but will not be an important effect at any significant distance from the point of detonation.

UNDERWATER BURST

An underwater burst (figs. 8-4 and 8-5) is a burst where the point of detonation is below the surface of the water. An underwater burst produces underwater shock and a water plume

Figure _{8-3.-Surface burst.}

Figure 8-5.-Deep underwater burst.

which then causes a base surge. Bursts with very shallow points of detonation can also produce air blast, initial nuclear radiation, fallout, and possibly some thermal radiation. These effects will be reduced in magnitude from those of a water surface burst and will become rapidly insignificant as the depth of the point of detonation is increased. The range of damage due to shock is increased as the depth of the point of detonation is increased. For a given weapon yield, greater hull and machinery damage will be produced by shock from an underwater burst than by air blast from an airburst or a surface burst. The reverse is true for topside equipment such as antennas and missile launchers.

When a high-yield weapon is detonated in deep water adjacent to a continental shelf, large breaking waves can be generated by the upsurge along the shelf slope. These waves will appear on the shallow-water side of the shelf edge. They are characterized by a long period with a sharp, possibly breaking, crest. They dissipate in amplitude as they progress toward the shore. Calculations and simulation experiments were conducted with the continental shelf off the east coast of the

Figure 8-6.-Underground burst.

United States. They indicate that in the near vicinity of the shelf edge (shallow-water side only), these waves may be large enough to damage the largest combatant ships and to swamp or capsize smaller ships. This shoaling phenomenon does not appear in deep water. Except in shoaling waters, water waves normally will not be a major hazard.