LEARNING OBJECTIVES Interpret SOCUS noise prediction graphs. Identify limitations and assumptions. Explain an example output of the explosive noise prediction plot.

In the atmosphere, sound waves propagating from an explosive blast are frequentl refracted toward the surface. Under certain atmospheric conditions this energy may be focused, resulting in minor property damage, such as cracked plaster and broken windows at these points of focus (caustics). Large-scale refraction of blast waves toward the surface, even without the presence of caustics, can contribute to increased overpressure levels at distances greater than 50 km from the blast, resulting in numerous complaints fom area residents. These large-scale refractive and focusing conditions are caused by temperature inversions or strong vertical wind shears.

The SOCUS program provides the following forecast products:

. A sound speed profile with respect to height

. A profile of maximum explosive noise (peak overpressure) with respect to range from the explosive source

. The range from the explosive source of caustics

. The minimum and maximum aircraft ground speed versus height

These products are provided for an operator-specified bearing of interest. Program input includes profiles of temperature, wind speed, and wind direction (for the time and location of interest from the EDFs), the explosive weight of the charge, and the bearing of the explosive source.

The SOCUS program allows METOC personnel to determine whether atmospheric conditions favor the formation of caustics (sound focus points) or the large-scale refraction of sound toward populated areas during explosive exercises. The appropriate action can then be taken to minimize the number of complaints or claims for minor property damage.

The restrictions as well as the principles taken for granted in using the SOCUS program areas follows:

. Sound focusing is quite sensitive to small temperature, wind direction, and wind speed variations with respect to height and time. Therefore, a valid sound focus forecast can be obtained only when accurate data from a sounding taken near the time and location of the explosive exercise are used.

. This SOCUS/Prediction model was developed using measurements of surface explosions where the airblast propagated several kilometers over water and then over flat land. The effects of barriers such as mountains or forests are not known when focusing is caused by low-altitude weather conditions. Channeling effects through mountains are also unknown.

. Maximum explosive noise levels in the vicinity of caustics are normally between 2 and 8 dB higher than the explosive noise levels plotted on the graphic output. (The locations of caustics are denoted by Xs on the plot.)

. To compute maximum explosive noise levels for muzzle blasts from 5-inch naval gunfire, an equivalent explosive weight of 66 pounds is used.

. To compute explosive noise levels for muzzle blasts from 16-inch naval gunfire, an equivalent explosive weight of 330 pounds is used for a reduced charge.

. To compute noise levels for muzzle blast from 16-inch naval gunfire, an equivalent explosive weight of 660 pounds is used for a full charge.

. Noise levels resulting from impact explosions of the HE-ET/PD, Mk 19 Mod O, HC, and AP projectiles may be computed using the respective equivalent explosive weights: 155, 27, 155, and 41 pounds.

. Maximum noise levels are to be found in the direction of tire from 5-inch and 16-inch naval guns.

. Maximum subsonic ground speeds are only computed using a headwind/tailwind. Operators must make an interpolation for headings that differ from these.

There are two outputs from this product, figure 7-6 and figure 7-7. Figure 7-6 shows an example output of

Figure 7-6.-Example output of the explosive noise prediction plot.

Figure 7-7.-Sample output of maximum subsonic aircraft ground speeds.

the explosive noise prediction plot. Output from this program consists of an explosive noise prediction plot that shows expected noise (dB) against range, sound speed profiles (total sound speed and speed due to wind) in the direction of interest with respect to height. Figure 7-7 shows an example of a tabular output of maximum subsonic aircraft ground speeds with respect to height. For instance, an aircraft flying at 681 knots at 5,000 feet with a tailwind, the explosive noise source would be 337 (relative) from the aircraft.

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