SOUND FOCUS (SOCUS)
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
. A sound speed profile with respect to height
. A profile of maximum explosive noise (peak
overpressure) with respect to range from the explosive
l The range from the explosive source of caustics
. The minimum and maximum aircraft ground
speed versus height
T h e s e p r o d u c t s a r e p r o v i d e d f o r 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.
LIMITATIONS AND ASSUMPTIONS
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
. 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
l 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
There are two outputs from this product, figure 7-6
and figure 7-7. Figure 7-6 shows an example output of