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 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 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. APPLICATION 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 X’s 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. 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 these. FUNCTIONAL DESCRIPTION There are two outputs from this product, figure 7-6 and figure 7-7. Figure 7-6 shows an example output of 7-14