DMSP—Defense  meteorological  satellite  program. DOWNWIND—The direction towards which the wind is blowing; with the wind. DRIBU—Drifting   buoy. DROPSONDE—A  radiosonde  instrument  dropped  by parachute from an aircraft. DSN—Defense   switched   network,   an   upgrade   and name  change  to  the  automatic  voice  network (AUTOVON). DUCT—A  layer  in  the  atmosphere  that  readily  traps electromagnetic   energy   permitting   extended transmission ranges. DUCTING—The process occurring within a duct, also known as trapping. E EDD—Effective     downwind     direction     (radioactive fallout). EDF—Effective  downwind  forecast. EDM—Effective    downwind    message    (radioactive fallout). F FAA—Federal aviation administration. AI-2 FATHOMETER—A    device    used    to    measure    the depth of the ocean. FNMOC—Fleet Numerical Meteorology and Oceanography Center, Monterey, California. FRONT—The interface or transition zone between two air masses of different density. Since temperature is  the  most  important  regulator  of  atmospheric density,   a   front   almost   invariably   separates   air masses of different temperature. G GEOPHYSICS —Used   to   mean   working   with   the physical properties of both the air, land, and water, this   term   is   occasionally   used   to   describe   the occupational   field   of   Navy   and   Marine   Corps weather personnel. GEOPOTENTIAL   HEIGHT—The  height  of  a  given point in the atmosphere calculated with respect to the energy in the column of air beneath the point, relative   to   sea   level.   In   other   words,   an approximation  of  the  height  based  on  measured temperatures,  pressures,  and  humidity  content  of the supporting air column, and not necessarily an exact measured height. GFMPL—Geophysics  fleet  mission  program  library. GHz—Gigahertz,  (1  billion  hertz) GMT—Greenwich   mean   time,   a   term   replaced   by coordinated universal time (UTC). GPM—Geopotential meters, also gallons per minute. GZ —round  zero,  the  detonation  point  of  a  weapon, usually  nuclear. H HDO—Horizontal    distance    out    (when    evaluating upper winds); or hurricane duty officer. HECTOPASCAL  (hPa)—A  unit  of  100  pascals  used to  measure  pressure,  exactly  equivalent  to  1 millibar. HF—High  frequency. HSA—Half-sector  angle. I ICAO—Abbreviation  for  international  civil  aviation organization. IFR—Abbreviation for instrument flight rules. INFRARED (JR)—The portion of the electromagnetic spectrum with wavelengths just slightly longer than visible  light  energy-thermal  energy. INVERSION—With     respect     to     temperature,     an increase   in   temperature   with   height.   Normally temperature   decreases   with   height   in   the atmosphere. IRCS—International  radio  call  sign. IREPS—Integrated     refractive     effects     prediction system. ISOTHERMAL—Having an equal temperature throughout. K KHz—Kilohertz; 1,000 hertz or cycles per second. KILOTON—(KT)  A  multiplication  factor  for  nuclear weapon   yields.   Each   kiloton   is   equal   to   the explosive  force  of  1,000  tons  of  trinitrotoluene (TNT) explosive.