observers  conducted  several  types  of  upper-air observations: Radiosonde   observations:  Pressure, temperature,  and  humidity  measured  by  a  balloon- borne  instrument.  Data  is  transmitted  in  the  TEMP, TEMP MOBIL, or TEMP SHIP code. Rawinsonde  observations:  Pressure, temperature,  and  humidity  measured  by  a  balloon- borne  instrument.  Wind  speed  and  direction  may  be obtained   from   a   ground-based   directional-tracking antenna  homing  in  on  the  radiosonde’s  transponder. Winds are also calculated by using remote Very Low Frequency  (VLF)  signals  or  by  the  satellite  Global Positioning   System   (GPS).   Collected   data   is disseminated  in  the  TEMP,  TEMP  MOBIL  or  TEMP SHIP code, with selected information distributed in the PILOT, PILOT MOBIL, or PILOT SHIP code. RABAL   observations   (RAdiosonde   BALloon): These observations measure wind speed and direction by using a theodolite or a fire-control radar to track a reflector   attached   to   a   radiosonde   train. When conducted  in  conjunction  with  a  RAOB,  data  is distributed  in  the  TEMP,  TEMP  MOBIL,  or  TEMP SHIP code. When only wind information is obtained, data  is  distributed  in  the  PILOT,  PILOT  MOBIL,  or PILOT SHIP code. PIBAL observations (PIlot BALloon): A balloon is  tracked  with  an  optical  theodolite  (or  radar)  to determine only low-level wind speeds and directions. No radiosonde is attached to the balloon. Heights are based on assumed ascension rates. When transmitted, data is encoded in PILOT, PILOT MOBIL, or PILOT SHIP  code. With  the  introduction  of  compact,  computerized rawinsonde  systems  containing  navigational  aid (NAVAID) receivers in the mid 1980’s, the Radiosonde and   Rabal   observations   became   obsolete.     Pibal observations   are   still   conducted   by   Marine   Corps observers  in  the  field  to  provide  low-level  wind observations in support of aviation operations and para- drop  operations. Pibal  observations  are  particularly important  in  situations  where  radio  emissions  would lead to detection by enemy forces. Throughout the world, other countries conduct and transmit  data  from  Radiosonde,  Rawinsonde,  Rabal, and  Pibal  observations.  Several  countries,  including  the United  States,  routinely  carry  out  additional  types  of upper-air observations as follows: Rocketsonde observations: A rocket containing pressure,  temperature,  and  wind  sensors  is  launched from a ship, land station, or aircraft. After the rocket reaches apogee, the instrument package, deployed on a parachute,  measures  the  atmosphere  as  it  descends. Observed data is transmitted in the ROCOB code. Dropsonde   observations: Aircraft   deploy   a parachute-carried sensor package; the sensors measure pressure,  temperature,  humidity,  and  winds.  This information is transmitted in TEMP DROP code. Aircraft  flight  level  observations:  Aircraft  flying routine  flight  levels  may  contain  an  automatic  sensor unit   that   measures,   encodes,   and   automatically transmits   an   Aircraft   Meteorological   Data   Relay (AMDAR)  message,  which  contains  pressure, temperature, dew point, and wind information. Similar data  may  be  gathered  manually  by  the  aircrew  from onboard  equipment  and  forwarded  by  voice  radio  or commlink in the CODAR code. UPPER-AIR  OBSERVATION PUBLICATIONS All U.S. upper-air observations, including military, are  governed  by  procedures  outlined  in  the  Federal Meteorological  Handbook  No.  3  (FMH-3), Rawinsonde   and   Pibal   Observations.   The   FMH-3 prescribes   federal   standards   for   conducting Rawinsonde and Pibal observations, and for processing, encoding,  transmitting,  and  archiving  observation  data. Also provided are procedures for quality control. All  information  in  the  FMH-3  is  consistent  with World  Meteorological  Organization  (WMO)  standards. WMO  publication  number  306,  Manual  on  Codes, Volume  1,  International  Codes,  contains  a  complete breakdown of all upper-air observation code forms. The following text discusses the Mini Rawinsonde System (MRS). REVIEW  QUESTIONS Q1.  Upper-air  observations  measure  what  two layers of the atmosphere? Q2. Which atmospheric elements does a radiosonde measure? Q3. What are the main uses of upper-air observation data? 1-3