CAUTION The  observer’s  eyes  will  be  permanently damaged  by  looking  directly  at  the  focused  sun image  through  the  theodolite.  Therefore,  the observer  must  use  extreme  caution  following the  balloon  while  it  is  near  the  sun’s  angular bearing. and never track the balloon across the sun’s disk. Balloons All  pilot  balloons  are  made  of  neoprene  and  are usually  inflated  with  helium.  A  100-gram  balloon  is used for a daytime scheduled Pibal that is expected to ascend 15,000 feet or more above the surface or during high-wind conditions. The 30-gram balloons are used for  all  other  Pibals,  including  nighttime  observations when  equipped  with  a  chemical  light.  The  choice  of color  is  to  some  extent  a  matter  for  the  individual  to decide. In general, white balloons are used with a clear sky; black balloons, with low or middle overcast, and red balloons, with high overcast. Usually, when haze, dust,  or  smoke  is  present  in  a  cloudless  sky,  a  white balloon remainsvisible longest. This is true because the sun shining upon it above a lower layer of haze creates scintillation—  a  twinkling  or  shimmering,  which  is absent when colored balloons are used. Pilot   balloons   are   inflated   to   achieve   standard ascension rates. The 30-gram balloons are inflated with helium  to  neutral  buoyancy  while  connected  to  the inflation  nozzle  weighted  to  exactly  139  grams  (192 night). The 100-gram balloons are inflated with helium to  neutral  buoyancy  while  connected  to  the  inflation nozzle weighted to exactly 515 grams (552 night). The length of cord used to tie the balloon neck is draped over the nozzle during inflation of the balloon. For nighttime observations, the additional weight of a chemical light is compensated for by hanging an unactivated light on the nozzle during inflation. The initial ascension rate (216 ft/min for 30-gram and 350 ft/min for 100-gram balloons) slows gradually as  the  balloon  expands. The  height  of  either  size balloon at any time is listed in the FMH-3, and is also printed  on  the  MF5-20  Winds  Aloft  Computation Sheet.   The   computer   evaluation   programs   calculate balloon  height  based  on  the  time  in  flight.  A  surface wind observation must be taken no more than 5 minutes before release. Lighting Units Tracking a night Pibal is made possible by attaching a lightweight chemical light to the balloon. The lighting unit  should  be  activated  just  prior  to  the  release  in accordance  with  the  manufacturers  instructions.  You may  use  any  color  high-intensity  chemical  light, although green is most often used. WIND  EVALUATION The  GFMPL  programs  that  evaluate  Pibal  winds only  require  the  size  of  the  balloon  used  and  the consecutive minute readings of azimuth and elevation to determine wind speed and direction by the minute and/or in 1,000-foot (AGL) increments. If the data is to be encoded for transmission, only standard pressure level and fixed level (or significant level winds) are reported. Pibal observations that do not extend  to  at  least  1,000  feet  are  not  transmitted. Guidance for the determination and selection of levels is contained in Appendix D and E of the FMH-3. These wind  levels  are  determined  after  the  consecutive  minute or  1,000  foot  winds  are  plotted  on  the  Winds  Aloft Graphing  Board  or  the  Winds  Aloft  Plotting  Chart. Normally, 5 consecutive minutes of missing data will necessitate a new launch in addition to any equipment problems, such as a loose base clamp, etc. Missing data for less than 5 minutes may be interpolated. If severe or unusual weather exists in the vicinity of the observation site, a second verifying Pibal should be taken as soon as possible.  After  the  observed  data  is  plotted  and evaluated, it is encoded in the PILOT code, as discussed later in this chapter. Earlier in this chapter, we introduced the different codes used to relay upper-air observation data. We have briefly  discussed  the  Mini  Rawinsonde  System observation  procedures  and  indicated  that  the  MRS automatically  encodes  the  observed  data  in  the appropriate  form  of  the  TEMP  code.  We  have  also mentioned  that  if  Pibal-observed  winds  are  encoded  for relay, the PILOT code form is used. Although not every Navy   or   Marine   Corps   observer   will   have   the opportunity to conduct upper-air observations, all will routinely   use   data   contained   in   coded   upper-air observation reports. REVIEW  QUESTIONS Q32.  What  is  the  primary  purpose  of  Pibal observations? Q33.    What instrument is used to track pilot balloons? 1-19