Chapter 10 — WATCH ROUTINES 



enough to cause the sounding to be considered 

 erroneous. The path that a balloon takes in 

 flight is governed by the direction and speed 

 of the winds through which it ascends. 



Routine land and shipboard station pibals 

 are taken by tracking the flight of the balloon 

 with a single theodolite. On board ship a the- 

 odolite designed to reduce the effects of the 

 pitch and roll of the ship is used. 



2. Radiosonde balloon (RABAL). A rabal ob- 

 servation is a measurement of the direction 

 and speed of the winds above the earth's sur- 

 face obtained by visually observing a radio- 

 sonde's ascent with a theodolite. This type of 

 sounding is more exact than pibals because 

 there is no assumption made of the ascension 

 rate of the balloon. The direction and speed 

 of the wind are computed from successive po- 

 sitions of the balloon as computed from the 

 angular readings of elevation and azimuth and 

 the calculated height of the balloon. 



3. Radio or radar wind (RAWIN). A rawin 

 observation is a measurement of the direction 

 and speed of the wind above the earth's sur- 

 face obtained by electronic means. The height 

 assumption of the pibal Is eliminated. When 

 radio direction finding equipment is used, the 

 wind is determined from the calculations which 

 combine the angular elevation and azimuth of 

 a radiosonde signal with the computed height 

 of the radiosonde. When radar equipment is 

 used, the successive positions of the balloon 

 are fixed by determining the azimuth angle and 

 a combination of slant range and elevation 

 angle, the slant range and heights, or elevation 

 angle and height. (See fig. 10-9.) 



4. Radiosonde observations (RAOBS). Raobs 

 are taken to determine the pressure, tempera- 

 ture, and relative humidity from the surface 

 to the point where the balloon bursts. The ra- 

 diosonde consists of meteorological sensors, 

 combined with a radio transm'tter, which are 

 assembled in a lightweight box. It is carried 

 aloft by a balloon filled with helium. 



Measurements of pressure, temperature, and 

 relative humidity of the air are secured from 

 signals transmitted by the radiosonde to a 

 ground receiver where they are automatically 

 recorded. The extreme altitude to which the 

 radiosonde ascends is determined by the burst- 

 ing point of the balloon. After the balloon has 



burst, the radiosonde is prevented from damag- 

 ing property and injuring persons on its descent 

 by a small parachute. 



5. Rawinsonde. Rawinsonde observations give 

 a simultaneous measurement of the pressure, 

 temperature, humidity, and wind direction and 

 speed of the air above the earth's surface. 

 Rawinsonde observations combine the elements 

 of the radiosonde and rawin observations. 



Observational Schedules 



The standard times for upper wind observa- 

 tions are 0000, 0600, 1200, and 1800 GMT. 

 However, delayed releases may be made within 

 specified time limits. 



Afloat, upper wind observations are desired 

 at 0000 and 1200 GMT, daily, when underway 

 greater than 180 nautical miles from a reg- 

 ularly reporting station. Ashore, at least two 

 upper wind observations must be taken and re- 

 corded daily. Special winds aloft observations 

 are taken and recorded afloat and ashore as 

 required and directed by competent authority. 



Forms and Charts 



The following forms and charts are used 

 to compute and record upper air data received 

 from various methods. Procedures for requisi- 

 tioning forms, along with a listing of them, are 

 contained in the NAVAIR Allowance List, Sec- 

 tion L , NAVAIR 00-35QL-22. Upper air charts 

 used to compute radiosonde data are found in 

 the DOD Catalog of Weather Plotting Charts, 

 NW50-1G-518. It is essential that entries made 

 on the forms be legible, and that the forms be 



^Q 



TRANSMITTER 



*0» 



( BASE ) 



HORIZONAL. DISTANCE ( b ) 



209.254 

 Figure 10-9. — Right triangle representing the 

 parameters of an upper air sounding. 



189 



