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Pilot Weather Balloon (Pibal) Optical Theodolites - Equipment - Operations and Related information.
Updated 01-22-2007

WAVE Aerographer's Mate 3rd Class Dorothy J. Baroch stands ready to launch a weather balloon from a theodolite platform, circa 1944-45. N.A.S. Moffet Field California.  Image from: Naval Historical Center

Quiz: For you pibal experts...This picture was posed, what is wrong with it?  & Extra Credit: What model is the theodolite? Answers

New items:  Technicolor Pilot Balloon Theodolite, Cary Model D theodolite, Seiler Model 2000 theoodlite, Met Office MK IV slide rule, updates to David White 6061 page and Warren Knight 20-8403 page

Below is a compilation of information and links that I have collected in research on Pilot Balloon (Pibal) Optical Theodolites procedures and related items.  Pibals and theodolites have a important history in meteorology.   They have been used to track upper level winds for over 125 years.  Their use is now restricted to a limited number of specialized but often critical applications, usually in remote locations where usable data from a Rawinsonde is not available.  Ironically pibals are still utilized  to support the flights of manned balloons, (hot air balloonists) the application they were originally developed for.  

Basic Definition:
A pilot weather balloon (Pibal) theodolite is a device that is similar to a surveyor's transit.  It consists of a telescope mounted on two movable axes.   One axis (vertical) rotates to change elevation, the other (horizontal) azimuth.   There are vernier scales and in some cases micrometers that give precise readouts of the relative position of the telescope to each axis.  Unlike the surveyor's transit a pibal theodolite utilizes a "bent axis telescope".  Additionally a pibal theodolite often has the facility to illuminate the crosshairs and readouts for night time use.  A diagram of a commonly used pibal theodolite is illustrated here.   Specialized units were produced for shipboard use, one is illustrated here.

Basic Operation:
The instrument is set up so that it is level and it is pointed towards true north with both scales reading 0 degrees exactly.  A balloon is released in front of the theodolite.   It is sighted at timed intervals (usually one minute apart) and the position of the theodolite's telescope (azimuth and elevation) is recorded. 

Why do we do this:
We can chart the direction and velocity of winds at various altitudes just by watching balloons.  The rate of ascent of a balloon is mostly dependant on the balloon's drag and its "free lift" (the vertical pull of the balloon).  We have some degree of control over these these factors, and as a result, know approximately how high our balloon will be at any given time after its release.   Given a known height and an angular direction (read off the theodolite) to the balloon, we can fix the horizontal movement component of the balloon's travel as it moves through different altitudes.  The horizontal movement is due to the winds blowing the balloon around at the altitudes that the balloon is traveling through. 

When better accuracy is desired, two spaced theodolites can be used to site the balloon in synchronized intervals.  The two theodolite solution does not require assumptions of the ascent rate.  The position is solved in 3D and the resulting wind data will tend to be more accurate.

Pages and topics on this site include:
Pibal Theodolite Manufacturers Info. (current production models)
Pibal Theodolite Models and Info. (historical models)
Pibal Accessories and historical items
Pibal publications, software and information
Pibal Theodolite procedures for set up and observation of a balloon  

Important information about this site:
This site contains information is for casual informational purposes only.  This site is not affiliated with any manufacturer or reseller of equipment or services.    I have attempted to summarize information that I have received on these products and make no official claims or representations of the product line offered by any company listed on this site.

Please send comments, corrections, additional materials that can be included to: mbrenner@csulb.edu Martin Brenner, Director of Technology, College of the Arts, California State University Long Beach, 1250 Bellflower Blvd. Long Beach CA 90840

Acknowledgements:
I would like to thank Mr. Graham Bartlett of the National Meteorological Library & Archive, London for providing materials essential to this site, Rick Marron at Warren-Knight, Bob Summersett of Customcraft  and Dr. Michael Douglas and the National Severe Storms Laboratory for providing information on US Weather Service (now NOAA) pattern theodolites.  My colleagues at California State University Long Beach, Library and the College of the Arts for allowing the use of facilities, equipment and Web space to support this research and Web Site.  Last but not least the folks at www.palosverdes.com for hosting the files and the website.