The observer is using type of theodolite you just don't see every day (unless you have one yourself).
pibal theo is the shorthand name
I assume that the painter took a few liberties with the instrument, but it looks like the Balloon Theodolite that David White made during WWII.
It has an endless tangent screw on the horizontal and vertical circles and a clever locking system.
Kent
Did you get this off the internet somewhere or is it a magazine cover you have? Can you read the date?
> Did you get this off the internet somewhere or is it a magazine cover you have? Can you read the date?
I don't have that magazine, but it appears to be the issue of March 21, 1944 (one of which is for sale on eBay, even).
Not to hijack..... but this old fashioned scribed vernier device is a theodolite? It doesn't have glass reading circles like modern day theodolites and it's a David White not a Wild or Kern. So why is it a theodolite and not a transit?
No reason other than they called them "Balloon Theodolites" in the day. They were used for tracking weather balloons.
I think it's because this instrument would not "transit" (plunge). But then that makes one wonder why a T-1 is a theodolite when it will transit.
Balloon Theodolite, Updated
A theodolite is a precision instrument for measuring horizontal and vertical angles, precision being a relative term. They're all theodolites. The scope can be inverted on a transit theodolite (transit for short) and can't be inverted on a non-transit theodolite. The balloon thingy is a non-transit theodolite. The T-1 is a transit theodolite.
BTW if that's the WWII David White Balloon Theodolite that I think it is, it has a couple of very unusual features. The main one is how the motion clamps on the circles operate. The tangent motions drive worm gears that engage gears cut around the peripheries of the horizontal and vertical circles, resulting in an endless tangent motion. Those same tangent motions are held in place by a hinged, spring-loaded connector. So to unlock the motion, you pulled the tangent screw away from the ring gear and the motion was free to turn. Snapping the tangent screw assembly back into place locked the circle again.
Yup. that's the way they work. But that is also a place that wears out quite easily and things will start slipping. Sometimes they will slip only one direction turn of the screw, sometimes both.
Nice post...
now can someone tell me what these were actually used for? Why is this gal observing a balloon?
Nice post...
> now can someone tell me what these were actually used for? Why is this gal observing a balloon?
The used the angles measured to the balloon to measure speed and direction of winds aloft (I assume).
Nice post...
Correct
Nice post...
So there must have been at least 2 observing stations to allow triangulation?
Nice post...
Not sure of the technique used, but that would make sense. However I doubt it. I suspect the "opposite" side of the triangle distance was calculated based on a known rate of rise of the balloon.
Also, these instruments weren't made for precision. Angles were read to 1/10 degree if I remember correctly. This was quick and dirty observations on a moving target.
Nice post...
> Not sure of the technique used, but that would make sense. However I doubt it. I suspect the "opposite" side of the triangle distance was calculated based on a known rate of rise of the balloon.
>
> Also, these instruments weren't made for precision. Angles were read to 1/10 degree if I remember correctly. This was quick and dirty observations on a moving target.
According to the aerographic surveying manuals I've skimmed, both one-theodolite and two-theodolite observations were used, with one-theodolite observations assuming the rate of ascent of the balloon to derive it's position from the Z and Hz angles.
The David White theodolite I owned once upon a time could easily be read to the nearest 0.01 deg by interpolation of the micrometer. Part of the key to making accurate angle measurements with an instrument of the endless-tangent worm-gear design was pointing the telescope with the motion screws turning in the same direction each time.
More info on Pilot-Balloon (PIBAL) weather theodolites
Jim,
Kent and Dave have the basics correct- I'm an ex- Air Force weather officer, so I have first-hand experience with these- and have several in my collection of surveying and weather theodolites. Some comments regarding their use- these types of non-electronic theodolites were still in use by the Marine Corps in the 1990's, but have been replaced by newer methods since then. A quick overview has already been linked to Martin Brenner's excellent Pilot-Balloon (PIBAL) Theodolite website, at http://www.csulb.edu/~mbrenner/
I can highly recommend it for general knowledge and review of the various types of pibal theodolites used throughout the world.
History of Pilot-Balloon Theodolites
The theodolite in the picture is the standard US-based weather theodlite, known as the 20-8000 or military ML-474 theodolite, made by several contractors- Seiler, David White, Warren-Knight, and others. In it's final, non-electronic form it was still being produced into the 1990's, with some small upgrades over the years culminating in a version with electronic-recording of vertical/horizontal circles observations. I know the Marine Corps still deployed with them into forward locations in the 1990's, and they were retained in US military inventory into the 2000's as new stock. Although seemingly obsolete by then, they were robust, non-electronic, basic field-repairable instruments that met the needs of their users.
Worldwide several other manufacturers also made similar instruments; similar to the land surveying instrument the majority of these manufacturers were primarily British, German, and Japanese- China also started in-country manufacture in the late 1960's. Brenner's comprehensive survey of known manufacturing examples is fascininating for the variety of designs and methods of recording (some used polar-plotting circular graph charts, others used a punch-tape design. see:
Pibal Theodolite Manufacturers and Models
As mentioned, the were used individually (not by dual-triangulation); their primary function is to observe a small, standard-sized weather balloon (balloon only, no payload) as it ascends upwards into the atmosphere; this was what both military and civilian weather services used to determine the vertical wind profile of the atmosphere starting in the 1930's and lasting even into the 1990's for some countries. The picture illustrates use of the Women's Army Corp (WACS) to perform the weather observing function- most of the US-based weather observers during WWII and later were women- both WAC's (Army) and WAVES (Navy).
The use of a single theodolite is possible because the vertical pressure profile of the atmosphere is relatively consistent- and if you inflate a balloon to a standard amount of buoyancy, it will ascend at a constant, known rate. Balloons are manufactured to be inflated to specific sizes, (for human observation the 10,30 and 100 grams were most commonly used)... larger sizes are useful for attaining higher altitudes or with heavier payloads.
Under clear, daylight conditions a balloon (colored either red,white or black) could be observed to at least 25,000 feet and within about 40 miles- but on days with strong upper-level winds the balloon could quick drift beyond the visual observing range. Primary use was either for basic weather forecasting- or for artillery use to determine the vertical wind profiles. Red color was preferred as all-purpose for scattered clouds; white/ natural latex color was good if cloud-free, clear blue skies existed- but a high deck of overcast clouds would make the white balloon indistinguishable from the cloud deck, so black colored balloons were used if releasing the balloon in daytime under a cloud deck.
The design of the instrument utilized an spring loaded-transit screw with endless tangent motion due to the fact that the observer had to follow the balloon around the 360 degree circle- when setting it up one had to align the telescope to follow the balloon, and needed to be able to move the telescope very fast in the first few minutes of the balloon's flight aloft to follow it. The observing site was usually at a fixed location with a circular pad around the theodolite post/ standard to allow the observer a complete 360° path to move. (the picture of the instrument on a tripod is incorrect if observing a a fixed weather station- they would have used a concrete base with an adjustable pier/ post to mount the theodolite on). The ML-474 instrument was designed with a wide-angle finder scope (4X) adjacent to the regular, higher-power scope (21X) for observations once the balloon reached higher altitudes- the finder scope was integrated and aligned with the optical path and was reflected into the the eyepiece with a toggle switch; thus the observer could maintain track of the balloon easily during it's entire flight.
(this is a posed photo, notice the observe is standing on a block of wood... not operationally feasible)
For weather service use, these balloons would be launched at all fixed weather stations simultaneously every 6 or 12 hours, at fixed times of 00Z, 06Z, 12Z and 18Z (UTC/ Greenwich time) around the world to obtain the vertical wind profile. Night time observations were available if needed with use of a battery-powered light, or search-light enabled balloon ascent. A solid cloud deck would eliminate the ability of observing the balloon once it reached the cloud height- hence their usefulness was highly dependent upon the current weather at the time of observations (low clouds/ fog completely precluded their use). Artillery usage needed only the first 5000-10000 feet of measurements; so high-altitude observations were not as critical for that application.
Even today, this is the simplest way to measure the wind profiles from earth-based observations; (hence some hot-air balloonists still use these).. There are also balloons with temperature/humidity/ pressure sensors that radio back their telemetry data- these are called radiosondes, and don't require a theodolite for observation- they determine the direction of the balloon by equipping the ground-based radio receiver with an automated tracking antenna, when used on the ground it could track and record the direction of the radiosonde centered on the strongest gain of the radio signal to determine wind velocity). Newer radiosondes also have GPS sensors onboard and provide wind data as well as temperature, humidity and pressure. Overall issue with the newer radio-GPS based radiosondes is the cost- each radiosonde runs about $100 (even with mass-purchasing power of the US government); and the corresponding ground stations and equipment run around $40,000. Hence, in the US radiosondes are still used but increasingly are supplemented or replaced by satellite or other types of upper-atmospere observations. Vaisala of Uppsala, Finland (US office in Boulder, CO) and Intermet Met Systems, Grand Rapids, Michigan are the two primary providers of the electronic radiosonde systems in use today worldwide.
The balloons were inflated to an exact lifting capability (as measured by their buoyancy, they would be inflated to where they could lift either 10,30, or 100 gram weight)... once released, the balloons ascended at a known, standard rate- so the vertical component was known by using tables of standard atmospheric height vs/ time of ascent. The vertical and horizontal angles would be recorded by a 2nd person (the observer/recorder- not shown in the magazine picture) at 1-minute intervals, or when a distinct directional change was observed, indicating a wind shift aloft at that point. The recorded data would be entered in the upper-air weather observation, then compiled with other weather balloon recordings to create a chart of the overall wind field aloft, usually specified by specific pressure levels (925mb, 850, 700,500,300,250 and 100mb- corresponding to approximately 1000,5000, 10k, 18k, 25k, 30k feet above ground level)
The vertical ascent rates were usually either 150 or 200 meters/ minute (or approx 500/ 650 ft/ min- see this chart for current specs; balloons are made primarily by Kaysam (US); Totex (Japan) or others.
NovaLynx meterological balloons
Pibal theodolites weres used by all services (Army, Navy, Marines) as well as Air Force weather observing units. (The Navy also had a pendulum-stabilized theodolite for ship-board use.) Army and Marines used them on the ground with their artillery forward-observing posts to determine winds aloft for computing artillery deflection/ wind corrections. In the picture shown, the women at the instrument was the observer- not shown was another person (the recorder)who would read and record the location of the balloon (horizontal and vertical readings) every minute.
There were also several versions of self-recording balloon theodolites made by various German/Swiss firms- Zeiss, Kern, Askania, Breipthaupt, etc - which used a plotting pen on a polar-coordinate type plot, as seen here on Brenner's website:
(The green circular platform at the base of the theodolite is where the circular plotting-chart paper was placed on which the pen would record in polar form the velocity of the balloon)
