This instrument was made by Warren-Knight and they are still in business (web page). Most of the pibal theodolites have electronic readouts, but they still make this 8403 model as well as another all mechanical model 8500.
This theodolite is designed to track a ceiling (pilot) balloon, it's also called a PiBal (Pilot Balloon) theodolite or a Radiosonde. Since the balloon is usually at a high viewing angle the optical design has a right angle bend so that the observer always looks horizontally into the eyepiece and the elevation of the balloon does not effect the observer. This is very different from a normal theodolite that you can not use at high elevation angles without a 90 degree eyepiece adapter.
This is a commercial version of the military ML-47 (?) pibal theodolite.
My interest is for looking at stars, and Polaris (Wiki) in particular but also for it's use in relation to weather.
There are a number of different things that can be determined using a balloon. The balloons are very standardized in terms of construction and inflation so that their rate of rise will be known. Balloons are also used to raise antennas like for the Gibson Girl lifeboat survival transmitter.
Cloud HeightThis is done using a ceiling balloon (Wiki) and a stop watch. Not sure if just by eye or if binoculars or a telescope is used in addition. Ceiling height is not when the balloon disapears, but rather when it starts to fade.
Ceiling height in feet = 460 * (minutes since launch)
Winds AloftThe balloon is tracked and data recorded for time since launch, azimuth relative to true North and elevation angle. For daytime observations it's just the balloon that goes up, nothing is attached to it. In times past a water activated reserve battery was used to light a flashlight bulb so the balloon could be tracked at night.
To determine weather parameters aloft a Radiosonde (Wiki) can be lifted by the balloon. It transmits back the pressure, temperature and humidity. The units used in the 1950s used the pressure change to switch between temperature and humidity so that only a single parameter was transmitted and by paying attention to the time and number of cycles the pressure could be determined and the pressure is related to the altitude. Not sure if these were tracked with a pibal theodolite. But later they were tracked by the SCR-568 radar (these used to be advertized in military surplus flyers).
These are microphones supported by springs which in turn are attached to a ring. That way a mechanical shock to the stand would not make as much of a noise. A short hand name for these microphones was "disk". So when the AF put out a press release sayhing that "flying disks" were what crashed in Roswell New Mexico in 1947 a newspaper reported who was not farmiliar with that termonology reported that a flying "sauccer" had crashed. See: Roswell Connection
Mounts on a standard 3-1/2"-8 surveying tripod.
There are three ways to aim at a target:
There is a level under the eyepiece that switches the optical path between the finder scope and the main telescope.
- Use gun type open sights (this part is in the transit case)
- Look through the low power inverting finder scope
- look throught the high power inverting main telescope
There is a through compass, i.e. a compass without a scale that's only used to indicate North or South. You can see it in Fig 1 on the right just under the main telescope tube.
The 20-8403 is a first generation analog type where the readout is a veneer. Battery holder is a separate item resembling a flashlight.
The 20-8353 (W-K web page) has shaft encoders added for azimuth and elevation. Battery holder is on instrument frame and uses side-by-side "D" cells. It's intended to be located near a radio aid to navigation (ILS, MLS, VOR, TACAN, VORTAC) and the encoders are used to modulate a UHF radio transmitter. A matching telemetry receiver is in the test aircraft so that they can easily compare the instrument reading with their actual position from the theodolite.
Setup and leveling is the same as for any surveying tripod mounted tranist or theodolite. And like a surveying instrument the elevation angle is relative to a bubble level. But unlike a surveying setup the azimuth scale needs to be referenced to true north. TM 11-6675-200-10 for the military ML-47 lists a number of ways of finding North in order to calibrate the azimuth scale. The ways of orienting the azimuth scale to North are: Compass, Sun, Polaris, Equal star/Sun Angles, Datum Lines or Transference.
Fig 1 Pibal theodolite mounted on 3-1/2-8 surveying tripod
Fig 2 Transit case with factory label.
Fig 3 bottom & Az cal assy
Installing Az cal assy requires special 2-pin spanner.
Fig 20 In packing case
The red ring at the lower right is a thread protector cap for the
Fig 21 Far side
2 vertical cylinders are battery box
There is a 1/4" phone jack for each encoder.
Fig 22 Observer's side
Light colored cylinders are shaft encoders.
Fig 23 on factory tripod, legs at minimum length.
33: Geometrical Instruments
73: MEASURING AND TESTING
340: COMMUNICATIONS: ELECTRICAL
342: COMMUNICATIONS: DIRECTIVE RADIO WAVE SYSTEMS AND DEVICES (E.G., RADAR, RADIO NAVIGATION)
356: OPTICS: MEASURING AND TESTING
702: DATA PROCESSING: MEASURING, CALIBRATING, OR TESTING
708: ELECTRICAL COMPUTERS: ARITHMETIC PROCESSING AND CALCULATING
940329 Optical instrument for determining the direction of travel of air-ships and the like, Otto Krell, Nov 16, 1909, 356/150; 33/318; 74/5.3 - gyroscopic stabalized right angle telescope for looking at the ground from the balloon.
1296477 Instrument for Recording the paths of Aeroplanes, G.J.N. Carpentier, Mar 4, 1919, 33/228 434/15-
1446574 Nephoscope (Wiki), Alexander McAdie, Feb 27, 1923, 33/284, 356/27, 33/1.00R - measuring the altitude, direction, and velocity of clouds
1913512 Meteorological indicator, Anita Reynolds, Jun 13, 1933, 73/170.11, 73/170.15, 73/170.8, 73/178.00R, 333/24.00C, 340/949, 340/870.1, 73/170.16, 341/173, 73/170.28 - radiosonde
2027367 System of determining meteorological conditions by radio, William R Blair, Jan 14, 1936, 342/450, 340/870.28, 73/170.28, 340/870.1, 455/61, 342/460 -balloon & radiosonde
2162582 Device and Method for Determining Upper Air Wind Direction and Velocity, H.B. Kaster, June 13, 1939 33/228, 33/274 - instrument for observing a free balloon and method of determining wind speed & direction
2216161 Apparatus for making meteorological observations, Allen V Astin, Leon F Curtiss, Oct 1, 1940, 340/870.28, 73/170.28, 346/33.0TP, 235/61.00B, 346/50, 346/33.00B - balloon & radiosonde
2347160 Radiometeorograph transmitting apparatus, Charles F Wallace (Wallace & Tiernan), Apr 18, 1944, 340/870.1, 340/870.28, 73/170.28, 340/870.13, 200/56.00R, 340/870.12, 200/19.21 - barometer switches temp and humidity
2381009 Chronometric radiosconde system, Joseph A Siderman, Aug 7, 1945, 340/870.1, 307/651, 455/91, 340/870.12, 340/870.16, 340/870.13, 307/650, 455/98 - radiosonde: uses clockwork to switch sensors & reference resistor for calibration
2519180 Wind data computer, William K Ergen, Aug 15, 1950, 702/3, 235/413, 708/809, 235/400 - convert free balloon observations more useful data
2651459 Velocity and direction computer, James M Brady, Athelstan F Sipilhaus, Sep 8, 1953, 235/413, 33/1.00R, 701/519 - convert free balloon observations more useful data
TM 11 6660-258-25P ML-474 (Pilot Balloon type) PIBAL
TM 11-6675-200-10 ML-247 (Pilot Balloon type) PIBAL
TM 11-6675-200-25P ML-247 (Pilot Balloon type) PIBAL
TM-11-6675-200-35 (Pilot Balloon type) (Wiki) PilotBalloon.com
Theodolites ML-47 - C through ML-47-R,
ML-247 and ML-247-A and
Double Center Theodolite ML-474/GM
Martin Brenner's, Pilot Balloon Resources -
Liberated Manuals - theodolite -