Martin Brenner's, Pilot Balloon Resources 

Pilot Balloon Observation Theodolite Setup

The following section relates to David White/Warren-Knight instruments which are the most commonly found instruments in the United States.  Procedures differ only slightly for instruments from different manufacturers. Check the operations manual for the instrument model you are using for information specific to your instrument. Please note that this section assumes that your instrument is properly collimated and aligned. If it is not you can either obtain a service/repair manual for your instrument and do the work yourself or bring the instrument to a qualified optical shop or surveying equipment maintenance facility.

Precautions:
Special care should be taken to avoid any situation that might result in the theodolite being dropped or otherwise subjected to a severe jar.

Inspect the theodolite for loose parts and screws. Remove dust from the objective lens and eyepiece with a lens brush and lens tissue using procedures consistent with delicate optics. Keep the lens covered whit the theodolite is not in use. Use a sun shade to protect the lens from the direct rays of the sun.

The graduated circles and venires are coated with a lacquer to retard oxidation. Avoid touching these parts. A thin film of oil applied with a lintless cloth will aid in keeping the surfaces clean.

Store the theodolite in its case or other dry dust free location when not in use.

If the theodolite is to be taken from a cool environment to a warm one (especially in humid conditions) allow the theodolite to warm up inside its case where it will not be subject to condensation.  

Mounting the theodolite
The mount or tripod should be adjusted for the height of the observer with the top of the tripod level and approximately 8" below eye level. Make sure that the theodolite tripod is well anchored and leg retaining screws tight before mounting the theodolite.

Remove the theodolite from its case and loosen the lower clamp so that the leveling plate and leveling head can be rotated independently of the centers.

While holding the theodolite have an assistant rotate the leveling plate and leveling head affixing it to the tripod.

Leveling the theodolite
Disengage the azimuth tangent screw (horizontal circle) and rotate the upper plate until one of the plate levels is directly over one of the leveling screws (the screw will be under the center of the level). Regard this as screw A., and the other three screws as B,C, and D, in that order proceeding in a counterclockwise direction from A. Adjust the two leveling screws B and D by turning them in opposite directions until the bubble level in-between them (over A) is centered (reads level).

The bubble moves in the same direction as that of the right index finger. Leaving the position of the theodolite unchanged, adjust the two leveling screws A and C until the other bubble is centered (reads level). You may have to repeat the step with screws B, and C for the other level (over A) if it has drifted slightly.

Rotate the instrument 180 degrees about its vertical axis, and observe whether both bubbles remain in the center of their respective levels. If not, readjust the leveling screws. and repeat. When the theodolite is finally leveled, the four leveling screws must be resting securely, with an even amount of pressure (but not too much - lightly finger tightened). If any one of the screw is tightened too much, the base plate will be distorted and the theodolite will be impossible to level.

If the above procedure does not allow the bubbles to remain centered when the theodolite is rotated, the plate bubble levels must be adjusted.

Plate Bubble Level Adjustment:
This procedure is similar to leveling the theodolite above. Do this one level at a time. With the azimuth tangent screw (horizontal circle) disengaged, rotate the upper plate until one of the plate levels is directly over one of the leveling screws (the screw will be under the center of the level). Regard this as screw A., and the other three screws as B,C, and D, in that order proceeding in a counterclockwise direction from A. Adjust the two leveling screws B and D by turning them in opposite directions until the bubble level in-between them (over A) is centered (reads level).

Rotate the instrument 180 degrees and observe the position of the level. Use an adjusting pin to reset the bubble level adjusting screw so that the bubble returns exactly 1/2 the distance to the centered position. Re-level the theodolite with the leveling screws. Rotate the theodolite 180 degrees again, the bubble should maintain its position in the center.

Repeat the Plate Bubble Level Adjustment procedure for the other bubble level. After doing both levels you should be able to level the theodolite using the procedure in the preceding section.

If the theodolite is in use for a long period of time it may require re-leveling periodically due to temperature effects on the tripod and theodolite base.  

Orienting the Theodolite
If your theodolite has an compass do the following: Disengage the azimuth screw, set the azimuth the value for the amount of the local magnetic declination if it is east (for example where I live in So Cal. it is E14.2 - so I set the azimuth to 14.2); if west then subtract the magnetic declination from 360 and set azimuth to this value (example if you are some place in Maine you might have a declination of W20 so you would set the azimuth to 340 degrees) engage the tangent screw. Center the slow motion adjustment on the base of the theodolite, loosen the wing screw in the base. Unlock the compass and rotate the theodolite base so that the compass shows that the theodolite is pointed very close to towards true north. Tighten the wing screw. Rotate the base with the slow motion screw so that the compass shows that that the theodolite is pointed exactly north.

Now the azimuth scale is correctly oriented to true north.

If your theodolite does not have an integrated compass you must use a bearing compass or a compass where you can take a sighting on a distant point and read its direction. Take this sighting from the location of your theodolite and note its bearing. If your declination is East add the degrees of declination to the bearing you read off your compass. Set this value on the azimuth scale of your theodolite and engage the tangent screw. If your local declination is West than subtract this value from the bearing. For example if I see a tower on the horizon at 87 degrees, I add 14.2 (my local declination) and set my azimuth to 101.2 degrees and engage the tangent screw. After engaging the tangent screw loosen the wing screw on the theodolite base and rotate the base so that you can site the object of known bearing in the cross hairs of the theodolite. Use the elevation tangent screw to get the object vertically aligned and rotate the base of the theodolite for horizontal alignment. When you are very close to centered horizontally tighten the wing screw. Use the slow motion control on the base to finish the centering. Once this step is complete the theodolite’s azimuth circle is oriented to true north.

The theodolite is now level, oriented and ready for use!