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Up Theodolite Setup

Pilot Balloon Observation Site Setup and Considerations

Selection of the observation point
The selection of an observation point for single-theodolite work will be determined by the following:

a. Geographical location

b. Low horizon.

c. Angular altitude of obstructions.

The shape of the earth’s surface and the obstructions on it influence the surface winds and the winds aloft in the lower levels - from the surface to 1,000 or 1,500 meters in elevation. Since we are generally interested the prevailing winds aloft and not extremely localized conditions choosing a site free of surface features and obstructions.

Note: in some situations such as ballooning, hang gliding and possibly fire weather the site is not an ideal under the criteria above. However the reason that soundings may be taken at this location may be to map the localized winds, so the above criteria are not applicable.

An ideal observation point would be in the open, level country, or on the crest of a slight rise. The ground should be form and the position well removed from buildings and tall trees that might interfere with the line of sight upon the balloon. The maximum angular altitude of obstructions such as building and trees should not exceed 6 degrees above level.

In developed areas where satisfactory ground conditions cannot be found, the next preference would be a position on a flat roofed, well-exposed building be aware that buildings can contain wiring systems carrying high current or metal trussing/sheeting that will effect compass readings..

Ideally the location will be large enough so that the balloon can be released a few feet down wind of and level with the theodolite.

Setup of the observation site
The accuracy of a theodolite depends primarily upon the instrument being perfectly level. Set the tripod and instrument on solid level ground. It is desirable to have a stationary platform for the tripod to rest on and to enclose the platform to protect the instrument and observer from wind and gusts. A four foot square or circular enclosure without roof, with walls five feet height and a door opposite the prevailing wind is suggested. A ground support for the tripod for use when the instrument is used repeatedly in the same locations is also recommended.

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Navigation through Pibal Observation Instructions
Table of Contents Introduction Equipment Requirements Observation Site Setup Theodolite Setup
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