Theodolite

My Dad, Chester, a weatherman at the old Sacramento Airport, using a Theodolite. I remember being at work with him when he did this measurement at night. I found this photo nestled in an album with a much later date. I don’t remember seeing it before.

There is a long history of theodolite use in measuring winds aloft, by using specially-manufactured theodolites to track the horizontal and vertical angles of special weather balloons called ceiling balloons or pilot balloons. Early attempts at this were made in the opening years of the nineteenth century, but the instruments and procedures weren’t fully developed until a hundred years later. This method was extensively used in World War II and thereafter, and was gradually replaced by radio and GPS measuring systems from the 1980s onward.

The pibal theodolite uses a prism to bend the optical path by 90 degrees so the operator’s eye position does not change as the elevation is changed through a complete 180 degrees. The theodolite is typically mounted on a rugged steel stand, set up so it is level and pointed north, with the altitude and azimuth scales reading zero degrees. A balloon is released in front of the theodolite, and its position is precisely tracked, usually once a minute. The balloons are carefully constructed and filled, so their rate of ascent can be known fairly accurately in advance. Mathematical calculations on time, rate of ascent, azimuth and angular altitude can produce good estimates of wind speed and direction at various altitudes. (Wikipedia excerpt)