Tracking pilot balloon with theodolite. Women's first opportunities in meteorology occurred as a result of WWII. Circa 1944. A pilot balloon is a meteorological balloon used to observe air currents. A theodolite is an optical instrument used to measure angles in surveying, meteorology, and navigation. In meteorology, it is used to track the motion of a weather balloon by measuring its elevation and azimuth angle. The earliest theodolite consisted of a small mounted telescope that rotated horizontally and vertically; modern versions are sophisticated computerized devices, capable of tracking weather balloons, airplanes, and other moving objects, at distances of up to 20,000 m (65,600 ft).