Position determination methods used to track superpressure balloons

International audienceThe method that has been used in the past to determine the position of superpressure balloons employed in long- term meteorological and technological experiments-projects GHOST (Global Horizontal Sounding Technique), EOLE (French, God of the Winds), SOMEX (Solar Monitoring Experiment), ctc.-was to measure the solar elevation during the daylight hours and then compute the balloon position at local noon: latitude by the noon solar altitude and longitude by the time of balloon noon. This method has disadvantages: it requires a lengthy series of measure ments during the day and has degraded accuracy when the maximum solar angle approaches 90’. Another method was therefore devised in which the solar angle data are complemented by data that indicate the local geomagnetic rigidity; the correlation of the two data yields an improved position determination algorithm. This method was applied to the trajectory determination of the SOMEX balloons with considerable success