French Expert of 
Upper Air Observation

Upper Air Observation also called Radiosounding is the only in-situ measurement process performed in the Upper Air (from ground to approx. 30 km). The radiosonde consists of an airborne device equipped with a set of sensors, that is released into the atmosphere under a latex balloon. The ascent usually lasts between one and two hours and allows to draw a vertical profile of the atmosphere. These soundings are called PTU-W type, because it measures the following physical parameters: P (pressure), T (temperature), U (humidity), as well as the parameter WF (wind force) and WD (wind direction). The data is sent by radiotelemetry to the ground and processing station. Sometimes specific sensors are added (stratospheric ozone measurements, for example).

 By extension, the term radiosonde also refers to all the launching operations, the follow-up of the sonde as well as the display in real-time or again the dissemination of the results.