Meteorological radiosonde balloon being released. OCEANOGRAPHER around the world cruise 1967. A radiosonde (Sonde is French for probe) is a unit for use in weather balloons that measures various atmospheric parameters and transmits them to a fixed receiver. A rubber or latex balloon filled with either helium or hydrogen lifts the device up through the atmosphere. The maximum altitude to which the balloon ascends is determined by the diameter and thickness of the balloon. Balloon sizes can range from 3.5 to 110 ounces. As the balloon ascends through the atmosphere, the pressure decreases, causing the balloon to expand. Eventually, the balloon will expand to the extent that its skin will break, terminating the ascent.