The Global Positioning System (GPS) dropwindsonde is frequently just called a dropsonde. This cylindrical instrument package is roughly 7 cm (2.75 in) in diameter, 40 cm (16 in) long, and weighs about 0.4 kg (0.86 lb). The instrument package is released from the aircraft and falls through the storm via a parachute, making and transmitting measurements of temperature, pressure, winds, and humidity every half-second.