A dropsonde is an expendable weather reconnaissance device created by the National Center for Atmospheric Research (NCAR), designed to be dropped from an aircraft at altitude to more accurately measure (and therefore track) tropical storm conditions as the device falls to the surface. The sonde contains a GPS receiver, along with pressure, temperature, and humidity (PTH) sensors to capture atmospheric profiles and thermodynamic data. It typically relays these data to a computer in the aircraft by radio transmission.