GPS Dropsondes are instruments deployed from aircraft to measure temperature, humidity, pressure, and especially winds between flight level and the surface. Use of the Global Positioning System for wind finding is a technical revolution. The sonde moves with the horizontal wind as it falls at 10 m/s (2000 ft/min) so that the wind can be determined from the Doppler shifts of the GPS signals. It carries capacitive temperature, moisture, and pressure sensors. Readings are telemetered to the airplane at half second intervals. Vertical resolution for all measurements is 5 m. The model illustrated was new in 1996. With its finer vertical resolution, superior thermodynamic sensors, and GPS navigation, it is a great improvement over earlier versions. It promises to revolutionize understanding of hurricane motion and intensity change.