A pilot measures the wind while flying by measuring the difference between progress through the air with progress across the ground.
Progress through the air is measured essentially by compass and instruments measuring air pressure (speed and altitude) and temperature (for air density measurement).
- Direction of travel - heading - measured by a compass.
- Speed of travel - True Air Speed, TAS - measured by the airspeed indicator, corrected by calculations involving altimeter and thermometer.
Progress across the ground is measured by getting two fixes a distance apart and assessing average direction of travel and average speed. There’s a wide range of techniques available.
- Direction of travel - track - measured by direct observation with a map, or by GPS, or by ground-based radio navigation aids (VOR, NDB etc), or by other more sophisticated systems such as Doppler radar.
- Speed of travel - Ground Speed, GS - measured by direct observation with a map and a timing device, or by ground-based radio navigations aids (DME, VOR cross-bearings), etc.