Airliners measure various parameters such as temperature, wind direction, humidity and turbulence. This allows for valuable information to be collected from the free atmosphere which is primarily used in real time by airlines and weather services.
The Aircraft Meteorological Data Relay (AMDAR) programme was launched in 1991 by the World Meteorological Organization, which has coordinated it ever since. The programme comprises a global monitoring network for the collection of meteorological data by aircraft. Around 40 airlines participate in the programme, including Air France, American Airlines, British Airways, Lufthansa and United Airlines. The on-board sensors of commercial aircraft are used here to determine the temperature, air pressure, wind direction and wind speed along the flight paths. Humidity and turbulence measurements are also increasingly being taken.
The data is pre-processed on board the aircraft before being transmitted to a receiver on Earth via radio waves or satellite. On the ground, the data are collected, checked and prepared for users (primarily for airlines and weather services). MeteoSwiss requires this information for assimilation and verification of the ICON numerical weather model.
The measurements taken by aircraft are very useful. On the one hand, they provide data in areas where there are no monitoring stations – similar programmes are also run with ships and buoys. On the other, information from the free atmosphere is gathered, where practically no other measurements are otherwise taken. During take-off and landing, the sensors also provide information on the stratification of the atmosphere and thus supplement/increase the density of the radio sounding monitoring network.
More recently, there has been increasing interest in novel methods for gathering aircraft-based observations, especially mode-selective (Mode-S) enhanced surveillance (EHS)-derived data allowing estimates of wind and temperature at the aircraft’s location.