The European AQUA Thermodynamic Experiment (EAQUATE) brought together collocated hyperspectral measurements from the Atmospheric Infrared Sounder (AIRS) on NASA’s Aqua satellite, as well as three airborne interferometers operating in the troposphere and stratosphere. Simultaneous observations of temperature, water vapour and trace gases have been used to constrain the atmospheric state, for validation of radiometric accuracy and radiative transfer modelling. The close agreement of observations with model spectra, in the 800–1200 cm−1 region, indicates that the accuracy of modelling AIRS spectra is sufficient for beneficial use of the data in operational weather forecasting. The variability of atmospheric water vapour was found to be a fundamental constraint in the modelling of the 1400–1600 cm−1 region, emphasising the requirement for a high density of observations in future validation campaigns. Copyright " c Royal Meterological Society and Crown Copyright, 2009.