Sensitivity studies toward the retrieval of ice crystal habit distributions inside cirrus clouds from upwelling far infrared spectral radiance observations

•Introduction to the modelling of the cirrus clouds infrared spectral radiances by using mixtures of different crystal habits.•Sensitivity study to the ice crystal habits of the upwelling infrared spectral observations simulated for the future ESA ninth Earth Explorer mission, named far-infrared outgoing radiation understanding and monitoring (FORUM).•Presentation of the new approach to retrieve the coefficients of the crystal habit distribution.