During Fall 2019, the FORUM mission was selected for being the 9th ESA Earth Explorer mission. FORUM will measure globally the Earth emitted Far-infrared spectrum between 100 and 1600 cm-1 (6.25 to 100 μm). This measurement will improve the understanding of the climate system by supplying for the first time most of the spectral features of the far-infrared contribution to the Earth radiation budget, particularly focusing on the water vapour contribution related to the continuum absorption in the rotational band, the cirrus cloud properties and the ice/snow surface emissivity.
HYGEOS is pleased to have participated to prepare the FORUM candidature in support of the Laboratoire d'Optique Atmosphérique. We developped a cloud retrieval algorithm focusing on ice clouds and showing that the information content from FORUM measurements should be sufficient to retrieve (i) the ice water path (i.e. total quantity of ice), (ii) the ice particle effective radius, the (iii) the cloud top altitude and eventually (iv) the cloud geometrical thickness. This algorithm uses an optimal estimation approach and was tested using synthetic data representative of various conditions encountered at global scale.