The ABC(t) (Atmosphere-Biosphere-Climatology by remote sensing) : team central theme is the study of climatic variables and processes based on the analysis of radiation emitted and scattered by the atmosphere and the surface, by active and passive remote sensing from the ground and space. In particular, the team has internationally recognised expertise in the analysis of multi-spectral satellite observations and in the development of innovative instruments, based on in-depth knowledge of spectroscopy, advanced modelling of direct and inverse radiative transfer, calibration/validation, various inverse methods (Bayesian, neuronal, etc.), analysis of data over long time series. The resulting restitution and understanding of atmospheric and surface variables is an essential resource for the study of climate variability and evolution as well as for the study of the planet’s radiation balance. They also represent key data for the validation of general circulation models. The scientific themes of the team focus on the study of the characterisation of the atmosphere and continental surfaces using the coupling of passive infrared sounders (at nadir and limbus) and active instruments (lidars): characterisation of greenhouse gases (CO₂, CH₄, H₂O), clouds, dust aerosols and the radiative properties of continental surfaces. In line with its scientific expertise and research themes, the team is strongly involved in the proposal, preparation and operation of space missions, in particular with CNES and ESA. It coordinates activities around the IASI, IASI-NG and Merlin missions, and participates in the MicroCarb, Flex and GeoCarb mission groups.