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Over the past 3 decades, satellite altimetry has been a key tool for dynamic ocean studies and for accurately estimating sea surface heights. The geodetic reference surface—the “geoid”—can be approximated as the mean sea surface height of an ocean corrected for dynamic terms such as tides and currents. It is an equipotential surface of the gravity field; and variations of this field are quantified as free‐air anomalies, from which density heterogeneities of the oceanic basement can be inferred. Using such data in combination with other geophysical data, scientists have improved their knowledge of the nature of submarine relief and underlying structures. In solid Earth geophysics, major breakthroughs came from the development of high‐resolution marine gravity models based on closely spaced altimetry profiles collected during the U.S. Navy's Geosat satellite geodetic mission (launched in 1985) and the first version of the European Remote Sensing satellite geodetic mission (ERS 1, launched in 1991). These were combined with other repetitive profiles from the international TOPEX/ POSEIDON satellite (launched in 1992); ERS 1; TOPEX/POSEIDON's successor, Jason (launched in 2001); and the European Space Agency's (ESA) Envisat missions (ERS's successors [see, e.g., Sandwell and Smith, 1997; Andersen and Knudsen, 1998]).

<p>The EUMETSAT Polar System (EPS) programme is composed of three polar orbiting meteorological METOP satellites. The main payload instrument on-board each METOP is an InfraRed Atmospheric Sounding Interferometer (IASI). METOP-A, the first one of this series, was launched in 2006. Then METOP-B and METOP-C were launched successively in 2012 and 2018. IASI instrument products are disseminated to meteorological institutions for numerical weather prediction, to laboratories for atmospheric and climate studies and also to space agencies for expertise and monitoring. Since their beginning of life, IASI on-board METOP-A and METOP-B continue to perform very well and therefore demonstrate IASI instrument great performances stability and its sturdiness over time. Since July 2019, IASI on-board METOP-C is operational. It will ensure the continuity of good calibrated data dissemination to the user community for the next decade.</p><p>The purpose of this paper is to present the current performances status of the 3 in-flight IASI instruments, up to the Level 1 data. The objective is to give a feedback on the validation and the monitoring performed on IASI instruments during its life time. Moreover, during the past few years, some operational improvements were applied like the update of the on-board non-linerity correction for the 3 instruments. The impact of this new correction will be presented, also the reprocessing of a huge amount of IASI-A data for climate series.</p><p>New improvements will be assessed, like the impact on the spectral calibration monitoring of the new release of the GEISA spectroscopic database and the 4A/OP atlases or improvements of inter-comparison techniques.</p>