QUANTIFYING RADIOSONDE SPATIAL AND TEMPORAL REPRESENTATIVENESS FOR VICARIOUS ICI/MWI CALIBRATION UNCERTAINTY

D. Cimini¹, F. De Angelis², F. Di Paola¹, S. Gentile¹, T. Hewison², S. Larosa¹, F. Madonna³, V. Mattioli², E. Ricciardelli¹, F. Romano¹, M. Viggiano¹

¹CNR-IMAA, ²EUMETSAT, ³Univ. Sannio

The Microwave Imager (MWI) and Ice Cloud Imager (ICI) are two conically scanning radiometers part of the EUMETSAT Polar System Second Generation (EPS-SG) program that will provide continuity of observations of the current EPS in the timeframe from 2026 onward. The combined use of MWI and ICI radiometers will provide an unprecedented set of microwave passive measurements, from 18 up to 664GHz.

The vicarious calibration is a post-launch calibration analysis based on the comparison against one or more reference observations, such as observations from well-calibrated sensors aboard other satellites. However, since several channels of the MWI/ICI suite are unprecedented, their vicarious calibration can only be performed indirectly, particularly against simulated clear-sky observations obtained by radiative transfer computations of atmospheric thermodynamical profiles measured by radiosondes (RS).

To this aim, EUMETSAT funded a study to develop a tool for the VIcarious Calibration for MWI and ICI using RadioSoundings (VICIRS). The VICIRS tool was designed to consider RS from the high-quality low-density Global Climate Observing System (GCOS) Reference Upper-Air Network (GRUAN) archive, as well as from a more comprehensive and higher-density archive, the Radiosounding HARMonization (RHARM) data set. NWP profiles are also handled to fill the gap of surface parameters and data above the RS top levels. In addition, NWP data are used to estimate the spatial and temporal representativeness uncertainty affecting the measurements of each RS launch, which is needed to evaluate the total uncertainty of the vicarious calibration. This contribution presents how NWP data are used to characterize the spatial and temporal representativeness uncertainty of each RS to be considered in the overall uncertainty budget of the post-launch vicarious calibration of ICI/MWI.