VICARIOUS CALIBRATION FOR MWI AND ICI USING RADIOSOUNDINGS (VICIRS)

E. Ricciardelli¹, C. Accadia², V. Barlakas², F. Carminati³, D. Cimini¹, F. De Angelis², F. Di Paola¹, S. Gentile¹, T. Hewison², S. Larosa¹, F. Madonna⁴, V. Mattioli², F. Romano¹, M. Viggiano¹

¹CNR-IMAA, ²EUMETSAT, ³Met Office, ⁴Università degli Studi di Salerno

The EUMETSAT-funded study VICIRS (“VIcarious Calibration tool for MWI and ICI using RadioSoundings”) developed a software tool (named VICIRS tool) for the vicarious calibration of the two conical-scanning radiometers, the MicroWave Imager (MWI) and the Ice Cloud Imager (ICI), planned to fly from 2026 onwards as part of the EUMETSAT Polar System (EPS) Second-Generation (SG) program (EPS-SG) aboard of the Metop-SGB satellite. The combined use of MWI and ICI radiometers will provide an unprecedented set of microwave passive measurements, from 18.7GHz up to 664GHz, on the same platform. Vicarious calibration using radiosoundings (RS) is particularly important for MWI and ICI channels that are unprecedented and, therefore, cannot be compared with reference observational data from space.

The VICIRS tool has been drawn up to search and collect clear-sky match-ups (MU) between MWI/ICI and 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, homogenized and higher-density archive, the Radiosounding HARMonization (RHARM) data set, which also provides an estimation of the measurement uncertainty at all pressure levels. NWP profiles are also handled to fill the gap of surface parameters and data above the RS top levels. The tool provides a statistical analysis of the difference between observed and simulated brightness temperatures (BTs), considering the total uncertainty emerging from the various sources (e.g., instrumental uncertainties, forward model uncertainties, spatial and temporal mismatches) for each MWI/ICI channel.

This paper will introduce the VICIRS tool design and functionalities, reporting the results obtained testing it with simulated data (MWI/ICI L1B test data product collocated with RHARM), and real observations from a currently operating conical-scanning radiometer (NASA’s Global Precipitation Measurement Microwave Imager (GMI)) and GRUAN/RHARM RS.