MiRS Rain Rate Retrievals from ATMS Onboard S-NPP and NOAA-20

NOAA-20 is the first of NOAA’s latest generation of U.S. polar-orbiting satellites of the Joint Polar Satellite System (JPSS). NOAA-20 was launched on November 18, 2017 and joined the Suomi National Polar-orbiting Partnership satellite (S-NPP) in the same orbit. S-NPP was launched on October 18, 2011. NOAA-20 operates about 50 minutes ahead of S-NPP, allowing important overlap in observational coverage. The Advanced Technology Microwave Sounder (ATMS) instrument is onboard both NOAA-20 and S-NPP, with 22 channels operating in a cross-track mode, providing observations needed to retrieve atmospheric temperature and moisture profiles, hydrometeors, and surface parameters.

The MiRS is a 1-DVAR physically-based algorithm using microwave measurements as input that minimizes a two-term cost function that simultaneously measures both the weighted departure from an a priori background and the degree of fit of simulated radiances with the observations. The forward model used in MiRS is the Community Radiative Transfer Model (CRTM). The MiRS rain rate is calculated from an empirical relationship between rain and vertical integration of retrieved precipitation parameter (hydrometeor) profiles.

In this presentation we use NOAA’s Microwave Integrated Retrieval System (MiRS) to retrieve rain rate over the CONUS from NOAA-20 and S-NPP ATMS observations for the period from December 1^st 2017 to December 31^st 2018. As part of ongoing calibration and validation activities, operational Stage-IV hourly rain rates were collocated each day with both satellites and used as a reference dataset. Performance of hourly, monthly, seasonal, annual rain will be compared between the two satellites. Regional performance will also be evaluated. Performance metrics will include statistical analysis, categorical skill scores, and spatial analysis using accumulated rainfall maps. Preliminary results indicate that the two satellites show comparable performance. In-depth analyses will be available at the time of meeting.