Seasonal Radiometric Assessment of NOAA-21 CrIS Operational SDR Using COSMIC-2 Radio Occultation Retrievals

The NOAA-21 CrIS sensor data record (SDR) products have been reliably produced by the Joint Polar Satellite System (JPSS) interface data processing segment (IDPS) since the first science data on February 10, 2023 and have provided critical capabilities needed for numerical weather forecasting and environmental monitoring. It is required for the NOAA-21 CrIS SDR products to achieve long-term radiometric stability and consistency with the CrIS sensors on S-NPP and NOAA-20. One quantitative method of assessing the long-term radiometric performance of CrIS SDR products is to use the collocated CrIS observations and the Constellation Observing System for Meteorology, Ionosphere, and Climate 2 (COSMIC-2) radio occultation (RO) retrievals and to compare the observations with the Community Radiative Transfer Model (CRTM) simulations using the COSMIC-2 RO retrieved profiles as input. Due to the slanted path of the RO data product, the 2211 CrIS channels are divided into three groups for spatial collocation based on the channel weighting function peak altitude. The inter-comparison for the stratospheric channels (the weighting function peak altitude > 15 km) is performed using the simulations over oceans to minimize the simulation uncertainty. Similar brightness temperature comparisons are performed for the upper tropospheric channels (the weighting function peak between 7 and 15 km) and the lower tropospheric channels (the weighting function peak below 7 km) but using the simulations over oceans and clear-sky condition. This paper will present time series of the daily inter-comparison results from the first light of the NOAA-21 CrIS observations for all stratospheric channels and selected upper and lower tropospheric channels. The double differences between NOAA-21 and NOAA-20 CrIS observations using the simulations as a transfer target will also be presented to show the seasonal radiometric consistency between the two CrIS sensors. The challenges and lesson-learned in the implementation of this method as a continuing monitoring tool for CrIS sensors will be discussed as well.

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