Noise and Relative Responsivity Trends of the JPSS-1/NOAA-20 and SNPP CrIS Interferometers

On November 18, 2017, the JPSS-1 satellite was launched into orbit and renamed NOAA-20. Included in the instrument suite is the Cross-track Infrared Sounder (CrIS), an interferometer that collects infrared (IR) data used for atmospheric soundings. These soundings provide valuable information for weather forecast models and other applications. CrIS creates radiometrically calibrated spectra at 0.625 cm-1 resolution in three spectral regions from 4 to 15 micrometers. It has a 3x3 focal plane array and a nadir footprint of 14 km. NOAA-20 joined the orbit of its predecessor, Suomi National Polar-orbiting Platform (SNPP), with a half-orbit delay to provide better near-nadir coverage for the globe. Both satellite systems carry a CrIS instrument, with each providing twice-daily global coverage. NOAA-20 CrIS is a copy of the SNPP CrIS instrument with a few electronics upgrades. The SNPP CrIS has performed well over more than six years on orbit and continues to collect valuable data. NOAA-20 CrIS has performed well since data collection began on January 4, 2018, and its data products are in provisional status.

The NOAA-20 CrIS sensor had extensive ground calibration and has been undergoing further on-orbit validation in preparation for advancing its data products to operational status, expected later in 2018 pending the results of final testing. Performance optimization tests while on orbit have resulted in only small changes to a few pre-launch settings due to the robust on-ground calibration. On-orbit noise characterization has shown both SNPP and NOAA-20 CrIS meet instrument specification regarding the Noise Equivalent change in Radiation (NEdN) and have been stable during their respective periods of operation. This presentation will cover the results of NOAA-20 CrIS noise characterization trending while on-orbit, as well as comparisons against SNPP CrIS NEdN. In summary, NOAA-20 CrIS has lower noise levels than SNPP, even when compared to the start of SNPP’s on-orbit operations. However, SNPP has had very stable noise levels, increasing by less than 1% per year. In addition, SNPP has maintained system responsivity very well, with relative responsivity (RR) values within 2% of initial values for all but the shortest wavelengths, which are still within 5% of initial values. RR is calculated as the difference between detector responses when viewing deep space and internal calibration targets. RR for NOAA-20 CrIS remains very good after 7 months of operation, but it has shown slightly faster RR degradation than SNPP at this stage of its lifecycle. The cause of this increased degradation rate is currently being investigated. NEdN and RR have been and will continue to be continuously monitored throughout on-orbit operations for both platforms. The latest updates on NOAA-20 and SNPP CrIS NEdN and RR, along with platform-to-platform comparisons, will be presented.