## 2 Joint Polar Satellite System
The VIIRS supports operational environmental monitoring and numerical weather forecasting, with 22 imaging and radiometric bands covering wavelengths from 0.41 to 12.5 microns [6], providing the sensor data records more than twenty environmental data records, including clouds, sea surface temperature, ocean color, polar wind, vegetation fraction, aerosol [7], fire, snow and ice, vegetation, and other applications. The Ozone Mapping Profiler Suite (OMPS) is composed of three spectrometers: a nadir mapper for total column ozone, a nadir profiler, and a limb profiler for ozone profiling. Since this article is about OMPS radiance assimilation, we will introduce the OMPS sensor data record in detail in the next section. The CERES is a three-channel radiometer [8], measuring radiance at a shortwave channel (0.3-5.0 \(\upmu\)m), a total channel (0.3-\(>\)50 \(\upmu\)m), and an infrared window channel (8-12 \(\upmu\)m). CERES products contain estimates of instantaneous filtered radiance, unfiltered radiance, flux at the top of the atmosphere (TOA), and scene type (see [[https://www.nasa.gov/feature/langley/ceres-at-20-a-continuous-record-of-earths-radiation-budget](https://www.nasa.gov/feature/langley/ceres-at-20-a-continuous-record-of-earths-radiation-budget)]([https://www.nasa.gov/feature/langley/ceres-at-20-a-continuous-record-of-earths-radiation-budget](https://www.nasa.gov/feature/langley/ceres-at-20-a-continuous-record-of-earths-radiation-budget)), accessed on 25 August 2021). SNPP and all JPSS satellites carry multiple sensors, simultaneously observing the Earth from the ultraviolet spectrum to visible, infrared, and microwaves. For historical reasons and heritage, the OMPS sensor data record (SDR) data uses a radiance unit of \(\mathrm{Wcm^{-3}sr^{-1}}\). The VIIRS SDR uses a radiance unit of \(\mathrm{mWm^{-2}sr^{-1}nm^{-1}}\). The unit used for the VIIRS SDR and OMPS SDR is equivalent or the same. Both CrIS and ATMS SDRs use a radiance unit of \(\mathrm{mWm^{-2}sr^{-1}cm^{-1}}\), which is the same as the unit used by numerical weather prediction (NWP) centers. Using a CRTM utility tool, we converted CrIS and ATMS radiance to the same unit as OMPS and VIIRS [9]. Figure 1 shows radiances of the OMPS nadir profiler (black line, NP) and the OMPS Nadir Mapper for total column ozone (blue line, NM), the VIIRS bands (red triangles, VIIRS) of a moderate spatial resolution, and the CrIS (black line, infrared) over the Libya desert I site on 2 March 2021. To display the figure of entire radiance clearly, we plotted the OMPS NP and NM radiances as well as the VIIRS radiance in reflective bands on the top panel of Figure 1. It is noted that VIIRS channel 6 over desert may be saturated because of the small dynamic range since the primary use of VIIRS channel 6 is over oceans. The VIIRS infrared radiance (red triangles) and CrIS radiance (black) are displayed on the middle panel. The green spectral line is the CrIS inner spectral gap filling using the CrIS gap filling algorithm [10]. The extrapolated CrIS spectrum to shortwaves beyond 2550 cm\({}^{-1}\) is not displayed here because of strong solar radiation contamination. Even though no new information is added, the CrIS spectral gap filling is still quite useful for us to compare the CrIS observations with the VIIRS broadband measurements. The collocated VIIRS measurements averaged over the CrIS field of view and the simulated VIIRS observations through the spectral convolution of the CrIS radiances with the VIIRS sensor response function data have been successfully used to estimate the CrIS geolocation accuracy [11]. The ATMS radiances for 22 channels are shown in the bottom panel. One may notice that the SNPP radiance changes from more than 200 mW\({}^{-2}\)sr\({}^{-1}\)nm\({}^{-1}\) for VIIRS channel 5 centered at 670 nm (i.e., 14,925 cm\({}^{-1}\)) and downward 10\({}^{-10}\) mW\({}^{-2}\)sr\({}^{-1}\)nm\({}^{-1}\) for ATMS channel 1 at 23.8 GHz. Even for ATMS itself, the dynamic range of radiance is more than 1000 times. This is also true for the CrIS radiance itself.