Assessment of the Consistency and Stability of CrIS Infrared Observations Using COSMIC-2 Radio Occultation Data over Ocean Remote Sensing

The accuracy of brightness temperature (BT) from the Cross-track Infrared Sounder (CrIS) onboard the Suomi National Polar-orbiting Partnership (S-NPP) satellite and NOAA-20 is estimated using the Constellation Observing System for Meteorology, Ionosphere, and Climate 2 (COSMIC-2) radio occultation (RO) wet retrievals (temperature and water vapor profiles) as input to the Community Radiative Transfer Model (CRTM). The matchup criteria between RO and CrIS observations are time less than 30 min, a distance less than 50 km, and over oceans to reduce the collocation and simulation uncertainty. Based on the information provided in the CrIS and RO observations, only upper temperature sounding channels with weighting function peak height (WFPH) above 200 hPa (~12 km) from the CrIS longwave infrared (LWIR) and shortwave infrared (SWIR) bands and water vapor channels from the CrIS mid-wave infrared (MWIR) band with WFPH above 500 hPa (~6.3 km) are selected for comparison to minimize the impacts from the surface emission, cloud absorption/scattering, and atmospheric gaseous absorption. The absolute differences between CrIS observations and their CRTM simulations using RO data as input are less than 1.0 K for the majority of those selected channels. The double differences between CrIS observations on NOAA-20 and S-NPP using CRTM simulations as transfer references are very stable. They range from −0.05 K to 0.15 K for LWIR channels and −0.20 K to 0.10 K for SWIR channels during the two years from 1 October 2019 to 30 September 2021. For MWIR channels, the double differences range from −0.15 K to 0.25 K but have significant variations in both daily mean and monthly mean time series. The results provide ways to understand the qualities of RO retrieval and CrIS measurements: RO data can be used to assess the consistency and stability of CrIS observations quantitatively, and CrIS measurements have the quality to assess the quality and stability of RO retrievals. Grant no. NA19NES4320002

本研究以星载Suomi国家极轨伙伴卫星（Suomi National Polar-orbiting Partnership, S-NPP）与NOAA-20搭载的跨轨红外探测仪（Cross-track Infrared Sounder, CrIS）所获亮温（brightness temperature, BT）的精度评估为目标，采用气象、电离层与气候星座观测系统2号（Constellation Observing System for Meteorology, Ionosphere, and Climate 2, COSMIC-2）无线电掩星（radio occultation, RO）反演得到的温度与水汽廓线作为输入，驱动社区辐射传输模型（Community Radiative Transfer Model, CRTM）开展模拟计算。
观测匹配需满足以下准则：时间差小于30分钟、空间距离小于50公里，且观测区域位于洋面之上，以降低配准与模拟不确定性。
基于CrIS与RO观测的可用信息，仅选取CrIS长波红外（longwave infrared, LWIR）、短波红外（shortwave infrared, SWIR）波段中权重函数峰值高度（weighting function peak height, WFPH）高于200 hPa（约12公里）的高层温度探测通道，以及CrIS中波红外（mid-wave infrared, MWIR）波段中权重函数峰值高度高于500 hPa（约6.3公里）的水汽通道进行对比，以最小化地表发射、云吸收/散射及大气气体吸收带来的影响。
在绝大多数所选通道中，CrIS观测值与以RO数据为输入的CRTM模拟值之间的绝对差值小于1.0 K。
以CRTM模拟结果作为传递参考基准，NOAA-20与S-NPP的CrIS观测值之间的双差值表现出极佳稳定性：在2019年10月1日至2021年9月30日的两年观测周期内，长波红外通道的双差值范围为-0.05 K至0.15 K，短波红外通道为-0.20 K至0.10 K。
对于中波红外通道，双差值范围为-0.15 K至0.25 K，但在日均值与月均值时间序列中均存在显著波动。
本研究结果可为理解无线电掩星反演与CrIS观测的性能提供支撑：RO数据可用于定量评估CrIS观测的一致性与稳定性，而CrIS观测数据也具备评估RO反演结果质量与稳定性的能力。
资助编号：NA19NES4320002