Applications of STAR Integrated Calibration/Validation Monitoring System for Long-Term Inter-Sensor Radiometric Bias Stability Monitoring among SNPP, NOAA-20, NOAA-21, and Legacy NOAA Instruments

The Integrated Calibration/Validation System (ICVS) web-based monitoring system in the Center for Satellite Applications and Research (STAR) (https://www.star.nesdis.noaa.gov/icvs/) has been operating in near-real time (NRT) mode for over ten years. In recent years, its capabilities have been significantly increasing over time, both in terms of the number of satellite instruments and the amount of instrument parameters being monitored. In particular, a new portal within the ICVS, the Long-Term Performance Assessment Sub-System on Inter-sensor Radiance Difference (LTPAS-IRD), has been well established to provide supplemental data quality information to sensor calibration scientists and the broad user community. The involved POES NOAA instruments include five JPSS instruments (OMPS-NM, OMPS-NP, ATMS, CrIS, and VIIRS) onboard the SNPP and NOAA-20 and NOAA-21satellites, as well as an AMSU-A instrument onboard legacy NOAA and Metop satellites.

This study first presents the LTPAS-IRD associated with three inter-sensor comparison components. The first component is the JPSS instrument inter-sensor comparison, including each of the abovementioned five JPSS instruments onboard the SNPP, NOAA-20 and NOAA-21 satellites. The other two components are the LEO-LEO and LEO-GEO inter-sensor comparison, currently covering the following pairs of instruments: OMPS-NM vs. GOME-2, ATMS vs. AMSU-A, CrIS vs. ABI, CrIS vs. IASI, and VIIRS vs. ABI. The JPSS instruments are categorized as an independent component, separate from the LEO-LEO component, to highlight their significance in supporting JPSS missions. The LTPAS-IRD employs four existing methods: Simultaneous Nadir Overpass (SNO) (Cao et al., 2004); Sensor-double difference (DD), which uses a third sensor on a different satellite as a transfer and is based on various SNO measurements; CRTM-DD, which uses the Joint Center for Satellite Data Assimilation (JCSDA) Community Radiative Transfer Model (CRTM) (Han et al., 2006; Liu and Cao, 2019) as a transfer; and 32D-AD (32-day averaged difference) (Yan et al., 2021). The use of multiple methods leverages the advantage of each in term of geographical coverage and channel usage for inter-sensor radiance difference assessment, therefore improving the detection of spacecraft anomaly or calibration issues affecting the quality of SDR data.

This study further explores several applications of the LTPAS-IRD to assess long-term (LT) inter-sensor radiometric bias stability among various instrument pairs. The first application, which is about the JPSS instrument inter-sensor comparisoncomponent, evaluates the LT performance of globally averaged inter-sensor radiance biases across all wavelengths for the five JPSS instruments, using one or more of the four methods. The results generally indicate LT stability of SDR data for these instruments, especially after the validated maturity review, with some exceptions due to satellite spacecraft issues. These findings are consistent with those reported by JPSS SDR calibration scientists. Additionally, the 32D-AD method demonstrates its advantages over the other three methods in terms of channel and geographical coverage. It also relies solely on SDR data for computation, without requiring pre-launch measurement data such as instrument spectral response functions in the CRTM. Consequently, the 32D-AD results help capture a deficiency in the CRTM simulation for ATMS brightness temperatures that was caused by using boxcar-assumed SRFs in CRTM (Sun et al., 2024). The 32D-AD method also successfully identifies other calibration problems in OMPS SDR data, such as the solar intrusion into NOAA-20 OMPS-NP at short wavelengths over the Northern Hemisphere and solar flux pre-launch calibration errors in NOAA-21 OMPS NM. The other three applications are related to the LEO-LEO and LEO-GEO components. One application is to evaluate the LT stability of the TDR data from NOAA-19 AMSU-A and Metop-C AMSU-A against SNPP ATMS data using the SNO method. This supports climate change analyses, as AMSU-A observations continually play an important role in atmospheric temperature climate trend analysis. The second application monitors the inter-sensor comparison between SNPP OMPS-NM and Metop-B GOMES-2 using the SNO method, where a significant degradation was detected in GOME-2. The final application evaluates the LT stability of the SNPP CrIS SDR data in comparison with GOES-16 and GOES-18. It detects the impact of the 2^nd SNPP GPS problem on SNPP CrIS SDR data quality, which occurred in July 2024.

In summary, the new ICVS LTPAS-IRD portal has demonstrated its scientific potential in effectively monitoring the LT stability of inter-sensor radiometric calibration biases among the JPSS instruments and legacy NOAA and Metop AMSU-A instrument using multiple analysis methods. The portal is currently being enhanced with new functions and improvements to fill in gaps in the LT monitoring record to better support JPSS missions and the broad user community. Therefore, the ICVS LTPAS-IRD portal with these ongoing enhancements will further benefit JPSS and GOES calibration scientists, and non-NOAA users, including the Global Space-Based Inter-Calibration System (GSICS) user community. Additionally, the ideas of using multiple methods for the same pair of instrument observations are applicable to LT monitoring and performance assessment of non-NOAA satellites.

Disclaimer: the presentation contents are solely the opinions of the authors and do not constitute a statement of policy, decision, or position on behalf of NOAA or the U. S. Government.

Acknowledgement: thank Jingfeng Huan for his long-term contributions to the ICVS VIIRS monitoring sub-system development and maintenance. The project is partially funded by the JPSS program.