Evaluation of VIIRS Thermal Emissive Bands Long-Term Stability and Inter-Sensor Consistency with Radiative Transfer Modeling

Following the launch of Suomi-NPP (S-NPP) satellite in November 2011, two other Joint Polar Satellite System (JPSS) satellites, namely NOAA-20 and NOAA-21, were launched in November 2017 and November 2022, respectively. These three satellites collectively provide sustained Earth observations over a decade. The Visible Infrared Imaging Radiometer Suite (VIIRS) instruments onboard S-NPP, NOAA-20, and NOAA-21 satellites are designed to provide radiometrically accurate global images across 22 spectral bands ranging from 0.41 to 12.5 μm. The stability and consistency of VIIRS thermal emissive bands (TEBs) are crucial for ensuring the data quality of downstream VIIRS environmental data record products such as sea surface temperature and cloud products.

This work employs radiative transfer modeling (RTM) to conduct two studies with different time scales: The first study evaluates the long-term (2012-2020) stability of the NOAA STAR version 2 reprocessed S-NPP VIIRS moderate-resolution (M12-M16) TEBs data; The second study focuses on analyzing the inter-VIIRS TEB data consistency among S-NPP, NOAA-20, and NOAA-21 over five months in 2023. The Community Radiative Transfer Model (CRTM) is used for the simulation of VIIRS TEB brightness temperatures (BTs) collocated with VIIRS observations. The European Centre for Medium-range Weather Forecasts (ECMWF) global atmospheric reanalysis data such as surface temperature, atmospheric temperature and water vapor profiles are used as inputs to the CRTM. By confining to clear-sky ocean surface between and as the areas of interest, both VIIRS TEB long-term stability from S-NPP and inter-sensor consistency among S-NPP/NOAA-20/NOAA-21 are evaluated in terms of the observation minus background (O-B) BT differences between VIIRS measurements and CRTM simulations.

S-NPP VIIRS monthly O-B BT difference time series from 2012 to 2020 provide the validation of the long-term radiometric stability for the reprocessed S-NPP VIIRS TEB data. In particular, the drifts of the O-B BT differences are found to be all less than 0.09 K/Decade for S-NPP VIIRS bands M12-M16. To assess the inter-sensor consistency among VIIRS TEBs on S-NPP, NOAA-20 and NOAA-21, we calculated the daily O-B BT differences for these three VIIRS sensors over five months from 2023-03-18 to 2023-08-07. Double-difference analyses are carried out by subtracting any pair of O-B BT differences among S-NPP, NOAA-20, and NOAA-21 to calculate the inter-sensor biases and then to evaluate their consistency. Our results show that for all moderate-resolution VIIRS TEBs (excluding M13), the means of inter-VIIRS BT differences all have values < 0.07 K. For M13, the Spectral Response Function (SRF) of NOAA-21 is significantly different from the SRFs of NOAA-20 and S-NPP. As a result, the inter-VIIRS BT differences between NOAA-21 and NOAA-20/S-NPP have values about 0.22 to 0.30 K.

By using CRTM simulation as the transfer reference, the study offers a comprehensive quality evaluation of VIIRS TEB data to assure the consistency among S-NPP, NOAA-20, and NOAA-21. Furthermore, the double-difference approach effectively mitigates uncertainties and biases inherent to CRTM simulations, establishing itself a robust mechanism for assessing inter-sensor consistency. This study demonstrates that the RTM-based TEB quality evaluation method can be applied not only to evaluate the long-term sensor stability, but also to assess inter-sensor consistency.

Acknowledgement: Changyong Cao and NOAA STAR VIIRS radiance team

Disclaimer: The scientific results and conclusions, as well as any views or opinions expressed herein, are those of the author(s) and do not necessarily reflect those of NOAA or the Department of Commerce.