Improving the Calibration of Suomi NPP VIIRS Thermal Emissive Bands During Blackbody Warm-Up/Cool-Down

The Suomi National Polar-orbiting Partnership Program Visible Infrared Imaging Radiometer Suite (VIIRS) thermal emissive bands (TEB) have been performing well during nominal operations since launch. However, small but persistent calibration anomalies are observed in all TEBs during the quarterly blackbody (BB) warm-up/cool-down (WUCD) events. As a result, the time series of daytime sea surface temperature (SST) (derived from bands M15–M16) show warm spikes on the order of 0.25 K. This paper suggests that VIIRS TEB WUCD biases are band dependent, with daily-averaged biases about −0.04 and 0.05 K for I4 and I5, and −0.05, −0.05, 0.11, 0.09, and 0.05 K for M12–M16, respectively. Two correction methods—Ltrace and WUCD-C—have been implemented and evaluated using colocated observations from the Cross-track Infrared Sounder (CrIS), radiative transfer simulations, and SST retrievals. Also an error in the National Oceanic and Atmospheric Administration operational processing was identified and fixed. Both correction methods effectively minimize WUCD-induced SST anomalies. The Ltrace method works well for I5, M12, and M14–M16, with residual biases about 0.01 K. The WUCD-C method, on the other hand, performs well to correct WUCD biases in all TEBs, with residual biases also about 0.01 K. However, it introduces warm biases relative to CrIS at cold scene temperatures, which requires further study. Applying nonequal BB thermistor weights improves calibration at BB temperature set points, but its impact on daily-averaged WUCD biases is small. The proposed methodologies may also be applied to the VIIRS onboard the follow-on Joint Polar Satellite System satellites.

I. Introduction

The Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi National Polar-orbiting Partnership (S-NPP) satellite was successfully launched on October 28, 2011. The National Oceanic and Atmospheric Administration (NOAA) VIIRS sensor data records (SDRs), produced operationally by the interface data processing segment (IDPS), became available on January 20, 2012 and achieved validated maturity on March 19, 2014. VIIRS has seven thermal emissive bands (TEBs), including two imagery resolution bands (I4 and I5) and five moderate resolution bands (M12–M16), covering spectral range from 3.697 to . S-NPP VIIRS TEB calibration has been performing well during nominal operations since launch. However, small but persistent calibration anomalies have been observed in all TEBs during the quarterly blackbody (BB) warm-up/cool-down (WUCD) events, which are performed to characterize on-orbit calibration offset and nonlinearity changes over time [1]–[3]. During such events, VIIRS daytime sea surface temperature (SST) product, which uses bands M15 and M16 as primary inputs, becomes anomalous with warm biases shown as spikes in the SST time series on the order of 0.25 K [4] as seen in the NOAA SST Quality Monitor system [5]. Accurate and stable satellite SST data are critical to numerical weather prediction, seasonal, and climate applications. The VIIRS TEB calibration anomalies during WUCD negatively impact the SST analysis according to the users, and therefore need to be addressed to better support these applications.