Orbital Variation of Blackbody Thermistor Temperature for S‐NPP VIIRS Thermal Emissive Band Calibration

The Thermal Emissive Bands (TEBs) on S-NPP VIIRS are calibrated with an onboard calibrator blackbody (BB). The BB temperature is controlled using heater elements and thermistors. The calibration algorithm, based on the measured BB temperature, emissivity, and spaceview, computes the blackbody radiances and relates them to counts to determine the gain. The TEB calibration can be affected by the thermal dynamics of the VIIRS instrument components and surrounding environment. It is observed that two of the platinum resistance thermometers (PRT) on the BB have an orbital temperature variation of ~0.03K. This behavior reflects non-uniform variations in the effective temperature of the BB-radiating surface. We investigated characteristics of orbital variation of PRT temperature and found that this orbital variation existed before the opening of the nadir door. In addition, analysis of occurrence of maximum orbital temperature change of PRT shows that peak PRT temperature variations occur at the day time. These analyses suggest that the orbital variation of the PRT temperature is likely due to the non-uniform warming up of the instrument during the solar illumination on the instrument during the day. Correlational analysis of orbital variation of PRT temperature with TEB radiometric measurements of BB and its effects on the NEDN of TEB measurements will also be given and discussed