In this paper, we report a new method for calculating the S-NPP VIIRS Day-Night-Band (DNB) detector dark offsets and gains look-up-tables. During the seven years of S-NPP operation, the NASA VIIRS Characterization Support Team (VCST) has generated detector gain and dark offset calibration coefficients to be used in the DNB L1B Earth view radiance retrieval.[1,2] There have been a few calibration algorithm updates during the mission, however, those changes were only applied to the L1B forward processing. In preparation for reprocessing the L1B data for the entire mission using a consistent calibration method, we have regenerated the DNB gains and dark offset coefficients for the entire mission by integrating all the algorithm updates. The newly obtained gain and dark offset coefficients curve fits as functions of time are smoother than the previous versions. The amplitude of the oscillatory features in the high gain stage calibration fits have been greatly reduced. The preliminary test results show improvements on the DNB Earth view images as expected.
KEYWORDS: Calibration, Sensors, Long wavelength infrared, Data analysis, Temperature metrology, Satellites, Black bodies, Infrared imaging, Infrared sensors, Mid-IR
The VIIRS instrument onboard the NOAA-20 satellite (launched on November 18, 2017) started to collect Earth-view data after its nadir door opened on December 13, 2017. Seven of the VIIRS bands, I4-5 and M12-16 are thermal emissive bands (TEBs), covering a spectral range from 3.6 to 12.5 μm. They began collecting valid data after the cold focal plane assembly (CFPA) cooled down to its nominal operating temperature on January 6, 2018. This paper will present the performance of each TEB, including calibration coefficients, noise equivalent differential temperature (NEdT), on-orbit calibration coefficient estimates from scheduled onboard blackbody warm-up and cool-down (WUCD) data, as well as related telemetry temperatures. Several methods are tested and compared in the WUCD data analysis for estimating the calibration coefficients. Based on the preliminary results, the NEdT of each band is well below the design specification and very close to that of the VIIRS onboard the Suomi National Polar-orbiting Partnership (SNPP) satellite. The detector gains appear stable for bands on the short- and mid-wave infrared CFPA, whereas the detector gains have larger than expected degradation for bands on the long-wave infrared CFPA during the early mission. All TEB related telemetry temperatures are stable. The on-orbit performance of NOAA-20 VIIRS TEB is compared with VIIRS onboard the SNPP.
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