NOAA-20 VIIRS thermal emissive bands on-orbit performance

Abstract

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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“…At 210K, the noise equivalent delta temperature (NEdT) for the VIIRS I5 band is 0.32K. Assuming the noise is independent of temperature, at 162K the NEdT will be ∼1.8K (Li, Xiong, McIntire, Angal, et al., 2018).…”

“…These coefficients are based on pre‐launch tests against a calibration target. On orbit, they are adjusted through measurements of an onboard black body, which is around 267K for VIIRS (Li, Xiong, McIntire, & Wu, 2018), and deep space that presents a radiance of near‐zero. As no specific calibration has been performed for the temperatures discussed in this study, it is hard to estimate the uncertainty in the calibration, but due to the use of a deep space target we expect it to be small.…”