VIIRS day/night band radiometric calibration stability monitoring using the Moon

Abstract

The Visible Infrared Imaging Radiometer Suite (VIIRS) is a passive scanning spectroradiometer on board the Suomi‐NPP satellite. It has 22 spectral bands including the day/night band (DNB), which is a panchromatic reflective solar band (RSB) covering a wavelength range of 500–900 nm. Similar to other RSBs, the radiometric calibration of the DNB is in reference to the sunlight reflected from an onboard solar diffuser (SD). As an independent validation to the SD measurement, lunar calibration has been regularly scheduled at nearly constant lunar phase. In this paper, the lunar calibration strategies developed for RSB are extended to DNB. The on‐orbit gain coefficient, or the so‐called F factor, is derived for DNB low‐gain stage (LGS) from lunar data for each lunar calibration event. Its on‐orbit change is compared with the change of the LGS SD F factor. For more accurate comparison, the impact of the on‐orbit relative spectral responses (RSR) change, caused by the wavelength‐dependent degradation of the optical throughput of VIIRS telescope mirrors, must be considered. This impact is more significant for DNB than other RSBs because of its wider bandwidth, and the impact to the SD and lunar calibrations are different due to different scene spectra. Simulation results show a gradually increased deviation of 1% between SD and lunar trends since launch till now and 0.3% deviation since 2 April 2012 lunar calibration, when the lunar F factor was firstly calculated, till now. Taking this effect into account, the on‐orbit changes of the SD F factor and lunar F factor agree with each other in less than 0.3%. Our results validate the stability of the DNB SD calibration while demonstrating how the on‐orbit RSR change should be considered in the radiometric calibration and data usage.

Artificially lit surface of Earth at night increasing in radiance and extent

“…This should be further investigated, but we note that it could potentially be due to a complete lack of cloud-free observations in some of their study areas, or perhaps more likely, an interaction in their model between location, cloud cover, and season. Long-term changes in the radiometric calibration of the DNB itself are well understood and corrected ( 43 ).…”

Improved NOAA-20 Visible Infrared Imaging Radiometer Suite Day/Night Band Image Quality by Upgraded Gain Calibration

“…The LGS gain coefficient either stored in the LUT or produced by RSBAutoCal is determined by using the onboard SD data described in Section 2. Calibration stability of the VIIRS DNB is actively monitored by various methods, including onboard SD [33,34], deep convective clouds [35,36], lunar observations [37][38][39], and bright stars [40,41]. Unlike the Suomi-NPP VIIRS DNB, the NOAA-20 VIIRS DNB LGS gain is stable since the launch in November 2017.…”

An Improved Method for Destriping of VIIRS Day/Night Band Images

“…The signal-to-noise ratio (SNR) of the VIIRS DNB sensor is increased by four different gain stages based on the time delay integration mode [15], such as 2 High-Gain stages (HGS), one Mid-Gain stage (MGS), and one Low-Gain Stage (LGS). The gain-calibrated data is aggregated into 64 along-scan aggregation zones with an adjustable instantaneous field of view (IFOV).…”

“…The VIIRS DNB sensor records data using a chargecoupled device (CCD) with 672 subpixels detectors, and these data are combined onboard into 16 along-track detectors [15]. Because the detector-to-detector response of these 16 detectors is not equal, periodic horizontal striping effects become pronounced across the scene.…”