Abstract
The unique feature of the Visible Infrared Imager Radiometer Suite (VIIRS) day/night band (DNB) is its ability to take quantitative measurements of low-light scenes at night. In order to monitor the stability of the high gain stage (HGS) of the DNB, nighttime observations over the Dome C site under moonlight are analyzed in this study. The Miller and Turner 2009 (MT2009) lunar irradiance model has been used to simulate lunar illumination over Dome C. However, the MT2009 model does not differentiate the waxing and waning lunar phases. In this paper, the MT-SWC (SeaWiFS Corrected) lunar irradiance model differentiating the waxing and waning lunar phases is derived by correcting the MT2009 model using lunar observations made by the Sea-Viewing Wide Field-of-View Sensor (SeaWiFS). In addition, a top of atmosphere (TOA) bi-directional reflectance distribution function (BRDF) model during nighttime over Dome C is developed to remove the angular dependence from the nighttime TOA reflectance. The long-term stability monitoring of the DNB high-gain stage (HGS) reveals a lower reflectance factor in 2012 in comparison to the following years, which can be traced back to the change in relative spectral response (RSR) of National Oceanic & Atmospheric Administration’s (NOAA’s) Interface Data Processing Segment (IDPS) VIIRS DNB in April 2013. It also shows the radiometric stability of DNB data, with long-term stability of less than 1.58% over the periods from 2013 to 2016. This method can be used to monitor the radiometric stability of other low-light observing sensors using vicarious calibration sites under moonlight illumination.
Highlights
The Visible Infrared Imager Radiometer Suite (VIIRS) onboard the Suomi National Polar-Orbiting Partnership (Suomi-NPP) spacecraft was successfully launched on 28 October 2011 [1]
The MT2009 SeaWiFS Corrected (MT-SWC) lunar irradiance model is derived by correcting the Miller and Turner 2009 (MT2009) model using lunar observations made by Sea-Viewing Wide Field-of-View Sensor (SeaWiFS)
It can be seen that the mean top of atmosphere (TOA) reflectance factor in 2012 is lower by 5.69% than that in the following years from 2013 to 2017, which is in agreement with the trend of daytime observations of day/night band (DNB) over deep convective clouds (DCCs) from 2012 to 2015 [43]
Summary
The Visible Infrared Imager Radiometer Suite (VIIRS) onboard the Suomi National Polar-Orbiting Partnership (Suomi-NPP) spacecraft was successfully launched on 28 October 2011 [1]. A unique feature of the VIIRS DNB sensor is its ability to provide quantitative measurements of low-light scenes over a sun-synchronous orbit 824 km above the earth. It is the first fully-calibrated nighttime low-light panchromatic channel covering wavelengths from 500 to 900 nm. The primary mission of DNB is to provide sensor data records (SDR) of clouds and other Earth features over illumination levels ranging from full sunlight to quarter moon [7,8] This wide dynamic range of radiance measurements made by DNB is possible through three gain stages: low-gain (LGS), mid-gain (MGS), and high-gain (HGS). The MGS values are determined by multiplying the LGS gains with the MGS/LGS and the HGS values are obtained by multiplying the MGS gains with the HGS/MGS gain ratios [9,10]
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