Abstract
In this study, the observations from S-NPP VIIRS Day-Night band (DNB) and Moderate resolution bands (M bands) of Libya 4 and Dome C over the first four years of the mission are used to assess the DNB low gain calibration stability. The Sensor Data Records produced by NASA Land Product Evaluation and Algorithm Testing Element (PEATE) are acquired from nearly nadir overpasses for Libya 4 desert and Dome C snow surfaces. A kernel-driven bidirectional reflectance distribution function (BRDF) correction model is used for both Libya 4 and Dome C sites to correct the surface BRDF influence. At both sites, the simulated top-of-atmosphere (TOA) DNB reflectances based on SCIAMACHY spectral data are compared with Land PEATE TOA reflectances based on modulated Relative Spectral Response (RSR). In the Libya 4 site, the results indicate a decrease of 1.03% in Land PEATE TOA reflectance and a decrease of 1.01% in SCIAMACHY derived TOA reflectance over the period from April 2012 to January 2016. In the Dome C site, the decreases are 0.29% and 0.14%, respectively. The consistency between SCIAMACHY and Land PEATE data trends is good. The small difference between SCIAMACHY and Land PEATE derived TOA reflectances could be caused by changes in the surface targets, atmosphere status, and on-orbit calibration. The reflectances and radiances of Land PEATE DNB are also compared with matching M bands and the integral M bands based on M4, M5, and M7. The fitting trends of the DNB to integral M bands ratios indicate a 0.75% decrease at the Libya 4 site and a 1.89% decrease at the Dome C site. Part of the difference is due to an insufficient number of sampled bands available within the DNB wavelength range. The above results indicate that the Land PEATE VIIRS DNB product is accurate and stable. The methods used in this study can be used on other satellite instruments to provide quantitative assessments for calibration stability.
Highlights
The reflectances and radiances of Land Product Evaluation and Algorithm Testing Element (PEATE) Day-Night band (DNB) are compared with matching Moderate resolution bands (M bands) and the integral M bands based on M4, M5, and M7
We use the first three full years available Relative Spectral Response (RSR) corrected Visible Infrared Imaging Radiometer Suite (VIIRS) DNB and M bands radiance/reflectance data (derived from Equations (2), (5), (8) and (9)) as the training data set in the kernel-driven bidirectional reflectance distribution function (BRDF) correction model to cover a complete seasonal oscillation cycle
Because of the DNB wide wavelength range, the DNB observed solar irradiance is quite sensitive to the incoming radiative spectrum as well as the RSR
Summary
The Suomi National Polar-orbiting Partnership (S-NPP) is one of the modern Earth-orbiting. Heritage, and is a wide-swath (3034 km), cross-track scanning radiometer which observes the Earth’s surface in 22 visible and infrared spectral bands (0.4–12.5 μm). Among the RSB, the DNB on VIIRS is a visible/near-infrared panchromatic band, which can observe the Earth during both daytime and nighttime. The spatial resolution of the DNB is 750 m at nadir and there are 32 aggregation zones through each half of the instrument swath on either side of nadir These aggregation zones are designed to maintain a near 750 m spatial resolution for pixels away from the nadir. In order to provide imagery of clouds and Earth targets from full sunlight to quarter moon illumination status, the DNB comprises three gain stages: the low gain stage (LGS), the medium gain stage (MGS), and the high gain stage (HGS).
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