Abstract
Aboard the polar-orbiting SNPP satellite, the VIIRS instrument has been in operation since launch in October 2011. It is a visible and infrared radiometer with a unique panchromatic channel capability designated as a day-night band (DNB). This channel covers wavelengths from 0.5 to 0.9 µm and is designed with a near-constant spatial resolution for Earth observations 24 h a day. The DNB operates at 3 gain stages (low, middle, and high) to cover a large dynamic range. An onboard solar diffuser (SD) is used for calibration in the low gain stage, and to enable the derivation of gain ratios between the different stages. In this paper, we present the SNPP VIIRS DNB calibration performed by the NASA VIIRS characterization support team (VCST). The DNB calibration algorithms are described to generate the calibration coefficient look up tables (LUTs) for the latest NASA Level 1B Collection 2 products. We provide an evaluation of DNB on-orbit calibration performance. This activity supports the NASA Earth science community by delivering consistent VIIRS sensor data products via the Land Science Investigator-led Processing Systems, including the SD degradation applied for DNB calibrations in detector gain and gain ratio trending. The DNB stray light contamination and its correction are highlighted. Performance validations are presented using comparisons to the calibration methods employed by NOAA’s operational Interface Data Processing Segment. Further work on stray light corrections is also discussed.
Highlights
It is estimated by an integration of the day-night band (DNB) relative spectral response (RSR), RSR(λ, t), and the reflective solar bands (RSB)-derived solar diffuser stability monitor (SDSM) H-factors; RVSSD denotes the response versus scan angle of the halfangle mirror (HAM) at the solar diffuser (SD) view center; BRDF (λ) denotes the bidirectional reflectance factor of the SD, and was estimated pre-launch using reference samples based on the National Institute of Standards and Technology (NIST) reflectance standards
In this paper we presented a review of the background, methodology, and performance of the DNB, which is part of the Suomi-national polar-orbiting partnership (SNPP) visible infrared imaging radiometer suite (VIIRS) instrument Earth observation portfolio
All gain stages show a gradual decrease, which is driven by the low gain stage (LGS) gain response, as the gain ratios seem to remain stable
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. This paper aims to present a review of the approach that the NASA VIISR Characterization Support Team (VCST) has taken with respect to calibrating and monitoring the trending behavior of the DNB gain responses and background offsets. This approach relies on the constantly collected OBC data from the SD, BB, and SV sectors, with continuous updates of the gain ratios and offset drifts over short- and long-term periods [7,8,9].
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