Abstract
The launch of VIIRS on-board the Suomi-National Polar-orbiting Partnership (S-NPP) on 28 October 2011, marked the beginning of the next chapter on nighttime lights observation started by the Defense Meteorological Satellite Program’s (DMSP) OLS sensor more than two decades ago. The VIIRS observes the nighttime lights on Earth through its day-night band (DNB), a panchromatic channel covering the wavelengths from 500 nm to 900 nm. Compared to its predecessors, the VIIRS DNB has a much improved spatial/temporal resolution, radiometric sensitivity and, more importantly, continuous calibration using on-board calibrators (OBCs). In this paper, we describe the current state of the NASA calibration and characterization methodology used in supporting mission data quality assurance and producing consistent mission-wide sensor data records (SDRs) through NASA’s Land Product Evaluation and Analysis Tool Element (Land PEATE). The NASA calibration method utilizes the OBCs to determine gains, offset drift and sign-to-noise ratio (SNR) over the entire mission. In gain determination, the time-dependent relative spectral response (RSR) is used to correct the optical throughput change over time. A deep space view acquired during an S-NPP pitch maneuver is used to compute the airglow free dark offset for DNB’s high gain stage. The DNB stray light is estimated each month from new-moon dark Earth surface observations to remove the excessive stray light over the day-night terminators. As the VIIRS DNB on-orbit calibration is the first of its kind, the evolution of the calibration methodology is evident when the S-NPP VIIRS’s official calibrations are compared with our latest mission-wide reprocessing. In the future, the DNB calibration methodology is likely to continue evolving, and the mission-wide reprocessing is a key to providing consistently calibrated DNB SDRs for the user community. In the meantime, the NASA Land PEATE provides an alternative source to obtain mission-wide DNB SDR products that are calibrated based on the latest NASA DNB calibration methodology.
Highlights
The VIIRS on the Suomi-National Polar-orbiting Partnership (S-NPP) is a bridge mission betweenNASA’s Earth Observing System (EOS) and the Joint Polar-Orbiting Satellite System (JPSS) [1,2]
We discussed the NASA S-NPP VIIRS day-night band (DNB) on-orbit calibration and performance assessment, the improvements made since launch, some remaining challenges and the calibration framework used to generate mission-wide look-up tables (LUTs) for Land PEATE reprocessing
As part of our long-term quality assurance, we examine the gain and offset trending, as well as selected sensor data records (SDRs) images to ensure out-of-family behavior is not caused by calibration artifacts
Summary
The VIIRS on the Suomi-National Polar-orbiting Partnership (S-NPP) is a bridge mission between. The calibration suite is capable of generating the mission-wide calibration look-up tables (LUTs) efficiently, and we currently are partnering with NASA Land Product Evaluation and Analysis Tool Element (Land PEATE) to reprocess historical data when a major update in DNB calibration occurs. The goal of the NASA VCST and Land PEATE (re)processing effort is to facilitate nightlight remote sensing by providing mission-wide DNB SDR products based on the latest calibration methodology and LUTs and to further advance DNB calibration through research and development collaboration. As the JPSS IDPS currently only focuses on forward processing, the Land PEATE mission-wide reprocessed data products provide an alternative data source for user applications, where calibration consistency and accuracy are of a key priority
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