The S-NPP VIIRS Day-Night Band On-Orbit Calibration/Characterization and Current State of SDR Products

Abstract

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 OPEN ACCESSRemote Sens. 2014, 6 12428 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.

VIIRS Day/Night Band—Correcting Striping and Nonuniformity over a Very Large Dynamic Range

“…In areas where the stray light correction is applied (over approximately the lower two thirds of the image) there are significant residual nonuniformities that were not corrected by the stray light correction. These nonuniformities are likely at least partly due to changes in the stray light between the time that the correction tables were determined and when they were applied [1,10,22]. There is also striping in the upper third of the image similar to what appears in Figure 1.…”

“…The analysis also revealed that differences in the details of the methodology for calculating the gain ratio look-up tables could change the amount of striping seen in the DNB radiances produced using those tables [34]. There were fluctuations in the gain tables reported during the first year [10] as the calibration methodology was being refined.…”

“…The DNB stray light correction works very well in removing the effects of stray light, but it is not perfect [1,10,22]. There are at least four shortfalls to this method:…”

“…In addition to the IDPS DNB SDR, NASA Land Science Investigator-led Processing System (Land SIPS) in coordination with the Suomi-NPP VIIRS Calibration Support Team (VCST) produces a DNB Level 1 product using a similar calibration process. Land-SIPS system is maintained separately from IDPS in order to develop new algorithms and to support reprocessing of data [10]. There have been some major changes to the DNB calibration, and both the original process and the recent changes are described here since both are relevant and depend on when the SDR used for imagery is created.…”

“…An improvement that is included in the Land SIPS version is filtering out lunar stray light contamination from the offset data, after they found that it created a small bias when the moon is more than half full [17]. However, because of concerns regarding stray light, the Land SIPS version of automatic calibration no longer computes the gain ratios using the SV or BB signals [10].…”