Automated calibration of the Suomi National Polar‐Orbiting Partnership (S‐NPP) Visible Infrared Imaging Radiometer Suite (VIIRS) reflective solar bands

Abstract

Suomi National Polar‐Orbiting Partnership (S‐NPP) Visible Infrared Imaging Radiometer Suite (VIIRS) reflective bands are currently calibrated via weekly updates to look‐up tables (LUTs) utilized by operational ground processing in the Joint Polar Satellite System Interface Data Processing Segment (IDPS). The parameters in these LUTs must be predicted ahead 2 weeks and cannot adequately track the dynamically varying response characteristics of the instrument. As a result, spurious “predict‐ahead” calibration errors of the order of 0.1% or greater are routinely introduced into the calibrated reflectances and radiances produced by IDPS in sensor data records (SDRs). Spurious calibration errors of this magnitude adversely impact the quality of downstream environmental data records (EDRs) derived from VIIRS SDRs such as Ocean Color/Chlorophyll and cause increased striping and band‐to‐band radiometric calibration uncertainty of SDR products. A novel algorithm that fully automates reflective band calibration has been developed for implementation in IDPS in late 2013. Automating the reflective solar band (RSB) calibration is extremely challenging and represents a significant advancement over the manner in which RSB calibration has traditionally been performed in heritage instruments such as the Moderate Resolution Imaging Spectroradiometer. The automated algorithm applies calibration data almost immediately after their acquisition by the instrument from views of space and on‐onboard calibration sources, thereby eliminating the predict‐ahead errors associated with the current offline calibration process. This new algorithm, when implemented, will significantly improve the quality of VIIRS reflective band SDRs and consequently the quality of EDRs produced from these SDRs.

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

“…It has been noted from several sources that the cause of striping may be that drifts occur over the long monthly cadence of the calibration table update [15,17]. This could explain the striping in the MGS and HGS scenes, but it does not explain striping in the LGS that has a much shorter cadence, the same as the other RSB.…”

“…For the other RSB bands, the RSBAutoCal process is relatively straightforward. The per-orbit SD events used to compute time dependent, per-detector gains are temporally filtered to produce smoothed gain corrections [15].…”

“…These ideas were incorporated into the operational VIIRS calibration algorithm at IDPS in December 2013 [15], but operationally it was placed in "manual mode" (as described in the previous section) until it could be fully tested off-line. In August 2015 the VIIRS RSBAutoCal was placed in automatic calibration mode for all bands except the DNB [20].…”

“…Both the BB and SV are predominantly stray light [5,15,22], so this method is based on the assumption that stray light illuminates the HGA, HGB, MGS and LGS sections of the CCD focal plane array equally. This assumption will be discussed later in the paper.…”

“…In particular, the DNB CCD read-out and signal aggregation process is complicated by the many ASNs that it cycles through and by its Time Delayed Integration [36]. Timing becomes critical, and is believed to be the cause of the fixed-pattern offsets in the Earth-view [12,15].…”