VIIRS Day-Night Band (DNB) calibration methods for improved uniformity

Abstract

The Suomi-NPP VIIRS Day-Night Band (DNB) offers quantitative measurements of visible and near-infrared light over a dynamic range from full daylight to the dimmest nighttime scenes. This range presents a challenge to radiometric calibration, but the instrument has exceeded all of its absolute radiometric requirements. Nevertheless, striping and banding are still visible, day or night, but especially in low-light scenes. The causes may be cross talk, stray light or hysteresis in the data used for calibration. These issues combine to reduce the utility of these unique observations for gaining new insight on the nocturnal environment. This paper presents methods for improving gain and offset uniformity for both day and night scenes while maintaining absolute radiometric accuracy. We evaluate removal of fixed-pattern non-uniformity in dark scenes on a per orbit basis using three different techniques: i) tracking the darkest 25 th percentile calibration sector signal; ii) taking the mean of filtered dark Earth-view scenes to determine offset; iii) minimizing correlated error for dark scenes within an aggregation zone. For gain uniformity we discuss some problems with the current calibration methods, and demonstrate a technique to minimize the correlated error between detectors and aggregation zones using the moment matching technique for moonlit scenes. A similar technique can be used for daytime and twilight scenes. An alternative cross-calibration technique between gain stages uses indirect illumination of solar diffuser view. The use of the space view and blackbody view for cross-calibration is also discussed. Histogram equalization is discussed for minimizing striping and banding. In all cases, data with stray light is filtered out to prevent contamination of the destriping process.

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

“…It also presents a methodology for eliminating most nonuniformity for daytime, twilight and nighttime. We previously published results demonstrating destriping for imagery using the Moment Matching (MM) method, but this correction was limited to nighttime scenes with limited dynamic range [5]. Here we demonstrate for the first time destriping over the entire dynamic range of the DNB using the Histogram Matching Method (HMM).…”

“…We have tested three techniques for removing striping, and have presented some of these results previously [5]. These techniques are:…”

“…All the cal sectors were found to be contaminated with stray light. However, during the periods when the satellite went into the Earth's shadow, there was no stray light signal, and it was suggested that averages of the data from these periods could be used to determine offset [5,16]. This has become the basis for automated DNB offset correction.…”

“…Since during the day the attenuation screen is not exposed to any direct sunlight, it was hypothesized that this strong signal was due to Earthshine (solar reflection off the Earth) coming through the attenuation screen and illuminating the SD. Looking for a technique to provide gain ratios using only the cal sector data, it was suggested that this daytime SD signal could be used for LGS-to-MGS cross-calibration and possibly MGS-to-HGS cross-calibration as well [5,19]. Concerns were raised, however, about whether sneak-path stray light might be contaminating the MGS-to-HGS gain ratios [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.…”