# VIIRS Day/Night Band--Correcting Striping and Nonuniformity over a Very Large Dynamic Range
## 5 Conclusions  
We have considered the design of VIIRS and the DNB with respect to the original DNB calibration algorithm and the new RSBAutoCal algorithm. A review of DNB scenes shows that visible striping exists in the DNB SDR radiances over large parts of the swath for all gain stages from full day through moonless nights, though striping is the worst in the HGS at night. Since striping in DNB daylight scenes (LGS) is much stronger than is seen in other RSB, there is a root cause specific to the DNB. There is strong striping in twilight and night scenes, but with twilight it is only evident when scenes are viewed using NCC. A study of the three cal sectors (SD, SV, and BB) shows that under dark conditions there are differences of up to 3.5 counts in the daily means of dark offsets. These differences are systematic and remain almost constant for a period of at least one month, and probably much longer. These may represent a proxy for the stability of the differences between the cal sector and the Earth-view, and so is significant in using the cal sector for Earth-view offset correction. Offset correction is key to reducing striping in the darkest scenes, and cal sector data, and because of nightglow, the offset is very difficult to determine using earth view data alone. The gain ratios between all four of the DNB stages, LGS, MGS, HGA, and HGB were considered for all three of the aforementioned cal sectors. The SD LGS-to-MGS gain ratios for the period when indirect Earthshine light leaks through the attenuation screen and illuminates the SD appear to be stable enough to be useful as an alternative source of cross-calibration data, but by itself, this would not reduce striping because of detector nonlinearity. The HGA and HGB signals are typically saturated except for a brief period which corresponds to strong sneak-path stray light. We believe that sneak-path stray light is responsible for most of the signal seen during the day in the BB and SV cal sectors. Therefore, this stray light does not illuminate the gain stages or the detectors evenly and is not useful for cross-calibration. If the RSBAutoCal algorithm uses these data for cross-calibration, it will likely introduce more striping. The authors therefore do not recommend implementing this part of the RSBAutoCal algorithm. Instead we recommend transmitting MGS and LGS data as a normal part of nighttime operations and using the MGS data for MGS-to-HGS cross-calibration. The root causes of striping in the DNB imagery were enumerated. These are: offset instability, stray light in the cross-calibration, detector nonlinearity, electronic transients and hysteresis, electronic crosstalk, residual uncorrected stray light in the Earth-view, and uncorrected HAM mirror side modulation. We have shown that stray light correction and destriping are related and should be addressed together. With 3 years of new moon data now available, stray light correction tables that are dependent on solar azimuth angle in addition to solar zenith angle could now be produced, and this would improve the continuity of the correction. Also, based on this study, the signal seen in the southern hemisphere that is associated with the illumination of the solar diffuser is electronic hysteresis. This has been previously treated as stray light, but if the calibration algorithm were to treat it instead as electronic hysteresis, nonuniformity would be reduced. We tested the effectiveness of various destriping techniques including moment matching and HMM. HMM was found to be the most effective, and the only technique that can cover the huge dynamic range of the DNB. HMM works well in removing most striping, although some striping artifacts remain. Therefore, we continue our investigation of enhanced destriping techniques for producing high-quality DNB imagery.