# VIIRS Day/Night Band--Correcting Striping and Nonuniformity over a Very Large Dynamic Range
## 3 Results
### Evaluating Causes of Striping and Nonuniformities
#### 3.2.3 Electronic Effects--Hysteresis and Crosstalk  
Another problem with the stray light correction is the so-called solar diffuser stray light. This is only seen in the southern hemisphere and begins when direct solar irradiance starts to shine on the SD [10; 22]. After studying this effect carefully, however, we now believe that it is probably not, in fact, stray light at all, but is actually an electronic effect. It is indeed related to the strong SD irradiance, but as noted in [22], there is a 72 scan aggregation mode dependent modulation in the SV which shows that this is at least partly an electronic effect. The effect begins abruptly on a single scan, which is not consistent with stray light. If this were, in fact, solar stray light, then the onset should be gradual, extending over about 0.5\({}^{\circ}\) (the diameter of the solar disk). Also, we would expect SD stray light to be at least somewhat correlated with the SD signal, but instead it is almost flat, except for the aggregation mode dependent modulation. Another effect that cannot be easily reconciled with the stray light hypothesis is the fact that the SV signal for this onset is about an order-of-magnitude higher than the EV signal for the same scans. There is no easy way to explain such a large change over the short angular distance between the SV and the start of the Earth-view. For these reasons, we now believe that this is caused by saturation of the high gain SD signal from the previous scan. The onset always appears on the next scan after the SD is saturated in high-gain. This saturation apparently is having some type of hysteresis effect on the detectors, causing a bias during the SV and Earth-view that follows it. The exact mechanism is not known, but it could be that saturation may be leaving excess charge on the DNB CCD, which is then discharged over time during the SV cal sector and the beginning of the Earth-view. This hypothesis is consistent with all of the observed effects and is also borne out by the fact that during the Earth-view the offset gradually decreases to almost nothing by the end of scan. If this hypothesis is correct, then the SD cal signal saturation should be used to determine the onset of what we will now high-gain SD saturation hysteresis. Rather than use solar angle to determine offset, the cal sector aggregation sequence number would be used to determine along-track dependence. Errors in determining the  
Figure 8: NCC image of stray light artifact on 22 September 2014 00:17 UTC over Antarctica. SD onset cause the dark vertical band near the bottom of Figure 6 and the light band near the top of Figure 8.  
Other hysteresis effects have been observed as well. A dark band appears in the lower left corner in Figure 4. We have observed in very dark scenes that these dark bands repeat every 72 scans and produce a negative bias with increased offset striping. They are associated the calibration cycle when ASN 1 to 4 are active, and so comprise eight scans. They are apparently associated with a negative hysteresis effect in these particular aggregation modes. The effect dissipates by the end of the scan, and this is also consistent with hysteresis. The negative bias is not large, about \(1\times 10^{-10}\) W\(\cdot\)cm\({}^{-2}\cdot\)str\({}^{-1}\), but because of the recent interest in studying scenes illuminated by nightglow, this is significant. Another artifact that is probably crosstalk is the zigzag (or repeating chevron) pattern noted in the LGS in Figure 2. In prelaunch ground testing these were found to be related to crosstalk from the delay in aggregation mode switching relative to the MGS, HGA and HGB. The delay is because the stages are offset on the array, which requires that they be delayed so that they are collocated spatially. The pattern repeats for every scan, and the \"zig\" is associated with the first eight detectors and the \"zag\" is associated with the last eight detectors.