# VIIRS Day/Night Band--Correcting Striping and Nonuniformity over a Very Large Dynamic Range
## 3 Results
### Histogram Matching Method Results  
We show here a representative example of destriped images from the HMM algorithm. In every case shown, most or all of the striping is removed. The twilight region remains the most challenging. Also, destriping is not shown for scenes where stray light correction has been made. Because the residual striping from the stray light correction varies with region, it is not easily removed using the current HMM technique. Figure 13 shows the results of this process for the scene shown in Figure 4. This image reveals remarkable detail regarding the cloud formations, given that the only illumination source here is nightglow. The striping has been almost completely eliminated, and this image is truly noise-limited rather than striping limited. The destriping of some of the nighttime scenes has already been shown in Figure 12. These are both scenes with no lunar illumination, and so the HMM destriping is mostly correcting offset error, except as was noted regarding the 72-scan horizontal dark banding and the mirror side modulations. Figure 14 shows a scene from 9 September 2014 when the moon is full. It is over the Sahara Desert in southern Egypt. In the uncorrected image striping dominates, but not as much as with new moon scene in Figure 4. This illustrates the magnitude of striping due to gain errors. Figure 15 shows striping in the part of the scan centered on nadir. Gain striping dominates across the entire swath for HGS, but most of it is corrected with HMM destriping. Figure 16 shows a daytime image, but even with the contrast stretching, there is no visible striping. Some discontinuities can be seen, however, at some of the aggregation zone boundaries. Figure 12: Gravity waves seen in nightglow nighttime scene over Africa, 28 May 2014 at 01:23 UTC. Image has been destriped but there appears to be residual mirror-side dependent banding. Figure 13: Nighttime scene (**a**) with striping and (**b**) with HMM destriping correction from 28 May 2014 at 01:38 UTC. Figure 14: Nighttime scene (**a**) with striping and (**b**) with Histogram Matching Method (HMM) destriping, from 17 June 2014 at 23:46 UTC in a region of the Sahara Desert in southern Egypt. Figure 15: (**a**) Nighttime scene before destriping and (**b**) after destriping, from 9 September 2014 at 00:32 UTC in the Sahara Desert in Libya. The radiances are plotted on a linear scale over the range of 0 to \(4.1\times 10^{-8}\) W\(\cdot\)cm\({}^{-2}\)\(\cdot\)sr\({}^{-1}\) from black to white. The image is 500 by 750 pixels and is centered at nadir. Figure 17 shows the same twilight scene over the Antarctic as shown in Figure 2 after HMM destriping. Most of the striping has been removed, but some remains. Six orbits of twilight data was used to produce the correction table, but this may not be enough. We are continuing to experiment to determine what ensemble size is sufficient to get optimum twilight striping correction. Also note that the zigzag pattern in the LGS still remain. HMM only deals with striping, not these complex crosstalk artifacts. There are also discontinuities at the boundaries between the aggregation zones. We are working on another algorithm to correct these but it is not yet complete. It has been successful in some cases that will be noted later. Figure 18 shows the twilight scene from Figure 3 after HMM destriping. Most of the striping that appears in Figure 3 has been removed, but there is still some remaining. Note that for there are some aggregation zones that had no striping where there is now some. Figure 16: Daytime scene (**a**) with striping and (**b**) with HMM destriping, from 28 May 2014 at 12:32 UTC in a region of the Sahara Desert in southeastern Libya. The radiances are plotted on a linear scale over the range 3.6 to \(5.8\times 10^{-3}\) W\(\cdot\)cm\({}^{-2}\cdot\)sr\({}^{-1}\) from black to white. The image is 434 by 744 pixels and the left edge is the start of scan. We also tested the HMM on scenes with strong lunar illumination.