## 5 Evaluation of FFNN-Based VIIRS Dust Detection off CALIOP Track  
### Entire VIIRS Granule Run for Days 75 and 224  
The previous analyses are all based on the CALIOP \"truth\" data, which is on its narrow track. To understand the ability of FFNN dust detection off the CALIOP track, we selected two days from the test days (day 075, which is March 16 and day 224, which is August 12). The same cloud mask that applied to the ADP product is used for masking the off-track VIIRS granule before feeding into FFNN to preserve clear-sky assumption. Figure 6 shows the dust distribution of CALIOP (collocated on track), FFNN (collocated on track), and FFNN (off-track) for days 075 and 224. As seen in the figure, on-track and off-track FFNN dust detection accuracies mostly have a 10% difference, which is comparable to the difference between FFNN and CALIOP on the CALIOP track (see Figure 4c). This is very encouraging because it indicates that, although FFNN method is trained on the CALIOP track, it can be applicable for off-track pixels and maintains a similar accuracy. Difference in dust proportion is about 2% and 4% for both days. Since the coverage of collocated track and entire granule are different, we cannot expect the dust distribution to be the same for on-track and off-track. However, we also cannot expect the distribution to be very different because collocated track is a subset of the entire VIIRS granule, and it is fairly well distributed over the globe. In that context, 4% difference in the dust distribution is reasonable to assume that the result of FFNN model is consistent in both on and off-track. Figures 7 and 8 show the dust occurrence frequency distribution of CALIOP product, on-track FFNN, off-track FFNN, and PHYS for day 075 (Figure 7) and day 224 (Figure 8). For day 075 (Figure 7), CALIOP and on-track FFNN shows a similar pattern of dust distribution, except for Antarctica, where FFNN overestimates dust frequency. Off-track FFNN also shows similar distribution with CALIOP in terms of both spatial distribution and occurrence of dust. Off-track FFNN also expands the small dust frequency over the ocean between south Africa and South America shown in an on-track CALIOP map. The visual inspection of RGB images of this region shows that transported dust exists and FFNN captures this feature. In on-track FFNN, there is couple elevated dust frequency pixels shown over the ocean west of Australia. These features are not shown in an on-track CALIOP map and is much reduced in off-track FFNN results. This indicates that the model may capture the feature better with more spatial coherence data. PHYS shows dust occurrence at similar geolocations with much smaller magnitude, which is consistent with our previous analyses. It is encouraging that none of the off-track results from FFNN and PHYS show any dust occurring over North and South America, as the CALIOP map indicates that there are no dust activities over these regions. Day 224 (Figure 8) shows a similar attribute to day 075 that both on- and off-track FFNN reproduce what CALIOP observes well at most of the region with one exception over North America, where CALIOP shows a small amount of dust occurrence over eastern North America, but off-track FFNN flags a lot more over this region. Another interesting observation is that both on-track maps show isolated high dust frequency in the middle of the Atlantic, where off-track FFNN shows the transport of dust plume from North Africa to this region. PHYS again captured a smaller amount of the significant dust activities that are identified by CALIOP. It barely shows the North Africa dust event with a very small magnitude, but yet we can still see that there is trace of dust plume from North Africa to the mid-Atlantic ocean. The PHYS also does not pick up the dust occurrence over South America, which is again visually identified using RGB images. It is worth mentioning that, over Asia, March is the active dust season and August is relatively calmer.