1. Is it appropriate to use the data to compare the ‘night’ activity of regions which have shorter vs longer daylight hours? (e.g. in certain winter months, Norway experiences 6-8 hours of daylight whereas Singapore has ~12 hours of daylight throughout the year) Or is the data processing able to account for this?
2. If certain country experiences a significant event e.g. armed conflict in a winter month (presumably with shorter daylight hours) and the conflict is reported to have ended in a summer month (longer daylight hours), do you see any issues with using nighttime light emissions data to observe changes/recovery in activity? Or would taking an average radian metric be sufficient?
VNP46A2 / Black Marble data
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LAADS_UserServices_M
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Re: VNP46A2 / Black Marble data
Here is response to your questions from product expert:
1. Is it appropriate to use the data to compare the ‘night’ activity of regions which have shorter vs longer daylight hours? (e.g. in certain winter months, Norway experiences 6-8 hours of daylight whereas Singapore has ~12 hours of daylight throughout the year) Or is the data processing able to account for this?
Answer: We account for the sunlit data by filtering pixels with solar zenith angle (< 108 degree). Above this threshold value, the sun light is well below the horizon and free from the effects of solar illumination. Keep in mind that this filter might result in black outs in high latitude regions during summer solstice.
2. If certain country experiences a significant event e.g. armed conflict in a winter month (presumably with shorter daylight hours) and the conflict is reported to have ended in a summer month (longer daylight hours), do you see any issues with using nighttime light emissions data to observe changes/recovery in activity? Or would taking an average radian metric be sufficient?
Answer: I would be more careful with seasonal variations due to vegetation and snow when comparing data between winter and summer months. We discuss about some of these uncertainties in our paper – https://www.sciencedirect.com/science/article/pii/S0034425721002777
1. Is it appropriate to use the data to compare the ‘night’ activity of regions which have shorter vs longer daylight hours? (e.g. in certain winter months, Norway experiences 6-8 hours of daylight whereas Singapore has ~12 hours of daylight throughout the year) Or is the data processing able to account for this?
Answer: We account for the sunlit data by filtering pixels with solar zenith angle (< 108 degree). Above this threshold value, the sun light is well below the horizon and free from the effects of solar illumination. Keep in mind that this filter might result in black outs in high latitude regions during summer solstice.
2. If certain country experiences a significant event e.g. armed conflict in a winter month (presumably with shorter daylight hours) and the conflict is reported to have ended in a summer month (longer daylight hours), do you see any issues with using nighttime light emissions data to observe changes/recovery in activity? Or would taking an average radian metric be sufficient?
Answer: I would be more careful with seasonal variations due to vegetation and snow when comparing data between winter and summer months. We discuss about some of these uncertainties in our paper – https://www.sciencedirect.com/science/article/pii/S0034425721002777
Regards,
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