The map’s FAQ has a discussion regarding the 2015-to-2014 data:
3. Why is on a 2015 map less light pollution than on 2014? Isn't it supposed
to get worse each year?
There are numerous reasons for this. One could be lack of good data. For
example some areas have always some clouds and as VIIRS overlay is composited
monthly, it is impossible to get good quality data coverage for that month. It
could simply be that the radiance actually decreased or that HPS lamps have
been replaced by high color temperature LEDs to which VIIRS sensor isn't too
sensitive.
Alex
On Nov 25, 2016, at 11:57 AM, Howard Moneta <hmoneta@xxxxxxxxx> wrote:
It is interesting to see when toggling 2014/2015/2016 that light pollution in
rural areas grew in past years then reduced in 2016. I wonder if the
accuracy is off in the 2016 measurement. Since the 0,25 - 0,40 reading is
consistently less all over the map in 2016, it might not mean much.
https://www.lightpollutionmap.info/#zoom=8&lat=3958151&lon=-12497799&layers=B0TFFFFF
<https://www.lightpollutionmap.info/#zoom=8&lat=3958151&lon=-12497799&layers=B0TFFFFF>
Howard
