NachtMeetnet is a tradename under Sotto le Stelle (Registered Utrecht Nr. 30167055)
After a ten year period from 2009 till 2019 NachtMeetnet has ended the on-line ground based monitoring of the darkness in the Netherlands on December 31st, 2019. Due to the availability of data from sensitive satelites which can monitor the upward light during the night, monitoring of the darkness can be performed with less effort and without equipment. Therefore Sotto le Stelle continues to monitor the darkness with satelite data.
The final monitoring report over the period 2009 - 2019 has been released. The report can be downloaded here. Abstract of the report: In the period between 2009 and 2019 we found a trend in the range between -3% per year to 16% per year. The mean of the all the trends at the individual measuring locations was an 0.6% increase of night sky brightness per year with a uncertainty of 0.8%.
The sky brightness is highest during the evening and during the night the sky brightness decreased with 30% to 50%, depending on the location.
In three locations the measurements was specifically made for a program to reduce the upward light. At those locations we see indeed an upward light reduction between 2 and 7%. So these programs were effective, but are not representative for the general development of the darkness in the Netherlands.
We compared the ground based SQM measurements also with the data from the Viirs-DNB-band of the Suomi-NPP satellite, which measures the upward light coming from the earth. The correlation between both results is very good. An increase of 1% per year for the whole of the Netherlands was calculated from the satellite data, although not statistically significant. Nevertheless this value is in line with the ground based measurements.
We show a map of the change of the upward light during the last 6 years, derived from the satellite data. The map shows big regional differences.
We conclude that the yearly increase in the Netherlands between 3% and 5% per year in the 20th century is not continued. In general we have a stabilization of the upward light when we compare it with the change in population or the Bruto National Product.