Editing Light pollution (section)

=== Ground-based monitoring ===
In addition to satellite-based observations, ground-based networks of photometers have become essential for monitoring light pollution over time. One of the most widely used instruments is the [[Sky Quality Meter]] (SQM), a compact device that measures night sky brightness (NSB) in magnitudes per square arcsecond. SQMs are deployed by both professional observatories and citizen scientists worldwide, providing high temporal resolution data that complements remote sensing approaches.

Long-term SQM datasets from urban, intermediate, and rural sites have revealed measurable increases in light pollution. A 2023 study analyzing over a decade of data from 26 sites across Europe - including cities such as Stockholm, Berlin, and Vienna - found average annual increases in NSB of 1.7% in rural areas, 1.8% in urban areas, and 3.7% in intermediate areas. These trends were corrected for sensor aging using twilight calibration methods and adjusted for atmospheric factors such as albedo, vegetation cover, and aerosols through an empirical regression model.<ref>Puschnig, J., Wallner, S., Schwope, A., Näslund, M. (2023). Long-term trends of light pollution assessed from SQM measurements and an empirical atmospheric model. ''Monthly Notices of the Royal Astronomical Society'', 518(3), 4449–4465. https://doi.org/10.1093/mnras/stac3003</ref>

Ground-based studies have also shown that high levels of artificial light at night can suppress the natural circalunar pattern in sky brightness. In urban areas where the NSB exceeds 16.5 mag/arcsec², the variation associated with the moon cycle becomes nearly undetectable, potentially affecting species that rely on moonlight for behavior or navigation.<ref>Puschnig, J., Wallner, S., & Posch, T. (2020). Circalunar variations of the night sky brightness – an FFT perspective on the impact of light pollution. ''MNRAS'', 492(2), 2622–2637. https://doi.org/10.1093/mnras/stz3514</ref>

National SQM networks have been established in several countries. In Austria, the provincial government of Upper Austria operates a dense SQM network to support both astronomical and environmental research.<ref>{{Cite journal | last1 = Posch
 | first1 = T. | last2 = Binder | first2 = F. | last3 = Puschnig | first3 = J. | title = Quantitative assessment of light pollution in Upper Austria | journal = Journal of Quantitative Spectroscopy and Radiative Transfer | volume = 211
 | pages = 144–153 | date = 2018 | doi = 10.1016/j.jqsrt.2018.03.010 | arxiv = 1803.09811 | url = https://doi.org/10.1016/j.jqsrt.2018.03.010 }}</ref> In Spain, coordinated efforts by researchers including Bará and colleagues have helped quantify the relative contributions of streetlights, traffic, and residential lighting to NSB.<ref>{{Cite journal | last1 = Bará | first1 = S.
 | last2 = Lima | first2 = R. C. | last3 = Zamorano | first3 = J. | title = Monitoring Long-Term Trends in the Anthropogenic Night Sky Brightness  | journal = Sustainability | volume = 11 | issue = 11 | pages = 3070 | year = 2019 | doi = 10.3390/su11113070 | doi-access = free
 | bibcode = 2019Sust...11.3070B
 | hdl = 10316/107395 | hdl-access = free }}</ref> In Italy, SQM data have been used to monitor urban and protected areas.<ref>{{Cite journal | last1 = Bertolo | first1 = A. | last2 = Binotto | first2 = R.
 | last3 = Ortolani | first3 = S. | last4 = Sapienza | first4 = S. | title = Measurements of Night Sky Brightness in the Veneto Region of Italy: Sky Quality Meter Network Results and Differential Photometry by Digital Single Lens Reflex
 | journal = Journal of Imaging | volume = 5 | issue = 5 | pages = 56 | year = 2019 | doi = 10.3390/jimaging5050056
 | doi-access = free | pmid = 34460494 | pmc = 8320935 }}</ref> The Netherlands also maintains a national monitoring program using SQMs to track long-term trends.<ref>{{Cite web | last1 = Schmidt | first1 = T. S. | last2 = Spoelstra | first2 = H. | title = Darkness monitoring in the Netherlands 2009-2019 | date = 2020
 | url = https://zenodo.org/record/4293366 | doi = 10.5281/zenodo.4293366 | access-date = 8 May 2025}}</ref>

These ground-based networks provide continuous data under varied weather conditions and offer a crucial complement to satellite observations, especially for evaluating local lighting policies and environmental impacts.