Intercomparisons of Nine Sky Brightness Detectors

Abstract

Nine Sky Quality Meters (SQMs) have been intercompared during a night time measurement campaign held in the Netherlands in April 2011. Since then the nine SQMs have been distributed across the Netherlands and form the Dutch network for monitoring night sky brightness. The goal of the intercomparison was to infer mutual calibration factors and obtain insight into the variability of the SQMs under different meteorological situations. An ensemble average is built from the individual measurements and used as a reference to infer the mutual calibration factors. Data required additional synchronization prior to the calibration determination, because the effect of moving clouds combined with small misalignments emerges as time jitter in the measurements. Initial scatter of the individual instruments lies between ±14%. Individual night time sums range from −16% to +20%. Intercalibration reduces this to 0.5%, and −7% to +9%, respectively. During the campaign the smallest luminance measured was 0.657 ± 0.003 mcd/m2 on 12 April, and the largest value was 5.94 ± 0.03 mcd/m2 on 2 April. During both occurrences interfering circumstances like snow cover or moonlight were absent.

Red is the new black: how the colour of urban skyglow varies with cloud cover

“…This SQM showed the same variability with cloud formation, but reported larger values of mag arcsec −2 , as the IR filter reduces the amount of light incident upon the sensor (a decrease in mag arcsec −2 corresponds to an increase in measured sky luminance). The agreement seen here is better than that reported in a recent comparison of nine SQMs (den Outer et al ). This could possibly be attributed to the fact that the SQMs used in this study were all from the same batch, and were installed very shortly after calibration by the manufacturer.…”

“…. We calculated the average deviation of each of the unfiltered SQMs from the mean value for the period in the right‐hand panel (similar to, but much less rigorous than, the intercalibration of den Outer et al ). The difference in mean deviation between the two largest outlying SQMs was 0.1 mag arcsec −2 , and the sample standard deviation was σ = 0.04 mag arcsec −2 , which is still less than half the quoted unit‐to‐unit uncertainty of 0.1 mag arcsec −2 .…”

Measuring night sky brightness: methods and challenges

“…The KIOS 2011 campaign showed an initial scatter between the individual instruments of ±14%, ranging from −16% to +20%. With intercalibration methods it was possible to reduce this to 0.5%, and −7% to +9%, respectively [55].…”

How Clouds are Amplifying (or not) the Effects of ALAN

“…Intercalibration consists in a cross-calibration method based in pairing all the instruments, so with this strategy all the devices will show the same value for the same situation. The initial accuracy of a SQM is around 10% and with the intercalibration could be improved to 1% [10,16,17].…”