Sky Quality Meter Research Articles

Ideal Data to Determine Accurate Fajr Time

Early fajr time research was carried out by various parties with various techniques, one of which was using a sky quality meter (SQM) photometric tool. Observational data from various regions that have varying night levels result in a varying early fajr time as well. By paying attention to the effect of sky quality represented by the night level at the observation location, this research wants to answer whether the 20 mpsas night level limit is ideal data by looking at the correlation coefficient between night level and the turning point solution. From 1068 data with varying night levels, the correlation coefficient ( ) between the night level and the turning point solution is 0,42 which means there is an effect, while for data with a minimum night level of 20mpsas the correlation coefficient is 0,07 which means there is no influence. Based on the results of the analysis, the night level of 20mpsas can be the minimum limit for conducting an ideal early fajr time research. From 241 ideal observation data from 6 LAPAN observation stations, early fajr time presents when the Sun's elevation angle is -16,51°. Early fajr time is also the beginning of subuh prayer time, with its standard used in Indonesia, which is -20° or 3,49° different from the analysis results, if it is converted there is a difference of 13 minutes 57 seconds.

Batas Kualitas Langit yang Ideal untuk Lokasi Observasi Awal Waktu Subuh

This article describes the ideal sky quality limit to be used as an early subuh prayer time observation location, considering that early subuh prayer time research using a Sky Quality Meter (SQM) is mostly carried out from various observation locations with different sky quality. The research method used is quantitative with a sample of 6 observation locations with a daily data amount of 945. The data analysis carried out is to find a correlation between the night level which represents the quality of the sky and the inflection point which represents the sign of the appearance of the early subuh prayer time. Based on the analysis, it is concluded that the ideal sky quality limit to be used as a location for observing early subuh prayer time data using SQM is 20.35 mpsas. This limit is an important consideration for all parties who will conduct observations at early subuh prayer time, must choose locations that have a minimum night level of 20.35 mpsas.

Monitoring Light Pollution with an Unmanned Aerial Vehicle: A Case Study Comparing RGB Images and Night Ground Brightness

There are several tools and methods to quantify light pollution due to direct or reflected light emitted towards the sky. Unmanned aerial vehicles (UAV) are still rarely used in light pollution studies. In this study, a digital camera and a sky quality meter mounted on a UAV have been used to study the relationship between indices computed on night images and night ground brightness (NGB) measured by an optical device pointed downward towards the ground. Both measurements were taken simultaneously during flights at an altitude of 70 and 100 m, and with varying exposure time. NGB correlated significantly both with the brightness index (−0.49 ÷ −0.56) and with red (−0.52 ÷ −0.58) and green band indices (−0.42 ÷ −0.58). A linear regression model based on the luminous intensity index was able to estimate observed NGB with an RMSE varying between 0.21 and 0.46 mpsas. Multispectral analysis applied to images taken at 70 m showed that increasing exposure time might cause a saturation of the colors of the image, especially in the red band, that worsens the correlation between image indices and NGB. Our study suggests that the combined use of low cost devices such as UAV and a sky quality meter can be used for assessing hotspot areas of light pollution originating from the surface.

Analysis of the evolution of urban nighttime light environment based on time series

• We have opened up a new time dimension in the study of urban light environment. • We analysed the factors of urban luminous environment in time series in northeast China. • We explored the research of future light environment prediction based on time series. Excessively bright nighttime light environment has become an increasingly serious environmental problem. The Sky Quality Meter isused to continuously monitor the urban night light environment at the commanding heights of the building for 5 years. This study used correlation analysis and control variables to analyze the evolution and seasonal changes of the night light environment in Dalian from 2016 to 2021. Meteorological data were combined to explore the mechanism of natural factors on the light environment. The results showed the following: (1) the closer the moon phase is to the full moon, the brighter the night sky is; (2) The night sky brightness becomes brighter with the increase of atmospheric pollution; (3) Cloudiness will double the magnification effect of artificial lighting on the night sky; (4) The nighttime brightness of the study area has shown a certain increasing trend in the past five years. The annual average brightness value has elevated year by year, from 3.3 × 10 − 2 cd/m 2 to 5.6 × 10 −2 cd/m 2 ; (5) Historical data can be used to predict the changing trend of the light environment in the future and provide a data basis for future urban ecological lighting planning .

The significant impact of shape deviations of atmospheric aerosols on light monitoring networks

ABSTRACT Aerosol particles are important modulators of night sky brightness (NSB) due to their manifold impacts on spectral and angular properties of scattered light. The majority of radiative transfer models currently in use are based on rigorous Mie theory for spherical homogeneous particles. This fundamental concept enables significant simplifications in theoretical formulae and numerical modelling. However, as known from many studies, spherical shapes are rare for both natural and anthropogenic aerosols. Therefore, the aim of this paper is to analyse the potential magnitude of the subsequent effect in skyglow modelling assuming that the aerosol particles are of different aspect ratios. The zero-order approximation to tackle the problem is to characterize the non-sphericity by the ratio of the largest to smallest size of an ellipsoidal particle. We use T-matrix formalism to perform light scattering calculations on spheroidal particles of arbitrary size, composition, and orientation in respect to the incident light. Results indicate that the particle-shape impact on NSB can be of significant size leading to both positive and negative amplitudes around the zenith. In the most extreme case, an increase of up to 70 per cent in zenithal luminance was displayed. As a consequence, especially light monitoring devices like the sky quality meter, usually measuring the NSB around the zenith, are particularly influenced by this effect. In summary, the paper underlines both the importance of treating non-spherical aerosols in theoretical modelling of skyglow and also the significance of including atmospheric parameters to analyses of light monitoring networks.

Instrument assessment and atmospheric phenomena in relation to the night sky brightness time series

Several networks of Sky Quality Meters show long-term trends in measuring the night sky brightness. Causes of this variation could be ageing of the instruments and variations of the sky emission. The data from Ekar Observatory (Italy) are here considered.No significant ageing effect was detected on 9-year-old housing windows. A 9-year-old IR blocking filter shows a variation of its spectral transmittance up to 80%.No trend on the SQM output was found due to only the variation of the spectral distribution of the night sky emission. Together with ageing of the IR blocking filter, it causes a reduction of the SQM output of about 0.01magSQMarcsec-2 per year.Slow trend of the aerosol optical depth suggests the air near the considered site is changing towards less polluted conditions. It reduces scattering of the artificial light and consequently sky glow in the light polluted considered site.

Report on seeing, sky brightness, and meteorological properties measurements at Timau National Observatory site

With the existence of the Timau National Observatory, the site testing of the observatory location must be carried out to provide supporting data regarding the quality of the National Observatory site. Some site testing that needs to be done are seeing, sky brightness, and meteorological properties measurements. In this paper, the seeing and sky brightness measurements in July-August 2021 are presented. These measurements were conducted using the Differential Image Motion Monitor (DIMM) method with a 20 cm telescope and a Sky Quality Meter (SQM) respectively. From the results of these measurements, it was found that the site of Timau National Observatory has good seeing conditions with median of 0.92 arcseconds and most sky brightness values are around 22.02 magnitude per square arcsecond. The monitoring results of meteorological properties, such as air temperature, barometric pressure, relative humidity, and wind speed and direction during August 2021 that recorded by an automatic weather station are also presented.

The feasibility study of Barus city as the new astrotourism destination from astronomical and meteorological aspect

Astrotourism is a tourist activity that shows attractions in the form of astronomical phenomena and outer space. Astrotourism activities that can be carried out by tourists are such as studying and exploring astronomical phenomena such as eclipses, meteor showers, and so on in the conditions of the night sky. An important condition for the advancement of astrotourism in an area is that the area has dark skies that are characterized by no severe light pollution and had adequate atmospheric conditions such as at least clouds covering the sky so that celestial objects can be observed properly, temperature, humidity, wind speed. and good rainfall so that visitors or tourists can comfortably be at astronomical tourist sites for a long time. We’ve done collecting atmospheric data using portable weather station and sky brightness data using Unihedron Sky Quality Meter LU-DL type device from July 10th - 11th 2021 and we collected data from windy.com for atmospheric particle content and cloud coverage during those dates. The results showed that Barus can become a new potential astrotourism destination specifically in Northern Sumatera or broadly in Indonesia where the Light pollution in Barus city is quite low, with a maximum value of brightness sky of 21.6, 20.8, and 21.8 MPSAS for the east, zenith, and west directions, respectively; Atmospheric conditions are quite good with an average temperature of 25.9 °C, the humidity of 89.2%, wind speed of 2.07 km/h, rainfall of 33.1 mm, amount of particles in the atmosphere 0.13 AOD and heat index of 27.2 °C Future study is needed from other aspects to make Barus become a new astrotourism destination in Indonesia.

The Effect of Sun Elevation on the Twilight Stages in Malaysia

This study is concerned with determining the altitude of the sun under the horizon to the beginning and the end of the true and pseudo dawn and dusk. In 2007 and 2008, the Sky Quality Meter (SQM) was used in four regions in Malaysia to measure the brightness at night, pseudo dawn, true dawn, true dusk and pseudo dusk. The measurements were taken when the device was directed to the position of sunrise and sunset at the horizontal angle of the sunrise or sunset and at five degrees above the horizon during the entire monitoring period. The altitude of the sun for the true dusk was found to be -14.38° ± 0.91° and for the beginning of the pseudo dusk was found to be -14.86° ± 0.91° and the end of the pseudo dusk is -17.8° ± 0.7°, while for the beginning of the true dawn it was found to be -14.19° ± 0.52° (for high confidence -14.71°) and for the pseudo dawn was found to be -18.62° ± 0.82°. The light magnitude of the full night after the pseudo dusk was found to be 20.77 ± 0.93 mag./arcsec2, while it was found to be 22.17 ± 0.1 mag./arcsec2 before the pseudo dawn.

The Effect of the Installation Angle of the Sky Quality Meter on the Night Sky Brightness and the Beginning of the Fajr Prayer Time

Measuring the brightness of the night sky and determining the start of Fajr prayer times can be done using SQM. Observations were made at OIF UMSU with coordinates 3o 34' 55.06" N and 98o 43' 17.09" E. The sky brightness was measured using three SQMs mounted facing the zenith, eastern horizon, and western horizon. The night sky brightness values for SQM directed to the zenith, eastern horizon, and western horizon are 18.23 mpsas, 15.82 mpsas, and 15.47 mpsas. The beginning of fajr prayer time produced by SQM is after the beginning of fajr prayer time obtained using the Accurate Times concerning the Sun's altitude 18o below the horizon. The difference obtained by SQM directed to the zenith, eastern horizon, and western horizon is 29.5 minutes, 36.7 minutes, and 39.5 minutes. In other words, the beginning of Fajr prayer time used in Indonesia is earlier than it should be.

Verification of Angular Response of Sky Quality Meter with Quasi-Punctual Light Sources.

Sky Quality Meter (SQM) is a commercial instrument based on photometers widely used by amateur astronomers for skyglow measurement from the ground. In the framework of the MINLU project, two SQM-LE units were integrated in an autonomous sensor suite realized and tested at University of Padova for monitoring light pollution from drones or sounding balloons. During the ground tests campaign before airborne measurement, the performance of both SQM units was verified in laboratory using controlled light sources as a reference input; the results showed that both units presented an angular response deviating consistently from the expected performance and that the sensors’ field of view was larger than the one declared in the manufacturer’s datasheet. This aspect in particular would affect direct skyglow measurements during flight as light sources close to the boundaries of the field of view would not be attenuated but instead detected by the sensors. As a direct consequence, the measurement of low-intensity skyglows at stratospheric altitudes could be affected by high-intensity punctual sources acting as lateral disturbances. A dedicated test campaign was therefore conceived and realized to investigate SQM unit response to light sources in the field of view and identify the true angular response curve; the setup consisted in a controlled rotatory stage moving the unit in front of a fixed diffusive light source. Different test conditions were used to validate the experimental procedure, demonstrating the repeatability of the measurements. This paper presents the experimental campaign and the resulting SQM angular response curve; results indicate for both SQMs a larger than expected field of view and the presence of a double peak in the angular response, which is likely related to a non-perfect alignment of SQMs collimation optics. Furthermore, the wider resulting curves suggest that the contribution of lateral sources is more prominent with respect to the response predicted by the manufacturer. For this reason, the utilization of baffles to restrict SQMs field of view is analyzed to minimize the disturbance of lateral light sources and two different geometries are presented.

Flight test of an autonomous payload for measuring sky brightness and ground light pollution using a stratospheric sounding balloon

Light pollution is recognized as an increasingly important issue not only for astronomical observations but also for the preservation of ecosystem and the quality of human life. Emission from ground sources is currently mapped using satellite images aided by local ground observations but information has limited resolution in space and time; especially now that blue “cold” LEDs, which are poorly detected from space, are being widely used for illumination, data need to be integrated with measurement from autonomous systems flying at lower altitude.MINLU (“Misurazione dell’ INquinamento LUminoso”) autonomous payload was designed and tested to provide complete and detailed aerial observations of all light pollution sources and monitor sky brightness with the capability to be integrated on stratospheric balloons, tethered balloons or drones. The payload's architecture includes three downward looking cameras with dedicated filters and two commercial Sky Quality Meter (SQM-LE) units, one pointing in horizontal direction and the other monitoring the zenith sky. The system can achieve a ground sample distance of 3 cm when integrated on drones flying at 200 m altitude, going up to 8 m at altitudes above 30 km in the use with balloons; this considerably improves the information provided by satellite images showing a ground resolution around 800 m.The payload was successfully launched with a sounding balloon from Tuscany on July 8th, 2021 during the astronomical night window, achieving the first continuous observation of sky brightness magnitude in Earth atmosphere from ground to stratospheric altitudes. In parallel, images of on-board cameras have been used to quantify ground emission in terms of luminous intensity and power density and allowed to track sources causing the artificial luminance of the sky.

Identifying distinct metrics for assessing night sky brightness

ABSTRACT Studying light pollution is an interest to researchers in a wide range of fields including astronomy, biology, civil engineering, ecology, and social science. Consequently, numerous sky brightness metrics have been developed over the years. However, what metrics are truly representative of the night sky quality and unique to the measured feature? The US National Park Service Night Skies Program has collected more than 1500 sets of night skies data throughout the United States. For each data set, a maximum of 56 metrics were measured through the combination of the captured images, Sky Quality Meter readings, and visual observations. This paper analyses these measurements and identifies a distinctive set of night sky brightness metrics based on the principal component analysis. Three major findings emerge. First, the commonly used metrics, such as the zenith brightness, horizontal illuminance, maximum vertical illuminance, all-sky light pollution ratio, Bortle class, and limiting magnitude, are highly correlated. Secondly, the observed sky brightness often offers a good estimate of the artificial light level despite the natural varying night sky background. Thirdly, a set of six metrics that consists of the zenith brightness and sky brightness percentiles are more distinctive when used to concisely describe night sky characteristics. These findings suggest that long-term night sky monitoring can be efficiently carried out by measuring the sky brightness percentiles on the observed all-sky images.

A Sky Brightness Contrast Measurement before Sunrise and after Sunset over a Baghdad Region, Iraq

In this work, an analytical study had been made of sky brightness variations using a photometer of Sky Quality Meter (SQM-LU). The sky brightness measurements were performed in Baghdad city of Iraq (Latitude: 33°20’N, Longitude: 44°23’E, and Altitude: 34m above sea-level). The values of sky brightness level were collected on 27 December 2019 as well as 10 January 2020 at sunrise and sunset. The aim of this research is to study on sky illumination contrast by taking moonlight (moonless/full moon) as a reference source. Additionally is to localize the direction of the sun during both sunrise and sunset. The results indicated that, in case of sunrise and moonless, the sky brightness level was obtained averagely at 13.60 ± 0.26 magnitude/arcsecond2 with sun’s altitude angle at -9.79° ± 0.12°. While, in case of sunrise and full moon, the sky brightness level was obtained averagely at 12.75 ± 0.25 magnitude/arcsecond2 with sun’s altitude angle at -8.87° ± 0.11°. Findings also showed that, in case of sunset and moonless, the sky brightness level was obtained averagely at 17.44 ± 0.26 magnitude/arcsecond2 with sun’s altitude angle at -10.66° ± 0.12°. While, in case of sunset and full moon, the sky brightness level was obtained averagely at 15.69 ± 0.25 magnitude/arcsecond2 with sun’s altitude angle at -10.25° ± 0.11°. In conclusion, the study shows a correlation between the sky brightness magnitude against sun’s altitude angle, moon’s phase, and weather conditions as well.

SG-WAS: A New Wireless Autonomous Night Sky Brightness Sensor.

The main features of SG-WAS (SkyGlow Wireless Autonomous Sensor), a low-cost device for measuring Night Sky Brightness (NSB), are presented. SG-WAS is based on the TSL237 sensor –like the Unihedron Sky Quality Meter (SQM) or the STARS4ALL Telescope Encoder and Sky Sensor (TESS)–, with wireless communication (LoRa, WiFi, or LTE-M) and solar-powered rechargeable batteries. Field tests have been performed on its autonomy, proving that it can go up to 20 days without direct solar irradiance and remain hibernating after that for at least 4 months, returning to operation once re-illuminated. A new approach to the acquisition of average NSB measurements and their instrumental uncertainty (of the order of thousandths of a magnitude) is presented. In addition, the results of a new Sky Integrating Sphere (SIS) method have shown the possibility of performing mass device calibration with uncertainties below 0.02 mag/arcsec. SG-WAS is the first fully autonomous and wireless low-cost NSB sensor to be used as an independent or networked device in remote locations without any additional infrastructure.

Natural Night Sky Brightness during Solar Minimum

Abstract In 2018, Solar Cycle 24 entered into a solar minimum phase. During this period, 11 million zenithal night sky brightness (NSB) data were collected at different dark sites around the planet, including astronomical observatories and natural protected areas, with identical broadband Telescope Encoder and Sky Sensor photometers (based on the Unihedron Sky Quality Meter TLS237 sensor). A detailed observational review of the multiple effects that contribute to the NSB measurement has been conducted with optimal filters designed to avoid brightening effects by the Sun, the Moon, clouds, and other astronomical sources (the Galaxy and zodiacal light). The natural NSB has been calculated from the percentiles for 44 different photometers by applying these new filters. The pristine night sky was measured to change with an amplitude of 0.1 mag/arcsec2 in all the photometers, which is suggested to be due to NSB variations on scales of up to months and to be compatible with semiannual oscillations. We report the systematic observation of short-time variations in NSB on the vast majority of the nights and find these to be related to airglow events forming above the mesosphere.

Towards the Compilation of the Global Twilight Pattern

This paper summarizes ISRN’s 3-years research on the occurrence of dawn and dusk to mark the timings of the Fajr and Isha prayers. We acquired the astronomical data not only in Indonesia but also in Malaysia, the US, Egypt, and Turkey. It will be an attempt to compile a global twilight pattern in the future. The main instrument used is a Sky Quality Meter (SQM) that records the sky brightness data. For quality assurance, ISRN-UHAMKA employed dozens of imaging sensors ranging from an All Sky Camera, different types of DSLR, and gadget cameras. From hundreds of astronomical data, we have collected; it seems that the occurrence of the real twilight to mark the Fajr prayer throughout the world is the same. That is when the sun is at its depression angle of around 120-130. Likewise, the dusk to mark the end of the Maghrib prayer also occurs when the sun is at a solar depression angle around 120-130. Meanwhile, Muslims in the world use different solar depression angles ranging from -150 to -200.fields.

Effect of Street Lighting on the Urban and Rural Night-Time Radiance and the Brightness of the Night Sky

In April 2020, due to the coronavirus pandemic and the tourism decrease in Cracow (Poland), the Road Authority of the City of Cracow, followed by the authorities of several neighbouring municipalities, decided to turn off street lighting at night. It is worth noting that this is the first time that street lighting has been turned off in such a large area on a longer time frame at this scale, including one of the most populated cities in Poland, which made it possible to make unique observations. During this period, with the help of small night-sky radiance meters (Sky Quality Meters (SQM)), many ground-based measurements were made, both within the city and in its vicinity. For this purpose, the existing light pollution monitoring stations in Cracow and neighbouring cities were used. It was found that after switching off street lighting, the zenith surface brightness of the cloudless sky decreased by 15–39%, and this value was proportional to the city’s population. The night-time light satellite data (VIIRS/DNB) on radiance from Cracow and neighbouring communes were also analysed, both their daily values as well as monthly and annual averages. It was found that in the case of a large city such as Cracow, turning off all street lighting reduces the amount of light energy radiated into the sky by about 50%, which is a relatively small decrease in radiance, while reducing the surface brightness of the night sky by about 40%, regardless of the state of the atmosphere. The effect of a significant decrease in radiance as a result of switching off street lighting was found in each of the analysed communes, especially the urbanised ones.

Presence of Light Pollution as a Latent Anthropogenic Influence of Bat Dispersal in Mindanao, Philippines

Background/Objectives: The study aimed to determine the extent of the presence of light pollution dispersal in Mindanao, Philippines that influences bat dispersal. Methods/Statistical analysis: Satellite imagery and radiance data (10-9 W/cm2*sr) from Visible Infrared Imaging Radiometer Suite (VIIRS) were processed using different python codes to identify the pixel count as the extent of light pollution radiance in Mindanao, Philippines from 2012 to 2019. The VIIRS was set at an overlay of 60 transparency levels thru Sky Quality Meter (SQM) at 85 transparency levels for a hybrid base map at an altitude of 100 km to cover the island of Mindanao. Findings: The increase and spread of pixel count as light pollution in the region from 2012 to 2019 have shown significant expanse in the region. Major cities were found to be predominating evidence of light pollution as it stretches from town to town with intensifying pixel counts year by year. Having a strong positive linear relationship as identified R2 value and the increase of pixel counts throughout the parameters of the study is also anticipated that the site shows possible progress towards the community. It shows the increasing radiance and the extreme dispersion on the amount of light being emitted from the ground is critical towards bats dispersion throughout the region. Novelty/Applications: This study fosters evidence the increasing light pollution in a bat-prone region might cause possible bat dispersal related to BtCoV and/or any disease-carrying species present in Mindanao, Philippines. Keywords: Light Pollution; Bat Dispersal; Mindanao; Philippines

Evolution of Brightness and Color of the Night Sky in Madrid

Major schemes to replace other streetlight technologies with Light-Emitting Diode (LED) lamps are being undertaken across much of the world. This is predicted to have important consequences for nighttime sky brightness and color. Here, we report the results of a long-term study of these characteristics focused on the skies above Madrid. The sky brightness and color monitoring station at Universidad Complutense de Madrid (inside the city) collected Johnson B, V, and R sky brightness data, Sky Quality Meter (SQM), and Telescope Encoder Sky Sensor-WiFi (TESS-W) broadband photometry throughout the night, every night between 2010–2020. Our analysis includes a data filtering process that can be used with other similar sky brightness monitoring data. Major changes in sky brightness and color took place during 2015–2016, when a sizable fraction of the streetlamps in Madrid changed from High-Pressure Sodium (HPS) to LEDs. The sky brightness detected in the Johnson B band darkened by 14% from 2011 to 2015 and brightened by 32% from 2015 to 2019.