Press Statement

Preasráiteas

19 November 2020

Go to release: “How dark is your sky?” Estimating artificial light in Ireland from satellite imagery, 2015-2019

The Central Statistics Office (CSO) has today (19 November 2020) released the Frontier Series publication, “How dark is your sky? Estimating artificial light in Ireland from satellite imagery, 2015-2019”.

As a CSO Frontier Series publication it uses new methods which are under development. Publishing outputs under the Frontier Series allows the CSO to provide useful new information to users and get informed feedback on these new methods and outputs whilst at the same time make sure that the limitations are well explained and understood.

Commenting on the release, Tim Linehan, Statistician, said: ‘This CSO Frontier Series publication analyses satellite data to estimate artificial light emissions in Ireland between 2015 and 2019. The source data is from the United States National Oceanic and Atmospheric Administration (NOAA) Earth Observation Group (EOG) and represents a high-quality, free source of satellite imagery. Satellite data analysis is a commonly used method measuring light emissions.

The analysis shows that Ireland in January 2019 has significantly lower average artificial light emissions with 0.92 units than the UK (1.78 units), Portugal (2.52 units) and the Netherlands (7.43 units). The units used are nW/cm²/sr. 

When comparing with international cities using the EU NUTS-2/3 geographical regions, Dublin city (24.29 units) has significantly lower light emissions in January 2019 than Paris (43.52 units), Inner London West (53.27 units) and Inner London East (46.78 units)

At a county level, in January 2019, Dublin has much higher measured average emissions (11.53 units) compared to the second highest county Louth (1.70 units). The counties with the next highest emissions are Kildare (1.49 units), Meath (1.15 units), Limerick (1.03 units) and Cork (0.91 units). The counties with the lowest emissions in 2019 were Leitrim (0.53 units), Mayo (0.55 units), Kerry (0.58 units) Roscommon (0.64 units) and Sligo (0.65 units).

A similar trend is seen at Local Electoral Area (LEA) as the 10 LEAs with highest emissions were located in Dublin. Pembroke South Dock had the highest level of emissions with 69.94 units. The two LEAs with lowest emissions were South and West Kerry (0.42 units) and West Mayo (0.45 units). 

Editor's Note:

This analysis was carried out by the CSO with Graphical Information Systems (GIS) software tools combining Ordnance Survey mapping information with satellite data on monthly cloud-free light emissions from the Visible Infrared Imaging Radiometer Suite Day Night Band (VIIRS-DNB) sensor on the Suomi-NPP satellite, operated by the NOAA.

When observing the apparent decrease between the 2015 and 2019 figures, the following should be noted. It cannot necessarily be said that light emissions have decreased. Firstly, there are differences in the number of cloud-free observations in each month. Therefore, the months may not be directly comparable. Another factor may be the increased use of LED lighting which the VIIRS-DNB system measures as less intense than traditional lighting.

Among the many acknowledgements, the CSO wishes to particularly thank the Earth Observation Group (EOG) of the United States National Oceanic and Atmospheric Administration National Center for Environmental Information (NOAA-NCEI) for producing the satellite datasets on which this report is based. Without this source, this publication would not have been possible. Detailed acknowledgements are contained in the publication.

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