A map to recover the night

Interactive ground map showing the distribution of light pollution from VIIRS night-time satellite data calibrated with night-time zenith photometers – SG and TESS – developed and installed in the EELabs and STARS4ALL projects.

The University of Las Palmas de Gran Canaria and the Instituto de Astrofísica de Canarias have developed a method for calibrating nighttime satellite images from measurements of nighttime photometer networks. The work, financed by the Interreg EELabs project, is aimed at a more precise evaluation of light pollution and its impact on the natural ecosystems of Macaronesia. The data are available to the scientific community through the project portal.

Since its inception in 2020, the Interreg EELabs project has deployed more than a hundred sensors in the natural areas of Macaronesia, in order to measure light pollution in places where it should not have reached. These completely autonomous and non-invasive devices, called night photometers, are extremely sensitive to the low brightness of the night. For this reason, they have been used to take measurements on the ground to calibrate, to within hundredths of an error, the nighttime images obtained by the VIIRS instrument aboard NASA’s Suomi NPP satellite.

“VIIRS is not sensitive enough to take precise measurements in very dark areas, unlike photometers, which do not have this limitation,” says Borja Fernández Ruiz, first author of the article and researcher at the University of Las Palmas de Gran Canaria (ULPGC), who emphasizes the extreme value of this calibration, which allows the integration of both photometers and the VIIRS instrument”, says Fernández Ruiz.

For the future, there are plans for improvement. On the one hand, with the creation of maps of other years and in real time, but also, focused on areas of special interest, as is the case of the island of La Palma, home of the Roque de los Muchachos Observatory, a place of reference for astronomy in the northern hemisphere. “La Palma has a network of photometers covering a large part of the island, including both dark areas and illuminated towns and villages,” explains Miquel Serra-Ricart, coordinator of the Interreg EELabs project and researcher at the Instituto de Astrofísica de Canarias (IAC). He adds: “The combination of satellite data and photometer networks will allow us to understand and control the evolution and distribution of light pollution in a place where it can seriously affect astronomical observations”.

EELabs (eelabs.eu) is a project funded by the INTERREG V-A MAC 2014-2020 Program, co-financed by the ERDF (European Regional Development Fund) of the European Union, under contract number MAC2/4.6d/238. EELabs involves 5 centers in Macaronesia (IAC, ITER, UPGC, SPEA-Azores, SPEA-Madeira). The objective of EELabs is to create Laboratories to measure the Energy Efficiency of Artificial Night Light in protected natural areas of Macaronesia (Canary Islands, Madeira and Azores). STARS4ALL was a project funded by the European Union H2020-ICT-2015-688135.

Scientific article: Fernandez-Ruiz, B., Serra, M., Alarcon, M. R., Lemes-Perera, S., Santana-Pérez, I., & Ruiz-Alzola, J. (2023). Calibrating nighttime satellite imagery with red photometer networks. Remote Sensing, 15(17), 4189. https://doi.org/10.3390/rs15174189.

ULPGC press release: ULPGC and IAC work together to assess the impact of light pollution.

Interesting links:

IoT EELabs Portal: https://data.eelabs.eu/

Light pollution map and photometer networks: https://data.eelabs.eu/map