Crowdsourcing is being used to identify cities, in tens of thousands photographs taken at night by astronauts, in an effort to reduce their energy consumption and light pollution.

Earth from space at night

This image of Earth’s city lights was created with data from the Defense Meteorological Satellite Program (DMSP) Operational Linescan System (OLS). Originally designed to view clouds by moonlight, the OLS is also used to map the locations of permanent lights on the Earth’s surface. Click here for a larger version

The Cities at Night project began when some staff and students at a university in Spain noticed that NASA was collecting hundreds of thousands of pictures of the Earth taken from space, of which many were of cities at night, that were unidentified. Geo-positioning information had not been added to the photographs.

The purpose of identifying them is to help the cities to reduce light pollution and energy use. Volunteers are helping to sort the pictures and identify the locations of the images to create maps.

Volunteers are enrolled to help classify the thousands of unpublished images because humans are much more efficient than computers at recognising patterns. Therefore it is possible for anyone to make a significant contribution.

A section on the website contains images of cities that have not yet identified. Volunteers can just click on image and on a location on a map to reconcile them. Then the cities must be geo-referenced, associating a physical map with spatial locations using longitude and latitude coordinates. So for 11,109 volunteers have between them completed 31,000 of the almost 41,000 identified tasks.

Most of the images kept on record have not been published but the website does display more than 1000 examples of images of cities at night.

 Paris, London, North West Europe, Aurora Borealis at night

It's easy to identify the cities in this picture: Paris and London, with the Aurora Borealis in the background.

The intensity and the colors of the images could be used to determine the type of lighting used in each city in a way that was not possible before, in order to help reduce the electrical consumption and improve the energy efficiency of street lighting.

According to Alejandro Sánchez de Miguel, before astronauts on the ISS began taking photographs with digital cameras, images were only available for large areas of the Earth that were provided by the DMSP satellite (NOAA), which did not have color information. It was not possible with these pictures to measure the brightness of the most populated areas because they were saturated. But digital cameras, because they are capable of recording in three colors (R, G, B), provide more information and can identify a greater range of light intensities.

Part of the research work is therefore to calibrate the images to determine the flux emitted into space from each region of the Earth. This will make it possible to calculate the lighting energy expenditure in the cities independently of official statistics. Already the research suggests that the minimum expenditure in the EU in street lighting could exceed 4,000 million euros/year.

 unknown city from space

This city is unknown.

The project also wishes to support the fight against light pollution, which destroys the sense that humans have had for thousands of years of their place in the cosmos by preventing a view of the night sky.

It is easy to pinpoint the sources of light from these images that are a very useful tool to fight against light pollution. The archive of images began in 2003, which permits a study of the evolution of the problem.

The photographs are taken by astronauts from NASA, ESA (the European space Agency), CSA-ASC (Canadian Space Agency), ROSCOSMOS (Russian Federal Space Agency) and JAXA (The Japan Aerospace Exploration Agency).

The project is led by staff at the Universidad Complutense de Madrid. Click here to join the Cities at Night project.