Tuesday, March 12, 2019

Mapping Changes in Global Light Pollution

Radiance Light Trends allows you to view how nighttime light emissions have changed worldwide since 1992. This interactive map uses data collected from satellites to show the current light emissions around the world during non-daylight hours. The map also allows you to examine how light pollution has changed over time.

Radiance Light Trends allows you to select any area in the world to see the levels of local light pollution as recorded over time. For example, if you select an area around Pyongyang in North Korea, you can view a summed radiance graph for the city, which shows how there seems to have been a gradual improvement in the city's night-time electricity supply since 2012. Although the summed radiance graph for Pyongyang also reveals that between 2014 and 2017 there was a distinct decrease in light radiance.

The global changes in light pollution over time can be more easily observed on the Urban Radiance map. The Urban Radiance map compares historical night-time satellite views of the Earth to analyse urban development across the world. By comparing recent nighttime satellite imagery with historical nighttime satellite views of the same locations Urban Radiance is able to show how countries have changed in terms of urbanization, electrification and population density.

Urban Radiance has compiled time-based nighttime satellite composites of Asia, the Middle East, North America, North Africa, Europe and the whole World. On each map the nighttime light view uses orange to show the newest light pollution while older light pollution is shown in blue. In this way it is easy to pick out areas on the map where light pollution has grown over time.

On each composite map Urban Radiance has picked out significant areas which have seen a growth in light pollution. For example in North America Urban Radiance highlights how the growth of shale gas fields in the Dakota and South Texas regions has led to more light pollution. Below each map graphs show the total growth (or fall) in radiance in each country shown on the map.

NASA's Black Marble map has also been recording nighttime light levels around the world for a number of years.  The so called 'Black Marble' map of the Earth is made up of the best cloud-free satellite images of each land mass captured by satellites around the world.

Digital Geography has created an interactive map which allows you to directly compare NASA's Black Marble map of 2012 with the more recent 2016 Black Marble map. The Black Marble: 2012 vs 2016 interactive map allows you to swipe between the two NASA maps and compare the changing scale of natural lighting around the world. For example, if you open the map using the link above you can clearly see the effect that the Syrian war has had on electricity supply in the country.

John Nelson has also compared NASA's 2012 and 2016 Black Marble maps to see where in the world lights have been going on and off. His Lights On & Lights Out map highlights the locations around the world where there have been significant changes in electric lighting since 2012.

Nelson points out in the text accompanying the map that there are many reasons why places might show an increase or decrease in electric lighting. The increase in India is due to the "massive electrification of northern India in recent years". Elsewhere reductions in night lighting may be due (among other reasons) to attempts to reduce light pollution.

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