Gallery: Cities of lights
NIGHT-TIME images taken from kilometres above the Earth could help us better understand the economies of some of the planet鈥檚 least developed countries. So say the US economists behind a method for measuring changes GDP using the intensity of street lights and other night-time lighting.
A better way of estimating GDP is badly needed, especially for poorer nations. Data collected by national governments is weak when it comes to informal sectors of the economy, such as street markets. In some countries, such as Liberia, economic information systems are so poor that meaningful data is sometimes non-existent.
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Satellite images could help plug the gap. Nations tend to build new roads and expand residential areas as they become more wealthy, both of which increase the number of lights that can be seen from space. See our gallery of examples
By comparing 11 years of satellite data on night-time light intensity with GDP estimates, and colleagues at Brown University in Providence, Rhode Island, developed a method for in GDP from light measurements alone. When applied to some far-flung places, the formula casts doubts on official figures. Their paper has been submitted to The American Economic Review.
In the Democratic Republic of the Congo, for example, World Bank figures suggest that GDP shrank by 2.6 per cent between 1992 and 2003. Weil鈥檚 findings point to a 2.4 per cent increase over the same period. 鈥淭hat inclines me to think that the Congo鈥檚 problems are with its statistical information, not its economy,鈥� says Weil.
GDP measurements could ultimately be improved by using a weighted combination of conventional data and light measurements, but Weil says that researchers need first to get a better understanding of the link between economic activity and light intensity. An increase in population, for example, can increase light intensity even during poor economic times.
Economists will also have to consider whether the link between GDP and light intensity, which was established using information on rich nations, works in the developing world. 鈥淭hey鈥檙e extrapolating the relationship to places we don鈥檛 know about, where it might not work,鈥� says Jan-Peter Muller, a remote-sensing specialist at University College London.
If such problems can be ironed out, the light data could become a rich source for economists. It is more regularly updated than traditional economic indicators and can be used to study how lighting levels in different localities change relative to each other 鈥� something that is often averaged out in national figures.
An even richer source of data may also become available: NASA researchers are developing a proposal for , a remote-sensing satellite designed to produce higher-resolution images of the light emitted from populated areas.
