As a consequence, in the past decade, a new research field has prospered using these observations of nighttime light and its dynamics in space and in time, aimed at studying economic activity, demographics, energy consumption, poverty and development, conflicts, urbanism and the environment. This has opened a treasure of data, available at no cost, to the scientific community. Since 1992, the images have been systematically digitized and are now freely downloadable from the web. In contrast, nighttime lights are remotely sensed from one single satellite, with the same resolution, at the same time-of-day, in a systematic way, covering the surface of the whole planet. In the standard approaches, biases, time lags and inaccuracies are unavoidable and the comparison between different countries is often problematic. This is in stark contrast to many widely used economic and demographic indicators, which are often based on estimates and censuses, such as the gross domestic product, energy consumption, population levels, or the degree of poverty. Light emission is a quantity that can be measured instantaneously, objectively and systematically. When the system was declassified in 1972, and the data made publicly available, this unexpected, but very convenient, side-effect, gradually gained more interest from the scientific community. After scrutinizing the first results, it was discovered that, besides the initial goal of measuring cloud coverage, nighttime light was also very well captured by the sensors. The main purpose of this enterprise was to provide the military with daily information on worldwide cloud coverage. ![]() Air Force started a research project called the Defense Meteorological Satellite Program (DMSP a).
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