"Temporary and seasonal migrants are very hard to measure," Balk said. "The night lights are an important source of data for Africa and Asia, especially, where data is sometimes absent or quite poor."
Pej Rohani, a University of Michigan professor who studies infectious disease ecology and evolution, said that responses to epidemics are more complicated in areas with migratory or unstable populations. Rohani said that he was unaware of any other application of nighttime imagery to epidemics.
"If you're thinking about a city with hundreds of thousands or millions of people, how can you know at any one time how many people are in the city, which is why these kind of proxy measures are clever and useful," said Rohani, who is familiar with the research but also had no role in it.
Beyond providing a unique method to gauge population density, Rohani said the Princeton-led project also is notable for the unusually clear relationship it shows between outbreaks and shifts in population density in the first place.
"Traditionally, we've been having to make inferences about what determines the patterns of seasonality we see in disease outbreaks," Rohani said. "The beauty of this study is that they were able to dissect with great precision how the presence of susceptible individuals in the population correlates with and determines the growth rate of the epidemic."
The difficulty of the project and the fact that night-lights data are largely associated with long-term studies of stable populations could explain why nighttime satellite images have not previously been used to gather information about short-term event
|Contact: Morgan Kelly|