An entire city’s population can be estimated from space to help speed up medical and disaster relief efforts.
For the first time, analyses of satellite images of disaster zones and famine, war, or disease-hit areas – where cities are unreachable or census data is unreliable – are helping researchers make quick and accurate estimates of who needs help. New Scientist reports.
"Population numbers are crucial to everything we do," says project collaborator Ruby Siddiqui of Medecins Sans Frontières (MSF). "We need to plan the size, scale and mode of interventions."
Groups like MSF have relied on the ‘quadrat method’ to estimate population size. That’s when a surveyor visits a sample of household to figure out how many people live in each type of building. Using this, they estimate the population of entire towns or refuge camps.
But that’s slow, requires lots of samplers and analyses, and could be hazardous to carry out in conflict zones.
So to overcome some of these obstacles, Chris Grundy of the London School of Hygiene and Tropical Medicine is leading a project to estimate the population of Am Timan in Chad using satellite images (pictured).
(The entire population will be receiving meningitis vaccinations, and MSF wants to know how many doses to order.)
Surveyors still had to visit households in Am Timan to estimate how many people typically lived in each kind of building, but then they could make a city-wide estimate by counting the total number of each type of dwelling in the satellite image, either through a computer automated analysis or by manual counting.
The satellite counting technique matched the quadrat method for accuracy – and it took half the time to deliver an answer (and has the potential to be even faster).
- The quadrat method, which required sampling visits to 1,160 dwellings, gave a population of 49,722.
- The satellite technique, which required sampling visits to 348 dwellings, gave estimates of 46,625 for the manual and 45,400 for the automated method.
Preliminary results were presented London at the annual research meeting of MSF in London a couple weeks ago.
[Via New Scientist]
Image: Am Timan, Chad / DigitalGlobe, supplied by European Space Imaging