Damage maps could help in future earthquake relief

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This image shows street-level photos in the Bhaktapur area of Nepal overlaid on a damage proxy map derived from satellite data. The colour gradation – yellow to orange to red – represents increasingly more significant change on the ground. – NASA / JPL-Caltech / Google / DigitalGlobe / CNES / Astrium / Amy MacDonald / Thornton Tomasetti

The Nepal earthquake, which struck in April 2015, killed more than 8,800 people and injured more than 22,000. Rescuers were still digging survivors from the rubble a week later.

As Cosmos reported a few months before the disaster struck, it was not unexpected, but predicting exactly where and when it would strike confounded scientists. After the quake, it became critical to locate the worst-damaged areas in the most need of assistance as fast as possible.

Where science could not prevent the catastrophe, it may be able to help in the future to ensure emergency workers locate and assess the hardest-hit areas. 

NASA scientists led by Sang-Ho Yun have developed a way to make damage maps using satellites. They published their software in the journal Seismological Research Letters.

The mapping system is especially helpful for isolated remote areas where there is no communication and the roads are blocked. “Those are the communities in desperate need of help, and our maps could help responders provide efficient assistance,” said Yun.

Yun and colleagues used data from two radar satellites that orbit Earth 630 kilometres above: the Italian Space Agency’s COSMO-SkyMed system and the Japan Aerospace Exploration Agency's ALOS-2 satellite.

Both satellites send out microwaves and receive reflections off the Earth. And unlike satellites that take photos with visible light, they can be used at night or through cloud cover.

Yun’s software produced “damage maps” based on the satellites’ imagery of an area near Kathmandu before and after the earthquake.

The maps overlaid coloured pixels onto Google maps – red pixels being sites that changed the most between the pre- and post-earthquake images, and therefore, the most damaged.

With a resolution of 30 metres, the maps could show damage to individual buildings, along with large landslides.

And while it took a few days to compile the maps – COSMO-SkyMed flew over Kathmandu four days after the earthquake while ALOS-2 followed three days later – the researchers say it might soon be possible to analyse an affected area in a day.

More radar satellites are on the horizon, with the NASA-ISRO Synthetic Aperture Radar satellite due for launch in 2020.

“I see the red pixels as people's beating hearts. I would like to continue developing this system to make it robust enough and rapid enough to save lives,” Yun said.

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