Scientists Measure Nepal Earthquake by Bouncing Radar Beams off Kathmandu From Space
A Buddhist monk catches an aerial view of Kathmandu from the damaged Swayambhunath Stupa premises in Kathmandu, Nepal. Niranjan Shrestha/AP
The ground has shifted beneath Nepal’s feet, and space agencies around the globe are rushing to measure it.
The ground has shifted beneath Nepal’s feet, and space agencies around the globe are rushing to measure it. But they’re not all hopping on airplanes to Kathmandu; many are simply downloading data collected in space.
Using satellites that bounce radar waves off the earth and listen to the echo, scientists are able to calculate the distance between those satellites and the earth. Comparing the measured distances before and after the earthquake shows how much the earth has changed shape.
Data collected by the European Space Agency’s Sentinel-1A satellite and analyzed by Deutsches Zentrum für Luft-und Raumfahrt, a research center of the German government, show that areas near Kathmandu were a meter closer to the satellite on April 29 than on April 17. Areas north of the city were found to be nearly a meter farther away.
This type of measurement isn’t perfect. Radar can be scattered by snow and heavy vegetation, according to NASA, making areas covered with those features hard to compare. Satellites also don’t look straight down on all areas of the earth, but at an angle while they orbit from pole to pole.
In the case of the Sentinel-1A over Nepal, the angle could be up to 50 degrees. That means that the change in distance—measured at an angle instead of straight up—may not correspond to the exact measurements of the land’s rise or drop. Still, it’s an indication that something has shifted.
The motion of the Nepal earthquake deformation was “almost entirely vertical” and “almost purely north-south,” according to Eric Fielding, a scientist at the NASA Jet Propulsion Laboratory. This, he says, is confirmed by data collected at GPS sites in the region and makes the data analysis less affected by the satellites’ angled view.