Paris, France: Interferometric Synthetic Aperture Radar (InSAR) data can be used to monitor volcanoes, according to the article, ‘Monitoring Volcanoes’, published in Science. The article explained that InSAR is a remote sensing technique where two or more radar images over the same area are combined to detect slight surface changes occurring between acquisitions. Tiny changes on the ground cause changes in the radar signal and lead to rainbow-coloured interference patterns in the combined image, known as a ‘SAR interferogram’. Movement of magma underground may cause deformation of the surface above, thus InSAR can be used to monitor volcanoes.
The article made reference to a study of over 440 active volcanoes in 16 developing countries. The study revealed that 384 have rudimentary or no monitoring, including 65 volcanoes identified as posing a high risk to large populations. Meanwhile, referring to this article the European Space Agency (ESA) claimed that earth-observing satellites, such as Envisat, can detect unrest on currently unmonitored volcanoes.
Active volcanoes are often dangerous and difficult to access, so satellite methods provide a global perspective not achievable using ground instruments. InSAR is particularly useful for tropical areas – where cloud cover can obscure visual observations – because the radar beam can see through clouds.
Satellite views also provide a global perspective, mapping tectonic strain across continents and allowing the exploration of volcanoes in remote or inaccessible areas.
As a result, many volcanoes previously thought to be dormant are now known to be showing signs of unrest. The resources for acquiring more detailed, ground-based monitoring can now be targeted at such volcanoes.
One example outlined in Science’s article was the uplift detected at Mount Longonot, Kenya. Using radar data from ESA’s Envisat satellite, scientists recorded a 9 cm uplift during the year 2004 to 2006.