Image from European Space Agency (www.esa.int)
Italian scientists are studying data from these satellites to map surface movements after the earthquake and the numerous aftershocks that have followed.
The scientists are using a technique known as SAR Interferometry (InSAR), a sophisticated version of 'spot the difference'. InSAR involves combining two or more radar images of the same ground location in such a way that very precise measurements – down to a scale of a few millimetres – can be made of any ground motion taking place between image acquisitions.
The InSAR technique merges data acquired before and after the earthquake to generate 'interferogram' images that appear as rainbow-coloured interference patterns. A complete set of coloured bands, called ‘fringes’, represents ground movement relative to the spacecraft of half a wavelength, which is 2.8 cm in the case of Envisat's ASAR.
"We produced an interferogram just a few hours after the Envisat acquisition by combining these data with data acquired before the earthquake on 1 February. We were pleased that we were able to immediately see the pattern of the earthquake," said Riccardo Lanari of IREA-CNR in Naples, Italy.
The Envisat interferogram shows nine fringes surrounding a maximum displacement area located midway between L’Aquila and Fossa, where the ground moved as much as 25 cm.
Read more: European Space Agency