Synthetic aperture radar satellite imagery (Synthetic Aperture Radar, SAR) to measure the permanent deformation of the ground caused by the earthquake of August 24, 2016, through the DInSAR differential interferometry. A technique already used for displacement measurements in many other earthquakes, such as that of Emilia in 2012, of Lunigiana in 2013 e of L'Aquila in 2009. Carrying out these investigations, from the very first hours after the earthquake, the INGV/IREA-CNR Working Group, established by the National Institute of Geophysics and Volcanology (INGV) and by the Institute for Electromagnetic Sensing of the Environment of the National Research Council (CNR-IREA of Naples), as centers of expertise of the Department of Civil Protection in the sectors of seismology and of satellite radar data processing. Objective of the study, the analysis of satellite data aimed at measuring the permanent movements of the soil produced by the earthquake and at studying the seismic sources.
During the seismic emergency, which began with the earthquake of August 24, the satellite interferometric analysis benefited from a large number of SAR images acquired, between the seismic event, by the Japanese satellite ALOS-2 (Japan Aerospace Exploration Agency, JAXA), operating in the L-band (wavelength 23.6 cm), from the C-band sensors (wavelength 5.6 cm) of the constellation Sentinel-1 of the European Copernicus Programme (European Space Agency, ESA) and from those in the X band (wavelength 3.1 cm) of the Italian constellation COSMO-SkyMed, developed by the Italian Space Agency (ASI) in cooperation with the Ministry of Defence.
The technique consists in the use of a pair of radar images acquired by the satellite from the same position: before and after a seismic event it is possible to produce a interferogram (Figure 1a), that is, one displacement map expressed in terms of phase differences, between the two radar images before and after the seismic event, of the electromagnetic signal emitted by the satellite, "reflected" by the earth's surface and captured by the sensor (represented with different color cycles). Each cycle, or fringe, represents a shift of the Earth's surface along the line of sight of the satellite by half a wavelength of the emitted signal.
Figure 1: example of interferogram (A) obtained by processing two SAR images from the Sentinel-1 satellite. Panel B shows the corresponding map of the displacement of the ground due to the earthquake of August 24, 2016. The images used refer to the dates August 21 and 27, 2016
Link to the INGVterremoti Blog: