Assessment of the use of SAR satellite images for detection and mapping of post-earthquake damages, for purposes of emergency response management
Maria Virelli, Valentina Nocente, Federico Lombardo, Stefano Frittelli
The increasing availability of synthetic aperture radar (SAR) satellite imagery has opened up new opportunities for operational support to predictive maintenance and emergency response. The first step in any emergency response is to assess the extent and the impact of the damage caused by the disaster. First responders need to recognize and to collect useful
information to mount their rescue operation effectively and quickly. There is indeed a strong link between timely rescue operations and the percentage of survived victims from natural disasters.
Therefore, it is extremely important to ensure effective deployment of rescue teams as soon as possible by means of the optimization of resources, accurate information on how to access and to settle in the affected areas, and the definition of operational priorities. To further optimize the activity on the field, it is possible to use the potential of SAR satellite analysis.
Today, several satellite SAR missions are available, characterized by different technical features in terms of wavelengths, and temporal and geometric resolutions
The COSMO-SkyMed constellation initially consisted of four identical satellites, each equipped with high-resolution microwave SAR operating in the X-band and positioned in a sun-synchronous orbit ~620 km above the Earth's surface. Subsequently, the four First Generation satellites were joined by two further Second Generation COSMO-SkyMed satellites, also based on identical satellites equipped with X-band SAR payloads and positioned on the same orbital plane as the First Generation satellites. Currently 5 COSMO-SkyMed satellites are operational, 3 of the first generation and 2 of the second generation. 2 more will be launched in the coming years.
In 2018, the Italian Space Agency (ASI) and the Italian National Fire and Rescue Service (CNVVF) signed an agreement to approve the collaboration between the two State Administrations. The aims of the Agreement are linked to the use of technologies that use satellite data to support urgent technical rescue, a fundamental mission of firefighters.
Under the agreement, in the event of medium and large-scale emergencies, ASI makes radar-type satellite products available to the CNVVF. Through the use of these data we want to facilitate an initial assessment of the affected area, a few hours after the event, with the delimitation of the most critical areas, in order to optimize the operational response. Thanks to the COSMO-SkyMed products made available by ASI, are developed by the cartographic office of the National Corps (the TAS Central Service) products in order to support the territorial VVF offices in the planning phase and monitoring of interventions.
With the aim of investigating the performance of SAR images characterized by different geometric resolutions for the detection and mapping of post-earthquake damages, three SAR image datasets (Sentinel-1, COSMO-SkyMed Spotlight and COSMO-SkyMed StripMap) were analyzed available in Norcia (Central Italy) in the areas that were severely affected by the strong seismic sequence in 2016. We compared pairs of images with equivalent characteristics collected before and after the principal seismic event on October 30, 2016 (at 06:00:40, UTC). The results were compared with each other and then measured against the results of the post-earthquake field surveys for damage assessment, carried out by the CNVVF. Thanks to the interesting and opportunity to have COSMO-SkyMed Spotlight images before the event, we have determined that the nominal geometric resolutions 1x1-m can provide a very detailed damage mapping of a single building, while the COSMO-SkyMed StripMap HIMAGE at 3x3 resolutions they give relatively good detections of damaged buildings. As reliable given the different spatial resolution of the Interferometric Wide Swath mode, the Sentinel-1 images did not allow acquiring information on individual buildings, but simply provided approximate identifications of the most severely damaged sectors. The main results of the performance investigation that have been carried out in this work can be exploited considering the exponential growth of the satellite market in terms of revisit time and image resolution.
Mazzanti P., Scancella S., Virelli M., Frittelli S., Nocente V., Lombardo F, Assessing the performance of multi-resolution satellite SAR. images for post-earthquake damages detection and mapping. Remote Sensing of Environment.