Sequential Earthquake Damage Assessment Incorporating Optimized sUAV Remote Sensing at Pescara del Tronto

Abstract

A sequence of large earthquakes in central Italy ranging in moment magnitudes (Mw) from 4.2 to 6.5 caused significant damage to many small towns in the area. After each earthquake in 2016 (24 August and 26 October), automated small unmanned aerial vehicles (sUAV) acquired valuable imagery data for post-hazard reconnaissance in the mountain village of Pescara del Tronto, and were applied to 3D reconstruction using Structure-from-Motion (SfM). In July 2018, the site was again monitored to obtain additional imagery data capturing changes since the last visit following the 30 October 2016 Earthquake. A genetic-based mission-planning algorithm that delivers optimal viewpoints and path planning was field tested and reduced the required photos for 3D reconstruction by 9.1%. The optimized 3D model provides a better understanding of the current conditions of the village, when compared to the nadir models, by containing fewer holes on angled surfaces, including an additional 17% surface area, and with a comparable ground-sampling distance (GSD) of ≈2.4 cm/px (≈1.5 cm/px when adjusted for camera pixel density). The resulting three time-lapse models provide valuable metrics for ground motion, progression of damage, resilience of the village, and the recovery progress over a span of two years.

Earthquakes Reconnaissance Data Sources, a Literature Review

“…These missions collect structural, geotechnical, seismological and damage information [29]. Earthquake reconnaissance missions are undertaken by national or international organisations such as the Earthquake Engineering Field Investigation Team (EEFIT) [10,27,35,58,62,63], the Geotechnical Extreme Events Reconnaissance Association (GEER) [10,27,32,33,62,64], and Earthquake Engineering Research Institute (EERI) [10,32,35]. In Italy, the European Centre for Training and Research in Earthquake Engineering (EUCENTRE) and the Italian Network of University Laboratories for Earthquake Engineering (ReLUIS) have organized earthquake reconnaissance missions and conducted follow-on seismic policy analyses.…”

“…Automated small unmanned aerial vehicles (sUAV) acquired images of damages in the mountain village of Pescara del Tronto after the earthquake in 2016 and later images of the progress of the reconstruction efforts in 2018 [64]. The imagery data was used for 3D reconstruction using SfM.…”

“…The imagery data was used for 3D reconstruction using SfM. The sequential 3D reconstructed models enable building identification, movement detection, and volumetric measurements and document the building identification, movement detection, volumetric measurements, and document recovery progress [64]. The 3D models were developed using Bentley TM ContextCapture.…”

“…This software establishes the 3D point locations in a scene using camera metadata and GPS. The photos contain the data utilized to calculate inter-spatial intersections [64]. A view-planning algorithm delineated optimized angles and photo locations through 'greedy heuristics' to capture better orthogonal views of Pescara del Tronto and solve the drawbacks of the nadir grid approach.…”

“…A view-planning algorithm delineated optimized angles and photo locations through 'greedy heuristics' to capture better orthogonal views of Pescara del Tronto and solve the drawbacks of the nadir grid approach. This view-planning algorithm identifies the best sensor location for observing a site or an object by planning oblique images for optimized SfM [64]. These computational tools together produce photogrammetric outcomes that look down vertically and at several oblique angles.…”