2015 Gorkha Post-Earthquake Reconnaissance of a Historic Village With Micro Unmanned Aerial Systems

Abstract eng:
The M7.8 Gorkha earthquake that occurred in Nepal in April 2015 and its resulting aftershocks caused extensive widespread damage to numerous built-up urban centers. One example is Bungamati, a small village approximately 12 kilometers south of Kathmandu, Nepal, that overlooks the Bagmati River. This village dates back to the 6th century and contains the Temple of Macchindranath within its city limits. Within this village, numerous, tightly-spaced masonry and earthen style structures exists in a non-grid pattern with many streets only passable by pedestrian traffic. Such a village presents significant challenges for efficient damage assessment following an extreme event, where both narrow streets and urban canyons limit vehicular access for equipment and the clear sky required to collect global navigation satellite system (GNSS) data. In the aftermath of the earthquake series, two unmanned aerial system (UAS) platforms characterized the structural damage experienced by the village. A lightweight digital camera mounted on each platform collected visual images and both platforms flew on semi-autonomous paths. The applications of these UAS platforms permit damage assessment at a detailed level that is not achievable through satellite imagery, which has significantly less physical image resolution and at times has occlusions due to inclement weather. With these two platforms, 1300 high-definition, digital images were used to reconstruct the village into a 3D model via structure-from-motion, a computer vision technique. The resulting 3D point cloud and imagery allows for digital assessment of the structural performance. These remotely generated damage assessments were completed in a time-efficient, cost-effective, and safe manner with limited exposure to the damaged village.

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