Post-Earthquake Damage Inspection of Wood-Frame Buildings by a Polarimetric GB-SAR System

Hai Liu,Christian Koyama,Qinghuo Liu,Motoyuki Sato,Jinfeng Zhu

doi:10.3390/rs8110935

Hai Liu, Christian Koyama + Show 3 more

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https://doi.org/10.3390/rs8110935

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Journal: Remote sensing	Publication Date: Nov 10, 2016
Citations: 10	License type: CC BY 4.0

Affiliation: Xiamen University, Tohoku University, Duke University

Abstract

Structural damage inspection after an earthquake is essential for safety assessment of the affected wood-frame buildings and for making knowledgeable decision regarding their repair, renovation, or replacement. We present a polarimetric radar system for sensing the concealed wood-frames damaged by earthquakes. This system employs an antenna array consisting of four linearly polarized Vivaldi antennas recording full-polarimetric radar echoes in an ultra-wideband ranging from 1 to 20 GHz. The detailed design of the system and the signal processing algorithms for high-resolution 3D imaging are introduced. We conducted a number of surveys on damaged wooden wall specimens in laboratory. The experiment results indicate that the high-frequency radar waves can penetrate the wooden walls. Deformations of wooden structures (about 2 cm displacement) inside the wall, as well as the concealed small metal nails (about 3 mm in diameter and less than 2 cm in length) and bolts can be clearly imaged. The shape and orientation of the wooden members have shown a great sensitivity to the radar polarization. It is concluded that radar polarimetry can provide much richer information on the condition of concealed building structures than the conventional single-polarization subsurface penetrating radar.

Highlights

Destructive earthquakes cause different degrees of damage to buildings all over the world each year
To detect the subsurface damage of the wooden structure with sufficient resolution, we developed a ground-based synthetic aperture radar (GB-SAR) system operating in an ultra-wideband (UWB)
A number of non-contact measurements were conducted by the developed GB-SAR system on the wood wall specimens to check the system performance and to image the concealed damage to the wood wall specimens to check the system performance and to image the concealed damage to the the wood structures

Summary

Introduction

Destructive earthquakes cause different degrees of damage to buildings all over the world each year. In the stage of post-earthquake reconstruction, there is a great demand for efficient and accurate assessment of the safety of in situ residential buildings. Space-borne and air-borne remote sensing techniques, including optical sensors [3] and synthetic aperture radar (SAR) [4,5], have been popularly used for the overall damage evaluation in a vast area. These remote sensing techniques can detect collapsed or obviously unsafe buildings. For the moderately and/or slightly damaged buildings, visual observation by experienced engineers is still the main method to evaluate their safety [6,7]. A visual inspection is restricted to check the superficial damages—e.g., crack, spalling, deformation, etc.—and the evaluation results highly depend on the engineer’s experience

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