Imaging the interior of the nathan hale monument in coventry, connecticut by gpr attenuation tomography

摘要

A GPR survey in tomographically transmitting mode with 400 MHz antenna was conducted on Base Level 2 of the foundation of the Nathan Hale Monument, Coventry, Connecticut. Using the attenuation tomography technique based upon the centroid frequency down-shift (CFDS) method, we obtained an attenuation tomogram to image the interior of the foundation. In contradistinction to intuitive wisdom that thinks the monument made by solid granite from foundation to capstone, which has been subjectively assumed for a long time, the GPR tomography results suggest that within the horizontal plane a level of the foundation may consists of 3 portions: (1) the granite periphery, (2) a rather holow or void middle layer with low dielectric constant and relatively high attenuation, and (3) a central piece whose electromagnetic (EM) propertie are similar to the granite exterior (so, a piece of granite?). EM were propagation modeling using pseudo-spectral finite difference algorithm supports this tomographically-derived interior model. Understanding the interior structure of the foundation is of great significance to layout the plan for maintaining this 152-year-old monument.