Imaging Structural Elements Of A CathedralUsing Ground Penetrating Radar

Abstract

The Basilica of the Assumption of the Blessed Virgin Mary in Baltimore, Maryland is the first Catholic cathedral to be established in the United States. The cathedral was designed by architect Benjamin Henry Latrobe and is an important religious building as well as a significant example of the Greek Revival style in the United States. As part of a condition assessment and historical research program, the configuration and condition of several critical structural elements of the cathedral were evaluated in the autumn of 2000. Ground penetrating radar (GPR) was used to nondestructively determine the thickness of the cathedral dome at numerous locations. The radar was also used to determine the configuration of a main supporting colu~nn for the dome and a column supporting one of the two bell towers at the cathedral. A comprehensive image of the columns could be reconstructed based on their accessibility from all sides. The results from the GPR investigations at the tower column agreed well with borescope observations and the results from a previously conducted investigation using acoustic tomography. Ground penetrating radar has been shown to provide valuable information about building components (structural and nonstructural) nondestructively. The radar data reveals voids, construction layers, the presence of other materials (e.g. metal inclusions), as well as the thickness of the element. In some instances, it is the only practical nondestmctive technique capable of providing the required information.