Two- and three-dimensional ground-penetrating radar surveys across a medieval choir: a case study in archaeology

Abstract

Excavations around the Prediger Church in Zurich (Switzerland) for a building project prompted interest in the region beneath the choir, which dates from the thirteenth century. To supplement archaeological information on the church, the hidden remains beneath the choir were investigated with ground-penetrating radar (GPR). An initial coarse GPR survey with shielded high-frequency antennae mapped the locations and dimensions of buried walls beneath the choir. The choir was determined to be rectangular and an altar was discovered. The rectangular ground plan of the historic choir is typical for a Cistercian church. To resolve the exact dimensions of structures, migration of the data was required. The most important parameter for this process is the velocity model of the ground, which was determined by different methods: constant velocity migration tests of the GPR data, common mid-point analyses, time-domain reflectometry in drill holes and network analyser measurements on samples. A second GPR survey with a very fine grid was carried out over a small area to test the resolution capabilities of this method. A three-dimensional display of semi-automatic selected interfaces allowed the identification of single rocks. Such detail provided an insight into the construction and the state of destruction or preservation of the walls. Copyright © 2000 John Wiley & Sons, Ltd.