During the month of June, 1998, a team from the Geophysics section of
the Centre national des recherches scientifiques was in Auxerre
to survey the area beneath the nave and transept of the cathedral. Two
data sets were generated that are being analyzed and compared with the
goal of locating elements of earlier buildings that may lie below the actual
cathedral. The view below shows the electrostatic apparatus and the team
that developed and operated it.
From left to right are: Alain Jolivet, Huynh Try, Michel Dabas, the leader of the team, and Mounir Abdo. The front pads of the apparatus (right) emit continuous low frequency waves, and the rear pads receive signals of a strength that is conditioned by the resistivity of the elements beneath the paving. The signals are recorded by a computer that rides on the upper platfrom. The apparatus is pulled along parallel trajectories spaced 20 centimeters apart. A reading is registered by the computer each 5 centimeters. When the signal returns are coordinated as a group, a general picture of resistivity differences gives an indication of the location of elements below the paving.
The second technique that was employed uses a device that is also pulled
over the area to be surveyed, emitting a radar pulse every 5 centimeters.
Like the electrostatic process, parallel sweeps are made 20 centimeters
apart. The rebounds of signals emitted are received at a fixed distance
from the emitter. The photo below shows the radar apparatus (at right)
being pulled along a line in the south nave aisle of the cathedral. The
results appeared on a computer screen set in a side chapel, visible in
the right background of the image. The radar team was under the overall
direction of Michel Dabas, and included Christian Camerlynck and Cedric
Panissod, each Maitre des Conferences at the University of Paris
VI.
Michel Dabas and his colleagues have superimposed the results of the surveys over a plan of St. Etienne. They have included an image of the Romanesque crypt in gray tones to show the relationship between the survey results and the profile of the crypt. An overview of the process and its interpretation can be found in Michel Dabas and Harry Titus, "Non-Destructive Sensing Projects beneath Auxerre Cathedral," GESTA, XL/2 (2001), 181-188. The image below is a small-scale example of the electrostatic longitudinal survey at 2 m.
There are four electrostatic maps and eight radar maps. Click on the example you wish to see.
1. Longitudinal electrostatic 1 m.
2. Longitudinal electrostatic 2 m.
3. Transverse electrostatic 1 m.
4. Transverse electrostatic 2 m.
5. Radar 30 cm.
6. Radar 50 cm.
7. Radar 70 cm.
8. Radar 90 cm
10. Radar 130 cm.
11. Radar 150 cm.
12. Radar 170 cm.
