Ground penetrating radar yields vertical sections of data sampled at a high density,
here every 2 cm (above). Ten 15 m transects were run over a 5 m length of the fortification
ditch (in the same area sampled by resistivity tomography), each separated by 50 cm
(only 5 of those profiles are illustrated in the scaled diagram below). Each transect
represents a 25 nanosecond (nS) two-way travel time with the fortification ditch
occurring at 12 nS. Interpolation and averaging between profiles at a "time-slice"
of 12 nS (about 1 m depth) yields a GPR plan view of this feature.
This project was supported by a technology transfer grant from the National
Center for Preservation Technology and Training, National Park Service.
