Ground penetrating radar (GPR) is widely used in archaeological prospection, allowing non-destructive high resolution 3D investigation of archaeological sites. The GPR data is frequently visualized as 2D time- or depth-slices extracted from a 3D data volume and also in form of isosurfaces. For the archaeological interpretation of the GPR data volumes Geographical Information Systems (GIS) provide powerful toolboxes. The paper presents an innovative GIS based approach for the archaeological interpretation of GPR data. This approach is based on the dynamic visualization and analysis of the data in GIS environment, combined with the creation of 3D digital models showing the virtual reconstruction of the located buried remains. The display of distinct depth slices in form of animated raster images as introduced by one of the authors in 1998 has become a standard and is increasingly applied to support GPR data interpretation. This dynamic way of visualisation allows for a better perception of the anomalies produced by the buried structures, and simplifies the detection of the main changes in the stratification. Nevertheless the animations are generally created outside the GIS environment, while the interpretation in GIS is often still conducted statically (turning the layers on and off, corresponding to the respective depth levels). In the present application the animated visualization of series of depth slices is created directly within the GIS project by using animation tools (layer animations as well as time animations) allowing for a more efficient data interpretation. The interactive graphical interpretation is conducted by using vector features (typically polygons) and by describing the archaeological structures by means of descriptive attributes documenting typology and relative chronology of the buried remains based on stratigraphic relations. The temporal data are used in order to display features dynamically in the fourth dimension according to different phases. The 3D interpretation is performed by extruding features in the ArcScene environment. Replacing them with textured 3D models offers a more
realistic'' visualization of the buried structures. A more comprehensive 3D interpretation of the GPR data is also performed by integrating isosurface representations in addition to the sequence of depth slices in the 3D display environment. The animation of the interpretative 3D visualisations within ArcScene represents an attractive method for the further analysis and presentation of the data investigating the invisible cultural heritage’’ by means of a ``virtual dig’’. The application developed within ESRI ArcGIS is exemplified by the 3D archaeological interpretation of GPR data recently collected by the Ludwig Boltzmann Institute for Archaeological Prospection and Virtual Archaeology in cooperation with its partners at the test site of the Roman Town Carnuntum (Austria).