Geophysical Anomaly Detection for Archaeology using Multimodal Volume Visualization Andrew Loomis

Tyler Parker

Margaret Waters

Computer Science, Brown University

Computer Science, Brown University

Joukowsky Institute, Brown University

Abstract—We present a multimodal volume visualization technique that allows for simultaneous interactive exploration of multiple geophysical surveys to aid in the detection and analysis of subsurface anomalies at archaeological dig sites. An initial survey of archaeological students revealed that our proposed technique is preferred for visualizing Ground Penetrating Radar (GPR) and Electrical Resistivity Imaging (ERI) over existing techniques used in software packages such as Radan and Geoplot.

I. I NTRODUCTION Archaeologists use multiple geophysical surveys to noninvasively measure different geophysical properties and identify buried features at archaeological sites. Current software tools used to analyze and visualize these surveys are targeted primarily towards a single survey type. In addition, these tools do not fully exploit the threedimensional nature of some of these datasets, and instead prefer to treat them as two-dimensional slices. Previous work has show that the integration of multiple surveys into a single visualization is a more effective technique for the exploration of a particular site than any one survey alone [5], [1], [3]. Additional work has also been done to visualize these datasets in a three-dimensional space [6], [2], [4]. We approach both issues within the framework of multimodal volume visualization, which allows us to highlight even subtle features of the subsurface. II. M ETHODS Our project is focused on the integrated visualization of two particular types of geophysical surveys, GPR and ERI. Both are collected as two-dimensional slices arranged on a grid. The slices combine to form three-dimensional scalar volumes. Our general approach was to use volumetric ray casting on modern graphics hardware to render both the GPR and ERI volumes simultaneously. The color at any given point in the space was assigned using the values of each volume as indices into a multidimensional transfer function. In order to evaluate the effectiveness of our multimodal visualization, we enlisted an undergraduate archaeology class. We presented them with data from the Catholme Ceremonial Complex, an archaeological dig site in the United Kingdom. The students had previously been investigating this site through the use of two software applications, Radan and Geoplot. The central features of this site include a ring ditch, postholes, and plow furrows [6]. We gave each student several minutes to explore the site using our application. They were able to control several aspects of the visualization including the density, lighting, transfer function lookup, and scaling between the two datasets. This allowed them to both highlight and diminish different features within the volumes. After they were finished we gave each student a short survey asking them to compare different aspects of our tool with their current tools by rating statements on a Likert scale. III. R ESULTS When asked if the proposed software was more effective for identifying archaeological features than their current software, 62%

Fig. 1. Combined GPR and ERI volume visualization. The diagonal blue line is a medieval plow furrow.

felt that it was for GPR data and 50% felt that it was for ERI data. When asked if the proposed software was more effective at visualizing features, 87% felt that it was for GPR data and 62% felt that it was for ERI data. All students felt that visualizing both datasets simultaneously was more effective than visualizing either dataset alone. IV. C ONCLUSION The results from the survey are promising, but there are a number of factors that may have influenced them. The students themselves were not experts in the field and potentially lack experience in analyzing these types of data. In addition, they were already familiar with the test data using their current software. Finally the proposed software had a user interface that was difficult to learn, which may have hindered their ability to use the application. Overall there was a great deal of enthusiasm among the students for continuing work in this area. R EFERENCES [1] R.B. Clay. Complimentary Geophysical Survey Techniques: why two ways are always better than one. Southeastern Archaeology, pages 31– 43, 2001. [2] S. Kadio˘glu and J.J. Daniels. 3D visualization of integrated ground penetrating radar data and EM-61 data to determine buried objects and their characteristics. Journal of Geophysics and Engineering, 5:448, 2008. [3] K.L. Kvamme. Integrating Multidimensional Geophysical Data. Archaeological Prospection, 13(1):57–72, 2006. [4] L. Nuzzo, G. Leucci, S. Negri, M.T. Carrozzo, and T. Quarta. Application of 3D Visualization Techniques in the Analysis of GPR Data for Archaeology. Annals of Geophysics, 45(2), 2002. [5] S. Piro, P. Mauriello, and F. Cammarano. Quantitative Integration of Geophysical Methods for Archaeological Prospection. Archaeological Prospection, 7(4):203–213, 2000. [6] M.S. Watters. Geovisualization: An Example from the Catholme Ceremonial Complex. Archaeological Prospection, 13(4):282–290, 2006.

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