Ultradense Topographic Correction by 3D-Laser Scanning in Pseudo-3D Ground-penetrating Radar Data: Application to the Constructive Pattern of the Monumental Platform at the Segeda I Site (Spain) TERESA TEIXIDÓ 1 * , JOSÉ ANTONIO PEÑA 1 , GLORIA FERNÁNDEZ 2 , FRANCISCO BURILLO 2 , TERESA MOSTAZA 3 AND JULIO ZANCAJO 3 1 Universidad de Granada, Instituto Andaluz de Geofísica, Granada, Spain 2 Universidad de Zaragoza, Ciencias de la Antigüedad, Teruel, Spain 3 Universidad de Salamanca, Escuela Politécnica Superior, Ávila, Spain ABSTRACT Three-dimensional ground-penetrating radar (3D-GPR) is one of the highest resolution geophysical methods for exploring the shallow subsurface and it is widely utilized in the diverse fields requiring this kind of information: for example archaeology, civil engineering and environmental studies. Currently, there are several ways to present 3D-GPR results: 2D vertical pictures (radargrams), time- and depth-slices, a mixture of radargram-slice images, GPR reflectivity maps and GPR isosurface images. All of these techniques, however, require the maximum number of details possible. When the recognition surface is not horizontal, the GPR image is distorted due the topographic irregularities. To eliminate these distortions, a classic topographic correction is applied to the GPR data set, particularly in 2D GPR profiles. Generally, this topographic information is obtained by laser levelling, total station, differential Global Positioning System (GPS) or similar equipment. This study uses a new method of topographic correction based on three-dimensional laser scanner (3D-laser scanner) technology that provides ultradense coordinates of the terrain. A strategy for applying this topographic correction to 3D-GPR vertical traces is discussed and evaluated by comparing corrected images with other uncorrected images obtained using the same standard processing flow. The GPR dataset used to test this method is from a monumental structure located in the Celtiberian site of Segeda I (Mara, Spain). The data were acquired using a 400 MHz antenna on 0.25 m spaced profiles. Although the relief of this structure is not overly complex, we demonstrate how the results obtained by applying this topographic correction technique allow a better archaeological interpretation of the internal architecture. The technique is therefore presented as a new archaeological tool to obtain clearer images of buried structures and/or their internal elements. Copyright © 2013 John Wiley & Sons, Ltd. Key words: 3D-GPR method; 3D-laser scanner; ultradense GPR topographic correction; Celtiberian site of Segeda I Introduction Topographic data are an important aspect of ground- penetrating radar (GPR) surveying and, in order to be useful, measured coordinates must be matched with GPR data. This topographic information can be obtained using traditional surveying tools: laser levellers (Jol et al., 2004), total station (Heincke et al., 2002), or real-time kinematic Global Positioning System (GPS) (Urbani and Baskaradas, 2010; Böniger and Tronicke, 2010). Usually these topographic corrections are applied to 2D-GPR data when the relief of the profiles varies more than 10% (Lehmann and Green, 2000), in which case the traces are moved according to the measured elevations. These corrections, however, are rarer in pseudo-3D GPR or 3D-GPR sets because a dense topographic grid * Correspondence to: T. Teixido, Universidad de Granada, Instituto Andaluz de Geofísica, Granada, Spain. E-mail: tteixido@ugr.es Copyright © 2013 John Wiley & Sons, Ltd. Received 8 May 2013 Accepted 11 September 2013 Archaeological Prospection Archaeol. Prospect. (2013) Published online in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/arp.1464