A new radiolocation method for precise depth estimation and its application to the analysis of changes in groundwater levels in Colonia Clunia Sulpicia

Underground mapping is of paramount importance at archaeological sites with natural or man-made caves. Techniques of different complexity are available for underground surveying, from compass and tape to light detection and ranging (LiDAR). However, there are scenarios where it is impossible to use heavy and/or delicate instrumentation, or with some of the more advanced techniques, long-distance and time-consuming fieldwork would be required. This is the case of the study of the height of water at key points inside the aquifer located in the subsoil of the Roman city of Colonia Clunia Sulpicia to assess its relation with the evolution of the city. Although subsurface radiolocation, a technique originally intended for cave mapping, seems promising for this application, its accuracy in depth estimation is not sufficient for this purpose. Therefore, the main objectives of this work are to improve the accuracy of depth estimation using radiolocation, to obtain sound data to study changes in water supply in the early centuries of the city and to hypothesize possible causes and probable consequences. Then, this work analyses the sources of error affecting the radiolocation process and develops a new method experimentally validated to improve the depth estimation accuracy. As a result, the depth of key points at Clunia has been accurately measured by radiolocation, where LiDAR or direct measurements from the water level are not possible. Finally, based on the resultant data, a chronology of the city in relation to the aquifer, and vice versa, is outlined. The new radiolocation and calculation procedure proposed in this paper is an improved subsurface location technique that can lead to a significant innovation in archaeological prospection.