Imaging of buried archeological structures in the Alabanda Ancient City using the edge detection analysis and inverse modeling of the magnetic anomalies

Keywords: Archaeogeophysics, magnetic gradient tensor (MGT), eigenvalue analysis, tilt angle, Euler deconvolution, magnetic potential, Alabanda ancient city In this study, it is aimed to determine the boundaries and geometric properties of buried archaeological structures by magnetic edge detection techniques. The buried structures of an ancient water structure in the ancient city of Alabanda, a Carian city presently located in Aydın, Western Turkey, were determined by geophysical studies. Tilt angle, Euler deconvolution solutions, Magnetic Gradient Tensor (MGT) Boundary Analysis techniques and then a new application of Gradient Tensor Eigenvalue Boundary Analysis applications were carried out in the study for edge detection analysis and depth information of magnetic anomaly causative sources. In this context, a new normalized approach NK operator, which normalized with vertical component of MGT matrix, was utilized as a new edge detector operator. All of the techniques have been tested on synthetic data, which were generated from prism models, and then implemented to the real field data. In addition, three-dimensional (3D) electrical resistivity tomography (ERT) inversion sections and two-dimensional (2D) magnetic inversion section were checked against the results of edge detection analysis. The buried structures, which unearthed in a part of the study area by archaeological excavations, were marked with white rectangles on the generated geophysical maps and used in assessment of the techniques performance and interpretation of the results. The zero contour of the tilt angle is highly compatible with the excavation area and the ERT sections with respect to determining of the boundaries of buried structures. In addition, the depth values calculated from half of the distance between the positive and negative 45° (0,785 radians) tilt angle values are also compatible with the depths obtained from the ERT and magnetic inversion sections. Euler deconvolution results are in great agreement with the zero contour of the tilt angle. The depths obtained from Euler solutions also coincide with both inversion sections. MGT components produced information about the geometric shape and corner points of the buried structures. The resolution of NK was compared with the tilt angle and it was seen that NK determined the boundaries more clearly. Furthermore NK produced more successful and cleaner results than the tilt angle technique in the presence of noise.