Currently, archaeologists perform excavations determined by previous geophysical studies to accurately establish the prospective targets and minimize site disturbance. Among others, one of the methods most widely employed is the Electrical Resistivity Tomography (ERT-2D, -3D). However, investigation of the subsoil of archaeological buildings is not possible to carry out with traditional geophysical methods, because the structure itself prevents it. Therefore, it is necessary to design non-invasive special arrays capable of characterizing the subsoil of such buildings, while preserving their historical context. Here we show how this procedure combined with sequences of resistivity observations at depth allowed us to detect a low resistivity body beneath the pyramid ofEl Castilloin Chichen Itza (Mexico). This feature may be associated with a cavity (karst) partially filled with sweet water. On the other hand, a natural cavity was discovered underEl Osariopyramid (south of El Castillo), at the end of the 19th century. Therefore, this pyramid was also studied to validate the effectiveness of this methodology, obtaining outstanding results. This method provides an interesting procedure to investigate the subsoil of archaeological structures for unveiling evidences that allow specialists to understand the religious meaning of these temples.

This work analyzes the progress that the degree of geophysical engineer has made in the last fifty years, specifically in the School of Engineering of the Universidad Nacional Autónoma de México (unam), Mexico. This raises the vision, a little history, the teaching, and learning process that gives identity to the geophysical engineer, the forms of learning and the competences that applicants must have and acquire to obtain the professional title; In addition, the experience in the Introduction to Geophysics course, at the beginning of the COVID-19 pandemic, is detailed; finally, some challenges and areas of opportunity are proposed that geophysical engineers will face in the near future. Se hace un análisis del avance que ha tenido la carrera de Ingeniería geofísica en los últimos 50 años, específicamente en la Facultad de Ingeniería de la Universidad Nacional Autónoma de México (unam), México. Se plantea la visión, un poco de historia, forma de enseñanza y proceso de aprendizaje que da identidad al ingeniero geofísico, formas de aprendizaje y competencias que deben tener y adquirir los aspirantes para obtener el título profesional; también, se detalla lo experimentado en la asignatura Introducción a la Geofísica, ante la COVID-19, en el primer confinamiento. Finalmente, se proponen algunos retos y áreas de oportunidad que enfrentarán los ingenieros geofísicos en el futuro cercano.

When collecting data using ERT2D (2D electrical resistivity tomography) and TDIPT2D (2D time domain-induced polarization), different phenomena can occur, which can cause natural or anthropogenic noise, contaminating the data and making its processing, analysis, and interpretation difficult. Different techniques have been developed to eliminate or reduce these effects on the data, such as noise filtering or the development of new techniques to improve data collection in the field. In the present work, an iterative, weighted, least-squares filter was employed after voltage normalization using current and geometrical factor correction on data collected in rough topographic terrains. The selected filter basis function should be able to represent the natural behavior of the function to be filtered. Stationary or variable voltages in electrical prospecting decay with the inverse of the distance, which can be represented by an expansion in Legendre polynomials. On the other hand, uneven spacing of the electrodes leads to using the incorrect geometric factor, resulting in an error in the calculation of the electrical anomaly. The efficiency of the proposed technique was analyzed and tested with field examples using different filters and by comparing applying and not applying the proposed correction factor. The results indicated low RMS and L2-Norm errors, and better definition of the inverted resistivity image was obtained. For the TDIP data, a better correspondence between the inverted images of resistivity and chargeability was obtained.