Analysis of ground penetrating radar data from the tunnel beneath the Temple of the Feathered Serpent in Teotihuacan, Mexico, using new multi-cross algorithms

Abstract

The ground penetrating radar (GPR) —a non-invasive method based on the emission of electromagnetic waves and the reception of their reflections at the dielectric constant and electrical conductivity discontinuities of the materials surveyed— may be applied instead of the destructive and invasive methods used to find water in celestial bodies. As multichannel equipment is increasingly used, we developed two algorithms for multivariable wavelet analysis of GPR signals —multi-cross wavelet (MCW) and Fourier multi-cross function (FMC)— and applied them to analyze raw GPR traces of archeological subsurface strata. The traces were from the tunnel located beneath the Temple of the Feathered Serpent (The Citadel, Teotihuacan, Mexico), believed to represent the underworld, an outstanding region of the Mesoamerican mythology, home of telluric forces emanating from deities, where life was constantly created and recreated. GPR profiles obtained with 100MHz antennas suggested the tunnel is 12–14m deep and 100–120m long with three chambers at its end, interpretations that were confirmed by excavations in 2014. Archeologists believe that due to the tunnel’s sacredness and importance, one of the chambers may be the tomb of a ruler of the ancient city. The MCW and FMC algorithms determined the periods of subsurface strata of the tunnel. GPR traces inside-and-outside the tunnel/chamber, outside the tunnel/chamber and inside the tunnel/chamber analyzed with the MCW and filtered FMC algorithms determined the periods of the tunnel and chamber fillings, clay and matrix (limestone–clay compound). The tunnel filling period obtained by MCW analysis (14.37ns) reflects the mixed limestone–clay compound of this stratum since its value is close to that of the period of the matrix (15.22ns); periods of the chamber filling (11.40± 0.40ns) and the matrix (11.40± 1.00ns) were almost identical. FMC analysis of the tunnel obtained a period (5.08± 1.08ns) close to that of the chamber (4.27± 0.82ns), suggesting the tunnel and chamber are filled with similar materials. The use of both algorithms allows a deeper analysis since the similarities of the tunnel and chamber filling periods could not have been determined with the MCW algorithm alone. The successful application of the new multi-cross algorithms to archeological GPR data suggests they may also be used to search water and other resources in celestial bodies.