GEO PHYSI CAL SUR VEY ( GPR ) IN WEST SAQQARA ( EGYPT ) : PRE LIMI NARY RE MARKS
Ab stract Geo phys i cal in ves ti ga tions in West Saqqara area were part of the ar chae o log i cal field work of the Pol ish-Egyp tian ar chae o log i cal mis sion dur ing the cam paign in 2012. The main pur pose of geo phys i cal prospection us ing the groundpen e trat ing ra dar (GPR) was to de ter mine the lo ca tion of po ten tial un der ground se pul chral struc tures. Dur ing the GPR sur vey, op ti mal depth pen e tra tion was achieved due to dry rocks and mono lithic struc ture of the lime stone pla teau on which the an cient cem e tery was lo cated. Us ing an tenna of 100 MHz, the depth of pen e tra tion was up to 45 m and with an tenna of 250 MHz, up to 15 me ters. Three main groups of ar chae o log i cal struc tures were iden ti fied: sar coph agi and mum mies, burial shafts; mo bile ob jects (solid rock blocks as frag ments of tombs). One of the main goal of the GPR sur vey was to track the route of the west ern part of the Dry Moat, ex pressed by a wide and shal low de pres sion spread ing to wards north-south. The re sults of geo phys i cal in ves ti ga tions sug gest that Saqqara pla teau is an ideal site for us ing GPR sur vey ing tech nol ogy.
Applicability of Ground Penetrating Radar on desert archaeological sites: a case study from the Saqqara necropolis in Egypt
Abstract This paper presents the preliminary results of ground penetrating radar sounding applied at the desert archaeological site in Saqqara (Egypt). The survey was carried out in 2012 within a project realized by Institute of Archaeology, Cardinal Stefan Wyszyński University in Warsaw and the Faculty of Geology, University of Warsaw. One of the key aims of the research was testing the application of ground penetrating radar to non-invasive surveys of desert archaeological sites. Radargrams obtained for area of so called the Dry Moat channel surrounding the Step Pyramid complex have shown the geological structure of its filling. It comprises among others debris-sand conglomerate of diluval origin characterized by a significant content of the clay fraction and clay minerals. Such lithological content strongly attenuate the propagation of EM waves, restricting the depth range of the GPR survey. The conducted geophysical prospection west to the Step Pyramid in Saqqara has confirmed the high applicability of the GPR method in non-invasive studies of vast architectural structures, such as the monumental ditch surrounding the Step Pyramid known as the Dry Moat. It should summarised that high horizontal resolution obtained during GPR survey is a result of local geological structure of the searched area, i.e. strong lithological contrast of the sediments filling the Dry Moat, which, depending on their mineralogical composition
Improving modelling and inversion in refraction seismics with a first‐order Eikonal solver
A first‐order Eikonal solver is applied to modelling and inversion in refraction seismics. The method calculates the traveltime of the fastest wave at any point of a regular grid, including head waves as used in refraction. The efficiency, robustness and flexibility of the method give a very powerful modelling tool to find both traveltimes and raypaths. Comparisons with finite‐difference data show the validity of the results. Any arbitrarily complex model can be studied, including the exact topography of the surface, thus avoiding static corrections. Later arrivals are also obtained by applying high‐slowness masks over the high‐velocity zones. Such an efficient modelling tool may be used interactively to invert for the model, but a better method is to apply the refractor‐imaging principle of Hagedoorn to obtain the refractors from the picked traveltime curves. The application of this principle has already been tried successfully by previous authors, but they used a less well‐adapted Eikonal solver. Some of their traveltimes were not correct in the presence of strong velocity variations, and the refractor‐imaging principle was restricted to receiver lines along a plane surface. With the first‐order Eikonal solver chosen, any topography of the receiving surface can be considered and there is no restriction on the velocity contrast. Based on synthetic examples, the Hagedoorn principle appears to be robust even in the case of first arrivals associated with waves diving under the refractor. The velocities below the refractor can also be easily estimated, parallel to the imaging process. In this way, the model can be built up successively layer by layer, the refractor‐imaging and velocity‐mapping processes being performed for each identified refractor at a time. The inverted model could then be used in tomographic inversions because the calculated traveltimes are very close to the observed traveltimes and the raypaths are available.