Du cas 1D au 3D : apport des simulations numériques à la notion de profondeur de détection et de réponse spatiale des principaux dispositifs employés en prospection électrique en Archéologie - Archive ouverte HAL Accéder directement au contenu
Chapitre D'ouvrage Année : 2001

Du cas 1D au 3D : apport des simulations numériques à la notion de profondeur de détection et de réponse spatiale des principaux dispositifs employés en prospection électrique en Archéologie

Résumé

DC electrical surveying is widely used by different teams for the detection of buried archaeological remains. Several devices, generally quadripoles, are used such as Wenner α, Wenner β (often quoted as Dipole-Dipole or DD), square or pole-pole (with two remote electrodes at infinite ans separated by an infinite distance). The aim of this paper is a simulation of the response of simple objects in order to better define the notion of depth of detection and spatial response of the above menlioned quadripoles in order to help the surveyor in defining the best electrode configuration as a function of the searched archaeological targets. The response of a quadripole as a function of depth was studied by different authors by means of different concepts such as depth factor, depth of investigation, depth of penetration and finally depth of detection. After a review of the meaning of these different depths, we have chosen to focus on the depth of detection because of its link to the apparent resistivity which can be measured directly by the surveyor. The depth of detection is defined as the minimum depth to which the target must be buried in such a way that the measured response at ground level is less than or equal 10% of the response which would be measured without the target. Numerical simulations were carried out using 1, 2 or 3D targets. Digital filtering was used for 1D simulation and the method of moments for the 2 and 3D simulations. By the use of these simulations, we have been able to define the depth of detection of these devices and plot it as a function of the electrical contrast of the structure compared to the background resistivity. Despite some similarities, the plot are different whether the target has a 1, 2 or 3D geometry. Except for the lD case, it is easier to detect a conductive target than a resistive one considering an identical resistivity contrast. Wenner and square quadripoles show equivalent depth of detectfon . For high resistivity contrast structures (K >0.5), Pole-Pole device has the greatest depth of detection. The Dipole-Dipole could be used for lower contrast structures. The spatial response of these different quadripoles was studied for different targets: a shallow or deep cubic structure and an elongated structure. The Pole-Pole and to a lesser extent, the square quadripole, were shown to have a response not related to the orientation of the structures. Consequently, they should be favoured during field works if the direction of the archaeological structures is not known. For 3D structures, the response of the square quadripole is high and is isotropic. For a 2D structure, despite the fact that anomalies obtained with a DD quadripole has a tendency to oscillate in the vicinity of the boarder of the structure, their wavelength are shorter than the wavelength of the anomalies of other quadripoles. This quadripole should be favoured for better defining the limits of structures in the case of the injection is perpendicular to the structure. The Pole-Pole device shows a broader but also a stronger anomaly and can be used in nearly all cases considering also the easiness of measurement. Only if 3D structure are suspected, square quadripole can be used. This type of device can be used easily if towed by a vehicle. The Dipole-Dipole will be used solely for better defining the limits of the structures.

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Dates et versions

hal-02924297 , version 1 (27-08-2020)

Identifiants

  • HAL Id : hal-02924297 , version 1

Citer

Michel Dabas. Du cas 1D au 3D : apport des simulations numériques à la notion de profondeur de détection et de réponse spatiale des principaux dispositifs employés en prospection électrique en Archéologie. M. Cucarzi ; P. Conti. Filtering, Optimisation and Modelling of Geophysical Data in Archaeological Prospecting, Fondazione Ing. Carlo Maurilio Lerici, pp.27-44, 2001, 1947_1997 50th Anniversary. ⟨hal-02924297⟩
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