Shallow depth geophysical investigation through the application of magnetic and electric resistance techniques: An evaluation study of the responses of magnetic and electric resistance techniques to archaeogeophysical prospection surveys in Greece and Cyprus.

摘要

The response characteristics of total intensity and vertical gradient magnetic techniques have been investigated in detail and compared with electric resistivity and other geophysical techniques.;Four case studies from archaeological sites of Greece and Cyprus have been used as the experimental basis of this research project. Data from shallow depth geophysical investigations in these sites were collected over a period of four years. Interpretation of the geophysical results was based on the integration of the various prospecting methods.;The results of the comparative study between the different techniques showed a strong correlation among all methods allowing the detection of certain features and the determination of their dimensions. The application of a large range of geophysical prospecting techniques in the surveyed archaeological sites has been able to detect the approximate position of the subsurface remains and to compare the different techniques in terms of the information that they reveal. Each one of these techniques has been used to examine the characteristic response of each method to the geophysical anomalies associated with the surveyed sites.;Magnetic susceptibility measurements at two frequencies have identified areas and levels of intense human activity. A number of processing techniques such as low, high and band pass filtering in the spatial and frequency domain, computation of the residuals and fast Fourier transformation (FFT) of the magnetic potential data have been applied to the geophysical measurements. The subsequent convolution with filters representing apparent susceptibility, reduction to pole and equator, Gaussian and Butterworth regional and residual distributions, and inverse filtering in terms of spiking deconvolution have revealed a wealth of information necessary to obtain a more accurate picture of the concealed features. Inverse modelling of isolated magnetic anomalies has further enriched the information database of the particular anomalies and helped in the systematic recognition of similar features. The proposed filtering processes yielded fairly good results delineating the dimensions of the concealed targets, emphasized different kinds of anomalies and helped considerably in the interpretation of the geophysical maps and the subsequent archaeological excavations.;The effectiveness of each technique to detect magnetic susceptibility and electric resistivity contrasts has been proven to be extremely successful. This research project has shown the potential importance of the geophysical investigations and imaging techniques in shallow depth prospecting. Image enhancement and mapping of the corresponding anomalies can reveal an accurate representation of the subsurface features. The re-evaluation of the geophysical data under the combination of different techniques has proven fruitful and instructive for future geophysical studies.