JOURNAL OF THE BALKAN GEOPHYSICAL SOCIETY, Vol. 2, No 4, November 1999, p. 100-111, 10 figs.Detecting small-scale targets
by the two-sided gradient transformation
M. Emin Candansayar, Ahmet T. Basokur and Ertan Peksen
Ankara Universitesi, Fen Fakultesi, Jeofizik Muh. B., Tandogan, 06100 Ankara, Turkey.
E-mails: email@example.com; firstname.lastname@example.org
Univ. of Utah, Dept. of Geology and Geophysics, 717WBB, Salt Lake City, USA.
( Received 21 July 1999; accepted 30 September 1999 )
Abstract: The two-sided three-electrode arrangement uses equally spaced electrodes permitting the use of automated devices for fast measurements. A new transformation method named as the 'two-sided gradient' (TSG) is derived by a modification of the gradient (G) transformation of Karous and Pernu(1985). The gradient transformations may remove the contribution of the 1-D earth from the apparent resistivity data, improving thus the effect of the lateral resistivity variation. This helps to the fast detection of small-scale targets. Tests on synthetic data show that the TSG transformation is superior to the G transformation in delineating the shallow lateral discontinuities. However, both transformations do not provide estimates for the depth and the exact size of the target.
A field application was carried out in the archaeological site known as 'Alacahoyuk', a religious site of Hittites hosting the ruins of temples. The two-dimensional inversion of the two-sided three-electrode apparent resistivity data lead to the location of a part of the city-wall. The archaeological excavation next unearthed the wall. Thus, the validity of our interpretation was checked. The 2-D inversion of the two-sided three-electrode data estimated correctly the location, the depth and the dimensions of the city-wall. The 2-D inversion results predicted the termination of the wall inferred by the results in some profiles. On the contrary, the TSG transformation indicated the continuation of the city-wall and the subsequent excavations proved this fact. The field survey proved that the TSG transformation is a fast and efficient method in delineating small-scale targets. Then, it can be used as a complementary method for the 2-D inversion methods.
Key Words: Small-scale Targets, Two-sided Gradient Transformation, Archaeological Survey.