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.


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.