A. J. Ogah, P. O. Sule and M. K. Aliyu
Some manmade features may be under soil cover as a result of flooding, erosion, gradual sedimentations over a long period of time, or even sudden natural phenomenon such as earthquakes and tsunamis. Because of the inherent problems associated with conventional archaeological search, the magnetic profiling method has become a major tool in searching for such concealed features if they have contrasting magnetisation with the host soils. To establish the level of uncertainty in the method of locating the cultural features or lost items, we created an artificial site on a flat land in the Kogi State University Campus, Anyigba, Nigeria. Here, objects such as a short iron rod, a steel cylindrical pot, a fired stone and a clay pot were buried at known locations and at different depths, varying between 0.5 m and 1 m. The site was allowed to pass through one season of rains for the sake of re-arrangement of the disturbed soils. Thereafter, vertical gradient of the total field data were acquired on a 25m by 25m grid using proton precession magnetometer (Geometrics model G-856AX). The readings were taken at interval of 0.5m along profiles that were also spaced 0.5 m apart. The lower and the upper sensors were positioned at 1.25m apart, with the lower sensor fixed at 0.3m above the ground. We analysed and inverted the gridded data using 3D Analytical Signal Technique and obtained the plan positions and depths of the known sources with maximum errors of 11.39% and 35.29% respectively.
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