Archaeo-Physics, LLC - geophysical survey and subsurface mapping

Case Study

Tell Ahmar (Til Barsib)

Urban Zone

See also: - Summary page - City Wall and Monumental Architecture - Isolated Farmstead - City Wall Resistance Data With Magnetic Overlay

Tell Ahmar urban zone magnetic survey results

Urban zone magnetic survey - data clipped with false relief
Download images as *.PDF file (zipped)

These images show a survey area within the urban zone of the ancient city. This area is used as a trash dump by the modern villagers. The many "sharp" (high- amplitude, short-wavelength) bipolar anomalies which are present in this data set are caused by modern metal debris. These are not of interest, and can obscure relevant data.

Architecture in this zone is probably mud brick or limestone, or a combination of the two. The buildings may have a first floor composed of many small rooms, or multiple building episodes may be superimposed. The walls appear as subtle magnetic lows in the data. These lows are typically around 5nT below the mean, while even very small ferrous metal objects can cause both positive and negative anomalies raging into the hundreds of nanoteslas.

Although the data in the shade plot image (top) has been clipped to display a reasonable range of data, any subtle features are obscured by the noise introduced by modern metal debris.

The shaded relief image (bottom) was created to better display subtle architectural features. The data was processed by replacing all data outside of the -2nT to -8nT range (which is typical of presumed mud brick or limestone architecture in this data set) with zeros. A median filter, which replaces each data point with the local median, was used to "smooth" the data, making a more coherent image when obliquely lit in false relief. It should be noted that this shaded relief plot of the data is mainly for display, rather than analysis. Relevant data which falls outside of the range being displayed is lost. For example, the linear feature that runs north-south from N20/E25 to N50/E25, and some large bipolar anomalies along the west edge of the survey area are thought to be ancient in origin, but do not appear in the shaded relief plot.

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