Tall Jalul

2004



Art Chadwick and Larry Turner were invited by Randy Younker to accompany a group from Andrews University to Tall Jalul in Jordan and to bring the GPS (Global Positioning System) and GIS (Geographic Information System) technology utilized in the Lance formation dinosaur excavation project to explore how these might be applied in the archeological arena.

The GPS system that was used is a standard high-precision surveying equipment that utilizes the constellation of GPS satellites, a base station, and a rover unit that is capable of determining quickly the three-dimensional position of the rover unit to within approximately 1 cm in all three dimensions relative to a set of known "control points."

The GIS software is a product produced by ESRI of Redlands, CA to analyze and produce a variety of computer-generated models and ways of looking at data.

The primary purpose of the GPS system was twofold:

  • make a detailed map of each of the five existing excavation fields
  • perform a general topographical study of the tall
The GPS data were analyzed using the GIS software to produce a three-dimensional model of the tall using a false-color method for evevations as well as producing a standard contour map. Later in the summer, aerial photographs of the site were taken. The software could then drap the photograph over the data points to produce a detailed three-dimensional model.

The first task was to perform a detailed mapping of the five fields using the GPS equipment. Points were taken along at the top and bottom of vertical surfaces, around the edges of the fields, and all major structures interior to the excavation fields. The GPS equipment is capable of centimeter precision. A total of several thousand points were recorded.

points taken in fields
GPS data points taken in the five fields

For the general typographic map, the rover unit of the GPS equipment was set to record automatically the three-dimensional position every two meters. The rover was then hand-carried over the Tall recording points. For this more rough work, the precision for the points is more like 10 cm. Features, such as depressions and peaks were mapped in greater detail. Over nine thousand points were taken during two mornings and part of an afternoon using two GPS units (a Javad and a Thales systems). When the data were download a simple two-dimension map of the data points could be produced quickly each day in order to check what areas might need additional coverage.

points taken on Tall
GPS data points taken on surface of Tall

Since the data were actually three-dimensional points, several models could be generated. A contour map is one of the simplest to provide a visual representation of the surface elevation features.

contour map
Contour map generated by the GIS software

Of greater utility is a false color three-dimensional image of the surface of the Tall where different elevations are represented by a different color.

elevation model
False color elevation model generated by the GIS software

An aerial photograph can then be drapped over the computer generated surface by matching several distinctive features that can be seen in the photograph with the corresponding measured feature; eg. a corner of one of the excavation fields.

aerial photo draped on elevation model
Aerial view draped over the elevation model with contours

The surface with the draped aerial photograph is a three-dimensional image that may be rotated and viewed from a variety of direction.

oblique view
oblique view from north generated by GIS software

Having this three-diensional surface with the aerial photograph showing surface features and details that can be viewed from a variety of directions and distances can be extremely helpful in identifying potential sites for additional excavation fields.

Note, in all diagrams and images, except the last, north is up.


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