As part of the Qatar Remote Sensing Project two of the most important heritage sites in Qatar, the fort at Al-Zubarah and the rock engravings at Al Jassasiya were selected for laser scanning.
THE FORT or Qal’at at Al-Zubarah is located in the north-west of Qatar in the municipality of Al Shamal and Al Jassasiya is situated towards the north east coast of Qatar in the municipality of Al Khor. Laser Scanning is the process of firing a structured laser line over the surface of an object in order to collect 3-dimensional data. The surface data is captured by a camera sensor mounted in the laser scanner which records a sub-millimetre 3D point cloud. This can be used to create a fully-rendered, three dimensional model, which is an indispensible tool for the documentation, study, preservation and publication of monuments and objects.
Helen evaluates the scanning results.
A LEICA HDS6000 was used to digitize both Al Zubarah and Al Jassasiya, this equipment is a high-speed, high-definition laser scanner which records three-dimensional positions at a pre-determined resolution over a chosen area, generating thousands of high-accuracy coordinates. The coordinates are stored as a series of XYZ measurements which visually constitute a point cloud, as a three dimensional representation of the geometric form of the scanned structure.
As well as these basic parameters, the strength (intensity) of the laser’s return signal is recorded. These ‘intensity’ readings help to map the differences in material, or material conditions, and are typically presented across a spectrum of colour from the highest recorded intensity return to the lowest.
As well as intensity data; ‘red, green, blue’ colour information was gathered in order to provide a full colour point cloud. This was collected in the field using a panoramic digital SLR (10Mp), calibrated to the height of the laser scanner.
For Al Zubarah, the additional ‘red, green, blue’ information gathered using the panoramic digital camera was then added for the purpose of the animation. It was decided not to apply colour mapping to the Al Jassasiya dataset as the sandy colour detracts from the visibility of the carvings. Using intensity values solely for this site highlights important areas of archaeology.
Qal’at Al-Zubarah serves as a pristine example of a typical Arab fort built using traditional Qatari techniques and is an extraordinarily important monument in the history of Qatar. The fort was constructed in 1938 by H. H. Sheikh Abdullah bin Qassim Al Thani on the site of a small settlement and earlier fort.
It was designed to provide defence to the northwest coast of Qatar, with soldiers (Frontier Corps) stationed at the fort until Qal’at Al-Zubarah was transferred to the Museums Authority in June 1986.
Al Zubara Fort.
The 3D data recovered from the laser scanning has already begun to identify areas within the structure that may require conservation in the future in order to ensure the long-term integrity of the monument. The 3D point-cloud has been used to highlight specific areas of structural degradation that will need further monitoring. Future scans of the fort could be compared with earlier scans in order to highlight structural changes over time.
Al Jassasiya is the site of parallel rock outcrops that host some 900 rock engravings. Despite the incredible scope of the site, the extent of the petroglyphs and irregular shape of the outcrop severely limits paper records. As such, little is known about the background and while many theories exist as to the origins or dates of the petroglyphs there is a lack of compelling evidence to support them. The shapes themselves vary from geometric patterns to representations of possible ships and boats. Along with providing an accurate sub-millimetre digital record of the plateau, the 3D geometric data will further enhance our knowledge of the understanding of this unusual site and create a comprehensive plan of the location of the rock engravings.