SHALLOW WATER MAPPING OF A SUBMERGED ARCHAIC-AGE HARBOR AT LIMAN TEPE, TURKEY USING DATA-FUSED MAGNETIC AND SIDE-SCAN SONAR IMAGES

Geophysical surveying of archaeological structures in very shallow water (ca. <2 m deep) can present many technical challenges, particularly where features projecting above the seabed present a hazard to navigation and towed instruments. At Liman Tepe, Turkey a multi-method geophysical survey was recently conducted to map a shallow submerged Archaic-age harbor (ca. 2800 yBP). The harbor remains include a constructed breakwater feature that lies in 0.5 to 3 m water depth. The harbor area was surveyed using a marine magnetometer, single-beam echosounder and 200 kHz side-scan sonar fixed to a small inflatable boat. The survey was collected with a line spacing of 3-5 m and D-GPS positioning in order to obtain detailed imaging of submerged structures.

Mapping and analysis was facilitated by overlay of the magnetics and side-scan sonar swaths on a digital bathymetric model (DBM) of the site created from the depth sounder data. The data-fused images clearly identify a rectangular mole feature (ca. 25 x 100 m) enclosing a small harbor basin. The magnetic and side-scan images also delineate several linear structures on the mole surface that were identified as masonry walls by diver survey. The magnetic response across the mole structure indicates that it is composed of high magnetic susceptibility materials, possibly basaltic and andesitic boulders mined from nearby wadis. Side-scan targets and magnetic lineaments also reveal the location of several possible buried architectural structures within the sediment-filled harbor basin. The results from Liman Tepe demonstrate that the fusion of magnetic and sonar data can provide important insights into the surface layout of underwater archaeological sites and the presence of buried features within seabed sediments.