Phase 2 - Evaluation & Predisturbance Survey
Archaeologists use a baseline/crossline system to form a grid over a shipwreck site |
Once a site has been found it may be selected for more intensive survey and evaluation. At this point, archaeologists must pose more site-specific questions. A Phase II, or predisturbance survey, is non-intrusive and involves recording the site as it is, generally with no excavation or retrieval of artifacts. Representative artifacts and construction features that may indicate a site's age or cultural significance are examined, sketched, and left in place. This level of documentation usually includes taking precise measurements and developing a detailed map of the site. Other evaluations, such as identifying potential threats (human and natural), recreational possibilities and preservation needs are also made during a Phase II survey. Ideally, a Phase II survey is done soon after a shipwreck is found, though many shipwrecks are popular dive sites for many years before they are archaeologically studied.
Phase II surveys employ a variety of mapping and documentation methods. In producing a site map, the simplest method is to use tape measures and graduated baselines to map out fixed points in relation to one another. Using basic geometry to measure trilaterated, triangulated, and offset distances, archaeologists are able to "tie" all of the wreck's different components together.
Hetty Taylor site plan |
A team of archaeologists working on a shipwreck site will utilize a system that involves a baseline and several intersecting crosslines, which together form a grid over the site. Each "square" in the grid serves as a frame of reference. Each member of the field crew will be assigned a different "square" and map the contents within his or her square using a pre-determined scale. Eventually, the individual scaled drawings will be pieced together to form an overall picture of the site, called a site plan.
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