When it comes to marine archaeology, the most common (and perhaps most popular) type of sites studied are shipwrecks. However, marine archaeologists also investigate other kinds of sites, such as flooded land sites or fishing structures.
The tools used to locate underwater archaeological sites are essentially the same ones used to explore the seafloor. The first step is getting a “big picture” view, often through the use of multibeam sonar or a magnetometer. Sometimes, we stumble upon potential archaeological targets accidentally using these tools and sometimes we have a good sense of exactly where to look.
Once a target is identified and mapped, scientists must visually survey the area, to verify if it is indeed an archaeological site and to document the site fully. Remotely operated or autonomous underwater vehicles can be used to collect a large number of images and videos of the site. If the site is at a depth shallower than ~45 meters (150 feet), photos/video of the site may be taken by SCUBA divers, who may also make measurements and hand-drawn maps.
Scientists also use oceanographic instrumentation to measure ocean currents, temperature, salinity, pH, and oxygen in the water around an underwater site, to assess environmental conditions and determine the long-term integrity of the site.
Collected imagery can be used to digitally reconstruct and preserve these sites. Recent advances in photogrammetry allow scientists to stitch together multiple images to create three-dimensional models of sites, providing different perspectives from all angles and distances. These and other emerging techniques allow for the non-invasive study of important cultural resources.
In instances where excavation is required, such as at a flooded land site, underwater archaeological excavation is very similar to traditional land archaeology. Marine archaeologists use similar tools, but will opt for the plastic version of the tool so that it does not fall apart in the salt water. Most “tools of the trade” used on terrestrial archaeological digs are used for underwater excavations as well. Hand trowels, square units, clipboards, pencils, tape measures, and other hand tools are all used underwater to excavate sites as they are used on land.