Singh, Hanuman t; Adams, Jonathan; Min dell, David; and Foley, Brendan 2000 Imaging Underwater for Archaeology. Journal of Field Archaeology volume 27 number 3: 319-328. The article by the various authors listed above concentrated on the various techniques that are used to locate and then to excavate these sites. They list and discuss the various techniques that they use. These vary from side-scanning to locate the sites to high resolution video to see how the site appears and the various locations of the artifacts. The Titanic and the Bismarck were just two of the examples that were given for recent excavations.
The article also discussed the numerous surveys of the Hamilton and Scourge that are located in Lake Ontario as well as those located in the Mediterranean and Black Seas. Acoustic mapping, high-resolution video, and robots were used in the excavations of the Titanic and the Bismarck. The article then goes on to describe the various techniques that are used in underwater archaeology. The first was acoustic imaging, which uses sound waves to map the sea floor by the reflections.
This method is useful where the area is too dark to use video cameras. Due to recent advancements in technology the images that this method can reproduce are the same quality as a photograph. The frequencies that are used in the archaeological surveys range from 10 kHz to 1 Mhz. Acoustic imaging can cover a width from several kilometers down to 10 meters. There is a trade off between range and resolution.
This depends on the frequency that is being used. Lower frequency models are either ship mounted or towed behind to give a broad picture of the site where the higher frequencies provide a much clearer image. The next method that was discussed in the article was side-scan sonar systems. This method uses an object that is shaped like a torpedo; this is then towed behind the ship at a depth that is around 10 percent of the width. The side-scan method uses two fan shaped beams, as the beams reflect off of the sea floor there is a scan line that when plotted with the other scan lines an image is created.
This method also has it's downsides as well radiometric artifacts are harder to distinguish than geometric artifacts, this can lead to some artifacts not being noticed or being confused with natural objects such as rocks. The third and final method that was discussed was optical imaging and photo mosaics. This method includes film, analog video, and digital imagery (which produces the best images). This method also has its limitations; it is subject to electromagnetic radiation as well as the fact that all of the lighting equipment must be supplied by the imaging platform.
The photo mosaic method involves moving along the predetermined gird while filming, the strips of film are then laid out in the format as the gird which then provided an overview of the area to be studied. The article went on to say that the future of underwater imaging for archaeology will use a combination of scan techniques and video imaging to create three dimensional images of the artifacts. Micro bathymetric measurements use one or more pencil beams in a certain direction in three dimensional space and records the returns to create a three dimensional image. The article concluded by stating that no one method is perfect. The authors state that in order to obtain the best images a combination of the various techniques listed above.