ship were documented At times putfor the first time as a ting an archaeologist single image. in the water is not feaMosaics have sible due because of the proven to be a valudepth of the sire or hazable tool by allowing ardous sea conditions. researchers on the surTechnology has taken the lead in those cirface to view the site in cumstances, and with its entirety. Features the aid of remotely that might not be as operated vehicles and obvious at 230 feet become much more ~ submersibles we can apparent on the sur~ glimpse a once hidden face. The mosaics are ~ and inaccesible world. also invaluable to div~ The public needs to ers, helping them ori~ be aware of the limi• tations of gadgets and entate themselves on NOAA divers swim over the remains ofthe captain's quarters toward the bow section. the wreck before they software, however. begin work. This is important because at rime. Finally, since few people have the Mosaics are a remarkable tool, but they 230 feet it can be a challenge just to get deep dive training and access to dive on are never a substitute for an archaeologist to the wreck; differentiating one area from Monitor, the mosaics provide a means to on the bottom. Perhaps one day, advanceengage the public without them having ments in ocean exploration will overcome to get wet. Nevertheless, mosaics are not these faults, but, for now, my eyes, a tape Deterioration of the USS Monitor an end unto themselves. They are just one measure, and a pencil are still the most acof several research tools to document a curate and reliable tools available. .1 shipwreck. While conducting USS MoniDivers prepare to enter the water and begin their tor field work in 2003, we compared the Long descent to the shipwreck 240 feet below. mosaics with the archaeological drawings that resulted from them. When a mosaic and its accompanying site drawing were sized to the same scale and overlaid, we instantly recognized a discrepancy. Even though they were representations of the same thing at the same scale, the images did not match. Certain portions of the mosaic were aligned correctly with the drawing, however, overall, the mosaic was skewed slightly to one side or the other. The problem lies in the fact that computer sofrware is raking several separate images another can be difficult in the dim light. and artificially stitching them together to The mosaics were used as a visable guide create one single image. This procedure to sketch the site. When coupled with works remarkably well to produce a genthe actual measurements taken by divers eral "big picture" view of the wreck, bur on the wreck, archaeologists created a se- the software cannot compensate for differries of very accurate site plans. These were ing focal lengths and oblique angles that drawings that were never possible before occur when the individual pictures are because of the limitations imposed by stitched together. The software attempts scuba diving. NOAA now has an accurate to solve these problems by making a best archaeological record of the site docu- fit, aligning the same feature in two immenting the changes caused by the major ages. This error compounds with the addiTane Casserley is a Nautical Archaeologist with NOAA's Monitor National Marine tion of every still image to the point that, artifact recoveries. Conducted over several years, mosa- when compared at the same scale to the Sanctuary in Newport News, VA. For more ics could also be very useful as a record to drawing, the mosaic will appear stretched information on USS Monitor, visit their web site: www.monitor.noaa.gov. determine how the Monitor decays over at either end. SEA HISTORY 108, AUTUMN 2004
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