Abstract
There is an increasing demand for high-resolution recording of in situ underwater cultural heritage. Reflectance transformation imaging (RTI) has a proven track record in terrestrial contexts for acquiring high-resolution diagnostic data at small scales. The research presented here documents the first adaptation of RTI protocols to the subaquatic environment, with a scuba-deployable method designed around affordable off-the-shelf technologies. Underwater RTI (URTI) was used to capture detail from historic shipwrecks in both the Solent and the western Mediterranean. Results show that URTI can capture submillimeter levels of qualitative diagnostic detail from in situ archaeological material. In addition, this paper presents the results of experiments to explore the impact of turbidity on URTI. For this purpose, a prototype fixed-lighting semisubmersible RTI photography dome was constructed to allow collection of data under controlled conditions. The signal-to-noise data generated reveals that the RGB channels of underwater digital images captured in progressive turbidity degraded faster than URTI object geometry calculated from them. URTI is shown to be capable of providing analytically useful object-level detail in conditions that would render ordinary underwater photography of limited use.
Highlights
The UNESCO convention on the protection of the underwater cultural heritage (UCH) (2001) establishes within the first sentence of rule 1 that “in situ preservation shall be considered as the first option.” This has precipitated a corresponding shift in disciplinary thought, with preservation in situ widely espoused as best practice.[1,2,3,4] as Maarleveld et al.[5] make clear, rule 1 should not be misinterpreted to mean that archaeological research is being discouraged, rather that we need to focus on improving practices for engaging with a finite resource
This paper demonstrates for the first time that underwater reflectance transformation imaging (URTI) offers a viable method to extract unprecedentedly high levels of diagnostic detail from the surface of in situ submerged objects
It should be noted that Reflectance transformation imaging (RTI) is typically used as an accessible, qualitative photography tool, not as a replacement for 3-D scanning or photogrammetry for example, and we argue for a similar qualitative value of Underwater RTI (URTI) here
Summary
The UNESCO convention on the protection of the underwater cultural heritage (UCH) (2001) establishes within the first sentence of rule 1 that “in situ preservation shall be considered as the first option.” This has precipitated a corresponding shift in disciplinary thought, with preservation in situ widely espoused as best practice.[1,2,3,4] as Maarleveld et al.[5] make clear, rule 1 should not be misinterpreted to mean that archaeological research is being discouraged, rather that we need to focus on improving practices for engaging with a finite resource. The UNESCO convention on the protection of the underwater cultural heritage (UCH) (2001) establishes within the first sentence of rule 1 that “in situ preservation shall be considered as the first option.”. This has precipitated a corresponding shift in disciplinary thought, with preservation in situ widely espoused as best practice.[1,2,3,4] as Maarleveld et al.[5] make clear, rule 1 should not be misinterpreted to mean that archaeological research is being discouraged, rather that we need to focus on improving practices for engaging with a finite resource. These systems are often expensive to acquire
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