Mapping the Historical Shipwreck Figaro in the High Arctic Using Underwater Sensor-Carrying Robots

Aksel Alstad Mogstad,Asgeir J Sørensen,Øyvind Ødegård,Jørgen Berge,Geir Johnsen,Stein Melvær Nornes,Martin Ludvigsen

doi:10.3390/rs12060997

Aksel Alstad Mogstad, Asgeir J Sørensen + Show 5 more

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https://doi.org/10.3390/rs12060997

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Abstract

In 2007, a possible wreck site was discovered in Trygghamna, Isfjorden, Svalbard by the Norwegian Hydrographic Service. Using (1) a REMUS 100 autonomous underwater vehicle (AUV) equipped with a sidescan sonar (SSS) and (2) a Seabotix LBV 200 mini-remotely operated vehicle (ROV) with a high-definition (HD) camera, the wreck was in 2015 identified as the Figaro: a floating whalery that sank in 1908. The Figaro is to our knowledge currently the northernmost wreck in the world to be investigated by archaeologists. As the wreck is protected by law as an underwater cultural heritage (UCH) site, only non-intrusive methods could be used during surveys. In this study, we demonstrate how using multiple complementary remote sensing techniques can be advantageous with respect to acquiring a holistic overview of a recently discovered wreck site. In January 2016, the wreck was revisited, and a full photogrammetric survey of the site was conducted with a Sperre Subfighter 7500 medium class ROV. In addition to stereo camera images, HD-video and underwater hyperspectral imagery was also obtained from the wreck site. In terms of data analysis and interpretation, the emphasis was in the current study put on the photogrammetric 3D model and the underwater hyperspectral imagery. The former provided an excellent general overview of the Figaro wreck site, whereas the latter supplied detailed information from a 14.65-m2 sub-area situated on the top of the wreck. By analyzing classified underwater hyperspectral imagery in context with supplementary information from the 3D model, the levels of biofouling associated with different marine archaeological substrate types were assessed. Our findings suggest that strongly protruding archaeological objects support significantly higher levels of biofouling than their surroundings, and consequently that high-density biological assemblages could serve as proxies for identifying human-made artifacts on the seafloor.

Highlights

The United Nations Educational, Scientific and Cultural Organization (UNESCO) estimates that there are approximately 3 million historical shipwrecks in the world that fall under the definition of Underwater Cultural Heritage (UCH) [1]
Other salient features that could be seen in the sidescan sonar (SSS) imagery were an anchor chain on the starboard side, the rudder lying flat on the seafloor next to the stern post, and parts of the rigging on the seafloor outside the port side of the wreck
The findings presented in the current study showcased the utility of combining different state-of-the-art sensor-carrying robots for assessments of wreck sites in harsh and remote areas with limited accessibility, such as the high Arctic

Summary

Introduction

The United Nations Educational, Scientific and Cultural Organization (UNESCO) estimates that there are approximately 3 million historical shipwrecks in the world that fall under the definition of Underwater Cultural Heritage (UCH) [1]. In the high Arctic areas surrounding the Svalbard archipelago, estimates suggest that more than 1000 historical wreckings have occurred [2]. Investigations of shipwrecks in the Canadian Arctic [3,4] indicate that the Arctic’s low-temperature environmental conditions are favorable for preservation of wooden wrecks and other organic materials. Technological advances within underwater robotics and remote sensing in the recent decades enable effective surveying and non-intrusive investigations of UCH in the Arctic, potentially yielding valuable knowledge and insight into less known fields of our common heritage and history [5]

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