The Advantages Of Underwater Photogrammetry: Famous Shipwrecks, SS Thistlegorm

Do you ever wonder how to scan, scale, and geo-locate a large underwater structure like the SS Thistlegorm with photogrammetry? The process of recording historical and archaeological sites is changing due to technological advancements. In the past, a pencil, paper, and some artistic skill were the standard method of recording a site.

However, modern cameras and software make it possible to record a large site, like the SS Thistlegorm, using underwater photogrammetry. Traditional documentation methods remain useful but have limited capacity to identify changes over time.

underwater photogrammetry of SS Thistlegorm
Viewed from the port side the 2017 survey covered the main wreck site. The port and starboard locomotive boilers were located and added during the 2022 fieldwork.

History of SS Thistlegorm

Accupixel believes that the Thistlegorm ranks among the world’s best shipwreck dive sites. However, it serves as a maritime grave for 9 sailors attacked by Luftwaffe aircraft in 1941. Today, at depths of 12-32 msw, the wreck functions as an underwater museum. Attracting Egypt’s Red Sea Tourism and providing a space to reconnect with shared cultural heritage, Thistlegorm is a bucket-list dive. Due to its extensive and encompassing history, this shipwreck remains a favorite for visitation, diving, and study.

A unique site for underwater photogrammetry…

What makes Thistlegorm a unique site for underwater photogrammetry is that it is too big to capture in one dive. Massive complex objects, like this iconic shipwreck, require an approach that ensures not only individual images align, but differing areas of the wreck assemble to form a single, continuous model over multiple dives.

Digital Elevation Model (DEM)
Digital Elevation Model (DEM) of the SS Thistlegorm as recorded in 2017 with colour shader applied in Global Mapper to highlight the depth of water.

Partnering with Maritime Archaeologists for marine surveys

In partnership with Professor Jon Henderson of Edinburgh University, co-authoring, the paper featured in the Journal of Marine Science and Engineering. Firstly, the paper covers planning, image capture, and post-dive data management of the photogrammetry scans of SS Thistlegorm.

Secondly, the paper also explores the validation of constraints applied to scale the wreck. Entitled, “Recording the SS Thistlegorm: Rapid Multi-Image Underwater Photogrammetric Survey of a Large Second World War Wreck,” Accupixel is proud to present this publication. By using Underwater photogrammetry of SS Thistlegorm, we can identify changes to the site. One full scan of the wreck was conducted in 2017 and in 2022 smaller areas thought to be at risk of disturbance and change were surveyed.

comparing ship blueprints to a model
Main site ortho mosaic overlaid in Global Mapper with manually rectified contemporary builders plans.
We added vector area data to emphasize the location of the holds (highlighted in yellow) and hold entrances (highlighted in green) Source: Tyne & Wear Museum DS.JLT.4.PL.599.9.2.

In the future, we will publish a separate paper providing a detailed review of the changes identified between 2017 and 2022. This paper reveals a range of differences, including discreet alterations, strong evidence of commercial salvage, and instances of live ammunition disturbance.

underwater photogrammetry
The distance between buffers of the port smoke box section of the Stanier 8F is measured to be 1.72m. Contemporary engineering drawings record this distance at 5′ 8″ (1.7272m).

Reading about Underwater Photogrammetry of SS Thistlegorm

We would encourage anyone working in the field of photogrammetry to have a read of the paper, for the methods and techniques discussed would apply to complex and challenging terrestrial projects, as well as those underwater.

underwater photogrammetry
Section of the wreck, taken at frame 94 looking forward, compared to contemporary builders plan section taken midships. Historical information and documentary evidence contribute key insights to the vessel and its history, as detailed in the paper. Blueprint © Lloyds Register Foundation

The issues encountered whilst establishing accuracy were challenging but highlight the extreme value of cultural archives, not least of which is the Lloyds Register Foundation whose contemporary documents have permitted direct comparison between the wreck today, and when constructed.

Moving forward with underwater surveys

In conclusion, we extend an invitation to explore history and technology through Accupixel’s underwater photogrammetry study on the SS Thistlegorm. Collaborating with Professor Jon Henderson, we reveal the secrets of this iconic World War II wreck. Our recent publication reflects our commitment and documenting the evolution of techniques.

Considering the nuances of planning, image capture, and post-dive data management, Thistlegorm transcends its role as a maritime grave. It emerges as an underwater museum, inviting enthusiasts to connect intimately with our shared cultural heritage.

Looking ahead, our commitment to unmasking Thistlegorm’s mysteries persists. Furthermore, a forthcoming paper will meticulously detail observed and measured changes over time, providing insights into discreet alterations, hints at commercial salvage, and instances of live ammunition disturbance.

Join us in this immersive journey, where technology intertwines with history, preserving the legacy of a bygone era in every scan.

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