Computer Vision Photogrammetry for recording and monitoring in visibilities of less than 50 centimetres

Feiko WILKES
(Christian-Albrechts-Universität zu Kiel, Kiel, Germany)

Keywords: Underwater Archaeology, Monitoring, Recording, Photogrammetry, Agisoft PhotoScan

Abstract:
Very low visibility of mostly less than 0.50 meters is the main obstacle for underwater archaeological work on sites in the limnic waters of Northern Germany. Coupled with the loose sediments and low natural lighting often encountered on such sites the toolset typically used for recording in underwater archaeology can’t be applied here for the most part. This paper shows the workflow and experience gained by applying Computer Vision Photogrammetry in such an environment for recording and monitoring with a cost-effective approach, using GoPro cameras and Agisoft PhotoScan. It is based on the archaeological surveys conducted on the Fahrdorf wreck site in the Schlei fjord from 2015 to 2017 by the Study Group for maritime and limnic Archaeology of the University Kiel (AMLA). This early 12th century wreck located in shallow waters with a visibility of usually around 30 and never exceeding 50 centimetres was documented by video with different camera and lighting configurations and settings. A georeferenced system of permanent markers was established, allowing us to link the results of different campaigns for monitoring purposes and to extend the survey area without the need for further measurements. Different ways of extracting single frames from video were tested and compared regarding the quality of the results and the time required both for generating the pictures and the duration of processing with Agisoft PhotoScan.