Closing in on the Fortuyn: using Fledermaus in planning and post-processing
The Australia-based non-profit organization ShipShapeSearchers (hereafter, SSS) has been a QPS-sponsored Fledermaus user since 2014. SSS is currently involved with a maritime archaeology project centered around Christmas and Cocos Islands in the Indian Ocean; the quest is being referred to as "Closing in on the Fortuyn" or the Fortuyn Project. Research of primary historic documents has provided evidence that the Dutch East Indiaman trading vessel, Fortuyn, was likely to have wrecked at Christmas Island in 1724. A second target, Dutch trader Aagtederke, disappeared in 1726 and may have wrecked on Cocos. This project includes finding and recording of submerged heritage material as it is discovered during the survey.
Surveys were conducted from January 19th through February 8th 2015, utilizing a proton magnetometer. Towed behind a vessel, this instrument detects changes caused in the earth's magnetic field by the presence of ferrous metal material, such as cannon and anchors. The most effective way to run such a survey is in straight parallel lines, or transects.
Bathymetric multibeam and lidar data for both islands were obtained from Australian Hydrographic Service, and GeoScience Australia. This data was viewed in Fledermaus and allowed planning of detailed survey transects. Regional scale bathymetry provided a key to understanding the geological context of the islands – how they rose up thousands of meters from the ocean floor (F ) and the ongoing environmental processes.
Figure 1: View of Christmas Island and surrounding multibeam batymetry. Data provided by Geoscience Australia.
Figure 2: Plan view of Christmas Island and surrounding multibeam bathmetry. Data provided by Geoscience Australia.
The bathymetric lidar data provided a more detailed view of the narrow shelving around the islands. Christmas Island is characterized by nearly continuous sea cliffs, which become a shelf with depths between zero and -50 meters extending out an average of 250 meters before plunging down. The target depth was six meters, the estimated draft of a laden trading vessel of the period. This, in addition to operational safety margins, meant tight restrictions for the transects were required.
Fledermaus allowed SSS to lay out transect lines very precisely. The requirements for effective archaeological survey were combined with those of the vessel in the very early stages of planning (F). Using fixed-depth colormaps set up to highlight specific depth ranges allowed SSS to carefully avoid areas that were too shallow for the survey vessel (Figure 5). The software also allowed the production of profiles for each transect, which assisted with further planning (Figure 6). Hard copies were taken into the field, where they were used for planning dive operations.
Figure 3: Survey transects surrounding Christmas Island, laid out in Fledermaus. Data provided by Australian Hydrographic Service and Geoscience Australia.
Figure 4: Survey transects surrounding Christmas Island, laid out in Fledermaus. Data provided by Australian Hydrographic Service.
Figure 5: Survey transects surrounding Christmas Island, laid out in Fledermaus. The colormap in this image highlights specific depths, allowing easy avoidance of shallow areas during planning. Data provided by Australian Hydrographic Service.
Figure 6: Example of profile image for survey transect, Cocos Island. Data provided by Geoscience Australia.
Now that this season's field data has been collected, analysis and interpretation is occurring. The location of anomalies has been inputted into Fledermaus to provide a greater understanding of these areas of interest, and at the same time provide information for further planning of the next season's fieldwork. QPS looks forward to hearing more about this ongoing project. To keep updated on this project, visit and like the Fortuyn Project Facebook page: https://www.facebook.com/FortuynProject
Thank you to Alex Moss of ShipShapeSearchers for providing us with this story.
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