Survey report for the inner Danish waters and the Baltic Sea around Bornholm, 2022. Geological screening for offshore wind farms, the Danish Energy Agency

GEUS has carried out fieldwork as part of a geological screening for offshore wind farms for the Danish Energy Agency (DEA) in 2022 in the inner Danish waters and the Baltic Sea. The purpose of the survey was to acquire geophysical data, with particular focus on multichannel sparker seismic data, in regions with lack of data and geological information in order to establish a better basis for developing conceptual geological models and mapping geological units of importance for offshore wind farm development.

The survey, hereafter referred to as the ENS 2022 survey, started November 14 and was
completed December 11. The ENS 2022 survey include six large areas: Læsø North, Læsø South, Anholt South, Køge-Kriegers Flak, Vejsnæs Flak and Bornholm. The activities were carried out using the survey vessel Fortuna Crane and involved three legs of geophysical mapping with single and multichannel seismic. Sub-bottom profiler, multibeam echo sounder and side scan sonar were obtained to support the seismic mapping.

Mobilization of the geophysical equipment took place in Hundested harbor from November 11 to November 14. The crew change between Leg 1 and Leg 2 took place in Skagen harbor on November 19 and the crew change between Leg 2 and Leg 3 took place in Køge harbor on December 2. Demobilization after the survey took place in Køge harbor on December 12.

The survey plan for the ENS 2022 survey included 4103 km of survey lines in Inner Danish waters and the Baltic Sea. Læsø North, Læsø South and Anholt South areas include 687 km, 909 km and 1109 km of planned lines in Kattegat, respectively. In addition, 530 km of lines were planned to be acquired in Køge-Krieger area, 126 km in the Vejsnæs Flak area and 742 km around Bornholm.

Leg 1 acquisition started off Hundested on November 14 surveying in the Anholt South, Læsø South and Læsø North areas. Weather conditions forced 70 hours of weather standby at Skagen harbor. A total of 407 km of data were acquired before Leg 1 ended with GEUS crew change in Skagen on November 19.

Leg 2 acquisition started off Skagen on November 20 surveying in the Læsø North, Læsø South, Vejsnæs Flak and Anholt South areas. Bad weather conditions on November 23 were used for transit to Vejsnæs Flak and picking up personnel in Fredericia. A total of 1604 km of geophysical data were acquired during Leg 2 before the GEUS crew change in Køge on December 2.

Leg 3 acquisition started off Køge on December 2 surveying in the Køge-Krieger and Bornholm areas. A total of 1280 km of data were acquired during Leg 3. The ENS 2022 survey finished in Køge on December 11, followed by demobilization of the geophysical equipment. A total of 3291 km of geophysical data were acquired along the planned survey lines (Figure 1) during the ENS 2022 survey. Details on the survey lines and transits are provided in the survey log included as Appendix A

A GAMS calibration of the positioning system for the geophysical data acquisition on board Fortuna Crane was performed on October 22 during another GEUS survey immediately prior to the ENS 2022 survey and a multibeam patch test was performed during Leg 3 on December 5 over the southern slope of the Bakkegrund Syd raw material area near Bornholm.