Preface The expedition ARK XIX/3 with the German icebreaking RV ...

During the leg ARKXIX/3a ground truths for the backscatter analyses were collected at
different sites along the eastern slope of the Porcupine Seabight southwest of Ireland.
One site is located in the Gollum Channel system and a second area is situated south of
the Belgica mound province (->reference to overview map). The locations have been
determined based on bathymetry and backscatter data recorded during leg ANTVII/4. The
sites were selected because of a significant change in backscatter characteristics. The
changes within the Gollum Channel may be due to the flow regime in the channel that
had driven the sedimentation. The segments south of the Belgica province are isolated
areas and represent different seafloor facies, such as a depression area, a sloped area
and a stripe of low backscatter indicating flowing activity. The focus of the cruise was to
get a complete data set of the selected seafloor areas. It includes bathymetry, micro
bathymetry and angular backscatter data, sediment samples and video observations.
The deployment of ROV "Victor" 6000 was realised in the northernmost Gollum Channel
(Fig. A4.2.2-2). Using the multibeam module of the ROV the micro-bathymetry of that
channel along with video observations and vertical images have been recorded to obtain
information about the microstructure of the seafloor along the track lines.
Due to bad weather conditions the planned transect could not be finished completely.
Finally, a transect of the Channel and grid surveys at three selected locations were
completed. The grid surveys were selected to investigate differences between the
Polarstern Hydrosweep system (15.5kHz) and the Seabat 8125 micro bathymetric system
(455kHz) in terms of accuracy and resolution of the depth measurements and backscatter
data. The application of a shallow water echo sounder onboard "Victor 6000" establishes
the opportunity of recording backscatter data in addition to the Hydrosweep data for
comparison of areas.
The grids have a size of approximately 150 x 150m that corresponds to 3x3 footprints of
the Hydrosweep system. Since the seafloor segments represent homogenous seafloor
cover (based on the Hydrosweep backscatter data), results of the grids can stand for the
entire segment. The data of the tracks between the grid sites are recorded to examine the
backscatter and micro bathymetry change along the bottom of the channel. The flight
height during the survey was 10m. Altogether approximately 7nm of micro bathymetry
survey line have been recorded. The depths range from 1700m to 1300m.
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