Gridded bathymetry from EM120 multibeam echosounder of RV SONNE cruise SO222 (offshore Japan)

Bathymetry data based on multibeam echosounder (MBES) KONGSBERG EM120 was conducted during R/V SONNE cruise SO222 between 09.06.2012 and 30.06.2012 (Leg A) and 04.07.2012 and 18.07.2012 (Leg B) in the Nankai Trough off Japan. The main objective of the cruise was MeBo drilling and long-term monitoring of active mud volcanoes in the northern Kumano Basin, which carry gas hydrates and are overlying an area of high strain. Hydroacoustic work on board aimed at a high spatial coverage of the Kumano Basin and its mud volcanoes. Furthermore, bathymetric mapping revealed additional features in the study area, of which five previously unknown mud volcanoes were identified. Additionally, coring with gravity corers and the MARUM-MeBo70 drill rig as well as the deployment of CORK observation instruments and the remotely operated vehicle (ROV) MARUM-QUEST helped to study the activity and products of mud volcanoes in the Kumano Basin.

CI Citation: Paul Wintersteller (seafloor-imaging@marum.de) as responsible party for bathymetry raw data ingest and approval.

Description of the data source: During the SO222 cruise, the hull-mounted KONGSBERG EM120 multibeam ecosounder (MBES) was utilized for bathymetric mapping as it is able to perform in water depths up to 11,000 m. Two transducer arrays transmit acoustic signals of 11.25 to 12.6 kHz in successive emission-reception cycles. 191 overlapping beams in a 2° (TX) by 2° (RX) footprint form each acoustic ping, resulting in a beam width of maximum 150° across track and 2° along track. For further information on the system, consult https://www.km.kongsberg.com/. The depth of the water column is estimated through the two-way-travel time, beam angle and ray bending due to refraction in the water column by sound speed variations. Combining lateral and center beams secures measurement accuracy practically independent of the beam-pointing angle. During the cruise SO222, the MBES and PARASOUND sub-bottom profiler were continuously acquiring data of about 1500 km track lengths. Two sound velocity profiles (SVP) were calculated based on SEABIRD CTD measurements and applied to the MBES, whereas no SVP was available for the southern Kumano Basin due to strong currents.

Responsible person during this cruise / PI: Paul Wintersteller (pwintersteller@marum.de)

Description of data processing: Postprocessing and products were conducted by the Seafloor-Imaging & Mapping group of MARUM/FB5, responsible person: Paul Wintersteller (seafloor-imaging@marum.de). The open source software MB-System suite (Caress, D.W., and D.N. Chayes, MB-System Version 5.5, open source software distributed from the MBARI and L-DEO web sites, 2000-2012.) was utilized for this purpose. CTD measurements were carried out to conduct sound velocity profiles (SVP), which were applied during the acquisition of the hydroacoustic data. A roll correction was applied to the SO222data. Tide, pitch and heave corrections were not applied. Using Mbeditviz, artefacts were cleaned manually. NetCDF (GMT) grids of the edited data as well as statistics were created with mbgrid. The published bathymetric grids of the cruise SO222 have a resolution of 30 m. No total propagated uncertainty (TPU) has been calculated to gather vertical or horizontal accuracy. A higher resolution is, at least partly, achievable. The grid extended with _num represents a raster dataset with the statistical number of beams/depths taken into account to create the depth of the cell. The extended _sd -grid contains the standard deviation for each cell. All grids produced are retrievable through the PANGAEA database (www.pangaea.de). Projection: Geographic Coordinate System / WGS84

Chief Scientist: Achim Kopf (a.kopf@marum.de) CR: http://elib.suub.uni-bremen.de/edocs/00103543-1.pdf CSR: https://www2.bsh.de/aktdat/dod/fahrtergebnis/2012/20120280.htm Raw data: https://doi.pangaea.de/10.1594/PANGAEA.901244