ALBERT

Description: Bathymetry data was acquired during R/V MARIA S. MERIAN cruise MSM4/4a in the Atlantic North West off Africa between 27.02.2007 and 16.03.2007. The cruise focused on the study of particle transport processes as well as the collection of sediments for the reconstruction of past environmental conditions in the upwelling area off NW Africa. CI Citation: Paul Wintersteller (seafloor-imaging@marum.de) as responsible party for bathymetry raw data ingest and approval. Description of processed data sources: During the MSM4/4a cruise, the hull-mounted KONGSBERG EM120 multibeam echosounder (MBES) was utilized to perform bathymetric mapping in middle to deep water depths. Two linear transducer arrays in a Mills Cross configuration transmit acoustic signals of a nominal sonar frequency of 12 kHz. The emission cone has a dimension of 130° across track and 2° along track. With a reception obtained from 191 beams, the actual beam footprint is 2° by 2°. Depending on the roughness of the seafloor, the swath width on a flat bottom is generally maximum six times the water depth. For further information on the system, consult https://www.km.kongsberg.com/. Throughout MSM4/4a the EM120 run continuously in a 24/7 schedule. In general the system worked reliable and only minor data gaps exist. The data quality is generally suitable; however, on some lines the central part of the swath, where depth detection is done using the amplitude and not the phase algorithm, is unusual noisy due to unknown reasons. Responsible person during this cruise / PI: Sebastian Krastel (sebastian.krastel@ifg.uni-kiel.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 (Caress, D. W., and D. N. Chayes, MB-System: Mapping the Seafloor, https://www.mbari.org/products/research-software/mb-system, 2017) was utilized for this purpose. Tide corrections were applied to the MSM4/4a data; but corrections for roll, pitch, and heave were not necessary. The sound velocity profiles taken during the cruise were sufficient for the MBES data. Using Mbeditviz, artefacts were cleaned manually. NetCDF (GMT) grids of the edited data as well as statistics were created with mbgrid. The published bathymetric EM120 grid of the cruise MSM4/4a has a resolution of 40 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. The DTMs projections are given in Geographic coordinate system Lat/Lon; Geodetic Datum: WGS84. All grids produced are retrievable through the PANGAEA database (www.pangaea.de). Chief scientist: Tim Freudenthal CR: https://www.tib.eu/de/suchen/id/awi%3Adoi~10.2312%252Fcr_msm04/ CSR: https://www2.bsh.de/aktdat/dod/fahrtergebnis/2007/20070089.htm