DOI: 10.1594/pangaea.901949
title: Gridded bathymetry from EM1002 multibeam echosounder of RV MARIA S. MERIAN cruise MSM20/1 (Walvis Ridge)

description: Bathymetric data was recorded during the R/V MARIA S. MERIAN cruise MSM20/1 between 06.01.2012 and 15.01.2012 at the Walvis Ridge in the Eastern South Atlantic. The aim of the cruise was to investigate critical geologic parameters for continental break-up and plume processes offshore northern Namibia, like crustal thickness and structure of the underlying Earth's mantle. Geophysical methods were utilized to visualize structures relating to fossil plume and/or deformation processes. Several broadband ocean-bottom seismometers were recovered from the seafloor to gather seismological data. Hydroacoustic work during MSM20/1 was carried out as part of the "floating university" in order to teach Master students the acquisition, processing and interpretation of hydroacoustic data. The data was derived from different water depths (from upper slope down to the deep sea basin) and environments (slope, abyssal plain, Walvis-Ridge) by two KONGSBERG multibeam echosounders (MBES) EM120 and EM1002 and the sub-bottom profiler PARASOUND. 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 MSM20/1 cruise, the KONGSBERG EM1002 multibeam ecosounder (MBES) was utilized to perform bathymetric mapping in water depths of maximum 1000 m. A semi-circular transducer array with a radius of 45 cm and an angular extent of 160° transmits and receives acoustic signals at a standard frequency of 95 kHz. The systems uses different pulse lengths of 0.2 ms, 0.7 ms and 2 ms to maximize coverage in deeper waters. If the angular exceeds 100°, the transducer array will operate in three sectors with specific frequencies. With 111 beams and a beam width of 2° by 2°, the EM1002 provides the possibility of high range sampling with a maximum ping rate above 10 Hz. For further information on the system, consult https://www.km.kongsberg.com/. The position and depth of the water column is estimated for each sounding through the two-way-travel time, beam angle and ray bending due to refraction in the water column by sound speed variations. During the MSM20/1 cruise, eight sound velocity profiles (SVP) were taken, of which two were applied to the EM1002 data. EM1002 hydroacoustic data was acquired simultaneously with EM120 and Parasound sub-bottom profiles. Due to a crash of the EM120, detailed surveying was carried out with the EM1002 in the shallow waters of the continental shelf. Responsible person during this cruise / PI: Wilhelm Weinrebe (wweinrebe@ifm-geomar.de), Tilmann Schwenk (tschwenk@marum.de) & Paul Wintersteller (pwintersteller@marum.de) Description of data processing: Postprocessing and products were conducted by participants of the Floating University and 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 5.3, open source software distributed from the MBARI and L-DEO web sites, 2000-2012.) was utilized for this purpose. Eight sound velocity profiles were conducted during the cruise, of which two profiles were applied to the EM1002 data. A roll-correction of -0.15° was applied to the EM1002 data, however, there were no tide, pitch and heave corrections. Using Mbeditviz, artefacts were cleaned manually. NetCDF (GMT) grids of the edited data as well as statistics were created with mbgrid. The published bathymetric grid from the echosounder EM1002 of the cruise MSM20/1 has a resolution of 5 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). Chief Scientist: Wolfram Geissler (Wolfram.Geissler@awi.de) CR: https://www.tib.eu/en/search/id/awi%3Adoi~10.2312%252Fcr_msm20_1/ CSR: https://www2.bsh.de/aktdat/dod/fahrtergebnis/2012/20120062.htm Raw data: https://doi.pangaea.de/10.1594/PANGAEA.901471 A special thanks goes to the participants of the Floating University during MSM20/1: Gesa Barkawitz, Johanna Bruckmann, Eva Eibl, Milen Iliev, Janina Kammann, Sofia Kufner, Irena Schulten, Daniela Wolf, Timo Zander, Andre Vollmert, Monika Tangeni Emvula, Justina Nafje-Ovanhu Hamalwa