DOI: 10.1594/pangaea.902708
title: Gridded bathymetry from EM120 multibeam echosounder of R/V METEOR cruise M76/3A (Eastern South Atlantic)

description: Between 07.06.2008 and 13.07.2008, bathymetric data was acquired in the Eastern South Atlantic during the R/V METEOR cruise M76/3a. The expedition was dedicated to giant deep sea pockmark structures on the West African margin (primarily in the lower Congo Basin), which represent sites of significant fluid and gas seepage, occurrence of gas hydrates and carbonate precipitates and host large seep-related ecosystems. The aim of the cruise was to study the external controls of seepage by structural seismic and acoustic studies and sampling. Bathymetric mapping with the multibeam echosounders (MBES) KONGSBERG SIMRAD EM120 and EM710 provided the basis for the identification of seep locations and therefore access to appropriate sampling sites in order to investigate control parameters of gas and fluid migration systems and associated vent communities. In addition to the MBES, a sub-bottom profiler, multichannel seismics, the MARUM autonomous underwater vehicle (AUV) SEAL 5000, a TV-sled and sediment sampling devices were utilized during the cruise. 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 M76/3a cruise, the hull-mounted echosounder KONGSBERG SIMRAD EM120 was utilized to perform bathymetric mapping. The EM120 transmits a nominal sounding frequency of 12 kHz and can perform up to full ocean depth. It generates 191 beams with a 1°(Tx)/2°(Rx) and a maximum opening angle of 140°. The system was set to obtain equally spaced soundings and to compensate the ship's yaw movements. The actual opening angle was limited either by the maximum angle possible, a maximum angle set or a maximum coverage on the seafloor and was adjusted to the requirements of individual surveys. For further information consult: https://epic.awi.de/26725/1/Kon2007a.pdf Responsible person during this cruise / PI: Volkhard Spieß (vspiess@uni-bremen.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 5.4, open source software distributed from the MBARI and L-DEO web sites, 2000-2012.) was utilized for this purpose. Surface sound velocity and sound velocity profiles were applied to the M76/3a data. There were no tide, roll, 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 of the EM120 during M76/3a has a resolution of 100 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: Volkhard Spieß (vspiess@uni-bre¬men.de) CR: https://www.marum.de/Binaries/Binary3720/Fahrtbericht-M76-1-3a-b.pdf CSR: https://www2.bsh.de/aktdat/dod/fahrtergebnis/2008/20080171.htm Raw data: https://doi.pangaea.de/10.1594/PANGAEA.901652