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 EM710 was utilized to perform bathymetric mapping. The EM710 transmits a frequency range of 70 to 100 kHz and is optimal for data acquisition in water depths shallower than 1,000 m. The swath width can reach 5.5 times the water depth. 256 beams with an acoustical 1°(TX)/1°(RX) footprint are formed for each ping. Combining phase and amplitude bottom detection algorithms allows achieving best possible accuracy. For further information, consult: https://epic.awi.de/id/eprint/26726/1/Kon2007b.pdf. The position and depth of the water column is estimated for each beam by using the detected two-way-travel time and the beam angle known for each beam and taking ray bending due to refraction in the water column by sound speed into account. During the M76/3a cruise, the multibeam echosounder EM710 served as an addition to the EM120. Since the working area was mainly located in water depths deeper than 1,000 m, the EM710 was only used episodically. Responsible person during this cruise / PI: Volkhard Spieß (vspiess@uni-bremen.de) Chief Scientist: Volkhard Spieß (vspiess@uni-bremen.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
