DOI: 10.1594/pangaea.902504
title: Gridded bathymetry from EM122 multibeam echosounder of RV METEOR cruise M84/4 (Northeast Atlantic)

description: Bathymetry data was acquired during R/V METEOR cruise M84/4 at the Galician Shelf off Northwest Spain in the Northeast Atlantic between 01.05.2011 and 28.05.2011. The main objectives of the cruise were the investigation of sediment transport processes from shallow to deep waters, understanding sediment dynamics, analysis of material downslope processes and the reconstruction of modern and past environmental conditions. The cruise comprised seismic, sedimentological, magnetic, geochemical and palaeoceanographic methods. Extensive bathymetric mapping during M84/4 based on the multibeam echosounders (MBES) KONGSBERG EM710 and EM122 provided the basis for sediment coring and additional investigations. Hydroacoustic data revealed the diverse morphology in the study area, driven by both sedimentary and tectonic processes, including contouritic deposits, slope gullies, canyon/channel systems, ridges and seamounts. The sub-bottom profiler PARASOUND, multichannel seismics, ADCP, several coring devices and the electromagnetic profiler MARUM-NERIDIS III complemented the research programme of 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 M84/4 cruise, the hull-mounted KONGSBERG EM122 multibeam ecosounder (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. With 432 soundings per swath, the emission cone has a dimension of 150° across track and 1° along track. With a reception obtained from 288 beams, the actual beam footprint is 1° 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/. 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 M84/4 cruise, the EM122 was running simultaneously with the EM710 and PARASOUND sub-bottom profiling system. Acquisition of EM122 data was reliable during the whole cruise, but data quality declined during rough weather conditions, causing wobbling in depths of more than 2000m. Responsible person during this cruise / PI: Tilmann Schwenk (tschwenk@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 5.7, open source software distributed from the MBARI and L-DEO web sites, 2000-2012.) was utilized for this purpose. Tide and roll corrections and a sound velocity profile were applied to the M84/4 data; there were no corrections for pitch and heave. Using Mbeditviz, artefacts were cleaned manually. NetCDF (GMT) grids of the edited data as well as statistics were created with mbgrid. The published bathymetric EM122 grid of the cruise M84/4 has a resolution of 35 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: Till J. J. Hanebuth (thanebuth@coastal.edu) CR: https://www.tib.eu/de/suchen/id/awi%3Adoi~10.2312%252Fcr_m84_4/ CSR: https://www.ldf.uni-hamburg.de/meteor/wochenberichte/wochenberichte-meteor/m84/m84-4-scr.pdf Raw data: not yet