DOI: 10.1594/pangaea.912719
title: Gridded bathymetry from EM710 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 EM710 multibeam echosounder (MBES) was utilized to perform bathymetric mapping of high resolution in water depths of 3 m to – theoretically – 2000 m. Best quality data is, however, achieved in water depths of less than 600 m, and in rough weather conditions less than 400 m. The EM710 operates at sonar frequencies of 70 to 100 kHz. Three to five sectors divide the transmit fan, where distinct frequencies or waveforms are transmitted sequentially. 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. The transmit fan is electronically stabilized for roll, pitch and yaw. 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, ray-traced through the water column, utilizing a proper sound speed profile. During the M84/4 cruise, the EM710 was running in a 24-hour watch mode, in addition to the EM122 and the PARASOUND sub-bottom profiling system. Acquisition of EM710 data was reliable during the whole cruise; however, problems occurred during rough weather conditions, since the EM710 lost the bottom signal in depths of more than 400 m.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 (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 and a sound velocity profile were applied to the M84/4 data; there were no corrections for roll, pitch and heave. A tide correction was applied, based on the Oregon State University (OSU) tidal prediction software (OTPS) that is retrievable through MB-System. CTD measurements during the cruise were sufficient to represent the changes in the sound velocity throughout the study area. Using Mbeditviz, artefacts were cleaned manually. NetCDF (GMT) grids of the edited data as well as statistics were created with mbgrid. The published bathymetric EM710 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. 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: 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