DOI: 10.1594/pangaea.860436
title: Gridded bathymetry from multibeam echosounder EM122 data of the cruise M84/2, off Georgia (2011)

description: Bathymetry based on data recorded during M84-2 between 26.02.2011 and 02.04.2011 in the Black Sea. The aim of the cruise was to investigate the gas hydrate distribution in sediments of the Black Sea by using several coring technics. In addition to the coring activities the installed EM122 and the PARASOUND system were used to detect gas emissions in the water column and to map large areas of possible seep sites.
description: Detailed description: During the M84-2 cruise the Kongsberg EM122 multi-beam echo-sounder was used. The EM122 uses a nominal sounding frequency of 12 kHz. 288 beams or 400 soundings with a 1°/2° footprint are formed for each ping while the seafloor is detected using amplitude and phase information for each beam sounding. For further information consult https://www.km.kongsberg.com/. The EM122 was recording constantly within the permitted areas, meaning either designated bathymetry surveys or flare imaging-surveys. Problems of proper bottom detection occurred during Leg 2a on EM122, where the inner approx. 60 beams were forming a tube form profile. Therefore the surveys during Leg 2a were done mainly with &lt;120% overlap and later during port time at Trabzon the PU-software was reinstalled to eliminate this problem. Responsible person during this cruise / PI: Paul Wintersteller (pwintersteller@marum.de), Christian Ferreira (cferreira@marum.de). Description of data processing:Postprocessing and products were conducted by the Seafloor-Imaging group of MARUM, responsible person: Paul Wintersteller (seafloor-imaging@marum.de). The open source software MB-system (Caress, D.W., and D.N. Chayes, MB-System Version 5, Open source software distributed from the MBARI and L-DEO web sites, 2000-2012.) was utilized for this purpose. A tide correction was applied, based on the Oregon State University (OSU) tidal prediction software (OTPS) that is retrievable through MB-System. In general, there is a tide differences of less than 20 cm in the Black Sea. Though CTD measurements were taken during the M84-2 cruise, these were not sufficient to represent the changes in the sound velocity throughout the transits and partial study areas, therefore a SVP correction had to be applied. The corrections of sound velocity is based on various SVP/CTD measurements throughout different cruises in the Black Sea within the last 15-20 years. In addition, the NATO Black Sea data base (http://sfp1.ims.metu.edu.tr/ODBMSDB/ODBMSDB.dll/querydb) was consulted for further CTD profiles in the given season/period of the year and in close position to the data set. The CTD data has then been used to calculate SVP by the usage of the UNESCO formula (G.S.K. Wong and S Zhu, Speed of sound in seawater as a function of salinity, temperature and pressure (1995) J. Acoust. Soc. Am. 97(3) pp 1732-1736). Changes in SVP were applied with the mbset function within mbsystem. Further roll, pitch and heave corrections were not applied for the M84-2 data, but a draft offset correction of -5 m was applied with mbset. Bathymetric data has been manually cleaned for existing artefacts with mbeditviz. NetCDF (GMT) grids of the product and the statistics were created using mbgrid. Quality assurance was furthermore proven by visual and statistical comparison of crossing survey-lines from different cruises throughout the Black Sea. No total propagated uncertainty (TPU) has been calculated to gather vertical or horizontal accuracy. The grid extended with *_num represents a statistical raster dataset with the 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 currently published bathymetric grid of the cruise has a resolution of 125 m. A higher resolution is, at least partly, achievable.