Wintersteller, Paul; dos Santos Ferreira, Christian (2016): Gridded bathymetry from multibeam echosounder EM120 data of the cruise M72/3a and M72/3b (2007) [dataset]. PANGAEA, https://doi.org/10.1594/PANGAEA.860094

Bathymetry based on data recorded during M72-3 between 17.03.2007 and 23.04.2007 in the Black Sea. This cruise concentrated on interdisciplinary work on gas hydrates with a main focus on the gas hydrate transition zone in and below 750 m water depth. Gas hydrate environments have been studied in various geological settings, mainly of the eastern Black Sea. Origins, distributions and dynamics of methane and gas hydrates in sediments and also methane fluxes from the sediment to the water column have been the focus. Main working areas were the Sorokin Trough, an area south of the Kerch Strait and the Andrusov Ridge in Ukrainian waters and the Gudauta Ridge and Gurian Trough in Georgian waters.

Detailed description:

During the cruise M72-3 the Kongsberg EM120 multi-beam echo-sounder was used. The EM120 uses a nominal sounding frequency of 12 kHz. 191 beams 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://epic.awi.de/26725/1/Kon2007a.pdf. The EM120 multi-beam was used continuously during M72-3. The vessel's speed was 8 kn during Surveys while the opening-angle was set to 140°. On transits with speeds up to 12 kn the EM120 was running with bad data quality especially for the outer beams. Responsible person during this cruise / PI: Markus Brüning (info@pk-engineers.de), Heiko Sahling (hsahling@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 M72-3 cruise, these were not sufficient to represent the changes in the SVP profile throughout the study area, 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). The changes in SVP were applied with the mbset function within mbsystem. Due to a negative offset within the data set a positive draft correction of 10 m had to be applied with mbset while further roll, pitch, and heave corrections were not necessary for the M72-3 data. 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 currently published bathymetric grid of the cruise has a resolution of 125 m. A higher resolution is, at least partly, achievable.