ALBERT

Description: Between 30.10.2007 and 28.11.2007, bathymetric data was acquired on the continental margin of Pakistan in the Makran subduction zone during R/V METEOR cruise M74/3. This expedition builds on the findings of the previous cruise M74/2, which was dedicated to a systematic seep search in the working area, where several bubble flares, backscatter anomalies and distinct seismic records were detected by using sidescan sonar, multi-channel seismics and a sediment echosounder. These findings provided the basis for detailed surveying during the cruise M74/3. The multibeam echosounders (MBES) KONGSBERG SIMRAD EM120 and EM710 were utilized for extensive mapping of the working area, which is essential for most investigations. Furthermore, bathymetric mapping during M74/3 significantly increased the resolution of previous bathymetry grids and provided information for the deployment of the remotely operated vehicle (ROV) MARUM-QUEST. The ROV was utilized to map the seafloor, take samples at potential seep sites and deploy and recover autonomous tools, such as a bubble-meter and in-situ pore water sampler. 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 M74/2 cruise, the hull-mounted multibeam ecosounder (MBES) KONGSBERG SIMRAD EM710 was utilized to perform bathymetric mapping. The system is optimised to survey with high resolution in water depths of maximum 1,000 m depth and uses a frequency range from 70 to 100 kHz. 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. As most of the working area during M74/3 was deeper than 1,000m water depths, the EM710 was used sporadically as an addition to the EM120. Systematically biased outer beams produced problems in areas with large overlap of parallel profiles. The applied sound velocity profile and a roll bias were tested as possible error sources, but no significant error was found. As the effect seems to be strongest on steep slopes, it might be a problem in yaw, which was not corrected for so far. Responsible person during this cruise / PI: Markus Brüning Chief Scientist: Gerhard Bohrmann (gbohrmann@marum.de) CR: https://www.tib.eu/en/search/id/awi%3Adoi~10.2312%252Fcr_m74/ CSR: https://www2.bsh.de/aktdat/dod/fahrtergebnis/2007/20070155.htm