ALBERT

Description: Raw Sub-bottom profiles based on acquisition recorded during Meteor expedition M167 between 17.10.2020 and 31.10.2020 in the Alboran Sea and Gulf of Cadiz. The aim of the cruise was to investigate the mud volcanoes of the region. The sub-bottom profiler Parasound P70 (Atlas Hydrographic GmbH) was operated to provide high resolution information of the uppermost 50-100 m of the subseafloor sediments. This system is a hull mounted parametric echo-sounder which utilizes the parametric effect based on non-linear relations of pressure and density during sonar propagation. Two high intensity waves with frequencies of 18‐20 kHz (primary high frequency, PHF) and 22-24 kHz were used to create a secondary high (about 40‐42 kHz) and a secondary low frequency (SLF) of about 4 kHz. While the SLF is used for the sub-bottom profiling, the PHF signal can be recorded synchronously to image potential gas bubbles, plankton, fishes or nepheloid layers in the water column. The footprint corresponds to size of about 7% of the water depth due to an opening angle of the transducer array of 4° by 5°. The chosen stetting of the P70 during cruise M167 are listed as follows: Desired SLF: 4 kHz (in the Alboran Sea), 3.5 kHz (in the Gulf of Cadiz) Desired PHF: 18 kHz Pulse type Continuous Wave with a length of 250 ms Pulse shape: Rectangular Depth Search Window: Mode Variable Min/Max Depth Limit System Sounding Depth: Other / EM122 For more details on data acquisition please see the M167 cruise report. Data quality: For the standard operation, a parametric frequency of 4 kHz in the Alboran Sea and 3.5 kHz in the Gulf of Cadiz as well as a sinusoidal source wavelet of 2 periods was chosen to provide a good relation between signal penetration and vertical resolution. The transmission sequence was established as a single pulse mode with manual system depth of the multibeam echosounder EM122 system. The PHF and SLF signal were recorded permanently. The Parastore software was used for the monitoring and quality control of the incoming data. It controls the data recording, processing, and visualization. All raw data were stored in the *.ASD data format, which contains the data of the full water column of each signal as well as the full set of system parameters. Additionally, the data was recorded in compressed *.PS3 files every 100 mb or 60 min, with the carrier frequency and the necessary geographical coordinates (UTM 29/30 and Lat/Lon).