DOI: 10.1594/pangaea.884111
title: Gridded backscatter mosaic of Venere mud volcano (MV), based on AUV MARUM-SEAL data acquisition during POS499

description: Gridded bathymetry and backscatter mosaic of Venere mud volcano (MV), based on AUV MARUM-SEAL data acquisition during the POS499 cruise, conducted between 13.10.2010 and 20.11.2010 in the Calarbrian Arc. / PI: Paul Wintersteller, Gerrit Meinecke, Markus Loher, Jens Renken, Ulli Spiesecke, Till von Wahl & Chief Scientist Gerhard Bohrmann.
description: Description of the AUV platform and the payload:The company International Submarine Engineering (I.S.E.) built the AUV MARUM-SEAL in 2005-2006 as #5 of its Explorer-Class AUVs. It is nearly 5.75 m long, with a diameter of 0.73 m and a weight of 1.35 tons in air.The AUV consists of a modular atmospheric pressure hull, designed as two hull segments and a front and aft dome. Inside the pressure hull, the vehicle control computer (VCC), the payload control computer (PCC), eight lithium batteries and spare room for additional "dry" payload electronics are located. The inertial navigation system IXBlue PHINS and the KONGSBERG multibeam-processor (VxWorks computer) are located as dry payload here. The tail and the front section, built from GRP-material, are flooded wet bays. In the tail section the motor, beacons for USBL, RF-radio, Flashlight, IRIDIUM antenna and DGPS antenna are located. The Seabird SBE 49 CTD, the Sercel MATS 200 acoustic modem, the Doppler Velocity Log (DVL, 300kHz), KONGSBERG Pencil beam (675kHz) as obstacle avoidance, the KONGSBERG EM2040 (200,300, 400kHz) implemented in 2014, the PAROSCIENTIFIC pressure-sensor and the BENTHOS dual frequency (100/400kHz) side scan sonar can be mounted as optional payload in the custom made aluminium front section. The SEAL AUV has a capacity of approx. 15,4 KWh main energy, enabling the AUV to conduct approx. 65 km mission-track lengths. However, mission-track lengths had to be reduced during POS499 due to the more energy consuming EM2040 MBES compared to former cruises.For security aspects, several hard- and software mechanisms are installed on the AUV to minimize the risk of malfunctioning, damage, and total loss. More basic features are dealing with fault response tables, including an emergency drop weight, either released by user or completely independent by AUV time-relays itself.MARUM put special emphasis on an open architecture in terms of hard- and software design of the AUV, in order to guarantee modular and flexible vehicle operations. Therefore, the VCC is based to a large extent on industrial electronic components and compact-PCI industrial boards and only few proprietary hardware boards have been implemented. The software is completely built on QNX 4.25 - a licensed UNIX derivate, open to large extents for user modifications. The payload PC is built on comparable hardware components, but running either with Windows and/or Linux. On the support vessel, the counterpart to the VCC is located on the surface control computer (SCC). It is designed as an Intel based standard PC, also running with same QNX OS and a Graphic User Interface (GUI) to control and command the MARUM SEAL AUV.Acquisition of Multibeam-Echsounder (MBES) Data:A MBES system on an AUV requires a number of auxiliary sensors for position, motion, sound velocity and depth of the vehicle. The INS PHINS delivers, based on complex Kalman filters, a position and attitude data for the AUV platform, while sound velocity (SV) is calculated utilizing a UNESCO SV equation on CTD sensor measurements. The pressure to depth calculation is based on a simplified equation, depending mainly on the latitude of the area of interest and a static factor for the recalculation. Therefore, the recorded data could be enhanced by post-processing of the pressure data with the UNESCO pressure to depth equation. The EM2040 system itself is controlled by the VCC of the AUVand records data directly on the control unit of the EM2040 (VxWorks computer) as *.all files including the option to store water column data. During former expeditions strong peaks and noise have been detected on the PAROSCIENTIFIC pressure-sensor data. Extensive lab-measurements revealed that the power supply caused this issue. During pre-cruise preparations the electrical grounding between the PHINS and the PAROSCIENTIFIC were separated, which solved this problem.A residual issue was related to the heave, which had been wrongly applied 3 times on top of the vehicles depth, through a standard form that is sent at the beginning of every acquisition from the VCC to the EM2040 control unit. In fact, MBES data recorded by AUV should avoid using any heave and simply take the depth of the vehicle plus the offset between in this case PAROSCIENTIFIC and the Tx/Rx-Array of the MBES as a valid dynamic sensor-depth.Description of data processing:The Seafloor-Imaging group of MARUM, responsible person & CI Citation Paul Wintersteller (seafloor-imaging@marum.de), conducted Postprocessing and products of the EM2040 data of AUV dives 71, 72 & 73.. The MB-system suite (Caress, D.W., and D.N. Chayes, MB-System Version 5, an open source software distributed from the MBARI and L-DEO web sites, 2000-2017) as well as QPS Fledermaus T were 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. Roll and pitch corrections were not required other than a correction for the heave and the sonar-depth, respectively. Bathymetric data has been manually cleaned for existing artefacts with MB-systems mbeditviz tool. No SV profile correction was applied.MBnavadjust, an MB-system tool, allowed rectifying for position-shifts due to e.g. DVL drift. The DVL (Doppler Velocity Log) is next to the propeller rotation the only consecutive information the INS PHINS uses to calculate the absolute position of the AUV during mission-mode. The MBnavadjust corrected navigation is evaluated with respect to plausibility e.g. to avoid strong, unrealistic tying or bending of the navigation track.NetCDF (GMT) grids of the product and the statistics were created using mbgrid. 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 6 m. A higher resolution up to 2m is achievable and used for current scientific investigations. 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. Post-processing and mosaicking steps of backscatter information in QPS Fledermaus tool FMGT (Geocoder Tools) require corrected navigation, which was extracted from MB-system after mbnavadjust corrections. This corrected navigation can be applied to the raw-data in QPS Qimera and the file can than be exported as *.gsf (Generic Sensor File). The latter was imported to FMGT and backscatter (beam time series) of these files were improved with an angular varying gain and beam-pattern correction. Finally a mosaic has been calculated within FMGT.