Multibeam and ROV Data from the Western Rio Grande Rise

- The two subbottom profiles were acquired aboard the N/Oc Alpha Crucis in February of 2018 with a Knudsen CHIRP 3260 operating at 3.5 kHz frequency and 2 kW power. Data was then converted to SEGY, and a simple burst noise filter was applied. Navigation was provided by an Applanix OceanMaster Inertial Navigation System (IMU) connected to two Trimble GPS antennas.

- Multibeam bathymetry data was acquired during the three expeditions: (1) For the Alpha Crucis, acquisition occurred using a Reson Seabat 7160 echosounder operating at 44 kHz. Navigation data was provided by an Applanix OceanMaster connected to two Trimble GPS antennas. Survey speed was between 4 – 4.5 knots. Sound Velocity Profiles were collected at least every other day during the survey and at least once per survey to full depth. The Patch Test was carried out in area north of the Cruzeiro do Sul Rift and applied retrospectively to the data already collected. Data processing was performed using Teledyne PDS 2000 software, following a basic workflow of spike removal, gridding, and interpolation of no-data cells. (2) For the NPqHo aboard the Vital de Oliveira, acquisition occurred using the Kongsberg SIS software with a Kongsberg EM122 echosounder operating at 12 kHz frequency and with navigation provided by a SeaPath 330 positioning system with two GNSS antennas without differential positioning. Survey speed was between 4 – 4.5 knots. Data processing occurred during acquisition on the software CARIS HIPS and SIPS and postprocessing on the software EIVA Navimodel. (3) For the operation aboard the RSS Discovery, acquisition occurred with a Kongsberg EM122 multibeam system equipped on the ship hull that used the Kongsberg SIS software and was processed in CARIS HIPS SIPS. Sound velocity data was acquired during two dips and incorporated into the data during processing. All multibeam datasets were merged and interpreted together using the software EIVA Navimodel Producer. All multibeam datasets were merged, interpreted together using the software EIVA Navimodel Producer and exported in ASCII format.

- Seafloor imaging was undertaken with the HyBIS from the UK National Oceanography Centre aboard the RSS Discovery in October of 2018. HyBIS is a ROV capable of reaching 6000 m of depth, controlled by a fibre optic cable connected to the ship, and equipped with two Super Scorpio HD cameras and one Sony HDR-CX560V camera (Murton et al., 2012). HyBIS dive objectives were to survey and sample the areas of high interest based on the analysis of the multibeam data. Depth range of the survey occurred from 620 m to 1480 m. Interpretation of ROV data occurred via the visual analysis of all video recordings post-survey, with the objective of identifying and interpreting the main geomorphological and seabed erosional structures recorded in the data.