Remotely Operated Vehicle (ROV) imagery - Caswell Sub-basin, Browse Basin Marine Survey (GA0345/GA0346/TAN1411)

Brief description

Geoscience Australia (GA) conducted a marine survey (GA0345/GA0346/TAN1411) of the north-eastern Browse Basin (Caswell Sub-basin) between 9 October and 9 November 2014 to acquire seabed and shallow geological information to support an assessment of the CO2 storage potential of the basin (see eCat record 83199 for full details: see link right).

The survey was conducted in three legs aboard the New Zealand research vessel RV Tangaroa, and included scientists and technical staff from GA, the NZ National Institute of Water and Atmospheric Research Ltd. (NIWA) and Fugro Survey Pty Ltd. Shipboard data (survey ID GA0345) collected included multibeam sonar bathymetry and backscatter over 12 areas (A1, A2, A3, A4, A6b, A7, A8, B1, C1, C2b, F1, M1) totalling 455 km2 in water depths ranging from 90 - 430 m, and 611 km of sub-bottom profile lines. Seabed samples were collected from 48 stations and included 99 Smith-McIntyre grabs and 41 piston cores. An Autonomous Underwater Vehicle (AUV) (survey ID GA0346) collected higher-resolution multibeam sonar bathymetry and backscatter data, totalling 7.7 km2, along with 71 line km of side scan sonar, underwater camera and sub-bottom profile data. Twenty two Remotely Operated Vehicle (ROV) missions collected 31 hours of underwater video, 657 still images, eight grabs and one core.

This catalogue entry refers to imagery data acquired from the ROVs downward facing camera during survey GA0345/GA0346/TAN1411. For the purposes of underwater imaging, the ROV was fitted with two video channels with pan and tilt, one colour Charged Coupled Device (CCD) camera, one low-light, black and white camera, one rear camera, one zoom camera, one downward facing digital HD video/stills camera, and two downward-facing lasers for scaling. Lighting was provided by four 150 W quartz-halogen lights. The ROV was deployed in a side entry garage Tether Management System (TMS) (100 m of tether cable) from the port side of the RV Tangaroa using a Launch and Recovery System (comprising a marine crane, umbilical winch and hydraulic power pack). During a `typical' deployment, the TMS was positioned approximately 20 m above the seabed, while the ROV surveyed a pre-determined transit line below the TMS at an altitude of 0.5 to 2 m above the seabed. Eight vectorised horizontal thrusters and two vertical thrusters controlled ROV motion once away from the TMS.

To correlate the position of seabed video and still images with physical features in the multibeam bathymetry, the position of the ROV was tracked using a HiPAP500 Ultra-short Baseline (USBL) acoustic tracking system. A beacon was initially attached to the ROV and on the latter half of operations to the TMS, which provided both Dynamic Positioning and ROV operators with a visual reference of the position of the TMS with respect to the ship and ROV. Video footage was transmitted in real-time via the ships network to various locations throughout the ship using the `Blue Iris' software package. Live video feed to the surface enabled science operators to monitor and broadly characterise the seabed environment and ROV operators to regulate the altitude of the TMS and ROV. High-resolution still photographs (captured opportunistically along each transect) were used in conjunction with the video footage to assist identification of biota and seabed features. Upon retrieval of the ROV, video and still images were downloaded and renamed by station and a sequential image number.

In the folder 'TAN1411_ROV', still images (.jpg files) and video (AVCHD .m2ts files) are arranged by study area with sub-folders named according to mission number, station number, gear code and camera number (e.g. M2_070_ROVCAM_022 = still images acquired during ROV mission 2 at station 070). USBL files (.csv) are located in each sub-folder and provide continuous navigational information on location, time (including UTC) and depth of ROV still and video imagery. Two master .csv files are located in folder 'TAN1411_ROV'.

Lineage

Maintenance and Update Frequency: asNeeded

Statement: Python scripts were used to extract relevant navigation data from `event log files supplied by NIWA and to georeference video and still imagery. The navigation data has now been embedded in the .m2ts videos and can be displayed using VLC media player by switching on subtitle track1.