Obliquely illuminated Digital Terrain Model of the Cape Hallett area surveyed by the Tangaroa during the Western Ross Sea Hydrographic Survey.

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Obliquely illuminated Digital Terrain Model of the Poverty re-entrant produced by Tangaroa’s new EM300 swath mapping system.

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Hull-mounted on the RV Tangaroa, the EM-300 multibeam echosounder maps the seafloor using a fan of 135 acoustic beams, providing 100% coverage of the seabed. The resulting surveys show far greater detail than the earlier method of multiple lines using a single-beam sounder, as well as greatly reduced ship survey time and cost.

A Simrad EM-300 multibeam echosounder was installed on the Tangaroa during 2000. This is a 30-kHz multibeam system, which produces excellent bathymetry and imagery in depths up to approximately 5000 meters, while complying with the performance standards defined in the International Hydrographic Organization’s performance standards, S-44 edition 4 as well as meeting Land Information New Zealand’s (LINZ) Hydrographic standards. Its beam width measures 1-degree along track by 2-degree across track and incorporates the facility to steer the 135 beams to produce variable angular swaths from approximately 150 degrees, down to 10 degrees as well as yaw stabilisation. Overall swath coverage is 5.5 times water depth, increasing with depth to a maximum width of 5000 meters at an approximate 1000 meters, where it remains relatively constant until 3500–4000 m, then decreasing until extinction.

The EM300 installation includes a POS/MV 320, which integrates positioning and motion compensation. The POS provides precise GPS navigation solutions, in addition to heave, pitch, roll, and yaw information for EM300. The precision of the POS/MV motion sensor allows for high calibration accuracy of the multibeam system and provides a freedom from acceleration errors induced when cornering.

Data are recorded and processed onboard using C&C Technologies HydroMap software along with ArcInfo, the end product being bathymetry data, geotiffs and backscatter imagery for use in both Hydrographic surveys and research programs.

After extensive calibration and acceptance trials the first survey with the system was a 6-week hydrographic program in the Western Ross Sea and around the Balleny Islands, Antarctica, for Land Information New Zealand (LINZ). Subsequently the system has been used extensively on FRST-funded marine geological research projects.

Note that no part of this figures is to be reproduced or interpreted without prior, written permission of NIWA.

Contact

John Mitchell [ j.mitchell@niwa.co.nz ]