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By ''painting the seabed with sound'', Land Information New Zealand (Linz) would create the most detailed picture of Fiordland's seabed ever produced, Linz hydrographic survey manager Stuart Caie said.
''It builds a picture of the seafloor in the same way you see hills and mountains on land, where the hills are, where the rocks are, maybe some deep holes.
''It helps scientists understand what the seabed is made of; is it hard rock, sand, gravel, are there weeds, what coral is there; so it's really what a land surveyor would do - map the land, but trying to remove the water.''
Using the latest technology, including a hydroacoustic echo-sounder, anything within the water columns would be revealed, including large uncharted rocks and any shipwrecks in the area, he said.
The most detailed seafloor mapping of a coastal region was recently completed in Queen Charlotte Sound which revealed 10 shipwrecks and previously unseen seabed structures, he said.
Delving into the unknown was like exploring for the surveyors.
''We know more about the moon and Mars than of our own seabed.
''I'm sure they would say they feel like latter-day explorers in revealing what is actually lying on the seabed.''
The survey work, expected to start in November, would focus on Thompson Sound, Doubtful Sound, Bradshaw Sound, down to Deep Cove, and then to Dusky Sound, inside the Five Finger Peninsula and surrounding islands.
Twelve people would be on the water at any one time.
The ''intensive work'' was expected to take about five to six months, he said.