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sunny weather
85°F (29.4°C)
Latitude: 25 deg 19’S
Longitude: 70 deg 02’E
Wind Direction: NW
Wind Speed: 12 Knots
Sea State 2
Swell(s) Height: 3 Foot
Sea Temperature: 79°F (26.1°C)
Barometric Pressure: 1011.3 MB Visibility: 18+ Nautical Miles

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Daily Update: Ocean Floor Mapping
April 10, 2001
By Amy Nevala

Geologists Susan Humphris and Dan Fornari spent last night making maps. Not just any maps, but special topographic maps of a portion of the Central Indian Ridge.

When people visit a new place on land, they use a map. The same is true in the ocean. Oceanographers map the seafloor to measure its depth and learn about the topography, or mountains, valleys and other physical features.

The maps we create guide us to interesting spots for studying hydrothermal vents in the Indian Ocean.

By using the different types of sonar systems on Knorr, we can make maps of the seafloor that cover both large and small areas. One of these systems, called the multibeam sonar, is mounted across Knorr’s hull and allows us to map areas covering hundreds of square miles.

Another type of multibeam sonar, the SM2000, is mounted on ROV Jason. It creates detailed maps of individual vent chimneys, which help scientists to locate biological, chemical and geological samples.

“The multibeam bathymetric maps we made earlier give us a bird’s eye view of the seafloor,” said Dan. “The SM2000 maps we made last night give us the gnat’s eye view.”

Bathymetric maps show depth and give us a sense of the orientation and shape of the seafloor. The maps outline features like the mid-ocean ridge, which rises like a mountain range.

When using multibeam sonar, the ship steams along a series of specific latitude and longitude points. Then Knorr’s sonar system sends sound to the seafloor, which bounces back to the ship as a depth signal. Our computers use this depth data to create the rainbow-colored bathymetric maps, with reds representing the higher peaks and blues the lower valleys.

Many people on board Knorr help Dan and Susan make the maps. Paul Johnson, Cindy Sellers, Amy Simoneau and Dave Sims are creating maps of our study area at different scales. Their work will be useful in the days ahead as we reconstruct our observations and sampling activities at this hydrothermal vent site.


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