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Archive of October 5th, 2007

Bathymetry Map of Kauai Region

 

 

Red star indicates current location of R/V Kilo Moana

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Science Update October 5th by Garrett Ito

Today I presented the work that I have been doing on gravity measurements that we have been making throughout the cruise. The Kilo Moana's "gravimeter" is an extremely sensitive instrument that measures very subtle changes in the downward pull of the Earth's gravity. These variations in gravity are caused by different amounts of mass pulling down on the ship. For example, a seamount is excess mass relative to the surrounding area where there is no seamount. For this reason, gravity will pull down slightly more over the seamount than far away from it.

The gravity measurements we are making are designed to remotely sense crustal structure beneath our survey lines. The above figure shows a map of "gravity anomaly." We have removed the effects of seafloor topography so that the variations seen in this image are caused by density structure below the seafloor. The measurement units are milliGals. One milliGal is equal to one millionth of a G-force (~980 Gals), or the normal pull of gravity. Thus, the changes between -20 and +20 milliGals that we are seeing are very small indeed. The red and pink areas are where gravity is pulling down more and could be caused by unusually dense crust. The blue areas are where gravity is pulling down slightly less and could be caused by less dense crust. The density of the volcanic crust changes with composition. Mapping out density variations using gravity will therefore help us understand how the different features that we are surveying were once formed.

Teacher at Sea log for October 5th, 2007 by Linda Sciaroni

Do you get to drive the ship? This a frequent question submitted by students and I wish I could say yes. This seems like an awesome job, and great for someone with quiet, calm confidence. All three of the ship's pilots and the three Jason navigators possess these qualities. To find out more about driving the ship I interviewed Second Mate Liz Scanland. She toured me though all the instruments and data she manages in order to keep the ship safely on course. Liz has been going to sea for 15 years and really loves her work. She is calm and professional and generous with her time. Her life at sea is steady work to get the Kilo Moana from point A to point B. This has required mastery of numerous systems and technical tasks. The ship has many operations automated and they frequently check manually to see if the automated data is correct. The ship uses the Global Positioning System (GPS), which is a satellite-derived position, to know where it is, and it uses the Dynamic Positioning System (DPS) to keep the ship at a chosen latitude and longitude. This is a computer-controlled setup, but the ship also includes more manual navigation systems like a gyrocompass to which gives true heading.

Other instruments redundantly double all of the automated instrumentation on the ship. Then there is another backup, human knowledge of celestial navigation and navigational mathematics. The boat has a helm to steer the boat, various measuring tools to get position, a chart room. Should the gyroscope fail, they could use the sun to find the true heading. There is also compass mounted on the roof that you must use a periscope to see. The bridge is designed to be functional in all kinds of weather; there are windshield wipers and heaters on the windows to keep the view clear, places to sit, and places to hold should the seas get rough.

When the Jason 2 is in the collecting mode at the bottom of the sea, it is important that the ship relatively above the Jason 2. During these times, the control of the ship is transferred to the Jason Van and the Jason navigator maintains the speed and the course of the ship. Once Jason is brought aboard the control goes back to the ship's bridge. It is a little unnerving when to think that someone in a windowless box is piloting the ship, but the instrumentation is sophisticated and there are always eyes watching from the bridge, so I am assured we are safe.

Brian and Liz Chart room
Liz inside the bridge Ships bridge
The Captain and David
Wave from the Captain

 

 

 

 


Presented by the School of Ocean and Earth Science and Technology at the University of Hawaii, with financial support from the National Science Foundation.

 

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