NOAA Teacher at Sea
Christine Hedge
Onboard USCGC Healy
August 7 – September 16, 2009
Mission: U.S.-Canada 2009 Arctic Seafloor Continental Shelf Survey
Location: Chukchi Sea, north of the arctic circle
Date: August 13, 2009
Weather Data from the Bridge
Long: 14809.54199W
Lat: 78017.31641N
Air Temp: 31.08 0F
Science and Technology Log
Sound waves travel at different speeds through different substances. If you look up the speed of sound in air you will find it to be about 300 meters/second, in water 1500 meters/second. But these numbers are not constants. In water, the temperature, the amount of salt, and the pressure can all impact how fast sound waves travel. In other words, all water is not created equal. Our mapping mission depends on data collected from bouncing sound waves off the sea floor. In order to get an accurate image of what the sea floor looks like and how deep it is – we need to measure precisely how fast the sound waves are traveling. This means we need to have a handle on any variable that might change the speed of the sound waves. Measuring the speed of sound in the water column is an important part of data collection for accurate mapping.
So, how does the Healy measure the speed of sound? Sometimes we use a Conductivity-Temperature-Depth instrument (CTDs). The ship needs to be stationary to deploy these instruments so they don’t happen very often while we are cruising. CTD measurements record conductivity of the water, which gives us the salinity (how much salt is in the water), temperature, and the depth at which these measurements were taken. Four times a day instruments called Expendable Bathythermographs (XBTs) are deployed off the moving ship. These XBTs measure the temperature as the device travels through the water. As pressure increases, (the deeper you go) the speed of sound increases. As temperature decreases, the speed of sound decreases. Four times a day the Healy science crew gets new data so that they can determine more precisely the speed of sound and therefore interpret what the sound waves are telling us.
Today, MST-2 (Marine Science Technician) Daniel Jarrett let me participate in the deployment of an XBT. As the device travels through the water it sends back temperature data from different depths to a computer on board.
The data travels through a very thin copper wire attached to the instrument. A graph of this data is observed and that information is used to create a profile of the speed of sound in that part of the Arctic Ocean at that moment in time.
Personal Log
All the things I do at home also have to be done on board ship. I eat, sleep, shower, exercise, and do laundry. The food is excellent so far. I love not having to cook or plan meals. There is fresh fruit, a salad bar, and a huge hot breakfast every day. It will be a rude awakening when I return home and have to plan and cook meals again! My daily routine does not involve much physical activity and I worry about gaining weight while on board. In order to stay in shape, it seems everyone uses the gyms or runs on deck. I have been working out on the treadmill or elliptical every day faithfully to avoid a severe weight gain.
The laundry and all other facilities are really nice. I have a 25-year-old washer/dryer at home and was pleasantly surprised to find state of the art, low-water-usage, front-loading washers on board the Healy. From what I can see the United States Coast Guard is working hard to become a “green” organization. Trash is separated and recycled when possible. People are encouraged to reduce their water usage. Extreme care is given to filtering and recycling wastewater and any kind of oil or lubricants. It is great to see the amount of thought and energy that is being put into helping the community on board the Healy to “walk lightly” on the Earth.
