Rita Salisbury: Underwater Navigation, April 24, 2013

NOAA Teacher at Sea
Rita Salisbury
Aboard NOAA Ship Oscar Elton Sette
April 14–29, 2013

Mission: Hawaii Bottomfish Survey
Geographical Area of Cruise: Hawaiian Islands
Date: April 24, 2013

Weather Data from the Bridge:

• Humidity 71%
• Wind SpeedS 8 mph
• Barometer30.07 in (1016.2 mb)
• Dewpoint65°F (18°C)
• Visibility

Science and Technology Log

I wish everyone could see how hard the scientists work on solving problems as they crop up. Their collaboration skills are top-notch. Everyone has something to contribute and their ideas are listened to respectfully. Solutions belong to everyone on the team. It also seems to me that there is a lot of “cross-training” going on, too. Everyone has a specialty, but others are capable of taking over or filling in for that person. That goes for the deck crew as well as the scientists. Every event has a planning meeting in which roles are defined and strategy determined.

One of the thrusters on the AUV had to be replaced and the new one is considerably heavier than the original one. That means that the whole buoyancy of the AUV is impacted. It needs to be a little light so its natural course is to float to the surface. The new thruster changed the weight of the AUV so the scientists had to calculate and design a remedy for the issue. They decided to add high density foam to the AUV to increase the buoyancy. They used high density foam because regular foam would compress at the depths to which the AUV submerges. This AUV is designed to go down 2000 meters, but others go as deep as 6000 meters.

In order to confirm that their calculations for the amount and placement of the new foam were correct, the AUV was put over the side of the ship and tests were run. It was always attached to the crane, as a precaution, but the cables were slack and the AUV had the opportunity to be tested. Once the tests were run, the scientists reviewed the results and decided to send the AUV out on a mission.

I asked Jeremy Taylor, one of the scientists, about how the AUV navigates underwater to the various coordinates pre-programmed into it. If it starts at Point 0, 0, how does it get to Point X,Y? Global Positioning Satellites are not any help since GPS doesn’t reach underwater.  Jeremy explained to me that the AUV actually navigates by altitude, not depth. It has 4 beams positioned on the frame in various locations that combine their information to tell the AUV how far above the sea bed it is. This kicks in when the AUV is about 35 meters above the bottom. From that information, the AUV keeps a certain distance above the sea floor and can then navigate over formations on the floor that stand between the AUV and its’ destination, the Point X,Y location. Using the altitude navigation system means the AUV’s navigation is fairly simple and the person who programs it doesn’t have to worry about going around or over obstacles.

Personal Log
As one of the scientists, Erica Fruh, explained the reasoning behind the high-density foam being used for buoyancy, it made me think of a video on the Galapagos Islands that I have shared with my students. In the video, an ROV is deployed in the depths off the coast of one of the islands in the Galapagos chain. Someone put a Styrofoam head (the type used to hold wigs) in a basket on the outside of the ROV. After the dive, which went to considerable depths, the head was retrieved and measured. The weight of the water had compressed the head to about 1/4 of its original size. It was a very graphic demonstration of the compression that occurs in the depths of the sea.

Did You Know?
The pressure at 3000 feet deep in the ocean is 100 times more that of air at sea level. Check out this link for a visual of wig heads and styrofoam cups: http://oceanexplorer.noaa.gov/explorations/04etta/logs/aug27/aug27.html