Eric Heltzel, October 6, 2005

NOAA Teacher at Sea
Eric Heltzel
Onboard NOAA Ship Ronald H. Brown
September 25 – October 22, 2005

Mission: Climate Observation and Buoy Deployment
Geographical Area: Southeast Pacific
Date: October 6, 2005

Eric on the bridge of the RON BROWN
Eric on the bridge of the RON BROWN

Weather Data from Bridge, 07:00 

Temperature: 19.1 degrees C
Sea level Atmospheric pressure: 1012 mb
Relative Humidity: 78%
Clouds cover: 8/8, stratocumulus
Visibility: 12 nm
Wind direction: 160 degrees
Wind speed: 6kts.
Wave height: 3 – 5’
Swell wave height: 3 – 5’
Seawater Temperature: 18.3 degrees C

Science and Technology Log 

The science team from the Upper Ocean Processes Group is busy preparing instruments to be deployed on the mooring of the Stratus 5 Buoy. Each instrument must be physically examined to ensure that it is properly mounted in its rack.  Then these instruments are awakened to make sure that they are working properly. They are hooked up to a computer so that their operation and calibration can be tested.

The Stratus Buoy
The Stratus Buoy

Today I had a look at a mechanical current meter.  These were designed by Senior Scientist, Dr. Bob Weller as part of his Doctoral work at Scripps Institute. The instrument is housed in an aluminum cylinder that is 2 feet long and 7” in diameter.  The canister is water tight utilizing two interior rubber seals. Extending from one end is a 3’ long PCV mast that has two propeller mounts on it. At each mount are two sets of propellers on either side of the hub.  The two mounts are set at 90 degrees to one another. When water flows through the propellers revolutions are measure and the data is stored in a chip inside the canister.  The number of revolutions per given unit of time gives the velocity of the current.  Having two sets of propellers set at 90-degree angles allows the direction of the current to be determined.

There is also a second type of current meter that uses measurements of sound waves to determine current velocity.  Several of these will be deployed on the mooring along with the mechanical current meters.  Using two types of instruments allows the team to compare results.  The mechanical units have been used for about 20 years and they are known to be reliable and accurate.  Placing the acoustic velocity meter nearby will help determine the accuracy of these devices.

Questions to Consider 

Why are all the instrument cases cylindrical in shape?

Why is a “sacrificial zinc anode” placed on each end of the mechanical current meter?

How could the direction of a current be determined using two sets of propellers at 90- degree angles to one another?

Why build canisters out of aluminum?

Eric Heltzel, October 4, 2005

NOAA Teacher at Sea
Eric Heltzel
Onboard NOAA Ship Ronald H. Brown
September 25 – October 22, 2005

Mission: Climate Observation and Buoy Deployment
Geographical Area: Southeast Pacific
Date: October 4, 2005

Acoustic releases
Acoustic releases

Weather Data from Bridge

Temperature: 25.5 degrees C
Clouds cover: 6/8, stratus, altocumulus
Visibility: 12 nm
Wind direction: 245 degrees
Wind speed: 13kts.
Wave height: 3 – 5’
Swell wave height: 3 – 5’
Seawater Temperature: 28.7 degrees C
Sea level Atmospheric pressure: 1005 mb
Relative Humidity: 82%

Science and Technology Log 

Today Senior Scientist Bob Weller and Senior Engineer Assistant Paul Bouchard showed me the acoustic releases.  These are devices that are placed on the tether that holds the Stratus Buoy to its anchor on the ocean floor. At the deployment location the ocean depth is 4425 meters (14,518 feet).  The acoustic release will be placed 30 meters from the anchor. Attached to the tether will be 35 instruments placed at a particular distance from the buoy. Their attachment distance will determine the depth at which they are located and will allow scientists to gather data about conditions at these particular depths of the water column.

The job of the acoustic release is to detach the buoy and tether from the anchor.  When we arrive at the currently deployed buoy a digitized acoustic signal will be sent through the water.  The acoustic release will “turn loose” of the anchor and allow our team to retrieve the buoy and the instruments attached to the tether. This is important because some of the instruments contain a year’s worth of data that must be downloaded and analyzed. Another reason is the cost of the buoy itself, all of the instruments, and the cable and line that have held it to the anchor. These things are worth about $500,000 dollars and would be difficult to replace. All of the instruments can be refurbished and used again.

Cornell Hill making a line splice.
Cornell Hill making a line splice.

When we arrive at the currently deployed Stratus Buoy the acoustic release that was put in place last year will be activated.  This should allow us to retrieve the system and replace it with the one we are carrying on board the ship. The acoustic releases we are carrying will be placed in the tether holding the new buoy and will not be activated until next year when that system is recovered. Acoustic releases are also used on drilling platforms and other objects tethered to the sea floor. These machines allow the objects tethered to be freed without the need to dive into the water and cut the line. These are an ingenious piece of technology that improves the safety and convenience of oceanographic research teams.

Ship Crew Activity 

I had the opportunity to watch Boatswain Group Leader Cornell Hill making a line splice.  He took the end of the line around a metal eye that is built with a groove on the outside. The line comes back on itself and Cornell braids the strands into the main part of the line. He has a knife with a spike on it to help lift the strands so he can braid it together.  What results is a closed loop with metal lining at the end of the line.  It’s very strong and is used as an attachment point. I have long wondered how this was done so it was very interesting to see the skillful way Cornell accomplished this feat.

Terms 

Acoustic signal – a particular blend of frequency and pattern of sounds that sends a message through the water to instruct a device to perform its operation. Example is the signal sent to activate the acoustic release.

Acoustic Release – a device that releases a line when given the proper sound signal. Used in the tether system of the Stratus buoy.

Bosun – crew member in charge of deck operations

Line – rope Line Splice – Braiding stands of a line back into itself.

Tether – attachment to a fixed object. This may be a combination of cable, chain, line, or wire. Example is the attachment of the Stratus Buoy so that it  doesn’t drift away.