Wes Struble: What in the World Is a CTD Cast? March 2, 2012

NOAA Teacher at Sea
Wes Struble
Aboard NOAA Ship Ronald H. Brown
February 15 – March 5, 2012

Mission: Western Boundary Time Series
Geographical Area: Sub-Tropical Atlantic, off the Coast of the Bahamas
Date: March 2, 2012

Weather Data from the Bridge

Position: 26 degrees 19 minutes North Latitude & 79 degrees 55 minutes West Longitude (8 miles west of Florida’s coast)
Windspeed: 14 knots
Wind Direction: South
Air Temperature: 25.4 deg C / 77.7 deg F
Water Temperature: 26.1 deg C / 79 deg F
Atm Pressure: 1014.7 mb
Water Depth: 242 m / 794 feet
Cloud Cover: none
Cloud Type: NA

Science/Technology Log:

There are four different ship’s stations that are involved in a CTD (Conductivity, Temperature, & Depth) operation: the bridge, the survey team, the winch operator, and the computer room. The bridge is responsible to keep the ship on position and stable over a predetermined latitude and longitude. The survey team is responsible for preparing the CTD platform for deployment and securing it back on deck at the completion of the cast. The winch operator controls the actual motion of the CTD platform by the use of a hoist.  The computer lab relays commands to the winch and survey team in reference to testing and sampling depths, and when to start and stop the ascent and descent of the platform. The CTD platform can carry many types of instruments depending upon the nature of the research being conducted. During this cruise our platform usually contained two each of a temperature gauge, conductivity gauge (from which you can obtain salinity), and oxygen gauge.  In addition there is one pressure gauge and a transmissometer (that measures the turbity of water which is an indicator of the phytoplankton), 23 Niskin water sampling bottles, and two Acoustic Doppler Range finders – one pointing toward the surface and one pointing at the sea floor.

The CTD (Conductivity, Temperature, & Depth) platform on the Ron Brown. The long grey cylinders are the water sampling Niskin bottles, the yellow and blue device at the bottom in the Acoustic Doppler Current Profiler (for measuring distance to the sea floor) for measuring the distance to the sea floor during descent phase of a cast, the grey cylinders are weights, and the green cylinder is the power supply.
A Niskin Bottle with my Nike shoe for scale
The CTD platform being lowered over the side for start of another cast.
The "downlooking" ADCP (Acoustic Doppler Current Profiler mounted on the CTD.
The "up-looking" ADCP (Acoustic Doppler Current Profiler) mounted on the CTD
The Niskin Bottle trigger release. This device is used to remotely close the Niskin bottles at depth
The bridge of the Ron Brown during a CTD cast

     A CTD cast begins when the ship arrives at prearranged coordinates of latitude and longitude. The bridge will announce that we are “on station”.

A photo of the Ron Brown off the coast of Grand Bahama Island

   The survey team acknowledges and then raises the CTD platform and places it is the water at the surface for a minute or two. Then after receiving a signal from the computer operator that all functions are operating within normal parameters the platform is lowered to 10 meters and held there for two minutes to allow the instruments to stabilize.

Here I am starting my midnight to 6 :00 am shift at the CTD computer control station in the computer lab of the NOAA Ship Ronald H Brown
The "brains" of the CTD. This device also contains the pressure sensor.

   After the two minute hold at 10 meters the entire platform is brought back to the surface and the log is started as the package is lowered. The descent begins at about 30 meters/minute and eventually reaches 60 meters/minute. Many of the deep water casts on this cruise were between 4000 m and 5500 meters (about 13000 ft and 18,000 ft) and take over an hour to reach the bottom. While the descent takes place all the instruments are recording data which is stored and plotted in real time at the computer monitor.   When the CTD platform is 10 meters from the bottom the descent is stopped and the first water sample is collected by sending a signal that closes the first Niskin bottle. At this point the CTD slowly begins its climb back to the surface (another hour or more) stopping at designated depths to collect water samples.After the last Niskin bottle is closed at the surface, the CTD platform is brought back on deck, the water samples are removed, and the entire platform is prepared for the next cast.

Here I am on the weather deck in my favorite chair on the ship. I enjoy relaxing here in the sun in the morning after a night shift at the CTD computer station.
Another beautiful western Atlantic pre-sunset. I enjoyed many of these during the cruise.
The early sun rising in the east off the stern of the Ron Brown brings another night of CTD's to an end.

Debra Brice, November 17, 2003

NOAA Teacher at Sea
Debra Brice
Onboard R/V Roger Revelle
November 11-25, 2003

Mission: Ocean Observation
Geographical Area: Chilean Coast
Date: November 17, 2003

Data from the Bridge

1.  171700Z Nov 03
2.  Position: LAT: 20-10.8’S, LONG: 085-05.1’W
3.  Course: Hove to
4.  Speed: 0 Kts
5.  Distance: 0 NM
6.  Steaming Time:  0H 00M
7.  Station Time:  24H 00M
8.  Fuel: 1845 GAL
9.  Sky: Cldy
10. Wind: 110-T, 18 Kts
11. Sea: 110-T, 2-3 Ft
12. Swell: 140-T, 3-5 Ft
13. Barometer: 1020.0 mb
14. Temperature: Air: 21.5 C, Sea 18.0 C
15. Equipment Status: NORMAL
16. Comments: WHOI buoy recovery in progress.

 

Science and Technology Log

The R/V REVELLE was positioned roughly 100 meters upwind from the anchor position.  The acoustic release was fired and it took approximately 40 minutes for the glass balls to come to the surface.  Once the glass balls were sighted the small a line was attached and they were pulled to the stern of the ship.  The line was threaded through the A frame, the winch hauled the glass balls over the stern of the boat.  Once all the glassfuls were onboard the process of uncoupling them to the mooring began, they were then loaded in groups of 4 into the shipping container to be sent back to WHOI.

Once the fantail was cleared, hauling began.  The polypropylene line was then spooled off using a winding cart and 7 empty wooden spools. (see photos) The line on the winch was off loaded into a wired basket which was then wound onto the wooden spools and then stored.  This process was repeated for several hours until all of the 2800 meters of line was recovered and the first instrument was brought aboard about 2pm.  Then we began to bring each instrument aboard and label it by depth and place it on the deck in the order it was recovered for labeling and photographing.  It is very important to document the exact condition of the instruments as they are recovered as it will help in the data analysis later.  For example if there are some strange readings in the data or the data suddenly stopped at some point during the year looking at the photograph could tell you that this instrument was covered in barnacles or tangled with fishing line that clogged or blocked the sensors. (see photos)

With 38 different sensors on the mooring it was a very long day just recovering all of them.  Once most of the sensors were all onboard and labeled they began the recovery of the buoy and the last 12 sensors.  The small boat was deployed and a line attached to the buoy. The ship’s knuckle crane was used in this part of the operation and the buoy was lifted and secured onto the port side of the ship (see photos).  Once the buoy was secured the retrieval of the last instruments began.  Again, labeling and photographically documenting the condition of the instruments was essential.  In the photos you can see the increase in bio-fouling as the instruments get closer to the surface.  The current meters nearest the surface were heavily clogged with fishing lines and although their temperature sensors were still functioning, the portion that measures the current direction and speed was completely jammed with the fishing line.

Although acoustic current meters are also used on the mooring, there has been some issues with the quality of their data and the mechanical current meters are still the most accurate, but they have the problems of being more susceptible to bio-fouling and  interference with fishing gear.  This emphasizes the need for redundant instruments for data collection and comparison.  Each year the sensors are evaluated and some changes in instrumentation and slight changes in buoy location might be made.  For example this year the buoy will be moved a little farther away from last years mooring to hopefully decrease the likelihood of being tangled by fishing lines. After all of the instruments were secured onboard and labeled and photographed, the cleaning began (see photographs).  Everyone participated in this phase with scrapers and , finally the power washer.  All of the instruments needed to be cleaned and many stored in the main lab for data analysis tomorrow.  All day tomorrow Nan, Lara, Jeff, Jason and Dr. Weller will be downloading and loading at the data from the sensors as well as preparing the new equipment for deployment on Wednesday.

Personal Log

An incredibly long day which began with my watch at 4am and ended sometime after 9pm.  It was great and I was fascinated by the differences in the instruments as they were recovered from different depths.  It was brought home to me yet again the importance of keeping meticulous and very detailed records of each stage of a operation and the condition of the environment and effect on the equipment.  Any of these variables have to be considered when analyzing the data and can only be collected immediately upon retrieval or deployment.  It is also essential to have a very detailed plan of operation and to work together well as a team.  I think we were also out there testing several brands of sunscreen….mine failed and and I have the racoon-eyes to prove it…ahh well, it was a wonderful day and loved it.  Tomorrow and preparing for the deployment will be equally interesting. Oh, and one of the benefits of bringing in the buoy was that all the fish who were living under the buoy were now around the ship and the crew and some of the science staff caught some very nice tuna…hmmm dinner is looking promising tomorrow too:)

Cheers