NOAA Teacher at Sea
Onboard NOAA Ship Ka’imimoana
July 8 – August 10, 2010
Mission: Tropical Atmosphere Ocean (TAO) Cruise
Geographical area of cruise: Equatorial Pacific from 110 degrees W Longitude to 95 degrees W Longitude
Date: Friday, 23 July 2010
Weather Data from the Bridge
Current location: 4 degrees South Latitude & 110 degrees West Longitude
Cloud Cover: 5/8
Cloud Type: Stratocumulus
Visibility: 10 nautical miles
Wind Bearing: 100 degrees
Wind Speed: 20 Kt
Wave Height: 2 feet
Swell Height: 5 – 7 feet
Barometric Pressure: 1015.5 mb
Temperature: 24.8 degrees C (76.6 degrees F)
Science and Technology Log
There are a variety of buoys used by NOAA in the Pacific Ocean. One of the more interesting is the ADCP buoy. ADCP stands for Acoustic Doppler Current Profiler. This buoy is anchored to the sea floor like most of the other buoys deployed on this cruise. The major difference is that the ADCP buoy does not float at the surface but rather is tethered with a line short enough to keep it submerged approximately 300 meters below the surface of the sea. In addition, it is only deployed with the TAO buoys at the equator and not at any of the other TAO buoy locations. The buoy’s name defines its function – current profiling – using acoustic signals (similar to sonar) the buoy provides a profile (or vertical map) of the ocean currents from the depth at which the buoy is tethered to the surface. The ADCP is able to measure both the speed of the current and the direction in which it is moving. Even though the TAO buoy at the same latitude is generally visited more often, the ADCP buoy is visited only once per year. During the visit the buoy is retrieved, cleaned, damaged parts replaced or repaired, data downloaded, batteries replaced, and sensors upgraded (if necessary).
The flotation component of the buoy is a large orange sphere just over four feet in diameter. This float is made of syntactic foam. In general, foam is a mixture of two substances: a gas phase in a solid or liquid phase. Syntactic foam should not be confused with the common foam with which we are all familiar (like the typical Styrofoam coffee cup). Most of these foams are generally composed of expanded polystyrene (a thermoplastic polymer) where the gas phase is air and the solid phase is polystyrene. Syntactic foams on the other hand use other substances for the components.
One of the more common syntactic foams uses small glass spheres 10 – 200 micrometers (millionths of a meter) in diameter. These glass spheres are filled with air during the manufacturing process. The spheres are then mixed in with some type of epoxy resin and allowed to cure to produce the foam. The buoyancy of the foam is affected by the size, number, and wall thickness of the glass spheres. Some of the applications that typically utilize syntactic foams are the manufacture of radar transparent materials, acoustic attenuating materials, and more specifically deep sea buoyancy floats. Our float is anchored to the sea floor with a large (several thousand pound) weight that prevents it from drifting. The material used to attach it to the anchor is very stable and exhibits little elongation under tension, thus keeping the buoy consistently at the same depth. The payload (the ADCP itself) is approximately 1 meter long and about 20 centimeters in diameter and is mounted in a circular well that is bored vertically through the center of the float. The ADCP has four sending/receiving units mounted at the top of the main body. One can see these in the photographs. These units send and receive a 75 kHz signal that reflects (echoes) off the sea/air boundary and returns to the buoy.
When we were close to the location of the ADCP buoy one of the scientists activated an acoustic trigger that released the buoy from its sea floor mooring anchor. Since it was almost 1000 feet under water it took a few minutes for the float to reach the surface. When the buoy was spotted the ship made a slow pass to visually inspect the float and to launch the skiff. The skiff towed a long and very strong line from the ship which was then attached to the top of the buoy. At this point the skiff was brought back aboard. The ship then came about so that the buoy was directly a stern. When all was ready the winch began to retrieve the line and slowly bring the buoy on board. When it reached the deck of the fantail it was made secure and the tether line (that attached the buoy to the anchor) was tied off to a chain on the ship’s deck.
The buoy was then disconnected from its tether line and the line was attached to a large winch and all several thousand meters of it was rolled onto a number of large empty spools and stored on board. While the anchor line was being retrieved the science crew downloaded the stored data from the ADCP and prepared the buoy for redeployment. When the deck hands were ready the process was reversed. First, the tether line was attached to the buoy and it was lowered over the fantail. Then the line was slowly played out. When the ship was in the appropriate position she began to move forward as the crew played out line. When they reached the end of the line a large (several thousand pound) anchor was attached, lowered, and released. This entire process took the better part of a day.
I have enjoyed getting to see the crew work together. One can tell that they clearly get along well and appear to enjoy working together because of all the friendly banter that passes between them. I have been impressed with how conscious they are about safety. I have been able to begin participating in some of the work deck activity during the buoy operations and it has helped in my understanding of what actually takes place. It has also helped me to get to know a number of the crew members better.
“Did You Know?”
Did you know that the greatest buoy equipment problem that occurs in this area of the ocean is vandalism? Many of the buoys are damaged, stolen/cut loose, or destroyed. This might be done either out of anger and frustration, for financial gain (the buoys have quite a large mass of aluminum framing and electronic equipment), or by accident. Regardless of the reason, much time, data, and financial resources are lost and consumed in maintaining TAO array in the Pacific Ocean.