Home | Contact ST  
Follow ST

Feature Article

Pilot Deployment of a Brazilian Deep-Ocean Buoy
Brazil, U.S. Scientists Collaborate in Testing Ocean Monitoring Platform


Edmo J.D. Campos

Leonardo Barreira

Francisco Vicentini Neto

The RV Alpha-Crucis and the Brazilian prototype of the ATLAS buoy (the ATLAS-B), just after its successful mooring operation at 28.5° S, 44° W, on April 23, 2013.
In March 2004, the evolution of an extra-tropical cyclone into a tropical system of hurricane strength in the South Atlantic, named Catarina, was confirmed for the first time by satellite imagery (http://earthobservatory.nasa.gov/IOTD/view.php?id=4369 ).That storm reached the coast of southern Brazil causing great damage and even some deaths. The timely prediction of its development was hindered by the presumption that the large climatological vertical shear in the atmosphere prevents the formation of tropical storms and by the lack of adequate observations in the ocean, particularly the subsurface layers. In the following years, a proposal for deploying a moored buoy system in the region was endorsed by GCOS (Global Climate Observing System), and in 2009 a project for building an ATLAS-B was approved by Brazilian funding agencies.

The ATLAS-B is a deep-ocean observing platform assembled entirely in Brazil, following the TAO (Tropical Atmosphere Ocean) and PIRATA (Prediction Moored Array for the Tropical Atlantic) ATLAS (Autonomous Temperature Line Acquisition Systems) in its structure, instruments and sampling schemes, but using commercial components. The mooring line was modified to a semitaut line format. The project is being conducted at the Laboratory for Modeling and Observation of the Ocean (LABMON), at the Oceanographic Institute of the University of Sao Paulo, with the technical support of AMBIDADOS (Rio de Janeiro, Brazil) and RDSEA International (St. Pete Beach, Florida).

Holos Brazil Inc. (Rio de Janeiro) fabricates the floating component, made of fiberglass over a foam core, and the aluminum and stainless steel structural frames.

The Guariroba
The first prototype of the ATLAS-B, nicknamed 'Guariroba,' was moored in April 2013 at 28.5° S, 44° W, in the region where Catarina gained the strength of a hurricane. The bottom depth at this location is approximately 3,700 meters. In this application, the surface buoy is equipped with a series of meteorological sensors and is anchored to the sea bottom. The top 700 meters of the mooring line is a 3/8-inch plastic jacketed 3-by-19 wire rope. Oceanographic sensors are clipped to this wire, transmitting data continuously to a Campbell Scientific (Logan, Utah) CR1000 datalogger in the buoy by means of electromagnetic inductive modems. Near the bottom, a sensor with internal storage capacity monitors continuously small variations in pressure, temperature and salinity.

The data collected by the underwater sensors and transmitted via inductive modems are organized in the datalogger and stored in a memory card. A string composed by the data from all sources, including the buoy position, is transmitted daily by means of satellite telemetry. A redundant positioning system was installed in a way totally independent of the buoy's electronics and batteries. The data stored in the deep sensors are retrieved by occasion of recovery and replacement of the whole system.

The Deeper Part of the Mooring Line
The Atlas-B project adopts a semitaut format for the mooring line, with a ratio between the length of the line and the local depth approximately 1.05. Moorings with scopes between 1.0 and approximately 1.1 are generally referred to as 'semitaut' designs. The depth in the Guariroba site is 3,700 meters. Below 700 meters, down to the acoustic release, which is at 50 meters above the seafloor, an 18-millimeter nylon rope was used, in sections of 500 meters length, interconnected with subsurface glass spheres with 17 inches diameter. Right above the pair of acoustic releasers was installed a set of eight glass spheres, for bringing these devices back to the surface upon recovery. The acoustic releasers are connected to the anchor by a 20-millimeter nylon rope and 3 meters of a 5/8-inch steel chain.

Results of the First Deployment
The first mooring was planned as a field test, intended to stay for up to a one-year period, with daily statistics transmitted through Inmarsat. Approximately four weeks after the deployment, data from the Sea-Bird Electronics (Bellevue, Washington) MicroCAT recorder at 300 meters stopped being received. A little more than one month later, the sensor at 500 meters was mute. On September 22, 2013, the entire data transmission was interrupted, except for the tracking system signal, which continued to show that the buoy was still moored at its original position. In late October 2013, though, the tracking system started to show the buoy was adrift and, after an emergency operation, the floating body and the upper 700 meters of the mooring line, with all underwater sensors, were recovered, all in good condition but without the mast and its equipments (meteorological sensors and satellite antenna). There was no sign of vandalism. So, it is most likely that the increased roll of the buoy after being freed caused the mast to break down and the loss of the associated sensors. The bottom part of the line is hopefully still anchored at the original mooring position. The accidental release of the buoy was due to a rupture of the shackles in the junction of the wire and nylon rope, for reasons not yet well understood. To continue this article please click here.

Edmo J.D. Campos has a Ph.D. in physical oceanography from the University of Miami. He is a professor and has been head of the Laboratory for Modeling and Observation of the Ocean (LABMON) at the Oceanographic Institute of the University of Sao Paulo, Brazil, since 1990. He is a member of the Brazilian Academy of Science.

Leonardo Barreira has a D.Sc. in ocean engineering and is the head of the Ocean Engineering Group at the Institute of Sea Studies Admiral Paulo Moreira. He is an officer of the Brazilian Navy, Arraial do Cabo, Rio de Janeiro, Brazil.

Francisco Vicentini Neto is a mechanical engineer and welding technologist. He has been a member of the Oceanographic Instrumentation Laboratory (LIO) of the Oceanographic Institute of the University of Sao Paulo, Brazil, since 1984.

Sea Technology is read worldwide in more than 110 countries by management, engineers, scientists and technical personnel working in industry, government and educational research institutions. Readers are involved with oceanographic research, fisheries management, offshore oil and gas exploration and production, undersea defense including antisubmarine warfare, ocean mining and commercial diving.