Instrumented Buoys

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Instrumented Buoys

An instrumented buoy being deployed during this year's field season. Photo by Steve.
An instrumented buoy being deployed during this year’s field season. Photo by Steve.

During previous years field cruises, we have deployed several instrumented buoys for data collection and field testing. This year we have five buoys that were deployed along the 90 m isobath to the east of Cape Shirreff on Livingston Island. Three of these buoys contain Acoustic Doppler Current Profilers while the other two have scientific echosounders. These buoys were planned to remain in the water until early March and provide a longer time series of measurements in this area than we can obtain through cruises. The data from the buoys should help us understand the physical and biological processes that occur in this region.

 

 

Buoy Features

The lower portion of the buoys laid out on deck prior to deployment.
The lower portion of the buoys laid out on deck prior to deployment. Photo by Derek.

The buoys are modular in design and assembled into two parts while on the ship. The main section [top picture] contains the flotation rings (the blue parts in the pictures), batteries for power, and the acoustic instrument. The top section (or mast) [bottom picture] contains a wireless radio transmitter (line-of-sight) which relays the buoy data to a shore station (located at the Cape Shirreff field camp) approximately 6 km away. The buoys’ mooring tackle consists of a plow-type anchor, several meters of chain, a mushroom anchor, a 100 m of line, and a 1/2 m diameter rubber flotation sphere. The buoys are attached to the float with several meters of a polypropylene line bridle. The bridle allows the buoy to float to the side of the mooring tackle which prevents the acoustic equipment from receiving reflections from the mooring line and chain.

While transiting to the survey site we tested the upper portion of the buoys on the deck of the ship. Photo by Derek.
While transiting to the survey site we tested the upper portion of the buoys on the deck of the ship. Photo by Derek.

The buoys have small windmills which convert wind power into electrical energy, which charges the batteries and extends deployment duration. Every 15 minutes the buoys transmit 3 minutes worth of data and then rest for 12 minutes of data. The data transmissions are staggered such that the buoy transmissions do not overlap while the shore station is continuously receiving and recording data.

 

 

Acoustic Echosounders

Acoustic echosounders (orange ovals) and acoustic Doppler current meters (four-circles) provide data that the buoys telemeter to shore. Photo by Steve.
Acoustic echosounders (orange ovals) and acoustic Doppler current meters (four-circles) provide data that the buoys telemeter to shore. Photo by Steve.

Two of the buoys (Moorings # 2 and 4) are equipped with SIMRAD ES 60 scientific echosounders (the orange rectangles on the two furthest right buoys in the picture). These instruments record acoustic backscatter in the water column at two frequencies (38 and 200 kHz). By using multiple frequencies we can discriminate between scattering caused by different types of animals which, generally, allows us to calculate what scatter is caused by krill in the water column. An identical instrument is used by the RV Ernest during the nearshore survey.

Acoustic Doppler Current Profilers

The buoys can be deployed by three people in a small boat due to their modular construction. Photo by Steve.
The buoys can be deployed by three people in a small boat due to their modular construction. Photo by Steve.

Three of the buoys (Moorings #1, 3, and 5) are equipped with RDI 300 kHz Acoustic Doppler Current Profilers (the three left most buoys in the above picture). These instruments provide vertical profiles of current velocities in the water column. In addition, they also provide data on the amount of backscatter in the water column. By combining the data from the ADCP buoys with data from the echosounder buoys and the small boat echosounder survey data, we hope to be able to use the ADCP backscatter information as a measure of biological scatterers in the water column.

 

 

Derek Needham and Sea Technology Services

Ground tackle which secures the buoys to the bottom is laid out on deck before the buoys are deployed. Photo by Derek.
Ground tackle which secures the buoys to the bottom is laid out on deck before the buoys are deployed. Photo by Derek.

Derek Needham and Dave Demer have designed several generations of these data collection buoys. Similar buoys have been deployed throughout the world (South Africa, Antarctica, Southern California) to collect bioacoustical information. Derek’s company manufactures the buoys and he has joined us at sea to deploy and work with the buoy data that are produced during this cruise.