An instrumented buoy being deployed during this year's field season. Photo by Steve. |
Instrumented
Buoys
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 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.
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.
|
The lower portion of the buoys laid out on deck prior to deployment
(top figure).
While transiting to the survey site we tested the upper portion of the
buoys
on the deck of the ship (lower figure). Photos by Derek. |
Acoustic echosounders (orange ovals) and acoustic Doppler
current
meters (four-circles)
provide data that the buoys telemeter to shore. Photo by Steve. |
Acoustic
Echosounders
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
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.
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The buoys can be deployed by three people in a small boat due to their
modular construction. Photo by Steve. |
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 Sea Technology
Services
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. |
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