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Moorings
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The Benguela system suffers from frequent
occurrences of a variety of toxic and otherwise harmful algal blooms (HABs).
Such blooms can have severe negative impacts on local marine ecosystems
and communities. The
mooring has been constructed as part of a BCLME (Benguela Current Large
Marine Ecosystem) project to
demonstrate the utility of real time bio-optical data as an integrated
management tool for coastal agencies, and an early warning system with
regard to HAB detection and ecosystem protection.
The mooring is deployed on the southern Benguela
Namaqua shelf, three and a half kilometers offshore from Lamberts Bay.
This
area is subject to frequent occurrences of HABs, predominantly composed of
dinoflagellate and ciliate species. The buoy has been deployed here as
research in the region is ongoing and the
area is perhaps the most studied and well understood region of the
Benguela system with regard to the dynamics, formative mechanisms and
typical assemblage structure of harmful algal blooms. |
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Trial Mooring
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The buoy provides real time ocean colour reflectance, temperature and fluorescence
data transmitted using cell phone telemetry. Considerations in the design
of the mooring were that it should be cost-effective and robust whilst minimising shading of the optical
sensors and allowing for field calibration and deployment from small
vessels.
The trial mooring was
deployed off Lamberts Bay from February to June 2004 providing a unique data set of hyperspectral
reflectance measurements and ancillary data relating to algal bio-mass and
water column structure.
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A
second buoy has subsequently been developed utilising a pencil buoy
design on a two anchor tight line mooring for enhanced sea-keeping
abilities. It was deployed in the same position as the trial
mooring off Lamberts Bay in January 2005.
The instrument package
on the buoy consists of two TriOS hyperspectral radiometers (one
radiance, one irradiance), a 50m Templine thermistor chain, a SCUFA
fluorometer and an RD Instruments ADCP. Power management, data acquisition and storage and data
transmission are controlled by a Saturn Solutions Ocean-i Sensor Unit. The buoy is powered by a 12Ah gel lead acid battery, which is charged by
solar panels. A GPS unit provides position information and
accurate time to Ocean-i . An inclinometer incorporated
into the radiance sensor allows for quality control of the data.
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Data are collected from all the instruments simultaneously for two
minutes every half an hour. These data are stored on a Compact Flash card
in the Ocean-i Sensor Unit. Data are retrieved from the buoy by dialing
into the buoy from an external modem. This process is automated at the
University of Cape Town so that the most recent data acquisition is
downloaded four times a day. Data are then processed using Matlab - remote sensing
reflectance is calculated from the radiometer data and locally developed
reflectance algorithms are applied to the data to calculate algal biomass and
effective assemblage size. The website is updated with
these data twice daily when data are available.
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