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Estimating the radiation environment in the Great Barrier Reef

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Masiri, IO (2008) Estimating the radiation environment in the Great Barrier Reef. PhD thesis, University of Tasmania.

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Abstract

There are a number of studies that have examined solar irradiance in the
environment above and below the ocean surface. Unlike other previous studies, this
thesis maps both surface and underwater irradiances using a combination of
geostationary and Sea WiFS satellite data and surface measurements. Detailed estimates
of broadband, PAR and UVB solar radiation, both above and below water, is obtained
for the Great Barrier Reef region in northeast Australia. The study area covers the Coral
Sea including the Great Barrier Reef (GBR), northeast of Queensland (1 0 o S - 26° S,
142" E - 155° E). Geostationary meteorological satellite (GMS) data collected for
periods between 1995 and 2005 are combined with the models to obtain broadband
solar radiation at the surface. PAR and UVB underwater irradiance are estimated from
the attenuation coefficients Kd derived from the Sea WiFS instrument for the period of
1998-2005.
In developing algorithms, a look-up table (LUT), which contains senes of
broadband surface solar radiation and the Earth-atmosphere reflectivity, is created from
the Streamer radiative transfer model. The broadband Earth-atmosphere reflectivity a llA
derived from the GMS data is used to estimate the surface solar radiation from the LUT
algorithms. The attenuation coefficients Kd for PAR, UVB and Sea WiFS wavebands are
obtained from Monte Carlo models, and relationships between these Kd values are
derived as a result. Using Sea WiFS-derived Kd data, PAR and UVB underwater
irradiance are estimated across the regions from the Kd relationships.
Comparisons between the satellite-derived surface solar radiation and the
measurements at Rockhampton and Cairns give good agreement with root-mean-square difference (RMSD) of 2.26 MJ-m-2-day"1 and 2.85 MJ-m-2-day" 1
, respectively. The
Sea WiFS-derived Kd at six different wavebands obtained from Monte Carlo models are
compared to the measurements at Heron Island, with a smallest RMSD value of 0.075
-I m.
Maps of solar radiation both above and below the water surface are provided for
the study area. On average, strong solar radiation is exhibited in summer and autumn
periods at latitude bands between 18 ° S and 26° S. The temporal information suggests
there is a small increase in solar radiation of about 1 percent per decade. The underwater
PAR and UVB irradiances along the GBR coastline at 2.5 m depth were in magnitude
of ~300 W-m-2 and ~120 mW-m-2
, respectively. Monthly distribution at 2.5 m depth
underwater for PAR shows an outstanding feature throughout between September and
February. There are patterns of high PAR irradiance throughout the summer months of
2001/2002 and 2002/2003. Results of the satellite-derived solar radiation are used to
examine the 2002 coral bleaching events. A correlation between maximum solar
radiation and the bleaching data are seen in summer months of 2001/2002.

Item Type: Thesis (PhD)
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Date Deposited: 18 Mar 2014 03:00
Last Modified: 11 Mar 2016 05:53
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