Chlorophyll and suspended sediment assessment in a ... - OzCoasts

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Chlorophyll and suspended sediment assessment using remote sensingSummaryRemote sensing data from satellites such as MODIS is often from the same timeof day; it is susceptible to prevailing cloudiness conditions and is therefore, nonuniformlydistributed throughout the year. Satellite images also may have partcloud cover and part visibility, or indeed may have some other errors throughoutthe scene causing ‘failed ‘ pixels. Nevertheless satellite images are by far thecheapest and most spatially and temporally complete datasets available, whencompared against any other measurement method.Archives of MODIS-like satellite images are available from 1997 onwards fromthe following satellite sensor systems: from 1997 SeaWiFS, from 1999 onwardsMODIS/Terra, and from 2002 onwards both MODIS/Aqua and MERIS. The MIMalgorithm can easily be adapted and applied to all these satellite data sets thusgiving the climatology of the FE–KB system from 1997 to present. Theapplicability to multiple sensors is another reason why it was well worth investingso much effort into developing regionally correct algorithms.Comparing MIM estimates of chlorophyll and suspended matter values anddistribution with the biogeochemical model outputThe concentration ranges determined from the MODIS/Aqua MIM images andthe output of the biogeochemical model are in a high level of agreement. Asthese two data products are produced independently of each other this is anindication that these two information sources are accurate for concentrationassessments, especially as the ranges in the FE–KB system are similar to thosemeasured in situ. This could mean a significant shift in the requirements for amonitoring program in the FE–KB system as remote sensing using MODIS orsimilar sensor data such as SeaWiFS and MERIS for TSM and CHL (and otherproducts such as Secchi disk transparency, turbidity, vertical attenuation oflight and coloured dissolved organic matter concentrations) can provide themonitoring data at an unsurpassed temporal and spatial scale.When the CHL and TSM dynamic in Keppel Bay is dominated by processesoccurring at a larger scale, the biogeochemical model (together with itsunderlying hydrodynamic model) is unable to appropriately recreate the spatialdistribution of those processes.The remote sensing images show how the assumption by the model of lowchlorophyll concentration along the coast misrepresents the likely true situation.In some cases there is a significant lobe of chlorophyll-rich water visible in thesatellite images, that passes across the top (north) of Curtis Island, travels to theeast and then after Curtis Island turns south-east. The model does not show this4
Chlorophyll and suspended sediment assessment using remote sensingSummarypattern although this may be a significant conduit of nutrient-rich waters notreturning into Keppel Bay after each tidal cycle. If this is the case, then thenitrogen and phosphorous budget of the FE–KB system to the Great Barrier Reef(GBR) lagoon as calculated by the model will be underestimated.The biogeochemical model output can be improved (forced/nudged) by theremote sensing–derived information to become more representative of theFE–KB system, in the first instance by improving the boundary conditions orexpanding the boundary.An improved biogeochemical model (with all its output variables) and the40 (minimum amount) to 100 (maximum current amount) of satellite images peryear (with its more limited set of output variables), can in combination give amanagement-relevant set of water quality indicators for the FE–KB system at arelatively low cost now that both the regional algorithms and the biogeochemicalmodel have been developed.The satellite images can cover a much larger area than shown here (typically upto 1000 km 2 ); the biogeochemical model can also become as large as required(although necessarily at a coarser scale). A nested approach of larger scale tofiner scale remote sensing and biogeochemical modelling would be appropriateto model and manage much larger parts of the Queensland coast. Such a nestedapproach would place the FE–KB system into a larger context, required tounderstand broader-scale issues (such as along-shore, coastal lagoon and evenoceanic waters) affecting the FE–KB system. Specifically this research showedthat significant amounts of chlorophyll may enter the FE–KB system from thenorth, whereas in some cases there could be large amounts of export acrossCurtis Island to the south-east.5
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Chlorophyll and suspended sediment assessment in a ... - OzCoasts

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