We present the first results of the assimilation of ocean colour datasets into coastal ocean biogeochemical models for the
tropical Fitzroy Estuary and Keppel Bay system (FEKB) contingent to the Great Barrier Reef lagoon. As part of the
Great Barrier Reef Monitoring Program, a regional algorithm for operational delivery of valid coastal ocean colour
products was recently developed for FEKB. A new generation of regional specific algorithm for the FEKB system had to
be developed for large satellite datasets of the MODIS sensors as the global algorithms failed. Concurrently, a
biogeochemical model was developed for the system, built upon a three-dimensional hydrodynamic and sediment
dynamic model, and simulating nitrogen and phosphorus dynamics including the dynamics of dissolved organic material
as well as pelagic and benthic primary production. One of the aims was to provide estimates of material fluxes from
Keppel Bay to the Great Barrier Reef Lagoon. The biogeochemical model was run first with fixed boundary conditions
based on the limited in situ measurements, then with boundary conditions derived from satellite datasets using the
region-specific algorithm. Several methodologies for linking of remote sensing observations to model variables were
evaluated over a period of one year (2004). When remote sensing information was used to inform the boundaries,
estimates of material fluxes in the model changed substantially in magnitude and direction.
Traditional approaches to remote sensing of coral reefs have been highly empirical, relying on classification of remote sensing images. We have chosen a physics based approach - the collection of reflectance spectra of different substrates and the determination of the inherent optical properties of the water column. This information, together with radiative transfer models of water and atmosphere as well as technical characteristics of different remote sensing sensors, allows us to estimate what benthic communities are spectrally resolvable with respect to water column depth and the sensor characteristics. A hyperspectral library of more than 140 different coral reefs substrates (living hard and soft corals, dead corals, rubble, sand, algae and sponges) were collected from the Great Barrier Reef. Hydrolight 4.1 model was used to simulate remote sensing reflectances above the water and a MODTRAN3 type in-house atmosphere model was used to simulate radiance at airborne and space borne sensor levels. Most of the spectral variability in reflectance of coral reef benthic communities occurs in the spectral range of 550-680 nm (green to red light). The water itself is a main limiting factor in remote detection of various reef substrates, as water itself is absorbing light strongly in the same part of the spectrum where most of the variability in reflectance spectra of different coral reef benthic substrates occurs. Hyperspectral information allows us to separate different substrates from each other more easily and in deeper waters than broad band sensors.
In order to obtain more information on the angular scattering behavior of algae and silt research was initiated to determine whether or not the volume scattering functions by Petzold of the San Diego Harbor are appropriate for use in other types of turbid waters as is often stated in literature. This paper presents a selection of the measured angular scattering distribution functions over the range 10 degrees-165 degrees, the extrapolated angular scattering distribution functions extended to the range of 0 degrees- 180 degree by fitting Mie functions and the calculated backward scattering to total scattering ratios. The San Diego Harbor measurements by Petzold may not be applied to other turbid waters; it is in the backscattering region where the samples deviate most from the San Diego ASD from Petzold. A large addition to existing literature values for backscatter probabilities is presented for 14 freshwater and marine algal species samples and 2 estuarine silt samples.
The availability of imaging spectrometers such as the airborne AVIRIS, CASI, ROSIS, HYDICE and future spaceborne instruments such as MERIS and MODIS has created a necessity for spectral methods and models which can predict the performance of these instruments for detecting and estimating chlorophyll-a (CHL) as a water quality indicator. The aim of this study is to gain insight into the performance of MERIS for estimating CHL in turbid inland waters. In such waters with CHL ranging from 10 to over 300 (mu) g 1-1 estimation of CHL using the fluorescence line height does not apply anymore. The research was carried out by means of bio-optical modeling, which yields the subsurface irradiance reflectance R(0-) from the water constituent concentrations, using the inherent optical properties as parameters. The inherent optical properties are measured with laboratory spectrophotometers and they are applied for simulation of water types ranging from clear drinking water to turbid eutrophic waters. These simulations enabled the quantification of the effect of increasing chlorophyll-a on R(0-). In addition a sensitivity analysis was applied. The change in R(0-) due to a change of 1 (mu) g 1- in CHL was compared to the noise equivalent reflectance as specified for ocean applications of MERIS< which gives an indication of the accuracy for estimating chlorophyll-a. From the simulation results it was concluded that MERIS can estimate chlorophyll-a in turbid inland water with an accuracy of 1 (mu) g 1- for CHL values of 10 (mu) g 1- for CHL values of 190 (mu) $g 1-. Furthermore, variations in the backscatter to scatter ratio of 25 percent, based on recent measurements of the volume scattering function, yielded a variation of 17-20 percent in the reflectance.
Conference Committee Involvement (1)
Coastal Ocean Remote Sensing
26 August 2007 | San Diego, California, United States
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