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1.
Traditional field techniques to monitor water quality in large estuaries, such as boat-based surveys and autonomous moored sensors, generally provide limited spatial coverage. Satellite imagery potentially can be used to address both of these limitations. Here, we show that satellite-based observations are useful for inferring total-suspended-solids (TSS) concentrations in estuarine areas. A spectra-matching optimization algorithm was used to estimate the particle backscattering coefficient at 400 nm, bbp(400), in Chesapeake Bay from Sea-viewing Wide-Field-of-view Sensor (SeaWiFS) satellite imagery. These estimated values of bbp(400) were compared to in situ measurements of TSS for the study period of September 1997–December 2003. Contemporaneous SeaWiFS bbp(400) values and TSS concentrations were positively correlated (N = 340, r2 = 0.4, P < 0.0005), and the satellite-derived bbp(400) values served as a reasonable first-order approximation for synoptically mapping TSS. Overall, large-scale patterns of SeaWiFS bbp(400) appeared to be consistent with expectations based on field observations and historical reports of TSS. Monthly averages indicated that SeaWiFS bbp(400) was typically largest in winter (>0.049 m−1, November–February) and smallest in summer (<0.031 m−1, June–August), regardless of the amount of riverine discharge to the bay. The study period also included Hurricanes Floyd and Isabel, which caused large-scale turbidity events and changes in the water quality of the bay. These results demonstrate that this technique can provide frequent synoptic assessments of suspended solids concentrations in Chesapeake Bay and other coastal regions.  相似文献   

2.
Measurement of dissolved oxygen using optodes in a FerryBox system   总被引：2，自引：0，他引：2  
Optode sensors can provide detailed information on concentrations of dissolved oxygen, which in turn may be used to quantify variations in net primary productivity. Throughout 2005 and 2006 the performance of commercially available oxygen optodes was examined, one in each year. The optode was part of an autonomous measurement system (FerryBox) on a ferry operating between Portsmouth (UK) and Bilbao (Spain). On crossings during which water samples were collected manually, the optode outputs were compared to measurements of dissolved oxygen made by Winkler titrations. The optodes maintained good stability with no evidence of instrumental drift during the course of a year. Over the observed concentration range (230–330 mM m−3) the optode data were approximately 2% low in both years. By fitting the optode data to the Winkler data the median difference between the optode and Winkler measurements is reduced to less than 1 mM m−3 (0.3%) in both years. The most appropriate calibration factor for 2005 was corrected O2 = Optode O2 × 1.018 and for 2006 the corresponding equation is corrected O2 = Optode O2 × 0.884 + 36.8. The standard deviation (95%) of the difference between the individual Winkler measurements was 5 mM m−3 and 3 mM m−3 in 2005 and 2006 respectively.Calculation of the oxygen saturation anomaly is required for calculation of the air sea exchange of oxygen and net biological production. This calculation requires the use of both salinity and temperature data. Salinity is measured to better than 0.1 so the corresponding error in anomaly is less than 0.2 mM m−3. Distortion of the temperature data is present due to warming of the water pumped to the optode. In winter this warming at the optode may be as great as 0.4 °C. The difference in the pumped water temperature can be corrected for by reference to other measurements of sea surface temperature reducing the error to less than 1 mM m−3.  相似文献   

3.
The direct photooxidation of coloured dissolved organic matter (CDOM) to dissolved inorganic carbon (DIC) may provide a significant sink for organic carbon in the ocean. To calculate the rate of this reaction on a global scale, it is essential to know its quantum yield, or photochemical efficiency. We have determined quantum yield spectra, φ(λ), (moles DIC/mole photons absorbed) for 14 samples of seawater from environments ranging from a turbid, eutrophic bay to the Gulf Stream. The spectra vary among locations, but can be represented quite well by three pooled spectra for zones defined by location and salinity: inshore φ(λ)=e−(6.66+0.0285(λ−290)); coastal φ(λ)=e−(6.36+0.0140(λ−290)); and open ocean φ(λ)=e−(5.53+0.00914(λ−290)). Production efficiency increases offshore, which suggests that the most highly absorbing and quickly faded terrestrial chromophores are not those directly responsible for DIC photoproduction.  相似文献   

4.
The changes in the phytoplankton absorption properties during a diurnal cycle were investigated at one station located in the north-western area of the Alborán Sea. The experiment was performed in spring when the water column was strongly stratified. This hydrological situation permitted the establishment of a deep chlorophyll a (chl a) fluorescence maximum (DFM) which was located on average close to the lower limit of the mixed layer and the nutricline. The relative abundance of pico-phytoplankton (estimated as its contribution to the total chl a) was higher in the surface, however, micro-phytoplankton dominated the community at the DFM level. Chl a specific absorption coefficient (a*(λ)) also varied with optical depth, with a* (the spectrally average specific absorption coefficient) decreasing by 30% at the DFM depth with respect to the surface. A significant negative correlation between the contribution of the micro-phytoplankton to the total chl a and a* was obtained indicating that a* reduction was due to changes in the packaging effect. Below the euphotic layer, a* increased three-fold with respect to the DFM, which agrees with the expected accumulation of accessory pigments relative to chl a as an acclimation response to the low available irradiance. The most conspicuous change during the diurnal cycle was produced in the euphotic layer where the chl a concentration decreased significantly in the afternoon (from a mean concentration of 1.1 μg L−1 to 0.7 μg L−1) and increased at dusk when it averaged 1.4 μg L−1. In addition, a* and the blue-to-red absorption band ratio increased in the afternoon. These results suggest that a*(λ) diurnal variability was due to increase in photo-protective and accessory pigments relative to chl a. The variation ranges of a*(λ) at 675 and 440 nm (the absorption peaks in the red and blue spectral bands, respectively) in the euphotic layer were 0.01–0.04 and 0.02–0.10 m2 mg−1 chl a, respectively. Approximately 30% out of this variability can be attributed to the diurnal cycle. This factor should therefore be taken into account in refining primary production models based on phytoplankton light absorption.  相似文献   

5.
The photochemical oxidation of colored, dissolved organic matter (CDOM) is important for carbon cycling in the ocean. This oxidation process produces a number of products, including carbon monoxide (CO). While the photochemical production efficiency of CO (apparent quantum yield, AQY, defined in terms of CDOM absorbance) has been reported to be similar for many water types, a full evaluation of the observed natural variability in CO AQY requires additional study. Here we use a polychromatic irradiation system to determine twenty AQY spectra at sea on fresh samples ranging from the near coastal waters of the Gulf of Maine to the offshore waters of the Northwest Atlantic. Despite the geographic variability of these marine samples the AQY of CO production in the Gulf of Maine and Northwest Atlantic exhibited only a small degree of variability, none of which was not correlated with measured environmental parameters. Consequently, a single aggregate AQY spectrum λ = e(−(9.134+0.0425(λ−290)))+e(−(11.316+0.0142(λ−290))) was found to adequately represent the entire data set. Significantly, the accuracy of an AQY spectrum determined using this multispectral/statistical technique was confirmed with data obtained from a monochromatic irradiation technique on a single open ocean sample. Taken together, the AQY spectra determined in this study were similar in magnitude and shape to those previously published for marine samples and, overall, were somewhat lower than those previously reported for freshwater studies.  相似文献   

6.
Vertical attenuation of light through the water column (Kd) is attributable to the optically active components of phytoplankton, suspended particulate material (SPM) and chromophoric dissolved organic matter (CDOM). Of these, CDOM is not routinely monitored and was the main focus of this study. Concentrations and spatio-temporal patterns of CDOM fluorescence were investigated between August 2004 and March 2006, to quantify the correlation coefficient between CDOM and salinity and to better characterise the contribution of CDOM to Kd. Sampling was conducted at a broad range of UK and Republic of Ireland locations; these included more than 15 estuaries, 30 coastal and 70 offshore sites in the southern North Sea, Irish Sea, Liverpool Bay, Western Approaches and the English Channel.An instrument package was used; a logger with multi-sensor array was deployed vertically through the water column and concurrent water samples were taken to determine salinity, CDOM fluorescence and SPM. Surface CDOM fluorescence values ranged between 0.05 and 16.80 S.Fl.U. (standardised fluorescence units). A strong, negative correlation coefficient of CDOM to salinity (r2 = 0.81) was found. CDOM absorption (aCDOMλ) was derived from fluorescence measurements and was in the range 0.02–2.2 m−1 with mean 0.15 m−1. These results were comparable with direct measurements of aCDOMλ in the same geographic regions, as published by other workers.Spatial differences in CDOM fluorescence were generally explicable by variation in salinity, in local conditions or catchment areas; e.g. CDOM at the freshwater end was 3.54–11.30 S.Fl.U., reflecting the variety of rivers sampled and their different catchments. Temporal changes in CDOM fluorescence were related to salinity. A significant and positive correlation was found between CDOM and Kd, and although CDOM was found to be less influential than SPM on Kd, it was still of significance particularly in coastal and offshore waters of lower turbidity.  相似文献   

7.
The ocean is an important sink for carbon and heat, yet high-resolution measurements of biogeochemical properties relevant to global climate change are being made only sporadically in the ocean at present. There is a growing need for automated, real-time, long-term measurements of CO2 in the ocean using a network of sensors, strategically placed on ships, moorings, free-drifting buoys and autonomous remotely operated vehicles. The ground-truthing of new sensor technologies is a vital component of present and future efforts to monitor changes in the ocean carbon cycle and air–sea exchange of CO2.A comparison of a moored Carbon Interface Ocean Atmosphere (CARIOCA) buoy and shipboard fugacity of CO2 (fCO2) measurements was conducted in the western North Atlantic during two extended periods (>1 month) in 1997. The CARIOCA buoy was deployed on the Bermuda Testbed Mooring (BTM), which is located 5 km north of the site of the US Joint Global Ocean Flux Study (JGOFS) Bermuda Atlantic Time-series Study (BATS). The high frequency of sampling revealed that temperature and fCO2 responded to physical forcing by the atmosphere on timescales from diurnal to 4–8 days. Concurrent with the deployments of the CARIOCA buoy, frequent measurements of surface fCO2 were made from the R/V Weatherbird II during opportunistic visits to the BTM and BATS sites, providing a direct calibration of the CARIOCA buoy fCO2 data. Although, the in situ ground-truthing of the CARIOCA buoy was complicated by diurnal processes, sub-mesoscale and fine-scale variability, the CARIOCA buoy fCO2 data was accurate within 3±6 μatm of shipboard fCO2 data for periods up to 50 days. Longer-term assessments were not possible due to the CARIOCA buoy breaking free of the BTM and drifting into waters with different fCO2-temperature properties. Strategies are put forward for future calibration of other in situ sensors.  相似文献   

8.
The effect of interaction between stratification and irradiance regimes on phytoplankton community structure was investigated in three shelf/coastal regions of the British Isles, each of which displayed ranges of vertical stability and light attenuation. Relationships between vertical stability, light penetration and community structure were indicated by the ordination of dominance (assessed using cell volume) of the main phytoplankton phyletic groups—diatoms, dinoflagellates and microflagellates—on a surface defined by a bulk stratification index () and water column depth, scaled by transparency (λh). Diatom- and dinoflagellate-dominated communities occupied distinctly different domains on the - λh surface, diatoms being favoured in well-mixed water columns with high values for λh and dinoflagellates dominating where stratification was strong and λh was low. Microflagellates were not abundant in any of the study areas and showed no clear ordination on the - λh surface. The domain of co-dominance of diatom and dinoflagellates on the - λh surface was narrow with small changes in the irradiance or stratification regime resulting in a switch to diatom or dinoflagellate dominance. It is suggested that loss of non-motile diatom communities in strongly stratified water columns might be a strong selective force in favour of dinoflagel-lates. However, in water columns with intermediate stratification and optical properties, the outcome of competition may be decided by physiological attributes of the two groups with respect to growth in low and fluctuating irradiances.  相似文献   

9.
Two models, a spectral refraction model (Longuet-Higgins) and a parabolic equation method (PEM) refraction-diffraction model (Kirby), are used to simulate the propagation of surface gravity waves across the Southern California Bight. The Bight contains numerous offshore islands and shoals and is significantly larger (≈ 300 km by 300 km) than regions typically studied with these models. The effects of complex bathymetry on the transformation of incident wave directional spectra, S0(f,θ0), which are very narrow in both frequency and direction are difficult to model accurately. As S0(f,θ0) becomes broader in both dimensions, agreement between the models improves and the spectra predicted at coastal sites become less sensitive to errors in the bathymetry grid, to tidal changes in the mean water depth, and to uncertainty in S0(f,θ0) itself. The smoothing associated with even relatively narrow (0.01 Hz-5° bandwidth) S0(f,θ0) is usually sufficient to bring the model predictions of shallow water energy into at least qualitative agreement. However, neither model is accurate at highly sheltered sites. The importance of diffraction degrades the predictions of the refraction model, and a positive bias [O (10%) of the deep ocean energy] in the refraction-diffraction model estimates, believed to stem from numerical “noise” (Kirby), may be comparable to the low wave energy. The best agreement between the predicted spectra generally occurs at moderately exposed locations in deeper waters within the Bight, away from shallow water diffractive effects and in the far-field of the islands. In these cases, the differences between the models are small, comparable to the errors caused by tidal fluctuations in water depth as waves propagate across the Bight. The accuracy of predicted energies at these sites is likely to be limited by the uncertainty in specifying S0(f,θ0).  相似文献   

10.
Four geosim families, with fully available resistance test results, have been re-analyzed to check the possible scale effect on the form factor. The form factor determined by Prohaska's method, with exponent n=4 and ITTC'57 correlation line, increases with the model size in all four cases analyzed. Because of its high correlation coefficient, a linear variation of the form factor with the scale is assumed. It is possible to have a first estimation of the ship's form factor extrapolating for λ=1 in the regression line. Form factor Reynolds number dependency will always be associated with a friction line. Using the ITTC'57 correlation line, the following equation KS−KM=1.91·(λ−1)·10−3 can be used to estimate the scale effect on the form factor. Calculations carried out, for axisymetric bodies, with some CFD codes are in good agreement with the experimental findings.  相似文献   

11.
This paper assesses the feasibility of applying remote sensing algorithms based on blue/green reflectance ratios to Case 2 waters. Two algorithms from the SeaDAS (NASA) image processing package, OC4v4 for surface chlorophyll concentration, Chl, and K(490) for the attenuation coefficient for downward irradiance at 490 nm, Kd(490), were investigated using an extensive set of observations from the Irish and Celtic Seas. In situ data from a profiling radiometer were used as inputs for the algorithms to avoid uncertainties in atmospheric correction procedures, and direct measurements of Chl and Kd490 and were used for validation purposes. The standard versions of the algorithms performed poorly: OC4v4 generally overestimated Chl (with a very low coefficient of determination), and K(490) progressively underestimated Kd490 for values greater than 0.3 m−1. A two-step procedure for level 2 product generation was therefore devised in which the numerical coefficients of OC4v4 and K(490) were tuned for the two optical water types known to occur most frequently in this region (McKee, D., Cunningham, A., 2006. Identification and characterisation of two optical water types in the Irish Sea from in situ inherent optical properties and seawater constituents. Estuarine, Coastal and Shelf Science 68, 305–316) by statistical regression on a data set of 102 stations from the Irish and Celtic Seas. The water types were distinguished by the magnitude of their normalised water leaving radiance signals at 665 nm, nLw(665), and appropriate versions of the tuned algorithms applied to each water type. When this procedure was tested on an independent data set of 19 stations from the Bristol Channel, Chl values were recovered with an RMS error of 0.36 mg m−3 and Kd(490) values with an RMS error of 0.095 m−1. The identification of water types from water-leaving radiance signals, and the application of band-ratio algorithms tuned for specific water types, may therefore provide a simple means of improving the quality of remote sensing products in optically complex shelf seas.  相似文献   

12.
An interaction of dissolved natural organic matter (DNOM) with copper ions in the water column of the stratified Krka River estuary (Croatia) was studied. The experimental methodology was based on the differential pulse anodic stripping voltammetric (DPASV) determination of labile copper species by titrating the sample using increments of copper additions uniformly distributed on the logarithmic scale. A classical at-equilibrium approach (determination of copper complexing capacity, CuCC) and a kinetic approach (tracing of equilibrium reconstitution) of copper complexation were considered and compared. A model of discrete distribution of organic ligands forming inert copper complexes was applied. For both approaches, a home-written fitting program was used for the determination of apparent stability constants (Kiequ), total ligands concentration (LiT) and association/dissociation rate constants (ki1,ki- 1).A non-conservative behaviour of dissolved organic matter (DOC) and total copper concentration in a water column was registered. An enhanced biological activity at the freshwater–seawater interface (FSI) triggered an increase of total copper concentration and total ligand concentration in this water layer. The copper complexation in fresh water of Krka River was characterised by one type of binding ligands, while in most of the estuarine and marine samples two classes of ligands were identified. The distribution of apparent stability constants (log K1equ: 11.2–13.0, log K2equ:8.8–10.0) showed increasing trend towards higher salinities, indicating stronger copper complexation by autochthonous seawater organic matter.Copper complexation parameters (ligand concentrations and apparent stability constants) obtained by at-equilibrium model are in very good accordance with those of kinetic model. Calculated association rate constants (k11:6.1–20 × 103 (M s)− 1, k21: 1.3–6.3 × 103 (M s)− 1) indicate that copper complexation by DNOM takes place relatively slowly. The time needed to achieve a new pseudo-equilibrium induced by an increase of copper concentration (which is common for Krka River estuary during summer period due to the nautical traffic), is estimated to be from 2 to 4 h.It is found that in such oligotrophic environment (dissolved organic carbon content under 83 µMC, i.e. 1 mgCL− 1) an increase of the total copper concentration above 12 nM could enhance a free copper concentration exceeding the level considered as potentially toxic for microorganisms (10 pM).  相似文献   

13.
A total of 1125 specimens of sardine, Sardina pilchardus, ranging in total length from 4.9 to 12.5 cm (mean 8.31 ± 1.41 cm) and in weights between 1.02 g and 11.18 g (mean 4.40 ± 1.87 g) were randomly sampled using a beach seine from the Krka River estuary. Samples were collected monthly according to their occurrence in this area from October to February during 2002/03, 2003/04 and 2004/05, which is during the spawning period of this species. Monthly fluctuations in the length frequency distributions of sardine were observed during that time. The length–weight relationship of all sardine specimens was described by the equation: W=0.007L2.9587(r2 = 0.9626); and the isometric nature of relative growth was established (t = −5.1495; p < 0.05). According to the allometric condition factor Ka, sardine specimens were in better somatic condition at the beginning of their appearance (spawning period) in the Krka River estuary. The length at which 50% of sardines were mature (L50) was calculated to be 7.9 cm.  相似文献   

14.
The wave transmission, reflection and energy dissipation characteristics of ‘’-type breakwaters were studied using physical models. Regular and random waves in a wide range of wave heights and periods and a constant water depth were used. Five different depths of immersion (two emerged, one surface flushing and two submerged conditions) of this breakwater were selected. The coefficient of transmission, Kt, and coefficient of reflection, Kr, were obtained from the measurements, and the coefficient of energy loss, Kl was calculated using the law of balance of energy. It was found that the wave transmission is significantly reduced with increased relative water depth, d/L, whether the vertical barrier of the breakwater is surface piercing or submerged, where ‘d’ is the water depth and ‘L’ is the wave length. The wave reflection decreases and energy loss increases with increased wave steepness, especially when the top tip of the vertical barrier of this breakwater is kept at still water level (SWL). For any incident wave climate (moderate or storm waves), the wave transmission consistently decreases and the reflection increases with increased relative depth of immersion, Δ/d from −0.142 to 0.142. Kt values less than 0.3 can be easily obtained for the case of Δ/d=+0.071 and 0.142, where Δ is the height of exposure (+ve) or depth of immersion (−ve) of the top tip of the vertical barrier. This breakwater is capable of dissipating wave energy to an extent of 50–80%. The overall performance of this breakwater was found to be better in the random wave fields than in the regular waves. A comparison of the hydrodynamic performance of ‘’-type and ‘T’-type shows that ‘T’-type breakwater is better than ‘’-type by about 20–30% under identical conditions.  相似文献   

15.
Microstructure measurements in natural waters: Methodology and applications   总被引：2，自引：0，他引：2  
Modern approaches to microstructure data processing, including wavelet denoising, are discussed. The wavelet procedure is applied to small-scale shear signals before estimating the dissipation rate ε and to the temperature/density profiles used to calculate Thorpe scales. Microstructure data obtained on the Mediterranean shelf of Catalonia are used to illustrate various approaches to the Thorpe displacement calculations. It is suggested that the Weibull probability function is an appropriate model for the Thorpe scale distribution. Microstructure measurements from the upper layer of the Boadella reservoir (Catalonia, Spain) support this finding.A new analytical approximation for the 1D Panchev–Kesich spectrum is deduced and the results of ε computation are compared with spectral fitting by the widely used Nasmyth spectrum. Applying the Kraichnan spectral model to compute ε from temperature spectra in the convective-viscous sub-range is examined as an alternative to the Batchelor spectrum. Microstructure measurements taken in Lake Banyoles (Catalonia, Spain) and in the North Atlantic were used for spectral calculations.Statistical analysis of eddy Kb and thermal Kθ diffusivities measured on a shallow shelf of the Black Sea shows the importance of process-orientated domain averaging of the diffusivities in obtaining good correspondence between Kb and Kθ in active turbulent regions. In weakly turbulent, stratified interior layers, the averaged Kb and Kθ differ significantly, which may point to the inapplicability of isotropic formulae used for ε and temperature dissipation χθ estimates, as well as to a dependence of the mixing efficiency γ on the Richardson number or in some cases on regions of fossil turbulence.  相似文献   

16.
This is a theoretical study of a breakwater-seawall wave-trapping system. The breakwater, being flexible, porous and thin beam-like, is held fixed in the sea bed and idealized as one-dimensional beam of uniform flexural rigidity and uniform mass per unit length. The seawall, being vertical, rigid and impermeable, is located behind the breakwater by a distance of L. The velocity potentials of the wave motion are coupled with the equation of motion of the breakwater. Analytical solutions in closed forms are obtained for the reflected and transmitted velocity potentials together with the displacement of the breakwater. The free-surface elevation, hydrodynamic forces acting on both the breakwater and the seawall are determined. It is found that the values of L, at which the minimum reflected-wave amplitudes reach, are in the range of λ to λ for breakwaters with different rigidity and permeability. It is shown that, when the spacing L maintains values in the range of λ to λ, the resultant amplitudes in both regions can be reduced to a favorable amount for any wave and structural parameters. It is also shown that the hydrodynamic forces on the breakwater decrease as the structural flexibility and porosity increase. However, with increases of the structural porosity and flexibility, the seawall experiences an increase of the hydrodynamic forces. Various results are presented in this paper to illustrate the effects of the structural and perous parameters together with the spacing on the response and efficiency of the breakwater-seawall wave-trapping system.  相似文献   

17.
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18.
The hydrolysis of silicic acid, Si(OH)4, was studied in a simplified seawater medium (0.6 M Na(Cl)) at 25°C. The measurements were performed as potentiometric titrations (hydrogen electrode) in which OH− was generated coulometrically. The total concentration of Si(OH)4, B, and log[H+] were varied within the limits 0.00075 B 0.008 M and 2.5 -log[H+] 11.7, respectively. Within these ranges the formation of SiO(OH)3− and SiO2(OH)22− with formation constants log β−11(Si(OH)4 SiO(OH)3− + H+) = −9.472 ±0.002 and log β−21(Si(OH)4 SiO2(OH)22− + 2H+) = −22.07 ± 0.01 was established. With B > 0.003 M polysilicate complexes are formed, however, with -log[H+] 10.7 their formation does not significantly affect the evaluated formation constants. Data were analyzed with the least squares computer program LETAGROPVRID.  相似文献   

19.
Measurements of the naturally occurring radioisotopes 223Ra (t1/2 = 11.4 days) and 224Ra (t1/2 = 3.66 days) in southern Rhode Island salt ponds were combined with a simple model to obtain independent estimates of the age of these coastal waters. Surface water and porewater samples were collected quarterly in Winnapaug, Quonochontaug, Ninigret, Green Hill, and Pt. Judith-Potter Ponds, as well as nearly monthly in the surface water of Rhode Island Sound, beginning January 2002 through August 2003. Surface water activities ranged from 1–78 dpm 100 L− 1 and 5–885 dpm 100 L− 1 for 223Ra and 224Ra, respectively. Porewater radium activities ranged from 3 to 715 dpm 100 L− 1 for 223Ra, and 57–4926 dpm 100 L− 1 for 224Ra. Results indicate seasonally varying water mass ages for Ninigret (5–12 days), Winnapaug (2–6 days) and Pt. Judith-Potter Ponds (1–9 days) and, in contrast, relatively constant ages for Green Hill (5–7 days) and Quonochontaug Ponds (3–6 days).  相似文献   

20.
Advanced remote sensing techniques and regional algorithms are combined to produce and analyze a 12-year multi-sensor time series of bio-optical properties for the Adriatic Sea. First, a multi-sensor series of normalized water-leaving radiance LWN is created with an optically-based merging technique applied to SeaWiFS and MODIS data, then distributions of inherent optical properties (IOPs) are obtained with a semi-analytical bio-optical model. Additionally, Chla is computed by two regional empirical algorithms associated with two classes of optical properties representative of open ocean waters and Adriatic coastal regions (Classes 1 and 2, respectively). The domain of applicability of each algorithm is dynamically determined on the basis of the LWN input spectrum by a novelty detection approach. The various satellite products are validated using a comprehensive bio-optical time series collected in the northern Adriatic. At the basin level, the frequency of occurrence of Classes 1 and 2 are 61% and 10%, respectively, with Class 2 waters particularly located in the northern part and characterized by higher levels of Chla and IOPs. The annual cycle of Chla over the 12-year period exhibits significant variations in amplitude and phase; moreover, the annual cycle shows a reduced amplitude during a period centered on 2004 for a time interval that varies with the region. In the northern Adriatic, the overall level of Chla appears lower between 2003 and 2008 compared to the beginning of the series.  相似文献   

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