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1.
An algorithm is presented to retrieve the concentrations of chlorophyll a, suspended pariclulate matter and yellow substance from normalized water-leaving radiances of the Ocean Color and Temperature Sensor (OCTS) of the Advanced Earth Observing Satellite (ADEOS). It is based on a neural network (NN) algorithm, which is used for the rapid inversion of a radiative transfer procedure with the goal of retrieving not only the concentrations of chlorophyll a but also the two other components that determine the water-leaving radiance spectrum. The NN algorithm was tested using the NASA's SeaBAM (SeaWiFS Bio-Optical Mini-Workshop) test data set and applied to ADEOS/OCTS data of the Northwest Pacific in the region off Sanriku, Japan. The root-mean-square error between chlorophyll a concentrations derived from the SeaBAM reflectance data and the chlorophyll a measurements is 0.62. The retrieved chlorophyll a concentrations of the OCTS data were compared with the corresponding distribution obtained by the standard OCTS algorithm. The concentrations and distribution patterns from both algorithms match for open ocean areas. Since there are no standard OCTS products available for yellow substance and suspended matter and no in situ measurements available for validation, the result of the retrieval by the NN for these two variables could only be assessed by a general knowledge of their concentrations and distribution patterns. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

2.
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   

3.
Quantitative algorithms for the remote sensing of suspended sediments in shelf seas and estuaries have traditionally sought to relate the signal sensed by the satellite radiometer to the mass of particles in suspension. In situ measurements presented in this paper, however, show that the irradiance reflection coefficient at the sea surface is more closely related to the cross-sectional area of particles in suspension than to their mass. Other optical properties (which in turbid water depend on particle area) can therefore be related directly to the reflection coefficient. To interpret satellite data in terms of mass concentration (for testing numerical models of suspended sediment transport, for example), it is necessary to know the relationship between the area and mass of the particles. For the 2008–2009 dataset presented here for western UK coastal waters, the particle cross-sectional area varies by a factor of 5 for particles of a given size and mass. The causes of this variation are currently poorly understood.  相似文献   

4.
By using the two-flow optical model, the variation in the irradiance reflectance of the ocean just below the surface has been calculated for varying water optical properties, for the interpretation of remotely-sensed ocean color data. The input variables used in our model are the concentration of phytoplankton (chlorophyll-a), the absorption coeffiicient of yellow substance, the particle scattering coefficient, the ratio of the back-scattering coefficient to the total scattering coefficient of particles, and the ratio of the absorption to scattering coefficients for particles.The irradiance reflectance increases monotonically with the ratio of the back-scattering coefficient to the total scattering coefficient. Spectral changes occur in the irradiance reflectance for increases in chlorophyll-a concentration and yellow substance as well as the ratio of the absorption to scattering coefficients.Because slightly different mathematical expressions have been derived by other investigators using the two-flow model, an evaluation of the resulting calculation differences is presented and discussed.  相似文献   

5.
This paper reports the initial steps in the degradation of chlorophyll-a in a temperate, sandy intertidal sediment from a low-energy coastline at Corner Inlet, SE. Victoria. The chlorophyll-a is shown to be derived primarily from diatom input into the surface layers and it is possible to show that in this environment, relative stabilities are: chlorophyll-a > chlorophyllide-C2 > chlorophyllide-C1. Traces only of chlorophyll-b are present, and little or no degradation of this pigment with depth was observed. Bacteriochlorophyll-a, bacteriopheophytin-a concentrations are inversely proportional to one another in the upper sedimentary layers and the depth profile suggests a stabilised environment. A depth profile of a range of chlorophyll-a derivatives, including pheophytin-a, provides no basis for accepting that they are intermediates on the direct degradative pathway of chlorophyll-a in this environment. Rather, the evidence favours the view that chlorophyll-a degrades primarily to colourless compounds.  相似文献   

6.
The solar light field within the ocean from the sea surface to the bottom of the mesopelagic zone was simulated with a radiative transfer model that accounts for the presence of inelastic radiative processes associated with Raman scattering by water molecules, fluorescence of colored dissolved organic matter (CDOM), and fluorescence of chlorophyll-a contained in phytoplankton. The simulation results provide a comprehensive characterization of the ambient light field and apparent optical properties (AOPs) across the entire visible spectral range within the depth range 200–1000 m of the entire mesopelagic zone for varying chlorophyll-a concentration and seawater optical properties in the mixed surface layer of the ocean. With increasing depth in the mesopelagic zone, the solar irradiance is reduced by ~9–10 orders of magnitude and exhibits a major spectral maximum in the blue, typically centered around a light wavelength of 475 nm. In the green and red spectral regions, the light levels are significantly lower but still important owing to local generation of photons via inelastic processes, mostly Raman scattering and to a lesser extent CDOM fluorescence. The Raman scattering produces a distinct secondary maximum in irradiance spectra centered around 565 nm. Comparisons of our results with light produced by the radioactive decay of the unstable potassium isotope contained in sea salt (40K) indicates that the solar irradiance dominates over the 40K-produced irradiance within the majority of the mesopelagic zone for most scenarios considered in our simulations. The angular distribution of radiance indicates the dominance of downward propagation of light in the blue and approach to uniform distribution in the red throughout the mesopelagic zone. Below the approximate depth range 400–500 m, the shape of the angular distribution is nearly invariant with increasing depth in the green and red and varies weakly in the blue. The AOPs at any light wavelength also assume nearly constant values within the deeper portion of the mesopelagic zone. These results indicate that the mesopelagic light field reaches a nearly-asymptotic regime at depths exceeding ~400–500 m.  相似文献   

7.
Satellite image studies and recent in situ sampling have identified conspicuous phytoplankton blooms during spring and summer along the Patagonia shelf-break front. The magnitudes and spectral characteristics of light absorption by total particulate matter (phytoplankton and detritus) and colored dissolved organic matter (CDOM) have been determined by spectrophotometry in that region for spring 2006 and late summer 2007 seasons. In spring, phytoplankton absorption was the dominant optical component of light absorption (60–85%), and CDOM showed variable and important contributions in summer (10–90%). However, there was a lack of correlation between phytoplankton biomass (chlorophyll-a concentration or [chl a]) and the non-algal compartment in both periods. A statistically significant difference was found between the two periods with respect to the CDOM spectral shape parameter (Scdom), with means of 0.015 (spring) and 0.012 nm?1 (summer). Nonetheless, the mean Scdm values, which describe the slope of detritus plus CDOM spectra, did not differ between the periods (average of 0.013 nm?1). Phytoplankton absorption values in this work showed deviations from mean parameterizations in previous studies, with respect to [chl a], as well as between the two study periods. In spring, despite the microplankton dominance, high specific absorption values and large dispersion were found (a*ph(440)=0.04±0.03 m2 mg [chl a]?1), which could be attributed to an important influence of photo-protector accessory pigments. In summer, deviations from general trends, with values of a*ph(440) even higher (0.09±0.02 m2 mg [chl a]?1), were due to the dominance of small cell sizes and also to accessory pigments. These results highlight the difficulty in deriving robust relationships between chlorophyll concentration and phytoplankton absorption coefficients regardless of the season period. The validity of a size parameter (Sf) derived from the absorption spectra has been demonstrated and was shown to describe the size structure of phytoplankton populations, independently of pigment concentration, with mean values of 0.41 in spring and 0.72 in summer. Our results emphasize the need for specific parameterization for the study region and seasonal sampling approach in order to model the inherent optical properties from water reflectance signatures.  相似文献   

8.
大鹏湾赤潮多发区的叶绿素a分布与环境关系初探   总被引：19，自引：2，他引：19  
根据１９９０－１９９１年大鹏湾盐海田域４个测站的观测资料分析结果表明，大鹏湾赤潮我发区海水中叶绿素α含量的测值范围为０．０６－８．２８ｍｇ／ｍ＾３，平均为１．３３ｍｇ／ｍ＾３。季切平均值以春，秋季较高，夏，冬季较低；表层的叶绿素α含量稍高于底层。采用多元逐步回归分析得知，影响叶绿素α含量变化的主要因子是Ｆｅ，ＣＯＤ，ｓ，其次是ＤＯ，ｔ，Ｔｂ；此，Ｍｎ，Ｓｉ（ＯＨ）４，ＰＯ４，ＮＯ２与叶绿素α的分布  相似文献   

9.
Chlorophyll-a (chl-a) concentration has an important economic effect in coastal and marine environments on fisheries resources and marine aquaculture development. Monthly climatologies the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) derived chl-a from February 1998 to August 2004 around Funka Bay were used to investigate the spatial and temporal variability of chl-a concentrations. SeaWiFS-derived suspended sediment, MODIS derived sea surface temperature (SST), solar radiation and wind data were also analyzed. Results showed two distinct chlorophyll blooms in spring and autumn. Chl-a concentrations were relatively low (<0.3 mg m−3) in the bay during summer, with high concentrations occurring along the coast, particularly near Yakumo and Shiraoi. In spring, chl-a concentrations increased, and a large (>2 mg m−3) phytoplankton bloom occurred. The spatial and temporal patterns were further confirmed by empirical orthogonal function (EOF) analysis. About 83.94% of the variability could be explained by the first three modes. The first chl-a mode (77.93% of the total variance) explained the general seasonal cycle and quantified interannual variability in the bay. The spring condition was explained by the second mode (3.89% of the total variance), while the third mode (2.12% of the total variance) was associated with autumn condition. Local forcing such as the timing of intrusion of Oyashio water, wind condition and surface heating are the mechanisms that controlled the spatial and temporal variations of chlorophyll concentrations. Moreover, the variation of chlorophyll concentration along the coast seemed to be influenced by suspended sediment caused by resuspension or river discharge.  相似文献   

10.
This paper focuses on the use of imaging spectroscopy for the mapping of sediment characteristics on a tidal sandbank in the Westerschelde, called the Molenplaat. On June 8, 2004, during low tide, a HyMap™ scanner recorded the Molenplaat at 4 m pixel resolution. The hyperspectral data were radiometrically calibrated, geometrically corrected, and atmospherically corrected to give apparent surface reflectance data. On the calibrated and corrected dataset a supervised binary classification was performed, based on linear discriminant analysis. Simultaneous to the flight, 25 sediment samples were collected in the field and analysed in the lab to define the median grain size, the water content, the total organic matter content and the chlorophyll-a concentration. These four parameters play a crucial role in sediment stability and macrofaunal habitat definition. Prior to the classification, a feature selection, based on sequential floating forward search (SFFS), was performed. For each of the four parameters two to three bands were retained for the classification. These bands were most frequently selected in the visible and near infrared parts of the spectrum, except for the organic matter content where also SWIR bands were used. The overall classification accuracy was highest for the water content (88%), the median grain size (88%) and the chlorophyll-a concentration (84%). The organic matter content, for which three instead of two classes were distinguished, scored somewhat lower but still reached 80%. The classifications were limited to a small number of classes in order to obtain reliable statistics with a small number of training samples. The spatial patterns in the classified images indicated that the four parameters under study are highly correlated. In most cases coarse sediment coincided with dry conditions, low organic matter and low concentrations of chlorophyll-a. The wet and muddy parts of the Molenplaat were in general characterised by a notably higher amount of organic matter and chlorophyll-a. The individual classification results for the median grain size, the water content and the chlorophyll-a concentration were combined to generate a sediment ecotope map. The presented study illustrates how airborne hyperspectral data can be used to achieve accurate classified maps of intertidal sediment ecotope types, applying feature selection and a binary classification approach.  相似文献   

11.
The often-rapid deposition of phytoplankton to sediments at the end of the spring phytoplankton bloom is an important component of benthic–pelagic coupling in temperate and high latitude estuaries and other aquatic systems. However, quantifying the flux is difficult, particularly in spatially heterogeneous environments. Surficial sediment chlorophyll-a, which can be measured quickly at many locations, has been used effectively by previous studies as an indicator of phytoplankton deposition to estuarine sediments. In this study, surficial sediment chlorophyll-a was quantified in late spring at 20–50 locations throughout Chesapeake Bay for 8 years (1993–2000). A model was developed to estimate chlorophyll-a deposition to sediments using these measurements, while accounting for chlorophyll-a degradation during the time between deposition and sampling. Carbon flux was derived from these estimates via C:chl-a = 75.Bay-wide, the accumulation of chlorophyll-a on sediments by late spring averaged 171 mg m−2, from which the chlorophyll-a and carbon sinking fluxes, respectively, were estimated to be 353 mg m−2 and 26.5 gC m−2. These deposition estimates were ∼50% of estimates based on a sediment trap study in the mid-Bay. During 1993–2000, the highest average chlorophyll-a flux was in the mid-Bay (248 mg m−2), while the lowest was in the lower Bay (191 mg m−2). Winter–spring average river flow was positively correlated with phytoplankton biomass in the lower Bay water column, while phytoplankton biomass in that same region of the Bay was correlated with increased chlorophyll-a deposition to sediments. Responses in other regions of the Bay were less clear and suggested that the concept that nutrient enrichment in high flow years leads to greater phytoplankton deposition to sediments may be an oversimplification. A comparison of the carbon flux associated with the deposition of the spring bloom with annual benthic carbon budgets indicated that the spring bloom did not contribute a disproportionately large fraction of annual carbon inputs to Chesapeake Bay sediments. Regional patterns in chlorophyll-a deposition did not correspond with the strong regional patterns that have been found for plankton net community metabolism during spring.  相似文献   

12.
Light attenuation (Kd) of photosynthetically active radiation (PAR) by chromophoric dissolved organic matter (CDOM), total suspended solids (TSS) and chlorophyll a (Chl a) were measured at nine stations along an estuarine gradient in the Swan River, Western Australia, over 15 months. There were strong spatial gradients associated with the marine-freshwater transition along the 32 km of estuary sampled, as well as seasonal gradients mainly associated with rainfall, 80% of which occurs between May and September. CDOM absorbances at 440 nm reached a maximum of 10.9 m−1 with the freshwater inflow but concentrations of suspended matter remained low throughout the sampling period (1.0–21.0 mg l−1) under the diurnal tides of the estuary. CDOM was the dominant constituent of Kd and a stepwise multiple regression showed that 66% (p < 0.0001) of the variation in Kd can be explained by CDOM and an additional 8% (p < 0.0001) by TSS. As a consequence of this result, analysis into the influence of river discharge rates on CDOM absorbance levels was examined for 2002 using data collected during this study, and for 2000 and 2001 using historical dissolved organic carbon (DOC) and river discharge data. The outcome of this analysis infers that greater river discharge rates result in increased CDOM absorbances in the Swan River estuary.  相似文献   

13.
The spectral measurements of the attenuation coefficient of sea water and the absorption coefficient of suspended particles and of yellow substance were made with a spectrophotometer for the sea waters sampled in Tokyo Bay. These parameters can be used to compute the expected spectral irradiance reflectance. Some relationships between the optical properties of sea water and the concentration of dissolved organic carbon, the dry weight of suspended matter and chlorophyll-a concentration are presented. On the basis of these results, the possibility of modelling the relationship between optical and material properties is discussed.  相似文献   

14.
Satellite-derived ocean color data of Coastal Zone Color Scanner (CZCS) on board the Nimbus-7 and Ocean Color and Temperature Scanner (OCTS) on board the Advanced Earth Observing Satellite (ADEOS) are jointly used with historical in situ data to examine seasonal and spatial distributions of chlorophyll a (Chl-a) and suspended particulate matter (SPM) concentrations in the East China Sea. Ocean color imagery showed that Chl-a concentrations on the continental shelf were higher than those of the Kuroshio area throughout the year. Satellite-derived Chl-a concentrations are generally in good accordance with historical in situ values during spring through autumn (although no shipboard in situ measurement was conducted at nearshore areas). In contrast, ocean color imagery in winter indicated high Chl-a concentrations (4–10 mg m–3) on the continental shelf where bottom depth was less than 50 m when surface water was turbid (2–72 g m–3 of SPM at surface), while historical in situ values were usually less than 1 mg m–3. This suggests that resuspended bottom sediment due to wind-driven mixing and winter cooling is responsible for the noticeable overestimation of satellite-derived Chl-a concentrations. The algorithm for ocean color needs to be improved urgently for turbid water.  相似文献   

15.
In this study, the CDOM absorption coefficient at 350 nm [aCDOM(350)] and CDOM excitation emission matrix (EEM) fluorescence were used to estimate annual fluxes of dissolved organic carbon (DOC) from the Cape Fear River to Long Bay in the South Atlantic Bight. Water samples were collected during a 3.5 year period, from October 2001 through March 2005, in the vicinity of the Cape Fear River (CFR) outlet and adjacent Onslow Bay (OB). Parallel factor analysis (PARAFAC) of CDOM EEM spectra identified six components: three terrestrial humic-like, one marine humic-like and two protein-like. Empirical relationships were derived from the PARAFAC model between DOC concentration and aCDOM(350), total fluorescence intensity and the intensities of respective EEM components. DOC concentration and CDOM optical parameters were very well correlated and R2 values ranged from 0.77 to 0.90. Regression analyses revealed that the non-absorbing DOC fraction, in DOC concentration estimated from CDOM optical parameters, varied with the qualitative composition of the CDOM. DOC concentration and intensity of the humic-like CDOM components characterized by excitation maxima at longer wavelengths have significantly higher estimated non-absorbing DOC compared to the analogous relationships between DOC and intensity of the humic-like CDOM components characterized by excitation maxima at shorter wavelengths. The relationships between DOC concentration and intensity of one of the protein-like components resulted in significantly reduced non-absorbing DOC fraction in DOC concentration estimation. Results of regression analyses between fluorescence intensities of specific EEM components and CDOM-specific absorption coefficients suggest that the relative proportion of humic-like CDOM components (characterized by excitation maximum at longer wavelengths) and the main protein-like component have the most impact on the values of a?CDOM(350). Based on the relationships between aCDOM(350), Cape Fear River flow, and DOC concentrations, DOC fluxes were estimated for 2002, 2003 and 2004. DOC fluxes varied from 1.5 to 6.2 × 1010 g C yr? 1, depending on river flow.  相似文献   

16.
The optical properties of coloured dissolved organic matter (CDOM) can be used, in some environments, to trace water masses and provide information about the dynamics of the dissolved organic fraction in natural waters. This work presents the results from a modelling exercise, laboratory experiment and field data, which describe the variations in the optical properties of CDOM during mixing. The exponential slope coefficient (S) is frequently used to characterise different CDOM pools; however, its behaviour during conservative mixing of two different CDOM types is often misunderstood. Identification of a theoretical conservative mixing line allows the rapid identification of non-conservative processes (e.g. in situ production, flocculation and degradation) acting on the pool during mixing. The results suggest that some of the patterns reported in the literature could purely be a result of conservative mixing rather than a product of non-conservative processes.  相似文献   

17.
用于海洋-大气辐射传递计算的光学参数数据库   总被引：1，自引：1，他引：1  
开发和建立了用于海洋-大气辐射传递计算的光学参数数据库.它包括海中主要成分(纯海水、浮游植物、悬移质、可溶有机物)的固有光学参数(光谱吸收系数、光谱散射系数等)及大气中主要气溶胶的有关光学参数.在这些光学参数中,大多数是来自现场的直接测量,一些是间接测量获取,还有一些是通过理论计算得到.  相似文献   

18.
叶绿素-α是湖泊浮游植物现存量的重要指标，其含量能反映水中浮游植物的丰度和变化规律。研究叶绿素含量的动态变化，可以有效防止、监控湖泊富营养化的发生。以太湖为研究对象，根据其营养水平进行分区，使得不同区域内叶绿素的浓度不同，而同一区域内浓度大体一致，然后利用地理信息系统技术对每个区域内未采样点的叶绿素浓度进行插值，取区域内所有栅格的平均值作为其最终浓度。应用时间序列分析方法对太湖1998-2004年每月的叶绿素含量进行动态模拟，建立各湖区的预测模型。结果表明，中营养区I符合MA（1）模型，轻富营养区Ⅱ和中富营养区Ⅲ符合AR（1）模型，富营养区Ⅳ符合MA（5）模型，重富营养区V符合AR（6）模型。由此预测出2005年各湖区总叶绿素的含量，经前10个月实测数据的验证说明，所建模型在一定程度上能反映太湖各区域叶绿素浓度的变化。  相似文献   

19.
An optical model is developed for the remote sensing of coloured dissolved organic matter (CDOM) in a wide range of waters within coastal and open ocean environments. The absorption of CDOM (denoted as ag) is generally considered as an exponential form model, which has two important parameters – the slope S and absorption of CDOM at a reference wavelength ag(λ0). The empirical relationships for deriving these two parameters are established using in-situ bio-optical datasets. These relationships use the spectral remote sensing reflectance (Rrs) ratio at two wavelengths Rrs(670)/Rrs(490), which avoids the known atmospheric correction problems and is sensitive to CDOM absorption and chlorophyll in coastal/ocean waters. This ratio has tight relationships with ag(412) and ag(443) yielding correlation coefficients between 0.77 and 0.78. The new model, with the above parameterization applied to independent datasets (NOMAD SeaWiFS match-ups and Carder datasets), shows good retrievals of the ag(λ) with regression slopes close to unity, little bias and low mean relative and root mean square errors. These statistical estimates improve significantly over other inversion models (e.g., Linear Matrix-LM and Garver-Siegel-Maritorena-GSM semi-analytical models) when applied to the same datasets. These results demonstrate a good performance of the proposed model in both coastal and open ocean waters, which has the potential to improve our knowledge of the biogeochemical cycles and processes in these domains.  相似文献   

20.
HY-1 CCD宽波段水色要素反演算法   总被引：7，自引：4，他引：3  
利用2003年春季黄海、东海区现场实测数据,建立了HY1卫星4波段CCD成像仪水色要素反演算法.由于HY1CCD的宽波段特性阻碍了黄色物质的反演,因此反演的水色要素仅包括水体表层的总悬浮物、悬浮泥沙(SS)以及叶绿素a的浓度.现场遥感反射率光谱由ASD地物波谱仪测量,对于叶绿素a的浓度利用现场萃取荧光法测量,总悬浮物、悬浮泥沙由实验室滤膜称重法获得.反演算法的拟合相关系数均大于0.88,平均相对误差在40%以下.对反演算法进行了误差灵敏度分析,结果表明对于总悬浮物、悬浮泥沙和低浊度水体中的叶绿素a的浓度反演算法能够满足日常的业务运行要求,但是对于高浊度水体中叶绿素a的浓度反演算法对某个波段组合比较敏感,仍需要进一步探讨.  相似文献   

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