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Estuary Water Suspended Matter Inherent Optical Property And Concentration Remote Sensing Inversion Model

Posted on:2009-05-02Degree:DoctorType:Dissertation
Country:ChinaCandidate:F WangFull Text:PDF
GTID:1118360242497539Subject:Use of agricultural resources
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Estuary is the key area connecting the exchange of materials and energy between continent and ocean.There is plenty of surface runoff to sea through estuary every year.The sediments,nutrients,and organic pollutants together with runoff have great impacts on the entironment of estuary.Due to the spatio-temporal variations of suspended sediments(SS)in waters of estuary,the traditional monitoring methods couldn't meet the management on spatial analysis and time frequency.With the development of remote sensing,remote sensing monitoring plays an important role in the study of water SS.The complex optical characteristics of SS result in their great spatial and temporal variations.Therefore,the optical characteristics and their correlations have to be investigated well when conducting SS remote sensing retrieval model.Meanwhile,the main impact factors in the ocean dynamical environment should be considered so that the high-precision inversion models combining the SS optical characteristics and water spectrum can be well applied.Affected by the turbid runoff with high sediment concentrations from the Yangtze River for long time,along with the function of suspended sediments induced by tide dynamics,the water SS concentrations in the Hangzhou Bay are pretty high and have complex spatio-temporal variations.The observation stations in this study were located in Zhapu of the North Hangzhou Bay and Cixi of the South Hangzhou Bay,and the database of time-series apparent optical characteristics parameters,inherent optical parameters,and the component concentrations of the water was obtained in the monitoring stations.Combined with the present bio-optical models,sensitive bands were selected based on the band configuration of common water color sensor.And the empirical model on suspended substance concentrations and semi-analysis model on inherent optical parameters were respectively developed to study the driving factors which affecting the short-term variations of surface water suspended substance concentrations and optical characteristics on the views of concentration and component,with the tide dynamics taken into account.This study is valuable on only on obtaining the inherent optical characteristics of suspended substances in the typical study area, but also on the knowledge of the scope and rules of their spatio-temporal variations so that we could analyze the driving factors from both microcosmic and macroscopical views.Moreover, this study could provide insight into developing the analysis models which are with higher precision and can be applied on secondary planet remote sensing.The major contents in this study and main results are the following:(1)In-situ spectrum measurement and laboratory absorption measurement.Above-water spectrum measurement method recommended by NASA ocean optical measurement criteria was employed to measure the in-situ Spectrum of surface water.The radiance of standard plate, water surface,and sky illuminance was measured,respectively,to calculate the remote sensing reflectance of the water surface.The results of spectrum measurements showed that the water reflectance spectrum in the study area had representative spectrum characteristics of the water with high sediment concentrations.The reflectance of water surface was pretty high and exhibited two reflectance peaks in the scope of visible light and near infrared spectrum, respectively.And the wavelength of the second reflectance peak present "red-shift" with the increasing of sediment concentrations.In-situ water samples were also collected and measured in laboratory to analyze their absorption spectrums,with quantitative filtration technology used for absorption spectrum measurements of suspended substances.The results of absorption measurements showed that the absorption values of the suspended substances in study area were high and the absorption spectrum in visible light scope was fitted with an negative exponential attenuation model.The time-series data obtained in Zhapu and Cixi illuminated that there existed obvious spatio-temporal variations for the suspended substance concentrations and their optical characteristics in the study area.(2)Remote sensing inversion model of water suspended substance concentrations.A database for analysis was developed based on in-situ spectrum measurements and the suspended substance concentrations data.The correlation relationships between suspended substance concentrations and corresponding bands reflectance were analyzed based on the traditional bands setting of MODIS and MERIS.The sensor bands with high correlation coefficients were selected as sensitive bands to develop statistical regression model.With suspended substance particle size as an impact factor of remote sensing reflectance,the fitting results of the regression model showed highest responsibility for the suspended substance concentrations in the bands of infrared and near infrared.For a single band,exponential regression and power function regression showed better fitting results compared to the simple linear regression model.Combined bands could not increase the fitting results and the fitting precision increased when the impact factor of particle size was added.Also,for the fitting precision,long wavelength bands were better than the short ones and dual bands better than single bands.Moreover,artificial neural network model got a satisfied prediction precision in the highly turbid ocean areas.With the bands of MODIS 250 m resolution as input and the suspended substance concentrations as output,the neural network model present higher prediction precision than statistical regression model.The neural network model using in-situ remote sensing reflectance to simulate the bands of MODIS and MERIS could also get a better prediction result.(3)Remote sensing inversion semi-analysis model of inherent optical characteristics of water suspended sediments.Database was developed using in-situ water components absorption data to analyze the correlationship between absorption coefficients of suspended substances and their concentrations in the water color bands of MODIS and MERIS reflectance,respectively.Based on the bio-optical theory models and the remote sensing retrieval semi-analysis algorithm of Carder-MODIS phytoplankton optical characteristics,the sensitive bands adapting to local water optical characteristics were selected to develop empirical models of inherent optical characteristics,apparent optical parameters and component concentrations.And the remote sensing retrieval of water inherent optical characteristics and concentrations in the Hangzhou Bay at the MODIS band was achieved by this model.The results showed that the good correlations between the absorption coefficients of water suspended substances and their concentrations,with the coefficients higher than 0.95. With MODIS band 1 as main sensitive band,empirical modes among inherent optical parameters,apparent optical parameters and suspended substance concentrations were simulated to obtain the remote sensing retrieval of suspended substance inherent optical parameters and their concentrations.(4)Spatio-temporal variations of water suspended substance optical characteristics. Spatial and temporal variations of water suspended substance particle absorption coefficients and backscattering coefficients were studied.And the spatio-temporal variation mechanisms were also studied from the two aspects of suspended substance concentrations and their components.The results showed that the inherent optical characteristics of the water suspended substance in the study area present high spatio-temporal variations.The inherent optical characteristics of suspended substances in Zhapu and Cixi exhibited short-term variations with the tide periods.Besides that suspended substance concentrations were the major driving factors affecting their inherent optical characteristics in the study area,particle size was also an important impact factor.However,the specific absorption coefficient didn't play an important role on it.
Keywords/Search Tags:Hangzhou Bay, Suspended sediments concentration, Inherent optical property, Spatio-temporal variation, Semi-analysis algorithm
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