| Water color remote sensing is an advanced technique to acquire the synoptic view of lake. It has big advantage in water quality monitoring, which is difficult to acquire by the traditional filed investigation for its hard accessibility. Water color parameters retrieved from remote sensing images can provide quantitative information about regional economic, social development and global change. It is significant to sustainably exploit lakes.As the largest freshwater lake lies in the middle reach of Yangtze River in China, Poyang Lake is a seasonal and throughput lake, which leads to its dramatic water area changes, complex water optical properties, and various bottom types. Therefore, it becomes a natural study area for the mechanism of radiative transfer process under water. Taking the most concerned water color parameter, suspended particulate matter concentration as an example, the dissertation discusses the seasonal and spatial variations of the optical properties in the Poyang Lake, and investigates the mechanism and method of quantitative retrieval of water color parameters based on radiative transfer theory.The main contributions are shown as follows:1. Measurement of aquatic optical properties and analysis of the applicability of different measurement methods in Poyang Lake.Four cruises of observation were performed in2005,2008,2009and2011, and the applicability of measurement methods for inherent and apparent optical properties were studied. Comparisons of methods of remote sensing reflectance measurements show that the above-water method was suitable for the shallow Poyang Lake. Due to the large number of small tiny mineral particles in Poyang Lake, the usage of current in-situ observation equipment was limited and in-situ particle scattering coefficients were only available for samples which the suspended sediment concentrations is less than75mg/L. For laboratory analysis the suspended particulate absorption, the transmission-reflection method was more efficient in the spectrum extracting in turbid waters than the transmission method, which is widely used in the laboratory determination of the absorption coefficient of suspended particulate matter in ocean and coastal waters.2. Inherent optical properties of suspended particulate matters and their optical contributions in Poyang Lake.Spectral features of Colored Dissolved Organic Matter (CDOM), non-algal particles and algae particles absorption properties were analyzed. Spatial and seasonal variations in absorption of each water components were also discussed. The study showed that non-algal particulate matter is the major contributor to the total absorption, and a good correlation relationship was existed between concentration of suspended particulate matters, total suspended particulate absorption coefficients and non-algal particulate absorption coefficients. Scattering properties of suspended particle were also investigated.A regional model was developed for partitioning total particulate scattering into the contributions of organic and inorganic particles. The results of scattering spectrum partition show that inorganic particles scattering plays a dominant role in Poyang Lake.3. Identification of optical shallow and deep waters by coupling the hydrodynamic simulation and remote sensing.Considering the seasonal variability of water depth and turbidity in Poyang Lake, advantage of hydrodynamic simulation and remote sensing technology was fully used to derive the real time water depth. Water clarity retrieval model was established based on the relationship between water clarity and remote sensing reflectance. Combining the retrieved water clarity and simulated water depth, the optical shallow water area, potential shallow water area, and optical deep water area can be identified. The distribution pattern for different water types in Poyang Lake indicated that the optical shallow water is mainly locates in the south Poyang Lake and the spatial distribution pattern of shallow water varies seasonally.4. Retrieval of suspended particulate matter concentration in optical shallow and deep water respectively, based on radiative transfer theory.According to water optical properties of Poyang Lake, the relationship between remote sensing reflectance and inherent optical properties was examined with in-situ data in the optical shallow and deep water areas. Based on radiative transfer theory, a semi-analysis model for inherent optical parameter retrieval was established in optical deep water area, while an iterative optimization model in the shallow water area. There is a significant correlation between inherent optical properties and suspended particulate matter concentration in different seasons and different regions, and retrieval model of suspended particulate matter concentration was constructed base on the relationships. The results indicated that the radiative transfer model performed well for the in-situ data, and it was more accurate and stable than the empirical model.5. Implementation of suspended particulate matter retrieval model on remote sensing images and error analysis.In the dissertation, method of neural network was used to remove the atmospheric affection on MODIS land reflectance images. Water type classification combined with hydrodynamic and remote-sensing was carried out on corrected images acquired on October20,2008and July20,2011. Considering the band setting of MODIS sensor, radiative transfer model of suspended particulate matter retrieval from MODIS image was established. Evaluation of radiative transfer model using in-situ simultaneous observation data showed that calculated concentration of suspended particulate matter in optical shallow and deep water separately can effectively improve the retrieval accuracy and make the results temporally stable. The model developed in this paper can approximately meet the needs of water quality monitoring. |
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