Study On Remote Sensing Estimation Of Suspended Solids Concentration Of Inland Waters Based On GOCI Data

Suspended solids concentration is an important water quality parameter. It is also one of the most important index of water quality and water environment evaluation. Select Lake Taihu, Lake Chaohu, Lake Dianchi and Three Gorges Reservoir as our study areas. Classify water in study areas into three types according to reflecting spectrum of sampling points by the method of Two-Step Cluster, then analyze apparent optical properties (AOPs) and inherent optical properties(IOPs) of water in each type, based on which, build different models of suspended solids concentration retrieval for different water types. At last, apply different models to GOCI data, which will realize remote sensing retrieval of suspended solids concentration. At the meanwhile, the spatial distributive characteristics and developing trends of suspended solids concentration in Lake Taihu are analyzed, and several conclusions are drawn as follows:(1) Classification of water type in study areas and analysis of its optical propertiesClassify water in study areas into three types with the method of Two-Step Cluster based on BIC(Bayesian Information Criterions),BIC change, ratio of BIC change and ratio of distance measures. Then, analyze suspended solids concentration and chlorophyll a concentration of each water type and define different waters as:type one with optical characteristic dominated by suspended solids, water type two with optical characteristic dominated by suspended solids and chlorophyll a, and water type three which is dominated by chlorophyll a.Different water types have different optical characteristics. There are significant differences in spectral shape and numerical value of remote sensing reflectance and absorption coefficient of pigment particles in different water types, while absorption coefficient of non-pigment particles, absorption coefficient of CDOM (Colored Dissolved Organic Matter) and back-scattering coefficient are similar in spectral shape but different in numerical value.(2) Remote sensing retrieval model of suspended solids concentration for different water typesBuild different remote sensing retrieval models of suspended solids aim at different water types. It is concluded that the best model for water type one is a quadratic function which variable is the ratio of remote sensing reflectance in band7 and remote sensing reflectance in band4described as B7/B4, the best model for water type two is an exponential function which variable is B7/(B8+B4) and the best model for water type three is a power function which variable is B7/(B8+B4), while the best model for water not classified is a quadratic function which variable is B7/B4. Model error of three water types are lower than retrieval model of water not classified by1.11%、6.75%and4.20%, meanwhile, average relative error of verify data drop markedly. Compared to retrieval model of water not classified, average relative error of models for three water type are felled by19.37%、8.96%and3.18%.(3) Remote sensing retrieval of suspended solids concentration based on GOCI dataAtmosphere correction is carried out by FLAASH and6S. Based on results of two methods, it is concluded that reflectance corrected by6S is more similar to measured data in spectral shape and numerical value, which is more appropriate for atmospheric correction of GOCI data.Classify pixels of GOCI data into different classes, and choose corresponding models to retrieve suspended solids concentration in Lake Taihu. The result shows that, from the perspective of time, variation of suspended solids concentration in one day is larger than variation in several days. Suspended solids concentration vary from day to day, even in the same day, the concentration is not the same. At the view of spatial distributive characteristics, suspended solids concentration is low in the north and east of Lake Taihu. while regions with suspended solids concentration are concentrated in west and southwest of Lake Taihu, and suspended solids concentration in the middle of Lake Taihu is somewhere in the between. One explanation for the results could be related to rivers flow into or out of Lake Taihu, meanwhile, meteorological factors such as wind speed and wind direction and topographic factors such as geography and physiognomy also might affect spatial distributive characteristics and developing trends of suspended solids concentration to a certain degree.