Remote Sensing Parameters Inversion And Dynamic Changes Of Colored Dissolved Organic Matter(CDOM) In The Changjiang Estuary And Its Adjacent Coastal Waters

The distribution,migration,and transformation of Chromophoric Dissolved Organic Matter?CDOM?in the offshore waters of the estuary have important links with the biogeochemical cycle.The study of optical parameters in turbid water bodies is great significance for water quality environmental monitoring and satellite remote sensing inversion.This study is discusses and analyzes the optical parameters inversion methods at home and abroad.Based on the CDOM absorption coefficient?a_g?in the Changjiang estuarine and coastal waters,semi-analytical algorithm and empirical algorithm are established for the Changjiang estuarine and coastal waters and the CDOM distribution is motivated in the Changjiang estuarine and coastal waters.The main results are as follows:1.Established an a_g inversion algorithm for turbid water bodies in the Changjiang Estuary region.Using the hundreds of measured data collected during the nine voyages of the Changjiang estuary and its adjacent coastal waters from 2011 to 2015,semi-analytical and empirical algorithms were established.In the semi-analysis algorithm?Quasi-Analytical Algorithm,QAA?is verified and calibrated,and the relevant part of the QAA algorithm is re-modified using the QAA_CDOM.Based on the QAA and the QAA_CDOM,we developed a new version of algorithm,named QAA_cj,which is more suitable to the inversion of the total absorption coefficients?a?and a_g.In empirical algorithms,the empirical relationship between remote sensing reflectance(R_rs)and a_g is established.The root mean square error?RMSE?,mean absolute relative error?MARE?and relative deviation?bias?were calculated by comparing the inversion results of the model and the remote sensing image with the measured data.The results show that the model inversion accuracy is significantly improved.After verification of the dataset test,RMES,MARE,and bias are lower than 1.17 m^-1,0.52,and 0.66 m^-1,and a_g at 443 nm are lower than 0.11 m^-1,0.58,and 0.03 m^-1,respectively.These results indicate that the calibrated algorithm has a better applicability and prospect for the Changjiang estuary and its adjacent coastal waters.In the algorithm comparison,due to the error accumulation of the empirical formula in the semi-analysis algorithm,the inversion result of the empirical algorithm is still slightly better than the semi-analysis algorithm.2.Combining remote sensing image with dynamic model FVCOM,this research is analyze the causes of a_g in the Changjiang estuary and its adjacent coastal waters.Using the established empirical formula of a_g???for the Changjiang estuary and its adjacent coastal waters,we are inversion the temporal and spatial distribution of a_g???in the Changjiang estuary and its adjacent coastal waters.Combining the Finite Volume Community Ocean Model?FVCOM?simulates the distribution of water level,temperature,salinity and tidal currents,this research is to analyse the spatial and temporal distribution of a_g???in the Changjiang estuary and its adjacent coastal waters in 2013.The results show that:?1?the a_g?443?diurnal variation is mainly affected by the ebb and drop;?2?the a_g?443?monthly variation are mainly affected by the wind.In winter,under the influence of the northerly winds,the Changjiang diluted water flows out the Changjiang estuary to south,a_g?443?gradually decreased along the coast of Zhejiang.In summer,under the influence of the southeast wind,the Changjiang diluted water flows out the Changjiang estuary to northeast,a_g?443?extension the northeast gradually decrease.In this process,due to the influence of wind in the monthly variation of a_g?443?,some water masses are separated from the diluted water from the Changjiang estuary,and high-value areas of a_g?443?appeare in these areas;?3?seasonal variation showed that the a_g?443?distribution trend had significant consistency in the four seasons.The concentration of CDOM is higher in estuaries and high suspended sediment areas,but CDOM concentrations in summer and autumn are slightly higher than winter and spring.The application of the high temporal resolution of the Geostationary Ocean Color Imager?GOCI?to inversion of a_g???breaks through the limitations of on-site measurements.The combination of remote sensing and physical ocean model has achieved a certain dynamic state the a_g???distribution.This method provides strong technical support for the observation and analysis of the daily and seasonal changes in a_g???distribution and transport processes.The remote sensing inversion a_g???can be used as an indicator to trace the spatio-temporal distribution characteristics and changes of the large amount of Changjiang diluted water into the ocean,and help to understand the biogeochemical processes in the offshore estuary.Estimating CDOM concentrations in water using remote sensing not only provides indicators of water quality parameters,but can also be used to study biogeochemical processes in aquatic organisms.