Research On Temporal And Spatial Differentiation Characteristics Of Offshore Phytoplankton Diagnostic Pigments From Remote Sensing Retrieval

Phytoplankton plays an essential role in global primary productivity,material cycle,and energy flow.Phytoplankton pigments are an essential component of phytoplankton.Phytoplankton pigment can better describe the changes in phytoplankton structure.Establishing a remote sensing model and monitoring pigment concentration has become a hot topic in Marine remote sensing research in recent years.This study has collected the measured data during seven cruise surveys in the Bohai Sea,Yellow Sea,and the East China Sea(2016 to 2018).The empirical models of 16 kinds of diagnostic pigment based on the combination form of R_rs and pigment covariation relationship were established.The semi-analytical models of 16 kinds of diagnostic pigments were established using the Gaussian Decomposition.The model was applied to the Sea Wi FS and MODIS satellite R_rs data(1998 to 2019)to obtain the diagnostic pigment concentration satellite products,and its spatiotemporal distribution characteristics were analyzed.Finally,the diagnostic pigment analysis(DPA)was used to fit the diagnostic pigment weight coefficient based on the measured pigment concentration data.Applied the satellite data of diagnostic pigment to obtain 6 kinds of phytoplankton functional type products,mainly including Diatoms,Dinoflagellates,Prymnesiophytes,Cryptoflagellates,Chlorophyta and Prochlorococcus,Cyanophyta and Prochlorococcus.The main conclusions are as follows:Firstly,based on the measured data,the empirical models based on the combination parameters of remote sensing reflectance bands and the covariant relationship of pigment,and the semi-analytical models based on the Gaussian decomposition parameters of phytoplankton absorption were established,respectively.At the same time,the phytoplankton size specific-absorption model is further used to invert the hyperspectral phytoplankton absorption coefficient,to realize the satellite application of the semi-analytical model.The inversion accuracy and application limitations of the three models were analyzed,and the semi-analytical model was finally selected for the follow-up study on the spatiotemporal differentiation characteristics of diagnostic pigment concentration.Secondly,through the analysis of the diagnostic pigment concentration satellite products in the study area,the spatial and temporal distribution trends of the 16 diagnostic pigment concentrations were similar,showing a decreasing trend from the nearshore to the offshore waters.The concentration of pigment in the Bohai Sea was high in winter and spring and low in summer.The peak concentration of pigment appeared in the coastal area from Jiangsu to Zhejiang-Fujian in summer.The concentration of pigment in the offshore deep-water area was relatively low and changed little with the seasonal concentration.The correlation between four Marine environmental factors and pigment concentration was analyzed.The diffuse attenuation coefficient(K_d(490))showed a strong positive correlation with each diagnostic pigment in most sea areas.SST and photosynthetically active radiation(PAR)were negatively correlated with the concentration of diagnostic pigment in the central Bohai Sea and the Yellow Sea region.In the Yangtze River estuary to the Zhejiang-Fujian coastal areas,the concentration of pigment was positively correlated with SST and PAR.Finally,by analyzing the satellite products of phytoplankton functional types,it can be seen that,Diatoms,Chlorophyta and Cyanophyta occupy a relatively high proportion,with Diatoms as the dominant species.Cyanophyta and Prymnesiophytes,Dinoflagellates,took a relatively low proportion.Cyanophyta is the dominant species in the continental shelf marginal sea region.The structure in the coastal area was relatively stable.The central area of the Yellow Sea and the East China Sea showed that the dominant Diatoms and Chlorophyta succeeded each other with the seasons.