The Preliminary Study On Estimation Of MC-LR Based On Sentinel-2

Microcystin is a kind of algal toxins wihic has highest frequency,largest production and most serious toxicity.It is a kind of strong liver tumor promoters and is harmful to the heart,kidney,stomach and intestines.It can cause deaths of livestock and poultry,and seriously endanger human health.Therefore,the monitoring of cyanobacteria toxin is critical.First of all,this study analyze the microcystin produced by aeruginosa which cultivated in medium with other biological optical factors.Then,based on this,we analyze the microcystin which sampled in Taihu Lake with other biological optical factors and then model the microcystin using the factor which has strong correlation with the microcystin.Then,this study apply the model to Sentinel-2 image and analyze the distribution of microcystin in north Taihu Lake.Through the research,we get the following conclusions:(1)Relation of Microcystin under the condition of laboratory in different growth stages and other biological optical factorsThrough the correction of microcystin and Chlorophyll a(Chla),phycocyanin(PC),Algal density,Chla:PC we know that microcystin concentration has hightest correction with Chla concentration,and followed by the Algal density.Then,correction of microcystin is analyzed with remote sensing reflectance(Rrs),absorption coefficient(a),specific absorption coefficient(a*),scattering coefficient(bbp).For the Rrs,540 nm and 710 nm has positive correlation with microcystin,628 nm remote sensing reflectance show strong negative correlation.These bands can be provided to the research of taihu lake microcystin concentration.microcystin concentration and total suspended solids absorption(at)and pigment particles absorption(aph)the correlation analysis shows that before 710nm,microcystin concentration has high correlation with at and aph,and at 710nm it reachs the maximum.The correlation of microcystin concentration and a*is not high at all bands.(2)Estimating model of microcystinIn the indirect model study,the correlation of microcystin concentration and Chla concentration,PC concentration,algae biomass are negative,mainly because that Chla and PC exsists in cells of algae and algae biomass is associated with number of algae.Measurement of microcystin concentration is extracellular microcystin and only after the cell disruption microcystin release into the water.This makes the microcystin concentration and Chla concentration,PC concentration,algae biomass present negative correction.Concentrations of microcystin concentration and Chla concentration,PC concentration,algae biomass in power exponent form.Combination of Chla and PC for microcystin conform to multiplelinear regression equation.In the three kinds of microcystin indirect model,the Chla concentration has the highest precision.In the optical model study,after respectively analyzing the correlation of microcystin concentration and optical factors(Rrs,a,a*,bbp),we found that microcystin concentration and Rrs has larger correlation in 450-500 nm and 678 nm,then 628nm.At around 706nm,microcystin concentration and Rrs has minimun correlation,followed by around 550nm.In 350-370 nm,550 nm and 710 nm,it present better positive correction,in 680nm the correction reach the minimum.Microcystin concentration and aph show the tendency of rapid decline in 350-400nm and keep stable in 400-800nm.Microcystin concentration and bbp present positively correlation in all bands.From 680-800nm,the correlation rapidly increases from 0.18 to above 0.60,then remain stable.At around 780nm the correlation reaches maximum.In these three optical indicators,the Rrs(707)/Rrs(490)has the highest recision and minimum error for estimating microcystin concentration.(3)The distribution of microcystin concentration retrieved from Sentinel-2 in Taihu LakeWe use spectral response function of the Sentinel-2 to simulate the remote sensing reflectance and finally determine B5/B2 as inversion factor.Eventually apply the model established by B5/B2 to Sentinel-2 image in April 5,2016 and get the distribution of microcystin concentration in Taihu Lake.The concentrations of microcystin in northern gulf MeiLiang and bay mouth and the west lake ZhuShan is relatively high.