Distribution Of Suspended Matters In Poyang Lake And Its Influence On The Optical Properties Of Water Body

Inland lake water color remote sensing research usually assumes that water components vertically distribute uniformly.For Poyang Lake,sediment gets transported and resuspended which is caused by river sand,lake circulation and sand mining,and vertical distribution of suspended particulate matter varies.By studying the influence of vertical distribution of different types of suspended particles on the optical properties of water body,we could provide technical support for high-precision remote sensing inversion of water components.In this paper,Poyang Lake is used as the research area.By measuring the intrinsic optical characteristics and concentration of water components and water color elements and the remote sensing reflectance above the water surface,an inversion model is established to obtain total the concentration of suspended particulate matter(TSM),inorganic suspended particulate matter(ISM)and chlorophyll-a(Chla).The HydroLight water body radiation transmission model is used to analyze the influence of the vertical structure changes of ISM and Chla concentration on the remote sensing reflectance.The main conclusions are as follows:(1)Analysis of the Apparent optical characteristics and intrinsic optical characteristics of water body.The summer,winter and spring water body remote sensing reflectance spectral curves show "double peak" characteristics,with peaks at 585 nm and 810 nm.In summer,the range of remote sensing reflectance of water body is large,and the overall level of winter reflectance is high.The backscattering coefficient decreases with increasing wavelength.The backscattering coefficient of water particles in summer is significantly lower than that in winter and spring.The total absorption coefficient decrease with increasing wavelength,and the total absorption coefficient of summer and spring is spectral curve.A weak absorption peak appeared at 675 nm in summer and spring.(2)Establishment and inversion of TSM,ISM and Chla concentration based on intrinsic optical properties and analysis of the vertical distribution characteristics.The vertical distribution types of TSM in summer include linear,exponential and divergent types.The linear vertical distribution of TSM in winter is 45.45%,as the proportion of linear type is 30.00% in spring,the proportion of exponential type is 20%;the vertical variation of ISM in summer is mainly exponential,linear and divergent,and the vertical distribution of ISM in spring The highest proportion is 35%.The vertical distribution of Chla in three seasons is mainly exponential type,accounting for 75.00%,63.64% and 50.00% respectively.(3)Analysis of the influence of uniform distribution of ISM and Chla on remote sensing reflectance.When the ISM concentration is linearly distributed with depth,the remote sensing reflectance increases as the slope increases.The maximum reflectance at 475 nm increases from 0.57% to 5.09%.The higher the ISM concentration,the greater the remote sensing reflectance.For the 585 nm reflection peak,when the ISM concentration increased from 5mg/L to 65mg/L,the remote sensing reflectance increased from 0.014sr-1 to 0.079sr-1,an increase of nearly 4.6 times.When the ISM is vertically distributed,the characteristics of the remote sensing reflectance are closer to those with ISM linear distribution.When the concentration of Chla is distributed with depth exponentially,the sensitivity of remote sensing increases with the increase of curvature for the same Chla concentration.The higher the Chla concentration for the same curvature,the greater the remote sensing reflectance.When the concentration of chlorophyll a increased from 1 ?g/L to 11 ?g/L,the remote sensing reflectance at 585 nm increased by about 3.2 times.The main influence of Chla concentration change on remote sensing reflectance range is 500~700nm.As the concentration increases,the peak position gradually moves toward the long wave direction.(4)Analysis of the influence of non-uniform distribution of ISM and Chla on remote sensing reflectance.The remote sensing reflectance decreases as the concentration of Chla increases.When the ISM concentration is low,the concentration of Chla increases from 1?g/L to 11?g/L,the peak reflectance of 575 nm continues to decrease,and the range of 400~700nm is the main affected band.The effect of Chla on the remote sensing reflectance is weakened as the ISM concentration increases.When Chla is vertically distributed,the remote sensing reflectance becomes larger with the increase of the added ISM concentration,the “stagnation peak” effect is obvious,and the peak position has a long-wave direction.the trend of.Inorganic particulate matter is the main component of water that affects the reflectance of remote sensing.The greater the gap between the concentration of Chla and ISM,the more remote sensing reflectance tends to be dominated by ISM.