Study On Vertical Variation Of Backscattering Coefficient Of Petroleum Water

The components of Class II water is complex.Under the influence of gravity and hydrodynamics,the vertical distribution of water component is non-uniform.As the pollution of petroleum in water,the oil particles diffuse vertically in water which cause the vertical non-uniformity of water components more complex.When the concentration of water component changes,the optical characteristics of water body,such as absorption and scattering spectral properties,will also change.Backscattering occurs under the effect of vertical non-uniform water components,which eventually bring about the water leaving radiation and carries the vertical structure information of water,which is received by remote sensing satellite sensors.The study of underwater optical field model is based on the water properties.If assuming vertical uniformity of water component structure is homogeneity,the accuracy of the model will be reduced to a certain extent,and the model can not be applied to offshore waters with obvious vertical heterogeneity of water body composition.Therefore,it is great significance to study the vertical variation of optical properties of petroleum water for the study of radiation transfer modes.In this study,the backscattering coefficient of petroleum water body is taken as the research object,and the vertical variation law of backscattering coefficient is discussed,three sites are selected along the research area-the coast of Dalian Port,and the following works has been done:(1)Describe the hydrological situation of water based on tidal forecast data and measured current data;(2)Described and analyzed the vertical distribution of suspended matter and petroleum concentration and their variation with time based on the measured data of them;(3)Describe and analyzed the horizontal distribution of suspended matter and petroleum concentration on the surface of water based on the OLI data of Landsat-8;(4)Establish a semi-empirical model for the vertical variation of backscattering coefficients based on the theory of vertical distribution of suspended load,the separation algorithm of backscattering coefficients and the empirical relationship between backscattering coefficient and suspended matter concentration and oil concentration;(5)Analyze the properties of backscattering coefficient changing with depth via the rate of backscattering coefficient vertical variation that calculated from the model;(6)Discuss the validity of the model by mean relative error and mean absolute error.The results show that:(1)At site A and site B,which are closest to the coast,the current is mainly along the coast,and the properties of the direction and value of the current are similar to half-diurnal tidal cycle,which indicates that the current in both places is affected by topography and tide.At site C,which is located on the east side of Sanshan Island channel,the current mainly point to the channel,but the direction and value of it may do not have the properties of half-diurnal tide cycle,which indicates that the current is mainly affected by topography;(2)The concentration of suspended matter increases with the increase of depth on the whole,while the concentration of petroleum decreases,which indicates that the suspended matter is tend to sink while the petroleum float.In addition,the concentration of suspended matter varies with tide but the rising and falling time lags behind it,while the concentration of petroleum changes rapidly under the fast speed current,but the concentration may increase or decrease;(3)The horizontal distribution of suspended matter and petroleum are similar,mainly concentrated in the area of coastal and behind the island relative the current,which indicates that environmental factors have similar effects on the horizontal distribution of both;(4)The relationship between backscattering coefficient and water depth is not a simple elementary function,but the sum of exponential and composite exponential;(5)In surface layer,the vertical variation rates of backscattering coefficients at sites A and B are similar,indicating that the trend of particle matter at two sites is similar.The rate at site C almost stable at a level slightly less than 0.0005 in the whole water body and smaller than those at the first two stations,indicating that the backscattering coefficient of C site changes uniformly on the whole;(6)The average relative errors of the three models at every site are 1.984,0.282 and 0.349,and the average absolute errors are 0.025,0.006 and 0.005,which shows that the model has different accuracy in different regions.The accuracy of site A with the shortest distance from coast is the lowest,followed by site B and site C.This model is great significance to the study of underwater optical field modes.