Inversion Of Water Depth And Bottom Reflectance By Remote Sensing Based On Radioactive Transfer Model

Water quality pollution is a serious problem,highly needed be solved,in China.Remote sensing monitoring of water-bottom,using the relationship between reflectance spectrum characteristics of water bodies and water bottom parameter,inverses water bottom parameter. There are three ways,which are customarily used to resolve the problem,including empirical,semi-empirical and mechanism modeling methods.At present,most researches are focused on the measurement of various water body spectrum characteristics,and regression analysis using remote sensing data and other methods to establish a visible light or the ratio of band parameters and the bottom of the empirical formula,in order to extract quantitative information of water bottom.The method can be carried out very easily,but it is depended upon the measured data of water surface and synchronous data of remote sensing. However,the accuracy of this method will be significantly influenced by the changing of the water sediment concentration.The principle of mechanism model,based on two relation ship: water component and amount of inherent optical,amount of inherent optical and apparent optical volume,simulates the distribution of light field in water and then inverse the bottom-water parameter.The theoretical basis of mechanism model is the principle of light transmission in water,therefore,mechanism model is an important method of remote sensing monitoring of water quality.The advantages of the mechanism model have a clear physical meaning,the bottom of the reliability of inversion parameters,and subjected to time and geographical constraints,applicability.Therefore,this study based on radioactive transfer model.According to the radiation from the water-leaving radiance,water depth and bottom reflectance modeling is to achieve the bottom reflectance effective way of quantitative remote sensing At depths greater(＞2m) under the assumption that,in the clear waters of the assumption that spectrum reflection occurs,the bottom reflectance is 1.According to the water depth and rate of water-leaving radiance to establish the relationship between the depth of the statistical model,the request will be incorporated into the water depth of reflection attenuation model,then inverse water bottom reflectance.To Shitoukoumen Reservoir as an example,inverse water bottom reflectance use of water attenuation model.Three dates of Landsat data are acquired for these models,that is,Landsat on 1993-09-07 and Landsat data on 2000-10-20 and 2001-09-21.Carries on the radiation to the ETM+/TM data to calibrate,DN(Digital Number) values the header files from the data obtained by are converted into dimensionless values of the radiance L(Radiance).Through the establishment of spatial distortion correction space and the corresponding relationship between the distortions of space will transform all the pixels to the calibration of space,using two sets of coordinates corresponding to the relationship between the remote sensing images of the geometric correction.Remote sensing image geometric correction is conducted with ground control points(GCP),eight points and features obvious points to control error in 0.5 pixels.Through the establishment the relationship of spatial distortion correction and the distortion of space,all the pixels transforms to the calibration of space,using the relationship of two sets of coordinates corresponding to geometric correction for remote sensing images.The purpose of atmospheric correction is to eliminate factors such as air and light reflection on the ground, gain ground reflectance and radiation ratio,temperature and real physical surface model parameters used to eliminate the atmosphere,water,oxygen and carbon dioxide and methane and reflection on the ground of ozone,eliminate air molecules and aerosol scattering effects. In remote sensing image processing,often requires the removal of atmospheric scattering effects of the image brightness,that is,the need for atmospheric correction.Using the atmospheric correction module FLAASH ENVI of ETM+/TM data,eliminates the atmosphere correction of remote sensing image by air,so as to obtain the true features of the radiation information.Corrected through a 1,2,3-band calculated from the water-leaving radiance.Assumptions in the clear waters of the spectrum reflection occurred underwater; input the inversed depth to water reflectance attenuation equation.The request will be incorporated into the water depth of reflectivity attenuation model,in order to inverse the underwater anti-reflectivity.By the relationship of water depth and the water-leaving radiance establish a statistical model so as to come up the depth of the reservoir in other areas.The depth of Shitoukoumen reservoir from the reservoir edge to middle deepens gradually deepened,which conforms to the reservoir actual water depth distributed condition. The average depth is 9.63014m,which is consistent with the calculated value.The water bottom reflectance of Shitoukoumen reservoir high area concentrates in north and south some areas but the reservoir's center of the lake area under water index of reflection is low.There is a low reflection strip obvious from Shitoukoumen reservoir west to middle,which is Shitoukoumen reservoir major activity regions.The artificial active influence causes the index of reflection to be lower than other areas obviously.But Shitoukoumen reservoir's actual situation is:the southern part of the reservoir sediment concentration was significantly higher than other region,which distribution is similar to the underwater terrain.And the waters near central reservoir suspended sediment concentration are high,north to gradually decrease.High in the southern area most distribution,which is mainly due to the shallows in natural conditions,the water in the sediment concentration distribution and underwater topography there exists the relationship of dynamic contact.The average water depth of 1993-09-07 remote sensing image of the error is 14.99%. The average water depth of 2000-10-20 remote sensing image of the error is 17.44%.The average water depth of 2001-09-21 remote sensing image of the error is 3.53%.Results show that water reflectivity attenuation model is accurate in inversion underwater parameter precision.From the table,Shitoukoumen reservoir bottom reflectivity in 2001 obviously lower than 2000 underwater reflectivity,and reservoir bottom reflectivity in 2000 obviously lower than 1993 underwater reflectivity.Shitoukoumen reservoir pollution becomes more and more serious.In order to verify the sensitivity of radioactive transfer model,the solar azimuth angle and the depth are evaluated for the inverse.The Vertex Angle with the depth of the value trend is same,increased significantly,and the trend is clear,viewing Angle from 30°to 90°,the depth increase about 2.7(m) in the other conditions remain unchanged.With the water bottom reflectance increasing,the zenith angle reduces,but the scope of minor changes in the 0.01 range.With the increase in water depth,bottom reflectance gradually becomes smaller.