Babushka A. The assessment of informativeness of airborne laser scanning for hydrographic tasks solving

The thesis discusses the theoretical foundations and applications of airborne laser scanning solutions for hydrographic tasks, in particular the modelling of hydrographic objects. The main factors which influence on the decrease of level of the returned laser signal are investigated and identified. Calculative study of the effect of the atmosphere on the signal loss is made. The aerosol attenuation for wavelengths 1064 and 1560 nm of laser scanners is determined. The analysis of process of reflection of laser beam from the water surface is implemented, the Fresnel reflection coefficients are calculated for the boundary "air-water" and their dependence on the incidence angle of the beam on the water surface is established. On the basis of the formula for calculating the level of recovered energy from the objects with diffuse reflection type it was proposed modified formula for the objects with a mirror reflection type. Using this formula there were calculated values of the returned optical energy from the water surface for determined values of atmospheric transmission coefficients and reflection coefficients of water surface. Considering obtained values of the returned energy there was calculated signal/noise ratio at the output of the receiver. Measurement accuracy of tilted distance depending on the signal/noise ratio was determined. It was found that for real conditions of survey the accuracy of determination of point coordinates may considerably differ from the accuracy declared by the producers. There is proposed and implemented method of optimization of input original DEM to correctly display it in the form of contour lines. The essence of the method is to create a regular grid with variable step depending on the complexity of surface. The resulting DEM is complement with structural lines of hydrographic objects.