The paper presents a hybrid classification method based on the determination of the optimal number of classes according to uncontrolled classification followed by image processing techniques of controlled classification. A criterion for determining the optimal number of classes is proposed based on the definition of averaged values differences of average spectral brightness among the classes. Space images from satellites Ikonos (2002, 2007) and QuickBird (2010) were used to study different time cuttings in the forests of the Carpathian region. A significant amount of ground observation was held for getting test information. A Hybrid Classification Method is used for different time cuttings by QuickBird satellite images and implemented in a software environment of ERDAS Imagine. In order to obtain acreage of cuttings made for the period of 2002-2007 and 2007-2010, a comparative analysis of cuttings is introduced in these time intervals and their area is determined on the basis of the digital images of polygons in the ArcGIS software environment.
The paper analyses the causes of riverbed shifts of the rivers Dniester and Tisza of the Carpathian region. Among these reasons are mostly climate, physical and geographical, and anthropogenic factors, including frequent floods, weak rocks and soils, logging, and removal of gravel and sand materials out of the channels. The research considers the transition of the Dniester and Tisza rivers from mountaineous area into the lowland. The analysis of these shifts has been carried out on the 100 km long sections over a 100-year period. We used topographic maps and space images, as well as special geological and soil maps, as materials for this research. We have determined that the shifts of the Dniester and Tisza riverbeds can reach up to 500-1000 m in some sections. We also analyze the risks and dangers that follow such shifts.
In this paper calculation of some physical parameters of the receiver of laser scanning system is presented. Basic physical principles of laser scanning of water objects are considered. Ranging standard deviation for typical parameters of laser scanning system are calculated. Formula for calculation of reflected optical power for specular reflective objects is proposed.
Space information, or information obtained by means of space remote sensing, is widely and effectively used by many countries to solve a lot of scientific, technical and applied problems. Most manufacturers of space remote sensing systems declared the high resolution values of their systems. However, these values are computed theoretically, without considering the various factors affected them. To determine the real resolution of the system, we have considered mathematical modeling which describes the influence of different factors on the satellite images resolution. Some of these factors are: atmosphere turbulence, image shift, residual defocusing, and diffraction. One of the most important characteristic of the images resolution is the modulation transfer function (MTF) which allows the estimation of different factors affected on the image resolution. The modulation transfer function (MTF) is a fundamental tool for assessing the performance of imaging systems. Various authors [Zhang et al. 2012, Hwang et al. 2008, Ryan et al. 2003] investigate different MTF assessment methods of high resolution satellite images: a slant-edge method, a knife-edge method, a sine wave method and a grill pattern. We propose a generalized approach for MTF assessment based on theoretical assumptions which allows to determine the influence of different factors. A comparative analysis of the modulation transfer function(s) for different space imaging systems shows that the image resolution depends mainly on the atmosphere turbulence and size of a sensor element. Additionally, we established that atmospheric turbulence significantly reduces the transmitting possibility of images. The parameters which describe the influence of turbulence required additional studies. The main goal of our researches is to show that real spatial image(s) resolution is much "inferior" than the value provided by the manufacturers of space remote sensing systems.
In recent decades, in the Pre-Carpathian region of Ukraine during the summer period, floods and flood events became more frequent. They were accompanied by significant economic and environmental loss. Especially powerful were the floods of 2008 and 2020, but the floods in 2014 and 2016 also had destructive consequences. Therefore, the study of river channel processes, river stability and assessment of flooded land areas due to floods is an urgent problem. The aim of the study is to propose a methodology for hydrological modeling of sections of riverbeds with complex morphometric and hydrological characteristics. The construction of a digital elevation model (DEM) and the selection of the distance between the cross-sections, as well as the determination of the Manning coefficients, have the greatest impact on the accuracy of the modeling, so these factors should be given maximum weight when calibrating the model. The object of the study was the section of the Dniester River in Ukraine in the place of transition from the foothill part of the channel to the hilly–marshy part with complex meandering and significant shifts of the river. The methodology of hydrological modeling includes three principal components: construction of the DEM, determination of the type of underlying surface and determination of the level of water rise in the riverbed. The research was carried out on the basis of imaging from unmanned aerial vehicles (UAVs). In 2017, the imaging of a section of the Dniester riverbed was carried out in the summer during a period of significant vegetation growth, which affected the accuracy of determining the heights of the model points. According to the results of this imaging, the residual mean square (RMS) for determining the heights of the points exceeded the permissible value of the RMS (0.25–0.3 m) by two times. In 2021, imaging was performed in the autumn period when there was no leaf cover. The RMS of the DEM for 2021 imaging was 0.26 m. According to the results of the survey in 2017 and 2021, orthophotoplans were created, which were used to determine the planned displacements of the river bed and clarify the Manning coefficients, which characterize the roughness of the underlying surface. The value of the water level rise was obtained on the basis of the graph on the date of the maximum rise of the water level on 24 June 2020 according to the hydrometeorological station located near the selected area. The result of the research is hydrological modeling using the HEC-RAS module for a site with complex hydrological and morphometric characteristics on the date of the maximum water rise. It was established that in order to achieve the required accuracy of the DEM, imaging should be carried out in the leafless period of the year, since the accuracy of constructing the DEM decreases by half during the growing season. On the basis of the obtained orthophoto plans, a methodology for determining refined Manning coefficients was developed, which allows taking into account changes in the underlying surface of the channel area. The area of the flooded area was calculated based on the level of water rise during the 2020 flood.
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