A methodology for determining land cover moisture content based on remote sensing data is offered in the thesis. The need to study land cover moisture content is increasing due to the global climatic change expressed mainly in the disruption of water and temperature regimes. In addition, land cover moisture content is an important parameter on the environmental safety and human life issues. An insufficient amount of land cover moisture content results in a disturbance of soil characteristics, intensifying their degradation processes, a long period of drought, loss of soil fertility and crop productivity.
When conducting monitoring work at a regional level, the use of large spatial coverage satellite images available to cover the whole territory of the state was suggested. Currently, such requirements are adhered to by the MODIS series satellites imagery, considered in the study. According to multispectral satellite imagery data, the use of various water indices is one of the most widespread methods of moisture level determination. Spectral channels of these indices are sensitive to moisture in the soil and vegetation cover.
To identify the most appropriate water index, five different water indices were analyzed. For regional level, NDII and RDI water indices were selected, as recorded by the MOD13C2 product data from the TERRA/MODIS satellite. The methodology for regional studies of determining land cover moisture content was based on the correlation of the remote sensing data with the climatic and physiographic regions.
The entire territory of Ukraine maps, reflecting the spatial distribution of the land cover moisture content, were calculated and compiled in accordance to water indices values. The physiographic regions shown on the maps represent the reference lines of typical natural and climatic conditions of Ukraine. According to the NDII and RDI water indices values distribution, significant lack of moisture in the steppe zone was observed during the selected years: 2007, 2015 and 2016. The forest-steppe zone was characterized by the low-moisture level. In 2007, the forest-steppe zone and the zone of deciduous forests acquired the signs of aridity, and the steppe zone become catastrophic drought, as such conditions could lead to desertification over the long run. If the trend towards the temperature increase and continuous decrease in precipitation be kept, the conditions of 2007 may become typical for Ukraine.
At the local level, the distribution of moisture is significantly influenced by the surface relief. The local landscape-forming elements of the territory are characterized by the micro-depression landforms, which determine the spatial variability of soil moisture and its transformation.
In the modern relief the micro-depression landforms accumulate small local catchment bases of erosion and places of increased moisture and soil mass transfer. This provokes transformation of soils’ composition, their swamping and changes in vegetation type in the central part of a micro-depression. According to the hydrogeological studies, micro-depressions represent the associated areas with the increased filtration and moisture migration (geodynamically active zones), which significantly complicates the land use conditions, causing the spatial variability of water regime in soils. Appearance of the micro-depressions on the land cover provokes great difficulties in agriculture.
Field observations, carried out within the Baryshiv landfill, held a valuable place in determining of the soil moisture at the local level. During April-July field observations period, the samples of the surface soil layer had been taken at the 10 cm depth. In laboratory conditions, soil moisture was determined by the thermostat-weight method that met the requirements of State Standards of Ukraine. While comparing the calculated water index NWI with actual soil moisture content, the linear regression equation was obtained.
The soil moisture content values obtained during the field observations are relevant to the values of water indices having been obtained on the basis of multispectral satellite imagery data calculations with correlation coefficient R2=0.82. Subsequently, the multivariate regression of the soil moisture content dependence on various meteorological and natural parameters was applied, which made it possible to establish the soil moisture content in the areas with similar meteorological and natural conditions, where the field observations were not performed.
Thus, the assessment of the land cover moisture content proposed in the thesis is of utmost importance while elaborating a national geoecological monitoring system. The devised method can be applied both as a component of geoecological monitoring, and be adapted for further research and solving various land use problems.
