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1

Zmiana fazy w falach elektromagnetycznych po przekroczeniu kąta Brewstera

Marcak H., Tomecka-Suchoń S.

Zeszyty Naukowe Instytutu Gospodarki Surowcami Mineralnymi i Energią PAN

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2016

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nr 93

35--48

PL

W pracach rolniczych istotne jest określenie rozkładu wilgotności w glebie. W artykule przedstawiono metodę badania tego rozkładu na podstawie analizy pomiarów georadarowych. Przedstawiono opis właściwości pola elektromagnetycznego na granicy dwóch obszarów o różnych właściwościach elektrycznych w zależności od wielkości kąta padania promienia radarowego. Okazuje się, że zachowanie pola elektromagnetycznego istotnie zależy od stosunku prędkości fali w warstwie nadległej i leżącej pod granicą odbijającą. W szczególności dla stosunku tych prędkości mniejszego od jedynki, to dla kąta zwanego kątem Brewstera zanika energia fali odbitej. W artykule zwrócono uwagę na istotną zależność wielkości współczynnika odbicia i zmiany fazy sygnałów elektromagnetycznych od tego, czy kąt padania przekroczył kat Brewstera i kąt graniczny. Po przekroczeniu kąta Brewstera następuje zmiana fazy w sygnale odbitym o 90 stopni. Znajomość kąta Brewstera pozwala wyznaczyć stosunek prędkości fali elektromagnetycznej po obydwu stronach granicy, na której nastąpiło odbicie. W praktyce badań georadarowych kąt Brewstera powstaje w sytuacji, kiedy warstwa nadległa jest bardziej nasycona wodą. Na przykładzie badań prowadzonych na polach uprawnych pokazano jak na podstawie zaproponowanego sposobu identyfikacji kąta Brewstera można określić zmiany właściwości elektrycznych na profilu pomiarowym. Zmiana fazy pola georadarowego może być wykorzystana do ciągłej kontroli wilgotności gruntu i optymalnego sposobu jego nawadniania.

EN

Information on moisture distribution in the soil is of great importance for agricultural projects. This article presents the GPR geophysical method for the study of water distribution in subsurface parts of rock formation. The analysis of the GPR measurements is used for a description of the electromagnetic field properties at the boundary of two areas of different electric properties, depending on the angle of incidence of radiation. It appears that the behavior of electromagnetic fields substantially depends on the ratio of the velocity waves in layers overlying and underlying the reflective border. In particular, for the ratio smaller than the ones disappears energy of the reflected wave. The article highlights the significant dependence of the reflectance and phase change of the electromagnetic signals on whether the angle of incidence exceeds the Brewster angle and the critical angle. Attention was focused on the Brewster angle and the critical angle for the size of the reflectance and phase change of the electromagnetic signals. In particular, after exceeding the Brewster angle a 90 degree change phase of the reflected signal occurs. Knowledge of this angle allows the ratio of GPR wave velocity in the neighboring soil regions to be determined. We demonstrate, on the example of tests carried out on cultivated areas, how the changes of dielectric properties on the investigated profile can be determined using the identification of the Brewster angle with the procedure proposed above. The phase change georadar field can be used for the continuous monitoring of soil moisture and its optimum method of irrigation.

2

Decomposition of Fine Woody Debris from Main Tree Species in Lowland Oak Forests

Ostrogović M. Z., Marjanović H., Balenović I., Sever K., Jazbec A.

Polish Journal of Ecology

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2015

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Vol. 63, nr 2

247--259

EN

Decomposition is an important carbon flux that must be accounted for in estimates of forest ecosystem carbon balance. Aim of this research is to provide estimate of fine woody debris decomposition rates for different tree species and sample sizes also taking into account the influence of specific microsite meteorological conditions on decomposition rates. In this paper we present results of the first two years of the experiment designed to last six years. Study was conducted in managed lowland oak forest in central Croatia. Decomposition rates (k) of fine woody debris (diameter 0.5–7 cm) for four species (Querus robur L., Carpinut betulus L., Alnus glutinosa Gaernt., Fraxinus angustifolia L.) in four size classes were estimated using litter bag method and mass loss equation of Olson (1963). Overall average k in our study was 0.182 ± 0.011 year-1. Results indicate that decomposition rate is affected by the size of the debris, with the smallest diameter branches (<1 cm) decomposing is significantly faster (k = 0.260 ± 0.018, P <0.05) than the larger one. Tree species from which debris had originated also affected decomposition, although to a lesser extent, with hornbeam samples having significantly (P <0.05) higher average decomposition rate (0.229 ± 0.028), compared to that of ash samples (0.141 ± 0.022). Proportion of variability in k explained by variables ‘species’ and ‘size class’ was assessed with general linear model (R2 = 0.644) also taking into account variables like soil temperature and soil water content. Sample size class explained 22.2%; species explained only 9.4%, while soil water content and temperature combined explained 32.8% of the variance of k. Rate constants obtained within this study might be useful in modelling ecosystem carbon balance for similar lowland forest ecosystems in Europe.

3

Altitudinal variability of the soil water content in natural and managed beech (Fagus sylvatica L.) forests

Pichler V., Durkovic J., Capuliak J., Pichlerova M.

Polish Journal of Ecology

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2009

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Vol. 57, nr 2

313-319

EN

European beech (Fagus sylvatica L.) ranks as one of the most adaptive species among European indigenous trees. Variable interactions between the trees and soil water depend on both phenotypic plasticity of the species and natural conditions. They are controlled through stomatal regulation and the ability of beech trees to accelerate quickly their growth if available resources increase. However, the effect of forest density at various altitudes on the soil water content in beech stands has been studied rather scarcely. Therefore, we monitored soil moisture by means of Time Domain Reflectometry in series of natural and managed stands located on sites representing the lower altitude (200-550 m a.s.l.), middle altitude (550-1050 m a.s.l.) and higher altitude (1050-1300 m a.s.l.) zones of the natural beech belt in the Western Carpathians, Slovakia. Forest stand density, expressed in terms of basal area, i.e. the sum of cross section areas of the tree stems at 1.30 m height, was unchanged in natural stands, but it was reduced by 60% in the shelterwood stands. In the clear-cuts, all trees were removed. Total soil water content (SWC) under forest stands was calculated in mm as the product of soil moisture and soil depth, the latter acquired by electrical resistivity tomography. SWC differences between natural and shelterwood stands of the lower altitude, middle altitude and higher altitude zones averaged 18 mm, 36 mm and -3 mm, respectively. According to the Friedman test on ranks, followed by post-hoc multiple comparison testing, the difference was only significant within the middle altitude zone. In it, soil water consumption by the natural stand was limited only by the hormonally controlled seasonal regulation. The comparatively low water loss in the shelterwood stand resulted from a small rainfall interception by forest canopy and a decreased soil water uptake due to reduced basal area, leaf area index and simple age-size forest structure. In the lower altitude zone, the precipitation deficit and limited extractability of soil water were responsible for the absence of larger SWC differences. As opposed to that, low potential evapotranspiration prevented any noticeable SWC differences within the higher altitude zone.