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Automated eddy covariance data quality control for long-term measurements
Šigut, Ladislav ; Mauder, M. ; Sedlák, Pavel ; Pavelka, Marian ; Špunda, Vladimír
Estimation of matter and energy exchange using the eddy covariance method is often organized into regional or global networks. To achieve comparability among sites, it is important to standardize and specify the methodology used. Currently, quality control (QC) is one of the most time-demanding steps in data processing within the Czech Carbon Observation System. Although manual QC (MQC) enables consideration of more complex test applications, it is often difficult to document. The aim of this study was to establish an automated QC (AQC) scheme based on available literature and post-processing software and test its effectivity and reliability on sites comprising an agroecosystem and a mature European beech forest. AQC successfully flagged low-quality CO2 fluxes and provided estimates of net ecosystem productivity similar to estimates based on MQC. The tests’ efficiency was particularly high for the agroecosystem, where AQC removed 13% less data than did MQC. We conclude that the adopted AQC displays satisfactory performance, especially for sites with low canopy heights.
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Effects of vegetation season and needles’ position in spruce canopy on emissions of volatile organic compounds
Večeřová, Kristýna ; Holišová, Petra ; Pallozi, E. ; Guidolotti, G. ; Calfapietra, Carlo ; Urban, Otmar
The main objective of this study was to investigate seasonal changes and vertical distribution in emissions of biogenic volatile organic compounds (BVOCs) within a Norway spruce canopy profile. Emissions were measured on current-year needles from the upper and lower canopy in early July and late August. Our results show that total BVOC emissions under standardized conditions (light intensity 1,000 µmol m–2 s–1, temperature 30°C) are higher in July than they are in August. BVOC emissions from upper canopy needles were approximately 3 times higher than were those from lower canopy needles. This difference was observed in July but not in August. The monoterpenes α-pinene, camphene, and terpinolene showed the most significant differences between emissions from upper and lower canopy needles.
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Interactive effects of UV radiation and drought on the accumulation of flavonols in selected herbs and grass in a mountain grassland ecosystem
Veselá, Barbora ; Surá, Kateřina ; Rajsnerová, Petra ; Klem, Karel ; Holub, Petr ; Urban, Otmar
The main objective of this 4-year experiment conducted in a mountain grassland ecosystem was to investigate the interactive effects of ultraviolet (UV) treatment and drought on changes in accumulation of UV-screening compounds (flavonols) in selected herbs (Hypericum maculatum Crantz, Rumex obtusifolius L.) and grass (Agrostis tenuis Sibth.). Inasmuch as drought and UV radiation induce similar protective mechanisms, we tested the hypothesis that UV radiation and drought elicit synergistic effects on flavonol accumulation. The experimental plots were manipulated using rainout shelters enabling the exclusion and transmission of incident precipitation and UV radiation. Generally, UV and drought treatments had similar effects on flavonol accumulation. For R. obtusifolius, UV exclusion resulted in a substantial reduction of UV-screening compounds, particularly under ambient precipitation conditions, while for H. maculatum and A. tenuis UV exclusion caused only a slight reduction of flavonol content. Similarly, the drought treatment caused an increase in flavonol accumulation.
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Flux footprints in different ecosystems
Macálková, Lenka ; Havránková, Kateřina ; Pavelka, Marian
Flux footprint is an upwind area where the atmospheric flux measured by an instrument is generated. Footprint size depends on measurement height, surface roughness, and atmospheric thermal stability. Our study focused on the flux footprints of four CzechGlobe ecosystem stations in a wetlands area, an agroecosystem, and young and mature spruce forests. Our aims were to prove that the sites were suitable for eddy covariance measurement and compare flux footprints under various atmospheric thermal conditions: stable, neutral, and unstable. Two computational models were used: the Kormann–Meixner (2001) and Kljun (2004)models. The outputs were processed graphically in site maps.
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Mathematical methods of modelling the morphology of spruce trees
Janoutová, Růžena ; Novotný, Jan ; Pivovarník, Marek ; Zemek, František
Radiative transfer (RT) models are simulation tools which can be used to quantify relationships between vegetation canopy properties and observed remotely sensed data. Th is study aims at creating a spruce tree growth model as a key input for use in RT models. Th e spruce tree model is built on data obtained from terrestrial laser scanning of spruce trees. Each tree model is unique. Th is uniqueness is achieved by using L-systems which are able to simulate natural randomness while complying with the given tree parameters. L-systems are established on a theory of grammar that enables rewriting a string of symbols according to specifi ed rewriting rules. In practice, our tree models are generated in Blender visualization soft ware, implementing an algorithm written in Python. Th e algorithm generates the basic parameters of the whole tree and then creates the parameters of the spruce trunk and initial branches. Th e parameters are generated randomly within a range that is calculated from measured data. Th en each branch is grown on the basis of annual increments defi ned by fi eld measurements. Tree needles are distributed with respect to the age of individual branches; therefore, the needles have diff erent colours according to their age. Cones and faces are graphical representations of the spruce model. Branches are represented by cones and needles are represented by faces around the branches. Th e faces are transparent, thus simulating light transmittance in-between the needles. The whole model is highly computationally demanding, especially with respect to computer memory.
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Hyperspectral image segmentation for estimation of biomass at reclaimed heaps
Pikl, Miroslav ; Zemek, František
This paper presents the preliminary results from a study that aims at estimation of above ground biomass and soil carbon content at reclaimed mining heaps in the Sokolov region. Two image segmentation methods are presented. We applied maximal likelihood (ML) and neural network (NN) classifi ers on airborne hyperspectral data. Th e objective of this part of the study was to prepare a land cover classifi cation of the region. Th e main focus was paid to discrimination of six classes with prevailing forest species cover. Th e classifi cation accuracy of the training sites was 93.75 % for NN and 79.12 % for ML respectively. But ML outperformed NN in overall classifi cation accuracy with 61.54 % compared to 40.9 % of NN. Th e more accurate results of the ML classifi er are probably infl uenced by properties of the training samples. Th e larger size of the training samples derived for ML enabled better representation of class histograms. Th e lower overall NN accuracy could result from high spatial resolution of HS data.
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Effects of UV radiation and drouhgt on the accumulation of UV-screening compounds and photosynthetic parameters in selected herbs and grasses of the mountain grassland ecosystem
Klem, Karel ; Holub, Petr ; Urban, Otmar ; Rajsnerová, Petra ; Kubásek, Jiří
The main objective of the experiment conducted on a mountain grassland ecosystem was to investigate the interactive eff ects of UV treatment and drought on the changes in accumulation of UV-screening compounds and photosynthetic parameters in selected herb (Hypericum maculatum) and grass (Agrostis tenuis) species. Th e experimental plots were manipulated using roof constructions enabling exclusion or transmission of incident precipitation and UV radiation, respectively. Generally, UV and drought treatments had a similar eff ect on the accumulation of fl avonols. UV exclusion resulted in a slight reduction of UV-screening compounds, particularly under the conditions of ambient precipitation. Likewise, drought treatment caused an increase in the accumulation of fl avonols per area unit. Under UV exclusion, drought slightly reduced the light-saturated CO2 assimilation rate (Amax) in both the species studied. Th e presence of UV radiation, however, led to less of a diff erence in Amax between [wet] and [dry] treatments. In addition to the increased induction of fl avonols, UV radiation increased water use effi ciency and alleviated thus the negative impact of drought on photosynthesis.
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Spatial heterogeneity of soil CO2 efflux in four different ecosystems
Dařenová, Eva
Manual measurements of soil CO2 effl ux on a larger number of positions can give precise estimation of CO2 effl ux from the investigated area and together with temporal dynamics, observed in continuous measurements, can provide a good view on the ecosystem carbon balance. In this study we investigated the spatial heterogeneity of soil CO2 effl ux in four diff erent ecosystems (spruce forest, beech forest, wetland, grassland). Soil CO2 was measured on a net of 25–65 positions using a manual measurement system. We tried to fi nd responsible factors for the heterogeneity and to determine a measurement protocol for the most precise estimation of soil CO2 effl ux. Th e highest respiration activity was observed in the spruce forest, the lowest in the wetland ecosystem, where it was caused by a high water table. In the wetland ecosystem, there was the highest spatial heterogeneity of respiration activity, which reached almost 60 %. Th is high heterogeneity was caused by the gradient of the water table depth. Contrary to this, the lowest heterogeneity was found in the grassland where it was only about 15 %. In the spruce and beech forest the heterogeneity ranged between 35 and 45 %. As infl uencing factors we investigated e.g. soil moisture, tree distance and amount of the above ground biomass.
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Potentials of the hyperspectral remote sensing - Aisa Eagle system and future perspectives
Lukeš, Petr ; Hanuš, Jan ; Kaplan, Věroslav ; Zemek, František
Since 2004 the Global Change Research Centre (CVGZ) operates a hyperspectral airborne imaging system AISA Eagle. A basic introduction to hyperspectral remote sensing and its potential applications in science as well as for commercial and military uses are presented, followed by a description of the system together with an overview of the key data pre-processing steps. The application of a rapidly developing technology, hyperspectral remote sensing, is presented within the field of quantitative remote sensing of plant health status. Finally, the future development of hyperspectral remote sensing at the CVGZ is outlined.
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