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  • 1
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    European Geosciences Union
    In:  EPIC3Earth System Dynamics, European Geosciences Union, 4(2), pp. 187-198, ISSN: 2190-4987
    Publication Date: 2021-07-19
    Description: Subgrid processes occur in various ecosystems and landscapes but, because of their small scale, they are not represented or poorly parameterized in climate models. These local heterogeneities are often important or even fundamental for energy and carbon balances. This is especially true for northern peatlands and in particular for the polygonal tundra, where methane emissions are strongly influenced by spatial soil heterogeneities.We present a stochastic model for the surface topography of polygonal tundra using Poisson– Voronoi diagrams and we compare the results with available recent field studies. We analyze seasonal dynamics of water table variations and the landscape response under different scenarios of precipitation income. We upscale methane fluxes by using a simple idealized model for methane emission. Hydraulic interconnectivities and large-scale drainage may also be investigated through percolation properties and thresholds in the Voronoi graph. The model captures the main statistical characteristics of the landscape topography, such as polygon area and surface properties as well as the water balance. This approach enables us to statistically relate large-scale properties of the system to the main small-scale processes within the single polygons.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 2
    Publication Date: 2020-05-27
    Description: The dataset is composed of AisaEAGLE airborne hyperspectral imagery data acquired during the AIRMETH2016 campaign on August 27th, 2016 within the Toolik Lake Natural Research Area on the Alaskan North Slope. The Toolik Lake Research Natural Area is representative of the North Slope physiographic province of the Southern Arctic Foothills (Walker et al., 1989). Dominant vegetation types are dictated by soil moisture and geology and include moist tussock tundra, wet sedge meadows, and dry upland heaths. The dataset includes three flight lines with 130 spectral bands ranging from VIS to NIR (451.7 – 897 nm) wavelength regions. The dataset also includes Level 2A EnMAP simulated imagery using the end-to-end Simulation tool (EeteS) with 78 bands from VIS to NIR (423 – 903 mn). The overall goal of the campaign was to acquire airborne imagery over the Toolik Vegetation grid encompassing 94 permanent 1 x 1 m vegetation plots where corresponding, comprehensive multi-seasonal spectral reflectance, photosynthetic pigment, and detailed species composition data exists. The remote sensing data are highly novel and can be used for vegetation mapping of species composition, plant biomass, and photosynthetic activity.
    Language: English
    Type: info:eu-repo/semantics/report
    Format: application/pdf
    Format: application/pdf
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  • 3
    Publication Date: 2020-02-12
    Description: The dataset comprises three tables: - Data Set 1: Half-hourly measurement dataset (quality controlled and filtered), derived variables and energy balance components (Franz_ds01.csv) - Data Set 2: Half-hourly fluxes and transfer coefficients derived by bulk aerodynamic transfer models (Franz_ds02.csv) - Data Set 3. Daily courses and cumulative sums of energy balance components for the average day per subperiod including measured and modelled H and LE (Franz_ds03.csv)Eddy covariance measurements were conducted from 23 April to 16 August 2014 on a thermokarst lake in the Siberian Lena River Delta, yielding direct measurements of sensible (H) and latent (LE) heat flux on half-hourly basis. Ancillary measurements including meteorological variables and water temperature measurements were gathered during the campaign. We derived bulk aerodynamic transfer coefficients in order to parameterize the heat fluxes and compare this in-situ model with independent heat flux parameterization schemes, which are also based on the common bulk transfer algorithm. We further investigated the components of a simple energy balance including measured and modelled H and LE. The dataset was created within the framework of a publication of the study results in Journal of Geophysical Research - Atmospheres (Lake-atmosphere heat flux dynamics of a thermokarst lake in arctic Siberia, by Franz et al.)
    Language: English
    Type: info:eu-repo/semantics/workingPaper
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  • 4
    Publication Date: 2023-02-08
    Description: This repository contains the codes produced for the article "Long-term observations reveal rise in early summer methane emissions from Siberian tundra" by Norman Rößger, Torsten Sachs, Christian Wille, Julia Boike and Lars Kutzbach. In the article, the authors report an increasing trend of methane emissions for June and July at a permafrost site in Siberia (Lena River Delta). Using the longest set of observational methane flux data in the Arctic, the authors demonstrate that the continuous warming has begun to trigger the projected enhancement of methane release in Arctic permafrost ecosystems. This software is written in MATLAB. Running the codes ([.m files](Code)) and loading the data files ([.mat files](Data)) requires the pre-installation of [MATLAB](/https://de.mathworks.com/products/matlab.html). IMPORTANT: The repository only contains dummy data. The data that is needed to run the code can be requested by Torsten Sachs and Christian Wille (contact authors). Although the scripts and the data files have been tested for newer versions of MATLAB (〉= MATLAB R2017a). The code might also run in older versions of MATLAB, but this has not been tested.
    Language: English
    Type: info:eu-repo/semantics/workingPaper
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  • 5
    Publication Date: 2024-04-22
    Description: This publication provides the codes produced for the article "Temporally dynamic carbon dioxide and methane emission factors for rewetted peatlands. Nature Communications Earth and Environment" by Aram Kalhori, Christian Wille, Pia Gottschalk, Zhan Li, Josh Hashemi, Karl Kemper, and Torsten Sachs (https://doi.org/10.1038/s43247-024-01226-9). In the article, the authors estimate the cumulative GHG emissions of a rewetted peatland in Germany using the long-term ecosystem flux measurements. They observe a source-to-sink transition of annual carbon dioxide (CO2) fluxes and decreasing trend of methane (CH4) emissions. This software is written in R and MATLAB. Running the codes ([R files and .m files](Code)) and loading the data files ([CSV files and .mat files](Data)) requires the pre-installation of [R and RStudio] (https://posit.co/downloads/) and ([MATLAB]. The RStudio 2022.07.2 Build 576 version has been used for the R scripts. The land cover classification work was performed in QGIS, v.3.16.11-Hannover. Data were analyzed in both MATLAB and R and plots created with R (R Core Development Team 2020) in RStudio®.
    Language: English
    Type: info:eu-repo/semantics/other
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  • 6
    Publication Date: 2024-04-22
    Description: The data provided here is an exemplary dataset for the flux site Zarnekow from one year (2018). The complete dataset that is needed to run the codes for all the years can be obtained from the European Fluxes Database Cluster under site ID DE-Zrk (Sachs et al., 2016) or provided upon request. This repository is intended to provide the necessary MATLAB and R code to reproduce the results by Kalhori et al. (2024). The data are provided as zip folder containing (1) a csv file with associated definition of variables and units (file: 2023-004_Kalhori-et-al_README_2018_units.txt), (2) a shapefile (file: 2023-004_Kalhori-et-al_2018_LAiV_DOP.shp) and (3) a Geotiff (file: 2023-004_Kalhori-et-al_2018_LAiV_DOP.tiff).
    Language: English
    Type: info:eu-repo/semantics/workingPaper
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