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  • 1
    Language: English
    In: Optics Communications, Nov 15, 2013, Vol.309, p.37(7)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.optcom.2013.07.003 Byline: Florian Spath, Simon Metzendorf, Andreas Behrendt, Hans-Dieter Wizemann, Gerd Wagner, Volker Wulfmeyer Abstract: A compact and rugged distributed feedback (DFB) laser system has been developed as online-offline injection seeder for the laser transmitter of a ground-based water vapor differential absorption lidar (WV DIAL) near 820nm. The frequency stability of this injection seeder system shows a standard deviation of only 6.3MHz and a linewidth of less than 4.6MHz during continuous operation of more than 14h. These values by far exceed the requirements for WV DIAL. By use of a novel technique based on an electro-optic deflector (EOD), alternating online-offline wavelength switching is achieved for each shot of the seeded laser with 250Hz with a response time of less than 10A[micro]s and very low crosstalk between the channels of only 33dB. As a result, a spectral purity of 99.95% is reached by the WV DIAL transmitter which again fulfills the requirements for WV DIAL measurements with high accuracy. Because moveable parts are not present in the seeding system, this setup is significantly less sensitive to acoustic vibrations and ambient temperature drifts during field experiments than other seeding systems which use external cavity diode lasers (ECDL) and mechanical switches. By our new seeding system not only the requirements for ground-based water-vapor DIAL are met but also for space-borne WV DIAL applications that pose even higher demands to the frequency stability and spectral purity of the laser transmitters. Author Affiliation: University of Hohenheim, Institute of Physics and Meteorology, Garbenstr. 30, 70599 Stuttgart, Germany Article History: Received 24 December 2012; Revised 29 May 2013; Accepted 1 July 2013
    Keywords: Vibration (Physics) ; Optical Radar ; Lasers
    ISSN: 0030-4018
    Source: Cengage Learning, Inc.
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  • 2
    Language: English
    In: Soil Biology and Biochemistry, February 2015, Vol.81, pp.291-303
    Description: Understanding enzyme activities could help clarify the fate of soil organic carbon (SOC), one of the largest uncertainties in predicting future climate. Here, we explored the role of soil temperature and moisture on SOM decomposition by using, for the first time, modelled enzyme activities as a proxy to explain seasonal variation in soil respiration. We measured temperature sensitivities (Q ) of three enzymes (β-glucosidase, xylanase and phenoloxidase) and moisture sensitivity of β-glucosidase from agricultural soils in southwest Germany. Significant seasonal variation was found in potential activities of β-glucosidase, xylanase and phenoloxidase and in Q for β-glucosidase and phenoloxidase activities but not for xylanase. We measured moisture sensitivity of β-glucosidase activity at four moisture levels (12%–32%), and fitted a saturation function reflecting increasing substrate limitation due to limited substrate diffusion at low water contents. The moisture response function of β-glucosidase activity remained stable throughout the year. Sensitivity of enzymes to temperature and moisture remains one of the greatest uncertainties in C models. We therefore used the response functions to model temperature-based and temperature and moisture-based enzyme activities to characterize seasonal variation in SOC decomposition. We found temperature to be the main factor controlling enzyme activities. To prove the relevance of our modelling approach, we compared the modelled enzyme activities with soil respiration data measured weekly. Temperature-based enzyme activities explained seasonal variability in soil respiration well, with model efficiencies between 0.35 and 0.78. Fitting an exponential response function to soil temperature explained soil respiration to a lesser extent than our enzyme-based approach. Adding soil moisture as a co-factor improved model efficiencies only partly. Our results demonstrate the potential of this new approach to explain seasonal variation of enzyme related processes.
    Keywords: Temperature Sensitivity ; Moisture Sensitivity ; Q10 ; Seasonal Variation ; Β-Glucosidase ; In Situ Activity ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 3
    Language: English
    In: International Journal of Remote Sensing, 19 May 2017, Vol.38(8-10), pp.3003-3026
    Description: In this study, high-resolution thermal imagery acquired with a small unmanned aerial vehicle (UAV) is used to map evapotranspiration (ET) at a grassland site in Luxembourg. The land surface temperature (LST) information from the thermal imagery is the key input to a one-source and two-source...
    Keywords: Geography
    ISSN: 0143-1161
    E-ISSN: 1366-5901
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  • 4
    Language: English
    In: Optics Communications, 15 November 2013, Vol.309, pp.37-43
    Description: A compact and rugged distributed feedback (DFB) laser system has been developed as online–offline injection seeder for the laser transmitter of a ground-based water vapor differential absorption lidar (WV DIAL) near 820 nm. The frequency stability of this injection seeder system shows a standard deviation of only 6.3 MHz and a linewidth of less than 4.6 MHz during continuous operation of more than 14 h. These values by far exceed the requirements for WV DIAL. By use of a novel technique based on an electro-optic deflector (EOD), alternating online–offline wavelength switching is achieved for each shot of the seeded laser with 250 Hz with a response time of less than 10 µs and very low crosstalk between the channels of only 33 dB. As a result, a spectral purity of 99.95% is reached by the WV DIAL transmitter which again fulfills the requirements for WV DIAL measurements with high accuracy. Because moveable parts are not present in the seeding system, this setup is significantly less sensitive to acoustic vibrations and ambient temperature drifts during field experiments than other seeding systems which use external cavity diode lasers (ECDL) and mechanical switches. By our new seeding system not only the requirements for ground-based water-vapor DIAL are met but also for space-borne WV DIAL applications that pose even higher demands to the frequency stability and spectral purity of the laser transmitters.
    Keywords: Laser Stabilization ; Injection Seeding ; Distributed-Feedback Lasers ; Water Vapor Differential Absorption Lidar ; Electro-Optic Deflector ; Fast Optical Switch ; Physics
    ISSN: 0030-4018
    E-ISSN: 1873-0310
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  • 5
    In: Journal of Agricultural Studies, 10/01/2014, Vol.3(1), p.79
    Description: Crop simulation is a modern tool used to mimic ordinary and extraordinary agriculture systems. Under the premise of continuing foreseeable climatic shift we combine adaptive field-level management decisions with their effects on crop performance. Price projections are used to examine yield and price effects on gross margins of the predominant crops in two specific regions of Southwest Germany into the coming decades. After calibration and validation to historic records, simulated future weather is used to explore how farmer behavior and performance of wheat, barley, rapeseed and maize could develop under anticipated global change. This development is examined based on a comparison of historic and projected gross margin variance. Simulations indicate that when yield levels increase, the relative variability of gross margins may decline in spite of some increasing variability of yields. The coefficient of variance of gross margins decreases even more due to the independence of price and yield fluctuations. This shows how the effects of global change on yields could be offset by economic conditions.
    Keywords: Agriculture ; Weather ; Historical Account ; Behavior ; Climate ; Simulation ; Economic Conditions ; Wheat ; Crops ; Hordeum Vulgare ; Triticum Aestivum ; Zea Mays ; Germany ; Issues in Sustainable Development;
    ISSN: Journal of Agricultural Studies
    E-ISSN: 2166-0379
    Source: CrossRef
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  • 6
    In: Water Resources Research, December 2013, Vol.49(12), pp.8200-8221
    Description: Six models with differing representation of the physical process in the coupled soil‐plant system are tested to simultaneously reproduce the dynamics of soil water contents, evapotranspiration, and leaf area index during a growing season of winter wheat at two contrasting field plots in the Kraichgau and the Swabian Alb regions in South‐West Germany. The main aim of the study is the assessment of the performance and the identification of structural deficits of the models LEACHN, SUCROS, CERES, GECROS, and SPASS as well as the land‐surface model CLM3.5. The calibration of each model is posed in a multiobjective framework with three different objective functions that summarize the fit between model simulations and the three observation types. The AMALGAM evolutionary search algorithm is utilized to simultaneously estimate the most important soil hydraulic and plant parameters. The six models exhibit a wide variability in the trade‐offs between the fitting to the data types. Mechanistic process description, particularly of the root system, reduces the trade‐off considerably for the SPASS and GECROS models. These models adequately simulate the reduction of root water uptake and transpiration during senescence under nonlimited soil water supply. The SPASS model in particular shows an overall better performance as compared to the more simpler models which is related to an adequate level of structural complexity in the interplay of all model compartments combined with a relatively low parameter sensitivity to the weighting scheme in the multiobjective optimization. The dynamic consideration of the root system formation is particularly important, which is simulated quite detailed in the SPASS model as a function of nitrogen (N) and water availability in the different soil horizons. The proposed multiobjective calibration procedure proved to be very useful to identify processes that are important to adequately simulate the coupled soil‐plant system. The consideration of these processes and our insights about the value of different data types for model calibration is expected to lead to more accurate, predictive land‐surface models. Over‐simplification of soil‐root processes result in biased simulations Soil moisture, plant development, & heat flux data are required for calibration A dynamic consideration of the root system formation is particularly important
    Keywords: Coupled Soil‐Plant Models ; Multiobjective Parameter Optimization ; Soil Moisture ; Pareto Analysis ; Model Structural Errors ; Evapotranspiration
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 7
    Language: English
    In: Biogeosciences Discussions, 09/24/2018, pp.1-36
    ISSN: Biogeosciences Discussions
    E-ISSN: 1810-6285
    Source: CrossRef
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  • 8
    Language: English
    In: Hydrology and Earth System Sciences Discussions, 07/09/2018, pp.1-36
    Description: The diurnal forcing of solar radiation is the largest signal within the Earth system and dominates the diurnal cycle of the turbulent heat fluxes and evapotranspiration (λE) over land. Incoming solar radiation (Rsd) also shapes temperature, vapor pressure deficit and wind speed known as important controls on λE. Current process-based λE schemes used in remote sensing and land–surface modeling differ in how these controls on λE are represented and which input variables are required. Here, we analyze how well different surface energy balance schemes are able to reproduce the diurnal cycle and how the diurnal signals of observed input variables actually influence the resulting diurnal pattern of λE. As additional constraint for model evaluation we estimate a linear and a non-linear phase shift component of a surface variable (e.g. λE) to incoming solar radiation. We illustrate our analysis with observations from an eddy covariance station at a temperate grassland site in Luxembourg with a focus on clear sky conditions. During the field campaign in 2015 a summer drought led to a dry-down of soil moisture which allows for studying the effect of wet and dry conditions on the diurnal cycle. We found a remarkable, almost linear relationship of λE with Rsd, which exhibits a significant positive phase lag during wet periods. This phase lag in λE was compensated by a preceding phase lag of the sensible heat flux. Vapor pressure deficit (Da, often used as input for Penman–Monteith based approaches) exhibits a strong phase lag, which is driven by air temperature reflecting large diurnal heat storage changes in the lower atmosphere. This large phase lag in Da, which is not seen in λE, explains why actual and potential evapotranspiration approaches can show systematic deviations from observations at the sub-daily time scale and highlight the need for a time-dependent non-linear compensation through the conductance parameterization. The surface to air temperature gradient used as input in energy balance residual approaches corresponds rather well with its linear response and phase lag to the observed sensible heat flux under both, wet and dry conditions. This simplifies the conductance parameterization and explains the better correlation of these models at the sub-daily time scale. We conclude that the analysis of phase lags at the sub-daily time-scale provides valuable information on the drivers of the surface–atmosphere exchange, which can be used to evaluate and improve the representation of land–atmosphere coupling in land–surface schemes.
    Keywords: Geography;
    ISSN: Hydrology and Earth System Sciences Discussions
    E-ISSN: 1812-2116
    Source: CrossRef
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  • 9
    Language: English
    Description: This dataset provides half-hourly surface energy balance measurements for a temperate grassland site in Luxembourg. The data were obtained during a field campaign in June and July 2015. The observations comprise multiple variables measurements by an Eddy-Covariance station, a net radiometer, soil moisture, temperature and soil heat flux probes and meteorological standard measurements. For details please see the reference article Renner et al., 2018 HESSD with the general setup described in Wizemann et al., 2015. The data are complemented by half-hourly model output of sensible and latent heat fluxes that are published as individual data publication (Renner et al., 2018). The data is provided as comma-separated-values (csv) format in a long table format. Columns represent Date, Time, variable, value, source. The column “variable” sets the name of the variable (following CEOP standards) with an information of the measurement depth for soil measurements. Column “source” describes the data source with an acronym(Observations “ObsEC”). The data contributes to the Joint Research Group "Catchments As Organized Systems" (CAOS) funded by the German Research Foundation. Methods: Eddy Covariance, Surface energy...
    Keywords: Land Surface Heat Fluxes ; Eddy Covariance ; Surface Energy Balance Observations ; Catchments As Organized Systems ; Caos ; Earth Science 〉 Biosphere 〉 Terrestrial Ecosystems 〉 Grasslands ; Earth Science 〉 Biosphere 〉 Terrestrial Ecosystems 〉 Grasslands ; Earth Science 〉 Atmosphere 〉 Atmospheric Radiation 〉 Outgoing Longwave Radiation ; Earth Science 〉 Atmosphere 〉 Atmospheric Radiation 〉 Incoming Solar Radiation ; Earth Science 〉 Atmosphere 〉 Atmospheric Radiation 〉 Longwave Radiation ; Earth Science 〉 Atmosphere 〉 Atmospheric Radiation 〉 Incoming Solar Radiation ; Earth Science 〉 Atmosphere 〉 Atmospheric Water Vapor 〉 Evapotranspiration ; Earth Science 〉 Atmosphere 〉 Atmospheric Radiation 〉 Heat Flux ; Research 〉 Scientific Research 〉 Meteorological Research ; In Situ/Laboratory Instruments 〉 Current/Wind Meters 〉 Eddy Correlation Devices
    Source: DataCite
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  • 10
    In: Water Resources Research, February 2014, Vol.50(2), pp.1337-1356
    Description: Interactions between the soil, the vegetation, and the atmospheric boundary layer require close attention when predicting water fluxes in the hydrogeosystem, agricultural systems, weather, and climate. However, land‐surface schemes used in large‐scale models continue to show deficiencies in consistently simulating fluxes of water and energy from the subsurface through vegetation layers to the atmosphere. In this study, the multiphysics version of the Noah land‐surface model (Noah‐MP) was used to identify the processes, which are most crucial for a simultaneous simulation of water and heat fluxes between land surface and the lower atmosphere. Comprehensive field data sets of latent and sensible heat fluxes, ground heat flux, soil moisture, and leaf area index from two contrasting field sites in South‐West Germany are used to assess the accuracy of simulations. It is shown that an adequate representation of vegetation‐related processes is the most important control for a consistent simulation of energy and water fluxes in the soil‐plant‐atmosphere system. In particular, using a newly implemented submodule to simulate root growth dynamics has enhanced the performance of Noah‐MP. We conclude that further advances in the representation of leaf area dynamics and root/soil moisture interactions are the most promising starting points for improving the simulation of feedbacks between the subsoil, land surface and atmosphere in fully coupled hydrological and atmospheric models. Selecting different model options strongly influences accuracy of simulations The ensemble size can be reduced by constraining Noah‐MP to different data types Considering dynamics of root growth results in more accurate simulations
    Keywords: Land‐Surface Model ; Structural Uncertainty ; Root Water Uptake ; Latent And Sensible Heat ; Ground Heat Flux ; Soil Moisture
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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