196,474 research outputs found
Comparing canopy-scale actual transpiration fluxes of a tomato crop as measured in the field and estimated by an agro-hydrological model
No full textRoot water uptake, and subsequently transpiration, is a main component of the hydrological cycle and, hence, a main input to hydrological models. Transpiration rates can be either measured in the field at leaf and/or canopy scale or can be estimated using numerical modelling with either microscopic or macroscopic approaches. The main purpose of this study is to compare the transpiration rates measured at the leaf scale and those calculated by a macroscopic approach embedded into the Agro-hydrological model FLOWS under variable soil properties and water availability. For this purpose, sixteen plots were cultivated with tomato crops in Metaponto Area in South Italy. Of those plots, 8 plots were irrigated with 100% of the potential evapotranspiration, ETp, (hereafter, the control group), and 8 plots were irrigated with 80% of ETp (hereafter, the Deficit Irrigation group or DI group). Soil Hydraulic Properties (hereafter, SHP) were collected using a new fast field measurement based on the infiltration from a point source. Leaf-Area Index, LAI, was also measured in situ using a leaf-area meter. The crop coefficients, Kc, were estimated from LAI based on the literature for tomato crops in Southern Italy. The daily macroscopic transpiration rates, Ta,m, were obtained using FLOWS Agro-hydrological model, which is based on solving one-dimensional Richards Equation (RE), using the soil and vegetation data. The leaf-scale stomatal conductance, gs,l, and transpiration rates, Ta,l, were measured in the field using the infrared Gas Analyzers (IRGA). For the sake of comparison with the macroscopic transpiration rates, gs,l was upscaled to canopy scale stomatal conductance, gs,c, by the big-leaf approach using LAI and an extinction factor accounting for radiation attenuation. Then, the canopy-scale transpiration rates, Ta,c, were obtained by the well-known Penman-Monteith equation using the gs,c. Multiple Linear Regression, MLR, was used to find the statistical correlation among transpiration rates (both Ta,m and Ta,c), the SHP and gs,c, The results emphasize the strength of the model as it smooths the spatial variability of transpiration rates reducing the uncertainties resulting from the erratic variabilities coming from leaf-scale measurements as well as the ability of the model to obtain the daily transpiration rates along the whole growth season, which are difficult to obtain from leaf-scale measurements. The results also showed the important role of SHP in transpiration rates. Both Ta,m and Ta,c are strongly affected by the saturated water content, θs, and the slope of the water retention curve, nvG. In addition, a reduction in transpiration rates was observed in the whole DI group and even in a plot in the control group. The stress experienced in the latter plot was due to the SHP and proved that stress periods can occur even when providing the roots with 100% of ETp
Comparing actual transpiration fluxes as measured at leaf-scale and calculated by a physically based agro-hydrological model
No full textThe primary purpose of this paper is to compare the actual transpiration rates from tomato crops, as measured at leaf scale and estimated by a macroscopic approach in an agro-hydrological model named FLOWS, under variable soil properties and water availability. To this aim, sixteen plots were cultivated with toma-toes in Metaponto, Southern Italy. Soil hydraulic properties (SHP) were obtained using a fast in situ characterisation method. Leaf-area index (LAI) was measured using a leaf-area metre. SHP and LAI were then used in the physically-based FLOWS, which allowed calculating the macroscopic transpiration rates, Ta,m. Single-leaf transpiration rates, Ta,l, and stomatal conductance, gs,l, were measured in situ. For comparison with Ta,m, gs,l was upscaled by the Big-Leaf approach to canopy scale stomatal conductance, gs,c, which was applied to the Penman-Monteith model to obtain the canopy-scale transpiration, Ta,c. Finally, multiple linear regression (MLR) was used to find the statistical relationship between Ta,m and Ta,c, and the SHP and gs,c. Results showed that the macroscopic approach smooths the spatial variability of transpiration rates. Ta,c increased with the saturated water content, θs, and the slope of the water retention curve, n, while Ta,m decreased with increasing θs and n. MLR improved significantly by introducing gs,c to predict Ta,m
Target tracking for UWB multistatic radar sensor networks
No full textA multistatic radar based on ultra-wideband (UWB), also known as a UWB radar sensor network, has been shown to represent a very promising solution to localize an intruder moving within a small surveillance area. In this paper, a tracking algorithm based on low-complexity particle filtering is proposed, specifically tailored to UWB radar sensor networks with one transmitter and several receivers. An expression to calculate the particle weights is first derived, combining observations from all receivers. The particle filter is then modified to solve problems caused by blind zones inherently associated with the use of the UWB technology and multistatic configuration. In the proposed improved algorithm, suitable low-complexity particle filtering is employed to estimate velocity. The proposed approach provides high accuracy even at low signal-to-noise ratios with either static or dynamic clutters and it can track complicated maneuvering trajectories
Maximizing allowable disturbances in uncertain, non-minimum phase unstable systems
No full textTypescript (photocopy)VitaMajor subject: Mechanical EngineeringA frequency domain design methodology for maximizing the allowable size of step disturbances for a class of uncertain plants subjected to hard time domain constraints on the control, internal states and the output is extended to Non-Minimum Phase (NMP) and unstable systems. The design technique is based on mapping the time domain constraints into the frequency domain to obtain point-wise constraints on the magnitude and phase of the nominal loop transfer function at each frequency. Once these boundaries are obtained, classical loop shaping realizes an acceptable nominal loop transfer function. To extend the design methodology to NMP and/or unstable systems, the effects of right-half-plane zeros and poles of the system on its feedback properties are studied first. Then, the design methodology is modified to accommodate such systems. For NMP systems, an inner-outer factorization is used to transform the frequency domain design boundaries on the nominal NMP loop transfer function into equivalent bounds on the corresponding MP transfer function. For unstable systems similar difficulties are also noted which in most cases can be dealt with as for the NMP case. Alternatively, prestabilization can be used, which in fact becomes necessary when the system has imaginary-axis poles. Consequently, issues regarding the type of stabilization technique that should be used, the desirable locations for placing the closed loop poles, and the effect of prestabilization on the maximum tolerable size of the step disturbance are addressed. Furthermore, a necessary condition for the existence of a solution is given which is based on transforming the design boundaries on the loop transfer function into equivalent bounds on the sensitivity function. As an application, the problem of controlling the position of a ball rolling on a beam is treated. Finally, a loop shaping algorithm is included. The algorithm is based on converting the loop shaping problem into a parameter identification scheme giving a discrete-time domain transfer function representation of the loop. The resulting pulse transfer function is then transformed back into the continuous-time domain giving an approximate transfer function for the nominal loop
Multiple target tracking with particle filtering in UWB radar sensor networks
No full textIn this paper, a particle filtering algorithm is proposed for the challenging problem of multiple target tracking in ultra-wideband (UWB) radar sensor networks. The particle weights are derived analytically for the case of one transmitter and several receivers. The performance of the proposed particle algorithm is then evaluated through numerical results with comparison to the well-known Kalman filter. The scenarios account for the spatial configuration of the receivers, propagation effects, presence of clutter and noise
Nonverbale Kommunikation im Videotranskript. Zu nonverbalen Aspekten höflichen Handelns in interekulturellen Konstellationen und ihrer Darstellung in computergestüttzten Videotranskripten.
No full textRehbein J, Fienemann J, Ohlhus S, Oldörp C. Nonverbale Kommunikation im Videotranskript. Zu nonverbalen Aspekten höflichen Handelns in interekulturellen Konstellationen und ihrer Darstellung in computergestüttzten Videotranskripten. In: Möhn D, Ross D, Tjarks-Sobhani M, eds. Mediensprache und Medienlinguistik: Festschrift für Jörg Hennig. Sprache in der Gesellschaft. Frankfurt am Main ; New York: Lang; 2001: 167-198
- …
