Die Time Domain Reflectometry in der Geotechnik Messung von Wassergehalt, elektrischer Leitfaehigkeit und Stofftransport

This thesis concentrates on the time domain reflectometry, an electromagnetic technique for the determination of water content in porous media, which is based on the measurement of the dielectric constant of the materials. Development, theories and measurement principles are presented, advantages and disadvantages compared to other measurement methods of water content are discussed. A new TDR-technique (TRIME) was investigated in laboratory and field experiments. The new method was calibrated with different soil materials, giving a wide range from heavy clays to fine sand. Only little dependence of soil type was found and a universal empirical calibration function was established. The clays and soils with high organic content showed a more pronounced deviation, which is due to a different dielectric behaviour of bound soil water. Influences of soil structure, density, temperature and salinity on the measurement were discovered and recommendations to avoid or correct these effects are given. The possibility to simultaneously measure the electrical conductivity with this technique was demonstrated. The results indicated a higher soil type dependence which - beside dielectric characteristics of the materials - was caused by technical specifications. In laboratory soil columns as well as in a loessy field plot the application of TDR in the measurement of soil transport properties was tested and break through curves of solutes (KCl) could be measured. The method showed a good temporal and spatial resolution and data could be collected automatically with only small perturbation of the soil. (orig.)145 refs.Available from TIB Hannover: RO 6603(40) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Bayesian methods for predicting LAI and soil water content

peer reviewedLAI of winter wheat (Triticum aestivum L.) and soil water content of the topsoil (200 mm) and of the subsoil (500 mm) were considered as state variables of a dynamic soil-crop system. This system was assumed to progress according to a Bayesian probabilistic state space model, in which real values of LAI and soil water content were daily introduced in order to correct the model trajectory and reach better future evolution. The chosen crop model was mini STICS which can reduce the computing and execution times while ensuring the robustness of data processing and estimation. To predict simultaneously state variables and model parameters in this non-linear environment, three techniques were used: Extended Kalman Filtering (EKF), Particle Filtering (PF), and Variational Filtering (VF). The significantly improved performance of the VF method when compared to EKF and PF is demonstrated. The variational filter has a low computational complexity and the convergence speed of states and parameters estimation can be adjusted independently. Detailed case studies demonstrated that the root mean square error (RMSE) of the three estimated states (LAI and soil water content of two soil layers) was smaller and that the convergence of all considered parameters was ensured when using VF. Assimilating measurements in a crop model allows accurate prediction of LAI and soil water content at a local scale. As these biophysical properties are key parameters in the crop-plant system characterization, the system has the potential to be used in precision farming to aid farmers and decision makers in developing strategies for site-specific management of inputs, such as fertilizers and water irrigation.Filtering method-based state and parameter estimation for crop model

Acurácia e calibração de sonda de capacitância em Latossolo Vermelho cultivado com cafeeiro

O objetivo deste trabalho foi determinar a acurácia da sonda de multisensores de capacitância "Delta-T Profile probe PR2/6", na avaliação do conteúdo de água do solo com uso de calibrações padrão do fabricante, realizar a calibração para condições específicas de locais e profundidades de amostragem do solo e obter coeficientes de calibração para medições acuradas em tempo real. Em janeiro de 2010, foram coletadas amostras de solo com estrutura preservada a diferentes profundidades, nas linhas de plantio do cafeeiro e nas entrelinhas. As análises foram realizadas em laboratório, com o sensor ML2x Theta probe. Após a obtenção das leituras do sensor, o teor de água foi determinado por meio do método gravimétrico. Foram utilizadas amostras de Latossolo Vermelho distrófico muito argiloso. As calibrações padrão do fabricante (mineral e orgânica) não não se mostraram adequadas para emprego nas condições de manejo (locais e profundidades de amostragem) avaliadas. Na impossibilidade de averiguar a acurácia obtida pelo método recomendado pelo fabricante, o uso de ajustes de regressão linear ou da ferramenta Solver mostrou-se útil no processo de calibração. São necessárias apenas duas equações de calibração para avaliação do teor de água das situações contrastantes de manejo