Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Development of probabilistic models for quantitative pathway analysis of plant pests introduction for the EU territory
    Douma, J.C. ; Robinet, C. ; Hemerik, L. ; Mourits, M.C.M. ; Roques, A. ; Werf, W. van der - \ 2015
    European Food Safety Authority - 435
    gewasbescherming - landen van de europese unie - plantgezondheid - siergewassen - stochastische modellen - bouwhout - vermeerderingsmateriaal - invasieve exoten - plantaardige producten - waarschijnlijkheid - risicoschatting - risicovermindering - plantenplagen - plant protection - european union countries - plant health - ornamental crops - stochastic models - building timbers - propagation materials - invasive alien species - plant products - probability - risk assessment - risk reduction - plant pests
    The aim of this report is to provide EFSA with probabilistic models for quantitative pathway analysis of plant pest introduction for the EU territory through non-edible plant products or plants. We first provide a conceptualization of two types of pathway models. The individual based PM simulates an individual consignment (or a population of such consignment) by describing the stochastic change in the state of the individual consignment over time and space. The flow-based PM, simulates the flow of infested product over time and space, without distinguishing individual consignments. We show how these two conceptualisations are mathematically related, and present, as a show case, both models for cut flowers. Second, we developed PMs for five product groups: round wood, sawn wood, cut flowers, plants for planting and seeds. For each product group we have developed a case-study (combination of product, origin and pest) to illustrate the use of the pathway models: (1) oak wood from the USA and Ceratocystis fagacearum, (2) Coniferous sawn wood from China and Bursaphelenchus xylophilus, (3) Cut orchids from Thailand and Thrips palmi, (4) Pot orchids from Thailand and Thrips palmi, and (5) Tomato seeds and Clavibacter michiganensis subsp. michiganensis from outside the European Union. An uncertainty analysis on the models shows that the pest species-specific parameters appear to be sensitive and uncertain. Third, a practical guidance is provided on i) how to develop a PM, ii) the application of PMs in @Risk (a plugin for MS Excel), and iii) application in R. Finally, future research topics are defined. Further work is needed on interpretation of results, linking quantitative outcomes of pathway modelling to pest risk scoring guidance, and evaluation of management options using pathway models.
    Kinetic modelling of enzymatic starch hydrolysis
    Bednarska, K.A. - \ 2015
    Wageningen University. Promotor(en): Tiny van Boekel; Remko Boom, co-promotor(en): Anja Janssen. - Wageningen : Wageningen University - ISBN 9789462573086 - 159
    hydrolyse - enzymen - zetmeel - stochastische modellen - verwerking - hydrolysis - enzymes - starch - stochastic models - processing

    Kinetic modelling of enzymatic starch hydrolysis – a summary

    K.A. Bednarska

    The dissertation entitled ‘Kinetic modelling of enzymatic starch hydrolysis’ describes the enzymatic hydrolysis and kinetic modelling of liquefaction and saccharification of wheat starch. After the background information about the enzymes, the substrate and the basics of the model in the first chapter, we describe a model predicting the outcome of wheat starch liquefaction by α-amylase from Bacillus licheniformis at 50°C in chapter 2. We demonstrate the ability of the model to predict starch hydrolysis products larger than the oligosaccharides considered in the existing models. The model in its extended version follows all the products of wheat starch hydrolysis separately, and despite the quantitative differences, the qualitative predictions are satisfactory. We also show that the difference between the experimental and computed data might stem from the inaccuracy of the subsite map.

    In the following chapters the model is used to find a better description of the hydrolysis data at two temperatures (50°C and 80°C), by varying the energy values of the subsite map and evaluating the inhibition. We hypothesize that a subsite map that is based on the cleavage patterns of linear, short molecules does not account for the complexity of hydrolysis of amylopectin. The branched structure of amylopectin molecules influences the composition of the hydrolysis products by restricting the access to some of the bonds. The presence of branches creates steric obstacles for the enzyme. The used α-amylase has difficulties hydrolysing and accommodating α-(1,6)-glycosidic bonds, which imposes on the hydrolysis of the α-(1,4)-glycosidic bonds located in its proximity. On this basis, we analyse the subsite maps in detail and suggest which of the subsites are crucial when making predictions about the product composition of starch hydrolysates. On top of that we propose new subsite maps that allow a quantitative description of the experimental data.

    After the model was shown to work at different experimental conditions, we also test it at increased the dry matter content during wheat starch hydrolysis. We follow both the liquefaction by BLA and the saccharification process by glucoamylase from Aspergillus niger at low moisture content. The liquefaction model, is used to predict all of the products of wheat starch hydrolysis at higher dry matter contents (30-60 w/w%). The liquefaction model also creates the substrate matrices representing maltodextrins to be used in the saccharification model. The saccharification of liquefacts to glucose is followed with a new mechanistic model, also using the assumptions of the subsite theory. The saccharification model predicts all of the reaction products using the subsite maps of glucoamylase available in literature.

    The findings described in the thesis are summarized and put in context in the general discussion. We demonstrate how the parameters of the liquefaction model at low moisture contents were chosen. The outcomes of the model are also compared with the experimental data at 30-60 w/w%. Next, we test our liquefaction model with starch hydrolysis data at 5 and 60 w/w% taken from literature, to verify both the approach we used and the validity of the parameters we obtained in previous chapters. The method used to improve the subsite maps is also tested on another enzyme, Bacillus amyloliquefaciens α-amylase. After discussing the factors that influence saccharification at high dry matter contents, we conclude the chapter with describing the potential of stochastic modelling and its practical use.

    Decision making under uncertainty in fisheries management: capital adjustment, fishermen behavior and stochasticity in fish stocks
    Dijk, D. van - \ 2013
    Wageningen University. Promotor(en): Ekko van Ierland, co-promotor(en): Rolf Groeneveld; Rene Haijema; Eligius Hendrix. - [S.l.] : s.n. - ISBN 9789461737304 - 103
    visserijbeheer - visserij - visserijbeleid - bedrijfsinformatiesystemen - besluitvorming - investeringsbeslissingen - onzekerheid - economisch gedrag - vissers - visstand - quota - stochastische modellen - fishery management - fisheries - fishery policy - management information systems - decision making - investment decisions - uncertainty - economic behaviour - fishermen - fish stocks - quotas - stochastic models
    The world’s marine fisheries are characterized by declining global catch, an increasing number of overexploited stocks and high natural variability in fish stocks. Policy makers are becoming more aware that effective management systems have to be implemented to rebuild overexploited fish stocks. The success of a management system is specified in terms of biological, economic, social and political objectives of policy makers and the fishing industry. However, the combination of these objectives makes the implementation of policies one of the main challenges in fisheries management. To prevent overfishing, different measures have been applied that limit catch and/or fleet capacity. Yet, the same management systems and economic behavior of fishermen may lead to an increase in investments in the fleet capacity, causing overcapacity. Decisions of policy makers and fishermen are made under uncertainty, such as uncertainty about fish stock dynamics and/or fish prices, and this can affect optimal management, investment decisions, healthy and productive fish stocks and resource rents. The objective of this thesis is to study the impact of different fisheries management systems on resource rents from the fishery, investment in the fleet capacity and fish stock under uncertainty about fish stock growth and the ex-vessel price of fish. Bi-level stochastic dynamic programming is used to model the interaction between the quota decision of a policy maker and fishermen behavior. The fisheries management systems of multiannual quota and a quota adjustment restriction are introduced and analyzed in terms of resource rents, overcapacity and fish stock. Real Options theory is used to determine for a fisheries management system of limited entry at what ex-vessel prices it is optimal for fishermen to make investment and disinvestment decisions.
    Towards stochastic simulation of crop yield: a case study of fruit set in sweet pepper
    Wubs, A.M. - \ 2010
    Wageningen University. Promotor(en): Leo Marcelis, co-promotor(en): Ep Heuvelink; Lia Hemerik. - [S.l.] : S.n. - ISBN 9789085856993 - 149
    capsicum annuum - paprikapoeder - simulatiemodellen - stochastische modellen - vruchtzetten - abortie (planten) - overleving - source-sink relaties - capsicum annuum - paprika - simulation models - stochastic models - fruit set - abortion (plants) - survival - source sink relations
    Crop growth simulation models are widely used in research and education, and their use in commercial practice is increasing. Usually these models are deterministic: one set of input values always gives the same output of the model. In reality, however, variation exists between plants of the same crop. A simulation model taking this variation into account is therefore more realistic. The aim of this thesis is to introduce a stochastic component into a dynamic crop simulation model. As case study, fruit set in sweet pepper was used, because large variation in fruit set between the plants exists. Competition with fast growing fruits causes abortion of flowers and young fruits, which results in periods with high and low fruit set, and consequently periods of high and low fruit yield. A literature review showed that most factors influencing fruit abortion can be expressed in the terms source and sink strength. Source strength is the supply of assimilates; a higher source strength increases fruit set. Source strength takes into account leaf area, radiation, and CO2 level and temperature. Sink strength is the demand for assimilates of the fruits and vegetative parts. It is quantified by the potential growth rate, i.e. the growth rate under non-limiting assimilate supply. Assimilate demand of the fruits depends on their number, age, and cultivar. If the total fruit sink strength of a plant is low, fruit set is high. Vulnerable for abortion were very small buds, buds close to anthesis and flowers and young fruits up to 14 days after anthesis. An experiment with six Capsicum cultivars with fruit sizes ranging between 20 and 205g fresh weight showed that variation in weekly fruit yield is highly correlated with variation in weekly fruit set. Fruit yield patterns resembled fruit set patterns, with a lag time being equal to the average fruit growth duration. Further investigation showed that the cultivars not only differed in sink strength of the individual fruits, but also that the source-sink ratio above which fruit set occurred was higher in cultivars with larger fruits. In the second half of the thesis, flower and fruit abortion was modelled. Survival analysis was used as the method to derive the abortion function. Source and sink strength were used as the factors influencing abortion. Their effect on the probability of abortion per day was non-linear: at high values of source and sink strength an increase did not further decrease or increase the probability of abortion, respectively. Flowers on the side shoots turned out to have a higher probability of abortion than flowers on the main shoot. Most flowers and young fruits aborted around 100°Cd after anthesis. The obtained function was used in a crop simulation model for sweet pepper. After calibration the model was able to simulate the observed fruit set pattern, although fruit abortion was not properly simulated when low source strength was combined with high sink strength. Validation with three independent data sets gave reasonable to good results. Survival analysis proved to be a good method for introducing stochasticity in crop simulation models. A case study with constant source strength showed asynchronisation of fruit set between the plants, indicating that fluctuations in source strength are an important factor causing synchronisation between individual plants.

    Bio-economic modeling of bovine intramammary infections
    Halasa, T. - \ 2009
    Utrecht University. Promotor(en): J.A. Stegeman, co-promotor(en): Henk Hogeveen; M. Nielen; T. van Werven. - [S.l.] : S.n. - ISBN 9789039350508 - 167
    melkvee - rundermastitis - melkproductie - stochastische modellen - ziektestatistieken - epidemiologie - gustperiode - modelleren - dairy cattle - bovine mastitis - milk production - stochastic models - disease statistics - epidemiology - dry period - modeling
    Stochastic forward and inverse groundwater flow and solute transport modeling
    Janssen, G.M.C.M. - \ 2008
    Wageningen University. Promotor(en): Sjoerd van der Zee; J.R. Valstar. - [s.l.] : S.n. - ISBN 9789085852414
    grondwater - grondwaterstroming - biochemisch transport - stochastische modellen - groundwater - groundwater flow - biochemical transport - stochastic models

    Keywords: calibration, inverse modeling, stochastic modeling, nonlinear biodegradation, stochastic-convective, advective-dispersive, travel time, network design, non-Gaussian distribution, multimodal distribution, representers

    This thesis offers three new approaches that contribute to the ability of groundwater modelers to better account for heterogeneity in physically-based, fully distributed groundwater models. In both forward and inverse settings, this thesis tackles major issues with respect to handling heterogeneity and uncertainty in various situations, and thus extends the ability to correctly and/or effectively deal with heterogeneity to these particular situations.
    The first method presented in the thesis uses the recently developed advective-dispersive streamtube approach in combination with a one-dimensional traveling wave solution for nonlinear bioreactive transport, to study the interplay between physical heterogeneity, local-scale dispersion and nonlinear biodegradation and gain insight in the long-term asymptotic behavior of solute fronts, in order to deduce (the validity of) upscaling equations. Using the method in synthetic small-scale numerical experiments, it is shown that asymptotic front shapes are neither Fickian nor constant, which raises questions about the current practice of upscaling bioreactive transport.
    The second method presented in the thesis enhances the management of heterogeneity by extending inverse theory (specifically, the representer-based inverse method) to determinations of groundwater age/travel time. A first-order methodology is proposed to include groundwater age or tracer arrival time determinations in measurement network design. Using the method, it is shown that, in the applied synthetic numerical example, an age estimation network outperforms equally sized head measurement networks and conductivity measurement networks, even if the age estimations are highly uncertain. The study thus suggests a high potential of travel time/groundwater age data to constrain groundwater models.
    Finally, the thesis extends the applicability of inverse methods to multimodal parameter distributions. Multimodal distributions arise when multiple statistical populations exist within one parameter field, each having different means and/or variances of the parameter of concern. No inverse methods exist that can calibrate multimodal parameter distributions while preserving the geostatistical properties of the various statistical populations. The thesis proposes a method that resolves the difficulties existing inverse methods have with the multimodal distribution. The method is successfully applied to both synthetic and real-world cases.

    Land rental, off-farm employment and technical efficiency of farm households in Jiangxi Province, China
    Feng, S. - \ 2008
    NJAS Wageningen Journal of Life Sciences 55 (2008)4. - ISSN 1573-5214 - p. 363 - 378.
    migratie - rurale migratie - stochastische modellen - grondmarkten - huurders - efficiëntie - landbouwhuishoudens - jiangxi - china - migration - rural rural migration - stochastic models - land markets - tenants - efficiency - agricultural households - jiangxi - china - agricultural productivity growth - tenure contracts - markets - ethiopia - reforms - determinants - models - impact
    Land rental market development and off-farm employment have important implications for agricultural production. This study examined the effects of land rental market participation, the resulting land tenure contracts, and off-farm employment on the technical efficiency in rice production in rural China, using the one-step stochastic frontier approach. Data from a survey held at household and plot level in three villages in north-east Jiangxi Province were used to estimate the stochastic frontier model. We found that the mean technical efficiency of rice production in north-east Jiangxi Province ranged from 0.36 to 0.97, with an average of 0.82. The determinants of technical efficiency show that households that rented land achieved higher technical efficiency than households that did not rent land. Rice production on rented plots was technically as efficient as on contracted plots. Additionally, participation in migration did not have an effect on technical efficiency
    Towards a soil information system with quantified accuracy : three approaches for stochastic simulation of soil maps
    Brus, D.J. ; Heuvelink, G.B.M. - \ 2007
    Wageningen : Wettelijke Onderzoekstaken Natuur & Milieu (WOt-rapport 58) - 90
    cartografie - bodemclassificatie - informatiesystemen - kaarten - stochastische modellen - simulatiemodellen - nauwkeurigheid - kriging - bodemkarteringen - geostatistiek - mapping - soil classification - information systems - maps - stochastic models - simulation models - accuracy - kriging - soil surveys - geostatistics
    This WOT report describes (geo)statistical methods for mapping soil type and soil properties from soil observations and explanatory information.
    Nutrient Digestion and Utilization in Farm Animals : Modelling approaches
    Kebreab, E. ; Dijkstra, J. ; Bannink, A. ; Gerrits, W.J.J. ; France, J. - \ 2006
    Wallingford, UK : CAB International - ISBN 9781845930059 - 480
    rundvee - schapen - varkens - pluimvee - vissen - voedingsstoffen - spijsvertering - voedingsfysiologie - deterministische modellen - stochastische modellen - modellen - cattle - sheep - pigs - poultry - fishes - nutrients - digestion - nutrition physiology - deterministic models - stochastic models - models
    This book contains 34 chapters on nutrition physiology and presents scientific research in modelling nutrient digestion and utilization in domestic animals, including cattle, sheep, pigs, poultry and fishes. It is divided into 6 parts that cover fermentation, absorption and passage; growth and development; mineral metabolism; methodology and model development; environmental impacts and animal production and feed evaluation models. Deterministic, stochastic, empirical and mechanistic modelling approaches are also described. This book will be of significant interest to researchers and students of animal science, especially those concerned with nutrition modelling.
    2.2 Kennis in waarschuwingssystemen: NemaDecide, een Beslissing Ondersteunend Systeem voor aaltjes: themavoordracht 4e Gewasbeschermingsmanifestatie 'Is het al tijd om te oogsten?'
    Been, T.H. ; Schomaker, C.H. ; Molendijk, L.P.G. ; Beers, T.G. van - \ 2005
    Gewasbescherming 36 (2005)sup. - ISSN 0166-6495 - p. 9S - 10S.
    gewasbescherming - plagenbestrijding - geïntegreerde bestrijding - nematoda - heteroderidae - aardappelen - informatiesystemen - stochastische modellen - wiskundige modellen - voorlichters - adviescentra - nematodenbestrijding - beslissingsondersteunende systemen - kennissystemen - kennismanagement - plant protection - pest control - integrated control - nematoda - heteroderidae - potatoes - information systems - stochastic models - mathematical models - extension agents - advisory centres - nematode control - decision support systems - knowledge systems - knowledge management
    Themavoordracht over het adviessysteem NemaDecide, waarin bestaande kennis betreffende aardappelcystenaaltjes wordt vastgelegd, geïntegreerd en systematisch uitgebreid. Het systeem kan worden ingezet om complexe modellen toe te passen in de advisering en Wageningse kennis kan snel doorstromen naar de praktijk
    Physiology of biological variation
    Schouten, R.E. - \ 2004
    Wageningen University. Promotor(en): Olaf van Kooten. - [S.l.] : S.n. - ISBN 9789058088512 - 137
    cucumis sativus - komkommers - fragaria ananassa - aardbeien - houdbaarheid (kwaliteit) - kleur - stochastische modellen - kinetica - modellen - systemen na de oogst - bewaarfysiologie - beeldverwerking - cucumis sativus - cucumbers - fragaria ananassa - strawberries - keeping quality - colour - stochastic models - kinetics - models - postharvest systems - postharvest physiology - image processing
    In agricultural products, variation exists in quality attributes between batches. Examples of this biological variation are well known and the general response is trying to suppress it as much as possible; to create uniformity using pre- andpostharvestmethods. This thesis shows a methodology that takes advantage of the biological variation, instead of treating it as a nuisance. This biological variation methodology was applied to understand the expected keeping quality of batches.

    The methodology currently consists of three steps. Firstly, repeated non-destructive measurements of quality properties of individuals need to be applied to find out how the quality attribute changes over time without having to worry about biological variation. Secondly, kinetic models need to be constructed that show the quality attribute changing over time as a combination of simultaneously occurring processes that, ideally, have a strong physiological background. The last step consists of translating the kinetic model that describes the behaviour of the quality attribute of individuals to batches usingstochastics. This methodology is applied for cucumbers and strawberries.

    Cucumber. The keeping quality for a cucumber, defined as the time the colour remains acceptable to the consumer, depends on the state of the chlorophyll metabolism. A generic model was build that describes thepostharvestcolour behaviour in time and temperature for individual cucumbers, irrespective of growing conditions and cultivar. The model enables prediction on the batch keeping quality, on the basis of initial colour measurements only. 

    Strawberry. Postharvestlife of strawberries is largely limited by Botrytiscinereainfection. A colour modelwasbuilt that describes the simultaneous development of the red colour and the anti-fungal function of individual strawberries over time. Batch keeping quality predictions could be derived on the basis of initial colour measurements or from the time between harvest dates.

    Batch model. The batch model describes the influence of one source of biological variation, here assumed to be variation in light conditions during thepreharvestperiod, on the distribution of precursor concentrations by combining (product specific) kinetic models and a generic stochastic part. The batch model described batch behaviour in terms of current maturity, biological variation and maximal maturity towards keeping quality of cucumbers and strawberries. Applications of biological methodology may be numerous: proposing protocols for keeping quality predictions, characterisation of cultivar specific influences on keeping quality or, in general, starting of a new field that is concerned with the 'hidden' information that is present in all biological batches.
    Simulation of 6-hourly rainfall and temperature by two resampling schemes
    Wójcik, R. ; Buishand, T.A. - \ 2003
    Journal of Hydrology 273 (2003). - ISSN 0022-1694 - p. 69 - 80.
    neerslag - regen - luchttemperatuur - stochastische modellen - nederland - precipitation - rain - air temperature - stochastic models - netherlands - daily precipitation - rhine basin - model - series
    The joint simulation of time series of 6-hourly precipitation and temperature using nearest-neighbour resampling is studied for Maastricht, the Netherlands. Two resampling schemes are considered: (i) straightforward resampling of 6-hourly values, and (ii) resampling of daily values followed by disaggregation into 6-hourly values using the method of fragments. Second-order statistics of the simulated values are compared with those in the observed data. It appeared that straightforward resampling of 6-hourly values does not adequately preserve the slow decay of the autocorrelation functions of precipitation and temperature. As a result the standard deviations of the monthly precipitation totals and monthly average temperature are strongly underestimated. A negative bias also shows up in the quantiles of the multi-day seasonal maximum precipitation amounts. The autocorrelation coefficients and the standard deviations of the monthly values are much better reproduced if the daily values are generated first. A good correspondence between the historical and simulated distributions of the seasonal maximum precipitation amounts is also achieved with this alternative resampling scheme. (C) 2003 Elsevier Science B.V. All rights reserved.
    VIDENTE 1.1: a graphical user interface and decision support system for stochastic modelling of water table fluctuations at a single location; includes documentation of the programs KALMAX, KALTFN, SSD and EMERALD and introductions to stochastic modelling; 2nd rev. ed
    Bierkens, M.F.P. ; Bron, W.A. ; Knotters, M. - \ 2002
    Wageningen : Alterra (Alterra-rapport 613) - 184
    grondwaterspiegel - bodemwater - tijdreeksen - stochastische modellen - modellen - beslissingsondersteunende systemen - automatisering - grondwaterstand - simulatiemodel - software - statistiek - water table - soil water - time series - stochastic models - models - decision support systems - software
    A description is given of the program VIDENTE. VIDENTE contains a decision support system to choose between different models for stochastic modelling of water-table depths and a graphical user interface to facilitate operating and running four implemented models: KALMAX, KALTFN, SSD and EMERALD. In self-contained parts each of these models is described. These descriptions also include an introduction to the practice of stochastic modelling. As each of the models can also be used in a standalone fashion, i.e. outside VIDENTE, input formats for each model are also given.
    Release of additives from packaging plastics
    Helmroth, I.E. - \ 2002
    Wageningen University. Promotor(en): W.M.F. Jongen; J.A. Wesselingh; M. Dekker. - S.l. : S.n. - ISBN 9789058087379 - 99
    verpakkingsmaterialen - voedselverpakking - kunststoffen - migratie - diffusie - diffusiemodellen - stochastische modellen - toevoegingen - packaging materials - food packaging - plastics - migration - diffusion - diffusion models - stochastic models - additives

    Keywords : migration, diffusion, additives, polymer, low density polyethylene, polymer swelling, Fick, stochastic modelling

    The diffusion of small molecules from polymers into food is studied. A better understanding of this process is important for the development of mathematical models to predict migration from packaging plastics into food. To study the effect of food absorption by the plastic on diffusion, the simultaneous diffusion of a migrant (Irganox 1076) and a solvent in low density polyethylene (LDPE) were measured. The migrant diffuses out of the polymer, while the solvent is diffusing inwards. For solvents with low molar mass the diffusion coefficient of Irganox 1076 increases with increasing solvent uptake. No increase in diffusion coefficient was found upon uptake of tri-glycerides such as olive oil. A method using microtoming and GC-analysis is tested for the measurement of migrant concentration profiles inside the polymer. The diffusion of Irganox 1076 and solvent in LDPE have been measured as a function of time. The Fick equation with a migrant diffusivity depending on the solvent concentration gives a good description of the results for isooctane and n -heptane. The description is less good for the measurements with cyclohexane (when the polymer swells strongly). The use of predictive modelling for legislative purposes is evaluated for a deterministic, a worst-case and a new stochastic approach. All approaches give a reasonable, but rough, estimation of the diffusion coefficient. The new stochastic approach has the advantage that an entire probability distribution may be obtained.

    Data assimilation by non-parametric local density estimation
    Torfs, P.J.J.F. ; Loon, E. van; Wójcik, R. ; Troch, P.A. - \ 2002
    In: Developments in Water Science : the XIVth International Conference on Computational Methods in Water Resources , Delft, The Netherlands, 23-28 June 2002 / S.M. Hassanizadeh, W.G. Gray and G.F. Pinder, Vol. 2 Amsterdam : Elsevier Science - ISBN 9780444509758 - p. 1355 - 1362.
    wiskundige modellen - stochastische modellen - hydrologie - hydrology - mathematical models - stochastic models
    In this paper, the use of Parzan densities in the different stages of an general non linear (ensemble) Kalman filter is discussed
    Development of a Stochastic Model of Rainfall for Radar Hydrology
    Uijlenhoet, R. - \ 2002
    Wageningen : Wageningen Agricultural University (Rapport / Wageningen University, Environmental Sciences, Sub-department Water Resources 110) - 54
    hydrologie - stochastische modellen - radar - neerslag - regen - remote sensing - meteorologie - hydrology - stochastic models - radar - precipitation - rain - remote sensing - meteorology
    Modelleringstechnieken gereed voor voedingsmiddelenproduktie
    Sman, R. van der - \ 2001
    Voedingsmiddelentechnologie 34 (2001)11. - ISSN 0042-7934 - p. 16 - 17.
    stochastische modellen - wiskundige modellen - voedselverwerking - voedseltechnologie - computer software - berekening - computers - stochastic models - mathematical models - food processing - food technology - calculation
    Regionalised time series models for water table depths
    Knotters, M. - \ 2001
    Wageningen University. Promotor(en): P.A. Troch; M.F.P. Bierkens. - S.l. : S.n. - ISBN 9789058084781 - 153
    grondwaterspiegel - grondwaterstand - meting - tijdreeksen - statistische analyse - stochastische modellen - simulatiemodellen - nauwkeurigheid - digitaal terreinmodel - water table - groundwater level - measurement - time series - statistical analysis - stochastic models - simulation models - accuracy - digital elevation model

    Index words: groundwater head, time series analysis, physical interpretation, resampling, stochastic simulation, accuracy, quantified uncertainty

    Because of its shallow depths, the water table is of significant importance for agriculture and nature conservation in the Netherlands. Water management therefore requires accurate information on the spatial and temporal variations of the water table depth. This information is preferably expressed in terms of probabilities, in order to enable risk assessment. Furthermore, to support strategic decisions in water policy, the information on the water table dynamics should reflect the prevailing climatic conditions (say, the average weather over a 30-year period). Since the number of observation wells and the lengths of the time series are limited for regional studies, spatio-temporal prediction methods should be able to incorporate additional measurements and additional information related to the water table depth.

    Stochastic methods are devised for estimating fluctuation characteristics representing the prevailing climatic and hydrologic conditions. These methods are based on various models for the dynamic relationship between precipitation surplus and water table depth: a physical descriptive, one-dimensional model, SWATRE, supplemented with a univariate time series model for the noise (SWATRE+ARMA), linear transfer function-noise models (TFN), dynamic regression models (DR) or autoregressive exogenous variable models (ARX), and nonlinear threshold autoregressive models (TARSO). These models are applied to extrapolate observed time series of water table depths, by using observed input series on the precipitation surplus having a length of 30 years. Uncertainty is accounted for by generating a large number of realisations using the stochastic model component. The models perform only slightly differently in simulating water table depths, despite their clearly different theoretical starting points. It is shown that a first-order ARX model can easily be expressed in terms of a water balance for a soil column. Moreover, the physically based ARX model can be applied in predicting the effects of human interventions in the hydrological regime on the water table dynamics.

    The ARX model is regionalised to a RARX model, by making its parameters dependent of the spatial co-ordinates. Because of their physical basis, the RARX model parameters can be guessed from auxiliary information such as a digital elevation model (DEM), digital topographic maps and digitally stored soil profile descriptions. Next, the guessed RARX parameters are used to transform a precipitation surplus series into a series of water table depths. Predictions obtained by this 'direct' method are compared with observed water table depths. The observed errors are used to correct the final predictions for systematic errors, and to perform stochastic simulations ('indirect' method). The RARX model is incorporated into a space-time Kalman filter algorithm, which enables predictions conditional to observed water table depths. A cross-validation experiment shows that Kalman filter approaches predict the temporal variation of the water table depths relatively precise, whereas the 'indirect' method yields relatively accurate estimates of expected water table depths, since systematic errors are small. The uncertainty about the temporal variation of the water table depth is underestimated by all methods evaluated. Given the sampling design, the accuracy of the uncertainty about the mean water table depth could not be assessed. Besides efforts to reduce uncertainty, it would be interesting to optimise sampling designs in order to obtain accurate estimates of uncertainty.

    VIDENTE: a graphical user interface and decision support system for stochastic modelling of water table fluctuations at a single location; includes documentation of the programs KALMAX, KALTFN, SSD and EMERALD and introductions to stochastic modellin
    Bierkens, M.F.P. ; Bron, W.A. - \ 2000
    Wageningen : Alterra (Alterra-rapport 118) - 183
    grondwaterstand - grondwaterspiegel - modellen - stochastische modellen - simulatie - tijdreeksen - analyse van besluiten - beslissingsondersteunende systemen - groundwater level - water table - models - stochastic models - simulation - time series - decision analysis - decision support systems
    The VIDENTE program contains a decision support system (DSS) to choose between different models for stochastic modelling of water-table depths, and a graphical user interface to facilitate operating and running four implemented models: KALMAX, KALTFN,SSDS and EMERALD. In self-contained parts each of these models is described. These descriptions also include introductions to the practice of stochastic modelling. As each of the models can also be used in a stand-alone fashion, i.e. outside VIDENTE, input formats for each model are also given.
    Non-linear stochastic methods for discharge prediction
    Wójcik, R. - \ 1999
    Warsaw University of Life Sciences (SGGW). Promotor(en): S. Ignar, co-promotor(en): P.A. Troch. - Wageningen : Landbouwuniversiteit Wageningen - 152
    afvoer - voorspellen - stochastische modellen - modellen - hydrologie van stroomgebieden - hydrologie - waterlopen - nederland - gelderland - discharge - forecasting - stochastic models - models - catchment hydrology - hydrology - streams - netherlands - gelderland
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