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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    Kalibratie pH meter Inolab
    Bom, Jesse ; Dijksman, J.A. ; Lageschaar, Luuk ; Galen, Martijn van; Hoogendam, C.W. ; Wegh, R.A.J. - \ 2016
    Wageningen : Wageningen UR
    ph - zuurgraad - meetinstrumenten - instrumenten (meters) - kalibratie - ph - acidity - indicating instruments - instruments - calibration
    Instructievideo over de kalibratie van de InoLab pH meter
    Kalibratie pH meter Schott
    Bom, Jesse ; Dijksman, J.A. ; Lageschaar, Luuk ; Galen, Martijn van; Hoogendam, C.W. ; Wegh, R.A.J. - \ 2016
    Wageningen : Wageningen UR
    ph - zuurgraad - meetinstrumenten - instrumenten (meters) - kalibratie - ph - acidity - indicating instruments - instruments - calibration
    Instructievideo over de kalibratie van de Schott pH meter
    Statistical modelling for exposure measurement error with application to epidemiological data
    Agogo, G.O. - \ 2016
    Wageningen University. Promotor(en): Hendriek Boshuizen; Fred van Eeuwijk, co-promotor(en): Hilko van der Voet. - Wageningen : Wageningen University - ISBN 9789462576223 - 160
    calibration - regression analysis - exposure assessment - validity - simulation models - statistical bias - epidemiology - kalibratie - regressieanalyse - blootstellingsbepaling - geldigheid - simulatiemodellen - statistische vertekening - epidemiologie

    Background Measurement error in exposure variables is an important issue in epidemiological studies that relate exposures to health outcomes. Such studies, however, usually pay limited attention to the quantitative effects of exposure measurement error on estimated exposure-outcome associations. Therefore, the estimators for exposure-outcome associations are prone to bias. Existing methods to adjust for the bias in the associations require a validation study with multiple replicates of a reference measurement. Validation studies with multiple replicates are quite costly and therefore, in some cases only a single–replicate validation study is conducted besides the main study. For a study that does not include an internal validation study, the challenge in dealing with exposure measurement error is even bigger. The challenge is how to use external data from other similar validation studies to adjust for the bias in the exposure-outcome association. In accelerometry research, various accelerometer models have currently been developed. However, some of these new accelerometer models have not been properly validated in field situations. Despite the widely recognized measurement error in the accelerometer, some accelerometers have been used to validate other instruments, such as physical activity questionnaires, in measuring physical activity. Consequently, if an instrument is validated against the accelerometer, and the accelerometer itself has considerable measurement error, the observed validity in the instrument being validated will misrepresent the true validity.

    Methodology In this thesis, we adapted regression calibration to adjust for exposure measurement error for a single-replicate validation study with zero-inflated reference measurements and assessed the adequacy of the adapted method in a simulation study. For the case where there is no internal validation study, we showed how to combine external data on validity for self-report instruments with the observed questionnaire data to adjust for the bias in the associations caused by measurement error in correlated exposures. In the last part, we applied a measurement error model to assess the measurement error in physical activity as measured by an accelerometer in free-living individuals in a recently concluded validation study.

    Results The performance of the proposed two-part model was sensitive to the form of continuous independent variables and was minimally influenced by the correlation between the probability of a non-zero response and the actual non-zero response values. Reducing the number of covariates in the model seemed beneficial, but was not critical in large-sample studies. We showed that if the confounder is strongly linked with the outcome, measurement error in the confounder can be more influential than measurement error in the exposure in causing the bias in the exposure-outcome association, and that the bias can be in any direction. We further showed that when accelerometers are used to monitor the level of physical activity in free-living individuals, the mean level of physical activity would be underestimated, the associations between physical activity and health outcomes would be biased, and there would be loss of statistical power to detect associations.

    Conclusion The following remarks were made from the work in this thesis. First, when only a single-replicate validation study with zero-inflated reference measurements is available, a correctly specified regression calibration can be used to adjust for the bias in the exposure-outcome associations. The performance of the proposed calibration model is influenced more by the assumption made on the form of the continuous covariates than the form of the response distribution. Second, in the absence of an internal validation study, carefully extracted validation data that is transportable to the main study can be used to adjust for the bias in the associations. The proposed method is also useful in conducting sensitivity analyses on the effect of measurement errors. Lastly, when “reference” instruments are themselves marred by substantial bias, the effect of measurement error in an instrument being validated can be seriously underestimated.

    Kalibratie van het Landelijk KRW-Verkenner Model 2.0
    Mulder, H.M. ; Cleij, P. - \ 2015
    Deltares - 41
    kaderrichtlijn water - kalibratie - modelleren - stikstofretentie - voedingsstoffenretentie - fosfor - water framework directive - calibration - modeling - nitrogen retention - nutrient retention - phosphorus
    Bij de laatste validatie van het Landelijk KRW-Verkenner Model (Cleij et al. 2014) is gebleken dat de concentraties voor N-totaal en P-totaal vaak matig tot slecht voorspeld worden. Eén van de manieren om de voorspellende waarde van een model te verhogen is kalibratie. Het LKM is echter modelparameter-arm, en de enige 'knoppen', waaraan wat betreft modelparameters gedraaid kan worden zijn de parameters van het eerste-orde afbraak proces voor -totaal en -totaal de a raakconstante ij en de temperatuurco ici nt De tot nu toe gebruikte retentieparameters zijn afkomstig van een vertaling van de retentieparameters van het KRW-ECHO systeem naar de retentieparameters voor de KRWVerkenner (Roovaart et al. 2012). Het in dit rapport beschreven onderzoek is via kalibratie gezocht naar een nieuwe set retentieparameters voor N-totaal en P-totaal, uitgaande van de tot nu toe gehanteerde parameterwaarden met als doel het voorspellend vermogen van het LKM op dit punt te verbeteren.
    Reactie op het artikel ‘Controle van kalibratiegegevens’
    Knotters, M. ; Hoogland, T. - \ 2013
    Stromingen : vakblad voor hydrologen 19 (2013)3/4. - ISSN 1382-6069 - p. 125 - 126.
    hydrologie - grondwaterstand - watervoorziening - informatiesystemen - kalibratie - hydrology - groundwater level - water supply - information systems - calibration
    Grondwaterstandsinformatie van goede kwaliteit vinden wij belangrijk. Iedere inspanning om deze kwaliteit vast te stellen en te verbeteren juichen wij toe, vooral als zo’n inspanning wetenschappelijk degelijk is onderbouwd. Wat betreft dat laatste willen wij graag twee opmerkingen plaatsen bij het artikel ‘Controle van kalibratiegegevens’ van Jaco van der Gaast in Stromingen 19(2), pag. 85-90
    On data requirements for calibration of integrated models for urban water systems
    Langeveld, J. ; Nopens, I. ; Schilperoort, R. ; Benedetti, L. ; Klein, J.J.M. de; Amerlinck, Y. ; Weijers, S. - \ 2013
    Water Science and Technology 68 (2013)3. - ISSN 0273-1223 - p. 728 - 736.
    afvalwaterbehandeling - afvalwaterbehandelingsinstallaties - riolering - watersystemen - stedelijke gebieden - monitoring - kalibratie - modellen - modelleren - oppervlaktewaterkwaliteit - noord-brabant - waste water treatment - waste water treatment plants - sewerage - water systems - urban areas - monitoring - calibration - models - modeling - surface water quality - noord-brabant - practical identifiability - simulation-models - optimization - uncertainty - quality
    Modeling of integrated urban water systems (IUWS) has seen a rapid development in recent years. Models and software are available that describe the process dynamics in sewers, wastewater treatment plants (WWTPs), receiving water systems as well as at the interfaces between the submodels. Successful applications of integrated modeling are, however, relatively scarce. One of the reasons for this is the lack of high-quality monitoring data with the required spatial and temporal resolution and accuracy to calibrate and validate the integrated models, even though the state of the art of monitoring itself is no longer the limiting factor. This paper discusses the efforts to be able to meet the data requirements associated with integrated modeling and describes the methods applied to validate the monitoring data and to use submodels as software sensor to provide the necessary input for other submodels
    Calibration and validation of land-use models
    Vliet, J. van - \ 2013
    Wageningen University. Promotor(en): Arnold Bregt. - S.l. : s.n. - ISBN 9789461734433 - 162
    landgebruik - modellen - kalibratie - verandering - beoordeling - stedelijke gebieden - modelleren - land use - models - calibration - change - assessment - urban areas - modeling

    Land use is constantly changing. For example, urban areas expand as a result of population growth, cropping patterns change to fulfil the demand for bioenergy and natural vegetation recovers in locations where farmers cease to farm. Understanding these changes is pivotal to explore future land-use scenarios and to design spatial policies. Land-use models are increasingly being used for these purposes. They function as virtual laboratories in which scientists or policy analysts can conduct experiments. In order to reliably apply models for these purposes, they need to be calibrated, where calibration is the adjustment of parameters to improve the model’s performance. Consequently, the value of modelled land-use scenarios and policy assessments depends on the quality of the calibration. Assessment of the quality of the calibration is termed validation, and is ideally performed independently in the sense that the data that is used for validation has not been used for calibration.

    The development of a land-use model can be described by four sequential phases: analysis and conceptual modelling, computer programming of the conceptual model, calibration of the computerized model, and experimentation with the calibrated model. The first three phases all have their own evaluation procedures: conceptual validation, code verification and operational validation, respectively. Operational validation provides insights into the strengths and weaknesses of a particular model application, and sometimes it can suggest directions for improvement. However, available assessment methods have limitations for their application in land-use modelling. Therefore, there is a demand to develop and apply more appropriate methods. The work presented in this thesis first considers the properties of land-use models that are important for their assessment, and subsequently presents and applies several methods that can be used for this assessment.

    Many land-use changes are directly or indirectly the result of human decisions. However, human decisions are inherently uncertain, and therefore land-use models cannot be expected to simulate these land-use changes exactly. This is acknowledged by many land-use models as they use a stochastic component to simulate land-use changes. Therefore, land-use models should not only be validated on their predictive accuracy, their capacity to accurately allocate land-use changes on the map, but also on their process accuracy, their capacity to realistically simulate land-use change processes. Moreover, many models start from an initial land-use map and simulate changes relative to this map. The amount of change for a simulation is typically small relative to the entire map, which means that a large part of the result is caused by persistence. For this reason, a benchmark, such as a naive predictor, is required to properly asses the accuracy of simulation results. This benchmark can be implicit to the assessment method itself, or explicit, i.e. another land-use model which serves as a reference model. Outperforming the benchmark can be considered a minimum threshold to pass; however, it cannot directly inform whether a model is acceptable as this depends on the purpose of the model, the requirements of the study and the application domain.

    The predictive accuracy of a land-use model is typically assessed by comparing a simulation result with the actual land-use map at the end of a simulation. A common method for this is the Kappa statistic, which expresses the agreement between two land-use maps corrected for the expected agreement from a random allocation given the distribution of class sizes. However, this is not an appropriate reference level to assess the predictive accuracy of land-use models, because it does not account for the amount of change. This thesis presents Kappa Simulation, a new map-comparison method that is identical in form to Kappa, but which instead applies a more appropriate reference model based on random allocation of class transitions relative to the initial map. This implicitly accounts for the amount of change, which truly allows gauging the predictive accuracy of changes in land-use models. However, Kappa Simulation cannot differentiate between near-hits and complete misses, while this distinction is often very relevant for land-use modellers. This thesis therefore presents Fuzzy Kappa Simulation. This statistic is an improvement of Kappa Simulation, as it applies a fuzzy interpretation of class transitions and their locations. This means that it can account for near-hits, which makes it arguably the most suitable map comparison method to assess the predictive accuracy of land-use models.

    Because of the intrinsic uncertainty underlying land-use change processes, a realistic land-use model does not necessarily generate a high predictive accuracy, which justifies a separate assessment of its process accuracy. Ideally, process accuracy is assessed directly from the values of model parameters. However, it is often impossible to observe real-world values for these parameters because drivers for land-use changes are correlated or they cannot be measured. Therefore, the process accuracy is typically assessed indirectly from the land-use patterns generated by the model. Two groups of methods exist to characterize land-use patterns: landscape metrics and fractal metrics. Landscape metrics are a collection of algorithms that have been applied in landscape ecology to characterize land-use patterns. In this thesis, landscape metrics have been used to compare the simulated land-use map with the observed land-use map instead. Fractal metrics, which have their origin in complexity science, are another type of measures to characterize regularities in (urban) land-use patterns. Examples are power-law distributions for urban clusters and fractal dimensions of patches of urban land. Moreover, fractal metrics can be interpreted in absolute terms since they represent general regularities in urban systems for which values are known from literature. Therefore, fractal metrics also allow evaluation of the process accuracy of a synthetic application for which no observed land-use pattern is available for comparison.

    Neighbourhood rules represent the influence of the existing land-use distribution on the location of land-use changes. This includes the persistence, conversion and attraction/repulsion of land uses in the neighbourhood of a location. Because neighbourhood rules cannot be estimated directly from data, they need to be set in a calibration procedure. The work in this thesis indicates that agents consider their neighbourhood at different spatial scales: the direct vicinity of a location has a strong influence on the allocation of new urban land, but neighbourhood rules over larger distance – typically the size of urban regions – also improve the model performance. This thesis also discusses a special type of neighbourhood rules: rules describing the influence of the existing activity distribution on the allocation of activity changes, where activities denote a quantity or density related to a land use, such as inhabitants for residential land use. This study shows that relatively simple rules can grow a realistic urban settlement structure, which confirms that neighbourhood rules improve the process accuracy of a land-use model.

    It should be noted that while the methods presented and applied in this thesis are objective, the selection of assessment methods remains subjective. Moreover, because no method is yet capable of describing land-use patterns satisfactorily, more subjective methods such as visual assessment of simulation results or interpretation of parameter values remain of added value in the calibration and validation of land-use models.

    Meten met ion specifieke meters: Praktijkervaringen in een gerbera- en paprikateelt
    Blok, C. ; Steenhuizen, J.W. ; Winkel, A. van; Ayik, A. ; Lekkerkerk, H. ; Klein, P. - \ 2012
    Bleiswijk : Wageningen UR Glastuinbouw (Rapporten GTB 1197) - 44
    glastuinbouw - cultuurmethoden - kastechniek - meetsystemen - meetapparatuur - kalibratie - gewasproductie - proefprojecten - efficiëntie - nederland - greenhouse horticulture - cultural methods - greenhouse technology - measurement systems - meters - calibration - crop production - pilot projects - efficiency - netherlands
    Het gebruik van een ionspecifieke meter in de tuinbouw maakt het naar verwachting mogelijk de behoefte van het gewas per dagdeel in beeld te brengen. Vervolgens kan snel en per element worden bijgestuurd. Hierdoor kan de uitstoot van meststoffen omlaag en kan mogelijk teeltvoordeel worden behaald in de vorm van productie of kwaliteit. Doelstellingen van dit project zijn: • Een gebruiksvoorschrift voor plaatsing, onderhoud en controle van de meters. • Het registreren en analyseren van voedingsaanpassingen met bestaande techniek. • Het beoordelen van de gewasrespons op voedingsaanpassingen.
    OSPAR-OIC Intercalibration Study on metals in produced water samples: a QUASIMEME Laboratory performance Study
    Velzeboer, I. ; Crum, S.J.H. ; Karman, C.C. - \ 2009
    IJmuiden : IMARES (Final report / Wageningen IMARES C014/09) - 23
    mariene constructies - offshore - marien milieu - zware metalen - kalibratie - kwantitatieve technieken - instrumenten (meters) - monitoring - bemonsteren - kwaliteitsnormen - verontreinigd water - marine structures - offshore - marine environment - heavy metals - calibration - quantitative techniques - instruments - monitoring - sampling - quality standards - polluted water
    The Offshore Industry Committee (OIC) of OSPAR discussed in its 2008 meeting the reporting of inputs of metals from offshore installations. INPUT is currently compiling data and information on discharges and emissions to the OSPAR maritime area to be used in the Quality Status Report (QSR). This includes an assessment of the inputs of cadmium, lead, and mercury in produced water. Initial estimates were considered by OIC to be unrepresentative, since many of the analyses recorded values below the analytical detection limits of the techniques used. Given the urgency of producing reliable information that could be used to prepare estimates of inputs of cadmium, lead, and mercury for the QSR, OIC agreed to conduct a further study, using the assistance of Quasimeme, to ensure quality assurance from sampling to measurement and reporting. This report focuses on the intercalibration exercise.
    Hydrologie op basis van karteerbare kenmerken
    Gaast, J.W.J. van der; Massop, H.T.L. ; Vroon, H.R.J. ; Staritsky, I.G. - \ 2007
    H2O : tijdschrift voor watervoorziening en afvalwaterbehandeling 40 (2007)19. - ISSN 0166-8439 - p. 65 - 68.
    hydrologie - grondwaterstand - simulatiemodellen - kalibratie - karteringen - toepassingen - klimaatverandering - bodemwaterbeweging - stroomgebieden - nederland - onderzoeksprojecten - hydrology - groundwater level - simulation models - calibration - surveys - applications - climatic change - soil water movement - watersheds - netherlands - research projects
    Onderzoek van de Commissie Waterbeheer 21e Eeuw (WB21) heeft o.a. geresulteerd in een wateropgave. In dit onderzoek is een methode ontwikkeld waarmee inzicht kan worden verkregen in de hydrologische variabelen van gebieden in Nederland. De methode kan een basis vormen voor het in beeld krijgen van de effecten van waterhuishoudkundige maatregelen en daarmee aangeven in hoeverre kan worden voldaan aan de wateropgave. In eerste instantie is een landsdekkende ruimtelijke schematisatie uitgevoerd en is de Gt-kaart 1 : 50 000 geactualiseerd. Vervolgens zijn SWAP-modellen voor een groot aantal mogelijke situaties geparametriseerd en gekalibreerd. Middels metamodellen, welke van de modelresultaten zijn afgeleid, kunnen verschillende hydrologische variabelen in kaart worden gebracht. Het kan hierbij bijvoorbeeld gaan om kwel, afvoer, berging in zowel grondwater als oppervlaktewater of fluxen. Validatie van enkele variabelen geeft aan dat de gegenereerde kaarten plausibel zijn
    Informatieblad Mest en Mineralen : DOVE 1. Nieuwe modelkalibratie- en validatietechniek voor het kwantificeren van de nutriëntenbelasting van het oppervlaktewater: veenweidegebied
    Walvoort, D.J.J. ; Hendriks, R.F.A. - \ 2006
    Wageningen : Alterra (Informatieblad mest en mineralen 02)
    grondwaterstroming - modellen - kalibratie - dierlijke meststoffen - uitspoelen - voedingsstoffenbalans - scenario-analyse - groundwater flow - models - calibration - animal manures - leaching - nutrient balance - scenario analysis
    Het Dove-project (Diffuse belasting van het Oppervlaktewater in de Veehouderij) heeft tot doel om de bijdrage van de melkveehouderij aan de diffuse nutriëntenbelasting (stikstof en fosfor) van het oppervlaktewater te kwantificeren in een veenweidegebied, een zandgebied en een kleigebied. Daarbij is ondermeer gebruik gemaakt van modellen die het transport van water en stikstof- en fosforverbindingen kunnen beschrijven. Deze procesmodellen maken het mogelijk om uitspraken te doen over de nutriëntenbelasting op tijdstippen waarop en voor omstandigheden waarvoor geen meetgegevens beschikbaar zijn (bijvoorbeeld in scenario- analyses). In dit informatieblad is beschreven hoe de procesmodellen zijn gekalibreerd en gevalideerd voor een proefperceel in het veenweidegebied. Hierbij zijn nieuwe methoden gehanteerd die tot voor kort niet gebruikelijk waren. Een toepassing van de gekalibreerde en gevalideerde modellen voor het analyseren van het hydrologische systeem en voor het doorrekenen van scenario's wordt beschreven in respectievelijk B0-05-infoblad 03 en B0-05-infoblad 04.
    Calibratie van de reductiefuncties in een eenvoudig denitrificatiemodel
    Heinen, M. ; Zwart, K.B. ; Hummelink, E.W.J. - \ 2005
    Wageningen : Alterra (Alterra-rapport 1216) - 33
    denitrificatie - bodem - nitraten - temperatuur - verzadiging - modellen - kalibratie - stikstof - zand - klei - veengronden - denitrification - soil - nitrates - temperature - saturation - models - calibration - nitrogen - sand - clay - peat soils
    In veel stikstofmodellen wordt denitrificatie vaak gemodelleerd met behulp van eenvoudige rekenregels. Actuele denitrificatie is gelijk aan de potentiële denitrificatie gereduceerd door het actuele nitraatgehalte, de actuele water verzadigingsgraad en de actuele bodemtemperatuur. Deze reductie vindt plaats aan de hand van een drietal reductiefuncties, welke gezamenlijk vier onbekende parameters bevatten. In dit rapport wordt beschreven hoe deze vier parameters zijn bepaald voor een zestal locaties in Nederland door denitrificatie te meten aan grondmonsters die onderling verschillen in nitraatgehalte, verzadigingsgraad en temperatuur. Uit deze studie wordt geconcludeerd dat de parameters locatiespecifiek zijn, en dat er geen relatie duidelijk wordt tussen de waarden van deze parameters en de hoofdgrondsoorten zand, veen en klei
    Calibration in a Bayesian modelling framework
    Jansen, M.J.W. ; Hagenaars, T.H.J. - \ 2004
    In: Bayesian Statistics and Quality Modelling in the Agro-Food Production Chain / Boekel, van, Stein, A., Bruggen, van, Dordrecht : Kluwer (Wageningen UR Frontis series vol. 3) - ISBN 9781402019166 - p. 47 - 55.
    bayesiaanse theorie - monte carlo-methode - wiskundige modellen - kalibratie - onzekerheid - beslissingsondersteunende systemen - bayesian theory - monte carlo method - mathematical models - calibration - uncertainty - decision support systems
    Bayesian statistics may constitute the core of a consistent and comprehensive framework for the statistical aspects of modelling complex processes that involve many parameters whose values are derived from many sources. Bayesian statistics holds great promises for model calibration, provides the perfect starting point for uncertainty analysis and provides an excellent starting point for decision support. The purpose of this paper is to draw attention to problems and possible solutions. It is not our intention to introduce ready-for-use methods
    Test of the Boreal Gasfinder 2.0 for methane measurements and Vaisala AMT-100 sensor for ammonia measurements in animal houses
    Hofschreuder, P. ; Ploegaert, J.P.M. ; Starmans, D.A.J. ; Top, S.G. van den - \ 2004
    Wageningen : Agrotechnology & Food Innovations, WUR (Rapport / Agrotechnology & Food Innovations nr. 295) - ISBN 9789067548557 - 48
    meteorologische instrumenten - ammoniak - methaan - emissie - huisvesting, dieren - kalibratie - binnenklimaat - meteorological instruments - ammonia - methane - emission - animal housing - calibration - indoor climate
    IJking Reinkstuw in de Buurserbeek
    Boiten, W. ; Dommerholt, A. - \ 2003
    Wageningen : Sectie Waterhuishouding (Rapport / Wageningen Universiteit, Omgevingswetenschappen, Sectie Waterhuishouding 117) - 31
    stuwen - afvoer - kalibratie - simulatie - hydrologie - hydraulische systemen - waterlopen - nederland - gelderland - twente - weirs - discharge - calibration - simulation - hydrology - hydraulic structures - streams - netherlands - gelderland - twente
    Surface fluxes over natural landscapes using scintillometry
    Meijninger, W.M.L. - \ 2003
    Wageningen University. Promotor(en): Bert Holtslag, co-promotor(en): H.A.R. de Bruin. - Wageningen : Wageningen Universiteit - ISBN 9789058088857 - 164
    meteorologische instrumenten - remote sensing - energiebalans - turbulentie - kalibratie - grenslaag - scintillometrie - meteorological instruments - remote sensing - energy balance - turbulence - calibration - boundary layer - scintillometry
    Motivated by the demand for reliable area-averaged fluxes associated with natural landscapes this thesis investigates a relative new measurement technique known as the scintillation method. For homogeneous areas the surface fluxes can be derived with reasonable accuracy. However, fluxes representative for large natural landscapes (comparable to the horizontal grid box size of numerical models or the pixel size of satellite imagers) are more difficult to obtain because at these scales the surface is mostly heterogeneous. At this moment only a few techniques are available that can provide flux information at spatial scales of several kilometres, such as the scintillation method. Based on the propagation statistics of EM radiation that has propagated through the atmosphere over a horizontal path of several kilometres it is possible to derive the surface fluxes of sensible heat, water vapour and momentum. In this study a Large Aperture Scintillometer (LAS) has been developed that can be used over distances up to 5 km. Since the LAS operates at a near-infrared wavelength hence it is primarily sensitive to temperature related scintillations, from which the sensible heat flux can inferred. In this thesis the following aspects regarding the LAS are investigated: The performance of the LAS over heterogeneous land surfaces The reliability of area-averaged water vapour fluxes provided by the LAS and in combination with a radio wave scintillometer over heterogeneous land surfaces Its practical applicability and usefulness in other scientific areas For the derivation of the sensible heat flux from the LAS signal one must rely on the Monin-Obukhov Similarity Theory (MOST). However, MOST requires homogeneous surface conditions. The question arises whether the LAS can be used over distances of several kilometres, since at these scales the surface is mostly heterogeneous. In order to test experimentally the applicability of the LAS over heterogeneous areas and the reliability of the derived fluxes of sensible heat a field campaign was carried out in Flevoland (The Netherlands). The general characteristics of the Flevoland area are as follows: a vast and completely flat area covered by four crops in a chessboard configuration of patches of 500 m ´ 250 m. Based on the horizontal length scale of the patches this landscape is classified as a Type A landscape, meaning that only the lower part of the surface layer is affected by the irregularities. Eddy covariance (EC) measurements were performed over the main types of farmland to provide to aggregation independent area-averaged fluxes. The EC observations reveal that the heterogeneity in the Flevoland area is primarily the result of spatial variations in the thermal properties. The fluxes of two large aperture scintillometers, installed at a height of 11.6 m and 20.4 m, respectively, show a close resemblance with the area-averaged EC fluxes, especially for the upper LAS. The lower LAS shows a slight underestimation of the sensible heat flux of approximately 7%. This underestimation is assessed using a blending height approach and an analytical footprint model for estimating the source areas and the associated fluxes. The blending height is considered as the level above the surface where the influences of the patches gradually decay. It is found, using a heuristic model that the blending height for the Flevoland area varies between 9 m and 14 m. Based on the found blending heights it is concluded that the upper LAS always measured above the blending height, which is consistent with the depicted LAS results. For the lower LAS the situation is more complicated as the individual fields influence the measurements, suggesting that the MOST may be violated. After dividing the Flevoland area into 8 wind-sectors and re-arranging the area-averaged fluxes for the entire area and for the 8 source areas, a closer agreement is found. These results indicate that from a LAS, which measures just below the blending height, still reliable area-averaged fluxes can be derived and that the violation of MOST is small. Next the performance of a combined LAS and radio wave scintillometer (LAS-RWS) over a heterogeneous land surface is studied. Although this scintillation technique, known as the two-wavelength method, provides both the sensible heat flux and the water vapour flux, most attention is focussed at the water vapour flux. The water vapour flux provided by a `stand-alone` LAS is evaluated also. In the latter case the water vapour flux is estimated as the residual of the surface energy balance equation using a simple parameterisation scheme (based on global radiation data) for estimating the area-averaged available energy (i.e. Rn - Gs). The LAS-RWS study is based also on data of the Flevoland experiment. As mentioned before the EC observations collected in Flevoland reveal that the heterogeneity in the area is primarily the result of spatial variations in the thermal properties and likewise in the buoyant production term of MOST. First, the water vapour fluxes from the combined LAS-RWS system are investigated. It was found that these fluxes agree well with the area-averaged water vapour flux aggregated from the in-situ observations. The found scatter is explained to be caused by: closure failure of the energy balance for the EC measurements, the non-linearity between the structure parameters and the inferred fluxes, and low frequency water vapour absorption fluctuations that affect the RWS. Finally, the water vapour fluxes derived from the stand-alone LAS are discussed. These results show that the `stand-alone¿ LAS can provide also reliable estimates of the area-averaged water vapour flux over heterogeneous areas (type A). In order to study the operational aspects of the LAS two LAS devices and a small micrometeorological station were installed in the Gediz Basin near Menemen (Turkey) in 1998 as part of an international experiment. The main objective of this experiment was to compare actual evapotranspiration estimates based on satellite remote sensing methods, hydrological models and field methods. This thesis deals only with the field methods, i.e. the variance method and in particular the LAS. One LAS was set-up over a transect of the valley of the Gediz river basin. For the derivation of the sensible heat flux additional wind speed and temperature data are taken from a nearby meteorological station. In addition a small micro-meteorological station was placed at an irrigated cotton field. The fluxes for this site are inferred from collected temperature fluctuation data using the variance method. Due to experimental problems with a second LAS installed at the same site these data are excluded from this study. The presented time series of 24-hour average fluxes for the valley clearly shows the seasonal trend of the sensible heat flux, including the irrigation events. This time series demonstrates from an operational perspective that the LAS, which was operational during the entire growing season, is a robust and reliable instrument that requires only occasional servicing. Finally, it is investigated whether the LAS fluxes collected in Turkey can be used as `ground-truth` data in other scientific studies such as remote sensing. For that purpose a large number of surface flux maps are generated using the SEBAL remote sensing algorithm, and are compared with the LAS results. In this validation study the in-situ fluxes and radiation measurements of the irrigated cotton field are included also. The SEBAL fluxes are derived from moderate resolution AVHRR visible and thermal-infrared images taken from the NOAA-14 satellite. Both instantaneous and daily average sensible heat fluxes are determined for the entire growing season. It is found that the SEBAL based instantaneous fluxes agree closely with the in-situ fluxes for the cotton site. However, the results for the valley site, i.e. SEBAL versus LAS, reveal a discrepancy. The following reasons are offered: the scaling mismatch between the source area of the LAS and the pixel size of the raw AVHRR images; a possible distortion by the dry slopes in the relative narrow valley compared to the resolution of the AVHRR imager. Therefore a convincing validation of SEBAL for the valley cannot be done. Finally, the daily average sensible heat fluxes for the cotton field are compared. It is found that only during the irrigation period the daily average results agree. Not actually dry reference pixels, which lead to underestimated evaporative fractions, are suggested to be the reason for the observed difference.
    Karakterisering van de freatische grondwaterstand in Nederland; bepaling van de GxG en xG3 voor 1995 op puntlocaties
    Gaast, J.W.J. van der; Massop, H.T.L. - \ 2003
    Wageningen : Alterra (Alterra-rapport 819) - 83
    bodemwater - grondwaterspiegel - monitoring - modellen - kalibratie - soil water - water table - monitoring - models - calibration
    In dit onderzoek is de freatische grondwaterstand landelijk gekarakteriseerd zodat deze gegevens gebruikt kunnen worden voor kalibratie van hydrologische modellen. Met tijdreeksanalyse is de klimaatsrepresentatieve GHG en GLG bepaald voor peilbuislocaties. Daarnaast zijn de HG3 en de LG3 voor het kalenderjaar 1995 berekend. Op basis van stambuisregressie zijn veldmetingen van grondwaterstanden die gedurende de winter en de zomer op een groot aantal gerichte opnamelocaties zijn verzameld, omgezet naar gemiddelde grondwaterstandskarakteristieken. Er is een databestand opgezet dat bestaat uit ca. 3100 buislocaties en ca. 9400 gerichte opnamelocaties waarvoor de HG3-95, LG3-95, GHG en GLG alsmede de onzekerheid is gekwantificeerd.
    IJking Aflaatwerk naar het Twenthekanaal in Lochem
    Boiten, W. ; Dommerholt, A. - \ 2003
    Wageningen : Sectie Waterhuishouding (Rapport / Wageningen Universiteit, Omgevingswetenschappen, Sectie Waterhuishouding 114) - 31
    stuwen - afvoer - kalibratie - simulatie - kanalen - hydrologie - hydraulische systemen - nederland - gelderland - achterhoek - weirs - discharge - calibration - simulation - canals - hydrology - hydraulic structures - netherlands - gelderland - achterhoek
    Calibratie van model LINBAL voor zetmeelaardappelen
    Jansen, D. - \ 2002
    Wageningen : Plant Research International (Nota / Plant Research International 213) - 40
    fabrieksaardappelen - aardappelen - gewasgroeimodellen - simulatiemodellen - kalibratie - akkerbouw - starch potatoes - potatoes - crop growth models - simulation models - calibration - arable farming
    In dit rapport wordt de calibratie beschreven van het model LINBAL, ontwikkeld in het kader van het AgroBiokon project om de groei en productie van zetmeelaardappelen te kunnen simuleren.
    Bepaling van de lekweerstanden met SWAP-PEST
    Bakel, P.J.T. van - \ 2002
    In: Moderne modelkalibratie in de praktijk; het automatisch ijken van grondwatermodellen; bundel van lezingen die op 7 maart 2001 zijn gehouden tijdens een bijeenkomst van de Nederlandse Hydrologische Vereniging / Boukes, H., Utrecht : NHV - ISBN 9789080356559 - p. 99 - 107.
    bodemwater - infiltratie - grondwaterstroming - grondwaterspiegel - drainage - modellen - kalibratie - soil water - infiltration - water table - drainage - groundwater flow - models - calibration
    Voor landelijke milieuverkenningen is het nutriëntenuitspoelingsmodel STONE ontwikkeld. Hierbij wordt Nederland opgedeeld in een groot aantal plots die een combinatie zijn van unieke combinaties van de hydrologie (UC) en andere indelingscriteria. Per UC wordt met een 1-dimensionaal model SWAP de hydrologie van het topsysteem berekend. In dit model is de interactie tussen grond- en oppervlaktewater binnen de plot en het oppervlaktewatersysteem integraal opgenomen
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