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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    Rainfall over the Netherlands & beyond: a remote sensing perspective
    Rí́os Gaona, Manual Felipe - \ 2017
    Wageningen University. Promotor(en): R. Uijlenhoet, co-promotor(en): A. Overeem; H. Leijnse. - Wageningen : Wageningen University - ISBN 9789463432009 - 124
    rain - remote sensing - satellites - estimation - netherlands - brazil - regen - remote sensing - satellieten - schatting - nederland - brazilië

    Earthlings like to measure everything (especially now that we are undergoing the era of big-data revolution) maybe because it is such a nice hobby... although a more serious school of thought believes that when measuring our environment we get to understand physics and ourselves.

    This thesis explores the uncertainties in rainfall measurements from state-of-the-art technologies like commercial microwave links (CML) and meteorological satellites. Rainfall has been measured by rain gauges since quite some time ago; and by weather radars since the end of WWII. Here we evaluate the performance of gridded-rainfall products for the land surface of the Netherlands. These gridded-rainfall products are CML-rainfall maps produced by the Royal Netherlands Meteorology Institute (KNMI), and the IMERG product developed by Global Precipitation Measurement mission (GPM).

    Overall, this thesis shows that CML-rainfall products are very reliable sources with regards to rainfall estimates for the land surface of the Netherlands... even better than the satellite products for rainfall estimation. We are also confident in the promising potential these technologies hold for places around the world where conventional technologies like gauges or radars are not scarce or not affordable.

    What happens in the bag? : development and evaluation of a modified in situ protocol to estimate degradation of nitrogen and starch in the rumen
    Jonge, L.H. de - \ 2015
    Wageningen University. Promotor(en): Wouter Hendriks, co-promotor(en): Jan Dijkstra; H. van Laar. - Wageningen : Wageningen University - ISBN 9789462574519 - 175
    herkauwers - pensfermentatie - stikstof - zetmeelvertering - pensvertering - protocollen - evaluatie - methodologie - schatting - voedingsfysiologie - ruminants - rumen fermentation - nitrogen - starch digestion - rumen digestion - protocols - evaluation - methodology - estimation - nutrition physiology

    The most widely used method to estimate the rumen degradation of dietary components in feedstuffs is the in situ or in sacco method. This method is based on rumen incubation of substrate (feed) in nylon or dacron bags followed by rinsing and analysis of the residue. Small pores in the bag allow microbes to enter the bag whilst a variable portion of the feed is retained in the bag. The results are used to estimate the ruminal effective degradation (ED) that is used in several protein evaluation systems. The weaknesses of the in situ method are its low precision, the lack of standardization, and its inaccuracy. The accuracy can be divided in a bias with respect to the in situ method itself, and the difference between the in situ and in vivo degradation. The bias of the in situ method itself is related to several assumptions regarding the size and degradation rate of the washable fraction, secondary particle loss, and microbial contamination. The aim of this thesis was to examine possibilities to reduce this bias by modification of the in situ methodology.

    The bias related to the assumptions regarding the washout fraction was successfully reduced by developing and using a modified rinsing method that involves less vigorously shaking conditions and a solvent which mimics the rumen pH and osmolality. This modified rinsing method markedly reduced the soluble (S) fraction of N, especially for legume seeds, and the non-soluble washout (W-S) fraction, especially for starch, compared to the conventional method. Consequently, the estimation of the ED became less dependent on the assumptions regarding the degradation of the S and W-S fraction. In vitro results did not support the assumption of a much faster degradation of the W-S fraction of starch than that of the non-washout fraction of starch. The modified rinsing method also allowed measuring the in situ degradation of products that contain mainly small particles such as wheat yeast concentrates.

    The bias related to the breakdown of particles was also successfully reduced by development and application of a combination of the modified rinsing method and an in vitro method that simulates particulate matter loss during incubation. This in vitro method was based on in situ results obtained with an inert marker (i.e., silica gel) which showed that particulate matter loss during incubation was moderate and limited to particles smaller than approximately 40 μm. Correction for these losses decreased the estimated ED of feed ingredients used. This study also showed that the fractional degradation rate of starch in grains was strongly affected by the process of secondary particulate loss when using the conventional method, and applying the modified rinsing method markedly reduced the error due to secondary particulate loss.

    In comparison to the conventional method, the modified method resulted in an increase of the bias related to microbial contamination of the residues. The ratio between diaminopimelic acid (DAPA), a marker for bacterial protein, and N in the residues was higher when using the modified method than that in the conventional method. The results obtained for the modified method also indicated lysis of bacterial cells during rinsing. This bias led to a lower ED when using the modified method with the impact greatly depending on the degree of lysis of bacterial cells.

    In summary, the modified method increased the non-washout fraction of N and starch of various feed ingredients, which offers the possibility to use it for a larger range of feed ingredients, and reduced the bias related to assumptions on the washout fraction and the breakdown of particles compared to the conventional method. On the other hand, the modified method increased the bias related to microbial contamination and enlarged the difference between the in situ and in vivo degradation.

    Leaching of plant protection products and their transformation products : proposals for improving the assessment of leaching to groundwater in the Netherlands : version 2
    Boesten, J.J.T.I. ; Linden, A.M.A. van der; Beltman, W.H.J. ; Pol, J.W. - \ 2015
    Wageningen : Alterra, Wageningen-UR (Alterra report 2630) - 105
    bodemchemie - adsorptie - pesticiden - uitspoelen - chemische afbraak - schatting - modellen - soil chemistry - adsorption - pesticides - leaching - chemical degradation - estimation - models
    Assessment of leaching of plant protection products to groundwater is an important aspect of the environmental risk assessment of these substances. Analysis of available Dutch groundwater monitoring data for these substances triggered a critical review of the current Dutch leaching assessment. As a result, proposals were developed for improving this assessment. These include: (i) a procedure for correcting systematic errors in measured sorption coefficients, (ii) a preliminary procedure for a quality check of Freundlich exponents, (iii) a flow chart for obtaining parameters describing the relationship between the organic-matter/water distribution coefficient, Kom, and the pH for weak acids, (iv) a procedure for obtaining a Kom endpoint from a population of Kom values including lower and upper limits, (v) a procedure for estimating the total amount of substance in soil from a concentration profile (needed for assessment of degradation half-lives from field experiments). This report is an update of the proposals reported in 2011 by the same authors based on testing the feasibility of the proposals to a few dossiers
    Vergelijking visserij - intensiteit op basis van AIS -VMS in de Voordelta
    Hintzen, N.T. ; Vries, P. de; Looije, D. ; Glorius, S.T. - \ 2014
    IJmuiden : IMARES (Rapport / IMARES Wageningen UR C068/14) - 50
    boomkorvisserij - nadelige gevolgen - visgronden - voordelta - schatting - voorspellen - beam trawling - adverse effects - fishing grounds - voordelta - estimation - forecasting
    IMARES voert samen met Deltares en een consortium van 4 partners monitoring uit binnen het project ‘PMR monitoring natuurcompensatie Voordelta’ in opdracht van RWS-WVL. Doel van het project is in kaart te brengen of de compensatiemaatregelen in de Voordelta, als compensatiegebied aangewezen voor de aanleg van de tweede Maasvlakte, daadwerkelijk een (positief) effect hebben op onder andere de bodemfauna. Onderdeel van de compensatiemaatregelen zijn verscherpte regelgeving voor de visserij en gedeeltelijke sluiting voor de visserij.
    Heteroaggregation and sedimentation rates for nanomaterials in natural waters
    Quik, J.T.K. ; Velzeboer, I. ; Wouterse, M. ; Koelmans, A.A. ; Meent, D. van de - \ 2014
    Water Research 48 (2014)1. - ISSN 0043-1354 - p. 269 - 279.
    sedimentatie - zwevende deeltjes - aggregatie - nanotechnologie - emissie - schatting - colloïden - waterstroming - zeewater - oppervlaktewaterkwaliteit - sedimentation - suspended solids - aggregation - nanotechnology - emission - estimation - colloids - water flow - sea water - surface water quality - engineered nanomaterials - silver nanoparticles - carbon nanotubes - manufactured nanoparticles - aggregation kinetics - aquatic environments - ceo2 nanoparticles - organic-matter - fate - exposure
    Exposure modeling of engineered nanomaterials requires input parameters such as sedimentation rates and heteroaggregation rates. Here, we estimate these rates using quiescent settling experiments under environmentally relevant conditions. We investigated 4 different nanomaterials (C60, CeO2, SiO2-Ag and PVP-Ag) in 6 different water types ranging from a small stream to seawater. In the presence of natural colloids, sedimentation rates ranged from 0.0001md-1 for SiO2-Ag to 0.14md-1 for C60. The apparent rates of heteroaggregation between nanomaterials and natural colloids were estimated using a novel method that separates heteroaggregation from homoaggregation using a simplified Smoluchowski-based aggregation-settling equation applied to data from unfiltered and filtered waters. The heteroaggregation rates ranged between 0.007 and 0.6Lmg-1 day-1, with the highest values observed in seawater. We argue that such system specific parameters are key to the development of dedicated water quality models for ENMs.
    Rainfall estimation for hydrology using volumetric weather radar
    Hazenberg, P. - \ 2013
    Wageningen University. Promotor(en): Remko Uijlenhoet, co-promotor(en): Hidde Leijnse; G. Delrieu. - S.l. : s.n. - ISBN 9789461736307 - 232
    regen - schatting - radar - hydrologie - meting - fouten - neerslag - rain - estimation - radar - hydrology - measurement - errors - precipitation
    This thesis focuses specifically on weather radar rainfall measurements in strati form precipitation. In North-Western Europe this type of precipitation is most dominant in winter and leads to the largest hydro logical response of catchments. Unfortunately, the quality of uncorrected radar rainfall estimates starts decreasing at relatively close range from the radar for this type of precipitation. Therefore, as a first approach, a number of previously proposed radar error correction algorithms were applied in this thesis. The implementation of these methods shows a positive impact on the quality of the obtained precipitation measurements as compared to rain gauges. However, the traditional approach of applying a uniform Eulerian based algorithm for the entire radar umbrella to correct for VPR, limits its impact to improve the corrected weather radar precipitation measurements
    Rainfall variability in the Netherlands from radars, rain gauges, and disdrometers
    Beek, R. van de - \ 2013
    Wageningen University. Promotor(en): Remko Uijlenhoet, co-promotor(en): Hidde Leijnse. - S.l. : s.n. - ISBN 9789461736437 - 128
    regen - neerslag - radar - regenmeters - hydrologie - meteorologie - schattingen - schatting - meettechnieken - meetsystemen - nederland - rain - precipitation - radar - rain gauges - hydrology - meteorology - estimates - estimation - measurement techniques - measurement systems - netherlands

    Chapter 1. This thesis presents studies on the variability of precipitation in the Netherlands from datasets collected by radars, rain gauges and disdrometers. Accurate rainfall estimates are highly relevant in hydrology, meteorology and climatology as precipitation has a large impact on society. Precipitation has been studied extensively in the past, although it is impossible to describe all processes and behavior involved. This thesis attempts to add to the knowledge on precipitation. In the first chapter a short overview of rainfall variability at different scales is presented together with the most common instruments for measuring precipitation.

    Chapter 2. The spatial variability of daily rainfall accumulations is studied. Ninety-day averaged semi-variograms are created based on a 30-year data set gathered by automatic stations operated by the Royal Netherlands Meteorological Institute (KNMI). This is complemented by a one-year dataset of 10 gauges within a 5 km radius around CESAR (Cabauw Experimental Site for Atmospheric Research) in the center of the Netherlands. It is shown that it is possible to derive an average semi-variogram that describes the climatology of daily precipitation for each day of the year.

    Chapter 3. The study of chapter 2 is extended by investigating accumulation intervals shorter than daily scales. These are at 12, 8, 6, 4, 3, 2 and 1-hour accumulation intervals. It is shown that at shorter temporal scales the behavior of semi-variograms of precipitation still shows a clear seasonal trend. At hourly and two-hourly accumulation intervals the signal of the range becomes fairly constant during the summer due to the limited accumulation period, the frequent occurrence of convective precipitation, and measurement errors. This illustrates the lower limit of using cosine functions to describe variogram parameters. By fitting a power-law function through the different cosine parameters it is possible to describe the semi-variance of precipitation at scales between 1 and 24 hours using a limited set of equations.

    Chapter 4. Different sources of error affecting rainfall estimates by weather radar are identified. By focussing on precipitation near a C-band radar some of these sources are reduced, which allows to focus on a limited set of error sources. These are radar calibration, ground clutter, wet radome attenuation and variations in rain drop size distribution. An event that caused high precipitation amounts in a band along the center of the Netherlands and more than 50~mm near the radar between the 25th and the 27th of August 2010 is studied. Without any correction and by applying a standard Marshall-Palmer Z-R relation the radar is found to underestimate by approximately 50% with respect to the rain gauge measurements. Using the sun for calibration a correction of 1 dB is applied. Clutter is corrected by subtracting a clear sky clutter map as this proves to provide better results than the standard doppler filter. Wet-radome attenuation is corrected by looking at the amount of attenuation at a known strong clutter pixel near the radar. Disdrometer data near the radar are used to derive accurate Z-R relations specific to the precipitation of the event. These corrections combined provide very promising results with a slight overestimation of the quantitative precipitation estimates (QPE) from the radar by 5 to 8%.

    Chapter 5. An extensive dataset of 195 precipitation events measured by an X-band radar (SOLIDAR) is used to study precipitation at a high spatial resolution of 120 m and a high temporal resolution of 16 s. This study shows the benefit of using such high resolution X-band radars over flat terrain. The errors in the radar measurements are first assessed and corrected as well as possible by considering different techniques. These errors are calibration, ground clutter and attenuation. Finally, five strongly different precipitation events are studied in detail to illustrate the strengths and weaknesses of the X-band weather radar.

    Chapter 6. The variability and possible measurement methods of precipitation have been studied. It was shown that precipitation spatial and temporal variability has a clear statistical signal by analyzing variograms for different accumulation intervals. Weather radars were also shown to be able to give good estimates of precipitation at ground level as well as detailed information on the spatial variability. Some recommendations are given to perform follow up studies. For chapters 2 & 3 it is recommended to use a larger and more detailed dataset, which also incorporates Belgian and German data. This would allow the study of anisotropy in the semi-variograms as well as extending the analysis to accumulation times shorter than 1 hour and longer than 24 hours. For chapter 4 it is recommended to study pixels located further away from the radar. While other error sources would become more pronounced it would be possible to study the applicability of the proposed corrections at longer ranges. Studying the wet-radome attenuation with several strong clutter pixels near the radar would allow the study of wind-effects on wet-radome attenuation, possibly allowing corrections using measurements of (Doppler) wind-speed and direction. Finally, in chapter 5 it is recommended to study the successor of SOLIDAR, IDRA, which is currently operational at CESAR. This radar is a polarimetric radar, allowing a more detailed study of precipitation together with the data from other instruments at this location and the C-band radar of KNMI, which is located close to this location at approximately 23 km.

    Methane : its role in climate change and options for control
    Amstel, A.R. van - \ 2012
    Wageningen University. Promotor(en): Rik Leemans, co-promotor(en): Carolien Kroeze. - S.l. : s.n. - ISBN 9789461732385 - 162
    methaan - klimaatverandering - emissie - schatting - broeikasgassen - controle - methane - climatic change - emission - estimation - greenhouse gases - control

    This study on CH4, (its role in climate change and options for control), aimed at a scenario analysis to assess future climate change under reduced methane emissions. At the same time improving the quality of CH4 emission inventories and estimating the costs of emission reductions between 2010 and 2100. In this thesis 28 major options to control or mitigate methane emissions from different sources were identified. The effectiveness and costs of these options were assessed. This resulted in a database of different options and costs for all the different sources of methane. This database was subsequently used to update the methane module of the Integrated Model to Assess the Greenhouse Effect and expand it with a simple costing module. The IMAGE model was further improved by this work by Van Amstel on methane reduction strategies.

    The thesis concluded that significant reductions in global methane emissions are both technologically feasible and, in many cases, very cost effective strategies for climate change mitigation. Their wider implementation in coming years and decades will largely depend on the policy and market signals delivered by the UNFCCC conferences of the Parties, but failing to make full use of the potential for methane mitigation globally will inevitably make effective mitigation of climate change through reduction of carbon dioxide emissions alone all the more difficult. The scientific community can provide improved methane flux estimates, reduce uncertainties and enhance our understanding of key climate change feedback mechanisms, such as methane emissions from high latitude wetlands and from clathrate deposits. The technology to deliver deep cuts in methane emissions from a host of important sectors is already available. To put methane mitigation at the heart of a robust and well-integrated framework for tackling global climate change, improved national and international policy is required to facilitate rapid technology transfer and provide financial incentives that will ensure that the myriad potential opportunities for the effective mitigation of methane emissions around the world are made real. It is therefore recommended to remove market barriers and to increase attention for methane abatement options through international cooperation and learning from proven technology. One possible route to overcome market failure in methane reduction is international cooperation between front runners and countries willing to learn. Public-private partnerships can be used to stimulate this international cooperation for example in the International Methane Initiative.

    Onzekere debietschattingen
    Mulder, H.M. ; Schipper, P.N.M. ; Jongman, E. ; Heijkers, J. - \ 2011
    Stromingen : vakblad voor hydrologen 16 (2011)3. - ISSN 1382-6069 - p. 33 - 43.
    hydrodynamica - afvoer - waterstroming - schatting - hydrodynamics - discharge - water flow - estimation
    De meest fundamentele en daarmee belangrijkste activiteit van hydrologen is het opstellen van waterbalansen. Immers, waterbalansen vormen het hart van elke watersysteemanalyse, inclusief het ontwikkelen, kalibreren en valideren van modellen. Naast de neerslag en verdamping vormen de aan- en afvoer van oppervlaktewater de belangrijkste componenten van de Nederlandse waterbalans. Die worden indirect afgeleid uit metingen bij klepstuwen, afsluiters, pompgemalen e.d. In dit artikel gaan wij in op de vraag hoe accuraat met zulke meetmethodes de debieten aan- en afvoeren in de praktijk kunnen worden geschat en hoe dit verbeterd kan worden. Wij concluderen dat de onzekerheden groot zijn en dat er veel te verbeteren is over het gehele traject: het uitvoeren van de metingen, het ijken van de formules van de meetopstellingen met alternatieve meetmethodes, de opslag en verwerking van de ruwe meetdata naar debieten en het kwantificeren van onzekerheden daarin.
    Uitsnijden van varkenskarkassen voor het opstellen van een formule om het vleespercentage met de HGP7 (Hennessy Grading Probe), CGM (Capteur Gras/Maigre-Sydel) en de CSB (Image Meater) te schatten = Lean meat equation for the Hennessy Grading Probe (HGP7), Capteur Gras/Maigre-Sydel (CGM and CSB-Image-Meater (CSB)
    Lambooij, E. ; Engel, B. ; Buist, W.G. ; Vereijken, P.F.G. - \ 2011
    Lelystad : Wageningen UR Livestock Research (Rapport / Wageningen UR Livestock Research 478) - 25
    varkenshouderij - slachtdieren - slacht - mager vlees - schatting - varkensvlees - vleessamenstelling - karkassamenstelling - pig farming - meat animals - slaughter - lean - estimation - pigmeat - meat composition - carcass composition
    For each of the instruments HGP7, CGM and CSB-Image-Meater a prediction formula for the percentage lean meat in a pig carcass was derived.
    Observation-based estimates of fossil fuel-derived CO2 emissions in the Netherlands using Delta 14C, CO and 222Radon
    Laan, S. van der; Karstens, U. ; Neubert, R.E.M. ; Laan-Luijkx, I.T. van der - \ 2010
    Tellus Series B: Chemical and Physical Meteorology 62 (2010)5. - ISSN 0280-6509 - p. 389 - 402.
    klimaatverandering - kooldioxide - emissie - brandstoffen - schatting - monitoring - nederland - climatic change - carbon dioxide - emission - fuels - estimation - monitoring - netherlands - atmospheric co2 - carbon-dioxide - regional-scale - europe - transport - methane - inversions - (co2)-c-14 - ratios - oceans
    Surface emissions of CO2 from fossil fuel combustion (¿FFCO2) are estimated for the Netherlands for the period of May 2006–June 2009 using ambient atmospheric observations taken at station Lutjewad in the Netherlands (6°21'E, 53°24'N, 1 m. a.s.l.). Measurements of ¿14C on 2-weekly integrations of CO2 and CO mixing ratios are combined to construct a quasi-continuous proxy record (FFCO2*) from which surface fluxes (¿FFCO2*) are determined using the 222Rn flux method. The trajectories of the air masses are analysed to determine emissions, which are representative for the Netherlands. We compared our observationally based estimates to the national inventories and we evaluated our methodology using the regional atmospheric transport model REMO. Based on 3 yr of observations we find annual mean ¿FFCO2* emissions of (4.7 ± 1.6) kt km-2 a-1 which is in very good agreement with the Dutch inventories of (4.5 ± 0.2) kt km-2 a-1 (average of 2006–2008).
    Aaltjesmanagement in de akkerbouw : achtergronden
    Aasman, B. ; Beers, T.G. van; Wolfs, A. - \ 2010
    Kennisakker.nl 2010 (2010)10 aug.
    akkerbouw - plantenparasitaire nematoden - nematoda - oogstschade - schatting - arable farming - plant parasitic nematodes - nematoda - crop damage - estimation
    In dit deel van de handleiding wordt ingegaan op schadedrempels. Exacte schadedrempels zijn helaas niet aan te geven, omdat veel andere factoren belangrijk zijn. Met behulp van de aangeboden informatie is het mogelijk om schaderisico's redelijk in te kunnen schatten.
    Seven years of recent European net terrestrial carbon dioxide exchange constrained by atmospheric observations
    Peters, W. ; Krol, M.C. ; Werf, G.R. van der; Houweling, S. ; Jones, C.D. ; Hughes, J. ; Schaefer, K. ; Masarie, K.A. - \ 2010
    Global Change Biology 16 (2010)4. - ISSN 1354-1013 - p. 1317 - 1337.
    klimaatverandering - kooldioxide - emissie - weersgegevens - schatting - europa - climatic change - carbon dioxide - emission - weather data - estimation - europe - north-atlantic oscillation - transport models - tracer transport - complex terrain - regional-scale - co2 inversions - part 1 - climate - fluxes - land
    We present an estimate of net ecosystem exchange (NEE) of CO2 in Europe for the years 2001–2007. It is derived with a data assimilation that uses a large set of atmospheric CO2 mole fraction observations (~70 000) to guide relatively simple descriptions of terrestrial and oceanic net exchange, while fossil fuel and fire emissions are prescribed. Weekly terrestrial sources and sinks are optimized (i.e., a flux inversion) for a set of 18 large ecosystems across Europe in which prescribed climate, weather, and surface characteristics introduce finer scale gradients. We find that the terrestrial biosphere in Europe absorbed a net average of -165 Tg C yr-1 over the period considered. This uptake is predominantly in non-EU countries, and is found in the northern coniferous (-94 Tg C yr-1) and mixed forests (-30 Tg C yr-1) as well as the forest/field complexes of eastern Europe (-85 Tg C yr-1). An optimistic uncertainty estimate derived using three biosphere models suggests the uptake to be in a range of -122 to -258 Tg C yr-1, while a more conservative estimate derived from the a-posteriori covariance estimates is -165±437 Tg C yr-1. Note, however, that uncertainties are hard to estimate given the nature of the system and are likely to be significantly larger than this. Interannual variability in NEE includes a reduction in uptake due to the 2003 drought followed by 3 years of more than average uptake. The largest anomaly of NEE occurred in 2005 concurrent with increased seasonal cycles of observed CO2. We speculate these changes to result from the strong negative phase of the North Atlantic Oscillation in 2005 that lead to favorable summer growth conditions, and altered horizontal and vertical mixing in the atmosphere. All our results are available through http://www.carbontracker.eu
    The influence of vegetation cover on the spectroscopic estimation of soil properties
    Bartholomeus, H. - \ 2009
    Wageningen University. Promotor(en): Michael Schaepman, co-promotor(en): Lammert Kooistra. - [S.l. : S.n. - ISBN 9789085854487 - 144
    bodemeigenschappen - vegetatie - spectroscopie - schatting - koolstof - landbouwgronden - ijzer - bodemchemie - geostatistiek - soil properties - vegetation - spectroscopy - estimation - carbon - agricultural soils - iron - soil chemistry - geostatistics
    Voor het bepalen van de kwaliteit van de bodem als hulpbron is er behoefte aan een regelmatige bepaling van de chemische en fysische eigenschappen, zowel in ruimte als tijd. Kwantitatieve schatting van de exacte hoeveelheid, ruimtelijke verdeling en temporele verandering van bodemeigenschappen is nog steeds een uitdaging. Het onderwerp van dit proefschrift is hoe spectrale reflectie informatie gelinkt kan worden aan bodemeigenschappen
    Methods for robustness programming
    Olieman, N.J. - \ 2008
    Wageningen University. Promotor(en): Paul van Beek, co-promotor(en): Eligius Hendrix. - S.l. : S.n. - ISBN 9789085048763 - 176
    wiskunde - operationeel onderzoek - schatting - programmeren - monte carlo-methode - computerwiskunde - mathematics - operations research - estimation - programming - monte carlo method - computational mathematics
    Robustness of an object is defined as the probability that an object will have properties as required. Robustness Programming (RP) is a mathematical approach for Robustness estimation and Robustness optimisation. An example in the context of designing a food product, is finding the best composition of ingredients such that the product is optimally safe and is satisfying all specifications. Another example is the investment in a portfolio of stock market shares. The number of shares to invest in is typically a controllable factor. The future shares prices and resulting portfolio return are typically uncontrollable factors. It is interesting to find the composition of shares for which the probability of reaching a predefined target return is as high as possible.
    In this research alternative methods for Robustness Programming are developed with favourable optimisation properties for finding a design with a Robustness as high as possible. Some of these methods are generally applicable, while other methods use specific problem characteristics. A framework for Robustness Programming is developed for modelling design problems from a wide application area and to select the applicable RP methods for such design problems.
    Reducing prediction uncertainty of weather controlled systems
    Doeswijk, T.G. - \ 2007
    Wageningen University. Promotor(en): Gerrit van Straten, co-promotor(en): Karel Keesman. - [S.l.] : S.n. - ISBN 9789085046134 - 174
    weersvoorspelling - weersbeïnvloeding - modellen - voorspelling - schatting - bedrijfssystemen - onzekerheid - weather forecasting - weather control - models - prediction - estimation - farming systems - uncertainty
    In closed agricultural systems the weather acts both as a disturbance and as a resource. By using weather forecasts in control strategies the effects of disturbances can be minimized whereas the resources can be utilized. In this situation weather forecast uncertainty and model based control are coupled. In this thesis a model of a storage facility of agricultural produce is used as an example for a weather controlled system.

    The first step in reducing prediction uncertainty is taken by reducing the uncertainty in the weather forecast itself. A Kalman filter approach is used for this purpose. Weather forecast uncertainty is significantly reduced up to 10 hours for temperature, up to 32 hours for wind speed and up to 3 hours for global radiation by using this approach.

    For a linearized model of the storage facility error propagation rules have been derived. The uncertainty of the output can therefore be analytically calculated. The medium range weather forecast, up to ten days ahead , consists of an ensemble of 50 forecasts. The mean and variance of these forecasts are used for model prediction and model output uncertainty prediction. Furthermore, by using optimal control in conjunction with a cost criterion, the uncertainty of the system state is incorporated into the cost criterion. As a result the control inputs shift towards parts with less uncertainty in the weather forecast. Finally, a numerical risk evaluation showed that if feedback is applied, as in receding horizon optimal control, the cost increase is limited to 5% for a 24 hour feedback interval.

    Mathematical models are always an approximation of the real system. Model uncertainties arise in the model structure and/or in unknown parameter values. If measurements from the system are present, the model is fitted to the data by changing parameter values. Generally, parameters that are nonlinear in system model output are estimated by nonlinear least-squares (NLS) optimization algorithms. For systems that rational in their parameters a reparameterization method is proposed such that the new parameters can be estimated with ordinary least squares. As a result a modified predictor appears. In the noise free case this leads to the exact parameter estimates whereas a nonlinear least squares approach might end up in a local minimum. If noise is present, however, the linear estimates might be biased and the modified predictor has only a limited range. Because after linear reparameterization the data structure generally becomes errors-in-variables a bias compensated total least squares approach is used. The predictive performance of the modified predictor in this case largely improves and is regarded as a powerful alternative to the existing least squares methods.

    Pilot study: Catches of North Sea cod by recreational fishermen in the Netherlands
    Keeken, O.A. van; Dijkman Dulkes, H.J.A. ; Groot, P.J. - \ 2007
    IJmuiden : IMARES (CVO report 07.002) - 28
    kabeljauw - noordzee - openluchtrecreatie - hengelsport - beoordeling - schatting - visvangsten - cod - north sea - outdoor recreation - angling - assessment - estimation - fish catches
    Stock assessment of North Sea plaice using surplus production models
    Machiels, M.A.M. ; Kraak, S.B.M. ; Borges, L. ; Bogaards, H. - \ 2007
    IJmuiden : IMARES (Report / Wageningen IMARES C032/07) - 33
    schol - beoordeling - schatting - modellen - onzekerheid - noordzee - visstand - plaice - assessment - estimation - models - uncertainty - north sea - fish stocks
    2006 stock assessment of North Sea plaice using a Bayesian catch-at-age model
    Borges, L. ; Kraak, S.B.M. ; Bogaards, J.J.P. ; Machiels, M.A.M. - \ 2007
    IJmuiden : IMARES (Report / IMARES C034/07) - 19
    vis vangen - noordzee - schol - beoordeling - schatting - bayesiaanse theorie - onzekerheid - visstand - fishing - north sea - plaice - assessment - estimation - bayesian theory - uncertainty - fish stocks
    Projectverslag over de verbetering van de toestandsbeoordeling van schol en tong. Problemen ronde de onzekerheid en bias in de toestandsbeoordeling en de gegevens die daar voor worden gebruikt zijn onderzocht. Dit verslag betreft de onzekerheid in de toestandsbeoordeling van Noordzee schol aan de hand van een Bayesiaans 'catch at age'- model (vangst per leeftijd).
    Spatial data quality: from description to application
    Oort, P.A.J. van - \ 2006
    Wageningen University. Promotor(en): Arnold Bregt, co-promotor(en): Sytze de Bruin. - Wageningen : Wageningen Universiteit - ISBN 9789085043393 - 125
    geografische informatiesystemen - gegevensanalyse - gegevensverwerking - kwaliteit - landevaluatie - verandering - schatting - gebruiksefficiëntie - geographical information systems - data analysis - data processing - quality - land evaluation - change - estimation - use efficiency
    The growing availability of spatial data along with growing ease to use the spatial data (thanks to wide-scale adoption of GIS) have made it possible to use spatial data in applications inappropriate considering the quality of the data. As a result, concerns about spatial data quality have increased. To deal with these concerns, it is necessary to (1) formalise and standardise descriptions of spatial data quality and (2) to apply these descriptions in assessing the suitability (fitness for use) of spatial data, before using the data. The aim of this thesis was twofold: (1) to enhance the description of spatial data quality and (2) to improve our understanding of the implications of spatial data quality.

    Chapter 1 sets the scene with a discussion on uncertainty and an explanation of why concerns about spatial data quality exist. Knowledge gaps are identified and the chapter concludes with six research questions.

    Chapter 2 presents an overview of definitions of spatial data quality. Overall, I found a strong agreement on which elements together define spatial data quality. Definitions appear to differ in two aspects: (1) the location within the meta-data report: some elements occur not in the spatial data quality section but in another section of the meta-data report; and (2) the explicitness with which elements are recognised as individual elements. For example, the European pre-standard explicitly recognises theelement'homogeneity'. Other standards recognise the importance of documenting the variation in quality, without naming it explicitly as an individual element.

    In chapter 3 we quantified the spatial variability in classification accuracy for the agricultural crops in the Dutch national land cover database (LGN). Classification accuracy was significantly correlated with: (1) the crop present according to LGN, (2) the homogeneity of the 8-cell neighbourhood around each cell, (3) the size of the patch in which a cell is located, and (4) the heterogeneity of the landscape in which a cell is located.

    In chapter 4 I present methods that use error matrices and change detection error matrices as input to make more accurate land cover change estimates. It was shown that temporal correlation in classification errors has a significant impact and must be taken into account. Producers of time series land cover data are recommended not only to report error matrices, but also change detection error matrices.

    Chapter 5 focuses on positional accuracy and area estimates. From the positional accuracy of vertices delineating polygons, the variance and covariance in area can be derived. Earlier studies derived equations for thevariance,this chapter presents a covariance equation. The variance and covariance equation were implemented in a model and applied in a case-study. The case-study consisted of 97 polygons with a small subsidy value (in euros per hectare) assigned to each polygon. With the model we could calculate the uncertainty in the total subsidy value (in euros) of the complete set of polygons as a consequence of uncertainty in the position of vertices.

    Chapter 6 explores the relationship between completeness of spatial data and risk in digging activities around underground cables and pipelines. A model is presented for calculating the economic implications of over- and incompleteness. An important element of this model is therelationship between detection time and costs. The model can be used to calculate the optimal detection time, i.e. the time at which expected costs are at their minimum.

    Chapter 7 addresses the question why risk analysis (RA) is so rarely applied to assess the suitability of spatial data prior to using the data. In theory, the use of RA is beneficial because it allows the user to judge if the use of certain spatial data does not produce unacceptable risks. Frequently proposed hypotheses explaining the scarce adoption of RA are all technical and educational. In chapter 7 we propose a new group of hypotheses, based on decision theory. We found that the willingness to spend resources on RA depends (1) on the presence of feedback mechanisms in the decision-making process, (2) on how much is at stake and (3) to a minor extent on how well the decision-making process can be modelled.

    Chapter 8 presents conclusions on the six research questions (chapters 2-7) and lists recommendations for users, producers and researchers of spatial data. With regard to the description, four recommendations are given. Firstly, spend more effort on documenting the lineage of reference data. Secondly, quantify and report correlation of quality between related data sets. Thirdly, investigate the integration of different forms of uncertainty (error, vagueness, ambiguity). Fourthly, study the implementation and use of spatial data quality standards. With regard to the application of spatial data quality descriptions, I have two main recommendations. Firstly, to continue the line of research followed in this thesis: quantification of implications of spatial data quality, through development of theory along with tangible illustrations in case-studies. Secondly, there is a need for more empirical research into how users cope with spatial data quality.

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