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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    Bias in lidar-based canopy gap fraction estimates
    Vaccari, S. ; Leeuwen, M. van; Calders, K. ; Coops, N.C. ; Herold, M. - \ 2013
    Remote Sensing Letters 4 (2013)4. - ISSN 2150-704X - p. 391 - 399.
    leaf-area index - digital hemispherical photography - forests - instrument - vegetation
    Leaf area index and canopy gap fraction (GF) provide important information to forest managers regarding the ecological functioning and productivity of forest resources. Traditional measurements such as those obtained from hemispherical photography (HP) measure solar irradiation, penetrating the forest canopy, but do not provide information regarding the three-dimensional canopy structure. Terrestrial laser scanning (TLS) is an active sensor technology able to describe structural forest attributes by measuring interceptions of emitted laser pulses with the canopy and is able to record the spatial distribution of the foliage in three dimensions. However, due to the beam area of the laser, interceptions are detected more frequently than using conventional HP, and GF is typically underestimated. This study investigates the effects of laser beam area on the retrieval of GF by using morphological image processing to describe estimation bias as a function of canopy perimeters. The results show that, using canopy perimeter, improvements in correlation between HP and TLS can be achieved with an increase in the coefficient of determination R 2 up to 28% (from an original R 2 of 0.66 to an adjusted R 2 of 0.85).
    Intercomparison of modis albedo retievals and in situ measurements across the global fluxnet network
    Cescatti, A. ; Marcolla, B. ; Santhana Vannan, S.K. ; Roman, J.Y. ; Moors, E.J. - \ 2012
    Remote Sensing of Environment 121 (2012). - ISSN 0034-4257 - p. 323 - 334.
    reflectance distribution function - broad-band albedo - surface albedo - boreal forests - climate-change - vegetation - products - feedbacks - validation - instrument
    Surface albedo is a key parameter in the Earth's energy balance since it affects the amount of solar radiation directly absorbed at the planet surface. Its variability in time and space can be globally retrieved through the use of remote sensing products. To evaluate and improve the quality of satellite retrievals, careful intercomparisons with in situ measurements of surface albedo are crucial. For this purpose we compared MODIS albedo retrievals with surface measurements taken at 53 FLUXNET sites that met strict conditions of land cover homogeneity. A good agreement between mean yearly values of satellite retrievals and in situ measurements was found (r2 = 0.82). The mismatch is correlated with the spatial heterogeneity of surface albedo, stressing the relevance of land cover homogeneity when comparing point to pixel data. When the seasonal patterns of MODIS albedo are considered for different plant functional types, the match with surface observations is extremely good at all forest sites. On the contrary, satellite retrievals at non-forested sites (grasslands, savannas, croplands) underestimate in situ measurements across the seasonal cycle. The mismatch observed at grassland and cropland sites is likely due to the extreme fragmentation of these landscapes, as confirmed by geostatistical attributes derived from high resolution scenes.
    Greenspace in urban neighbourhoods and residents’ health: adding quality to quantity
    Dillen, S.M.E. van; Vries, S. de; Groenewegen, P.P. ; Spreeuwenberg, P. - \ 2012
    Journal of Epidemiology and Community Health 66 (2012). - ISSN 0143-005X - 5 p.
    environment - areas - instrument - benefits - validity - spaces
    Background Previous research shows a positive link between the amount of green area in one's residential neighbourhood and self-reported health. However, little research has been done on the quality of the green area, as well as on quantity and quality of smaller natural elements in the streetscape. This study investigates the link between the objectively assessed quantity and quality of (1) green areas and (2) streetscape greenery on the one hand and three self-reported health indicators on the other. Methods 80 Dutch urban neighbourhoods were selected, varying in the amount of nearby green area per dwelling, as determined by Geographic Information System analysis. The quality of green areas, as well as the quantity and quality of streetscape greenery, was assessed by observers using an audit tool. Residents of each neighbourhood were asked to complete a questionnaire on their own health (N=1641). In multilevel regression analyses, we examined the relationship between greenspace indicators and three health indicators, controlling for socio-demographic and socioeconomic characteristics. Results Both indicators for the quantity of greenspace were positively related to all three health indicators. Quantity and quality indicators were substantially correlated in the case of streetscape greenery. Nevertheless, the quality indicators tended to have added predictive value for the health indicators, given that the quantity information was already included in the model. Conclusions The quantity and also the quality of greenspace in one's neighbourhood seem relevant with regard to health. Furthermore, streetscape greenery is at least as strongly related to self-reported health as green areas.
    A review of the use of information and communication technologies for dietary assessment
    Ngo, J. ; Engelen, A. ; Molag, M.L. ; Roesle, J. ; Serra-Majem, L. - \ 2009
    The British journal of nutrition 101 (2009)Suppl. 2. - ISSN 0007-1145 - p. s102 - s112.
    personal digital assistant - physical-activity - assessment-tool - history - intervention - validation - instrument - behaviors - children - validity
    Presently used dietary-assessment methods often present difficulties for researchers and respondents, and misreporting errors are common. Methods using information and communication technologies (ICT) may improve quality and accuracy. The present paper presents a systematic literature review describing studies applying ICT to dietary assessment. Eligible papers published between January 1995 and February 2008 were classified into four assessment categories: computerised assessment; personal digital assistants (PDA); digital photography; smart cards. Computerised assessments comprise frequency questionnaires, 24 h recalls (24HR) and diet history assessments. Self-administered computerised assessments, which can include audio support, may reduce literacy problems, be translated and are useful for younger age groups, but less so for those unfamiliar with computers. Self-administered 24HR utilising computers yielded comparable results as standard methods, but needed supervision if used in children. Computer-assisted interviewer-administered recall results were similar to conventional recalls, and reduced inter-interviewer variability. PDA showed some advantages but did not reduce underreporting. Mobile phone meal photos did not improve PDA accuracy. Digital photography for assessing individual food intake in dining facilities was accurate for adults and children, although validity was slightly higher with direct visual observation. Smart cards in dining facilities were useful for measuring food choice but not total dietary intake. In conclusion, computerised assessments and PDA are promising, and could improve dietary assessment quality in some vulnerable groups and decrease researcher workload. Both still need comprehensive evaluation for micronutrient intake assessment. Further work is necessary for improving ICT tools in established and new methods and for their rigorous evaluation
    Stress responses investigated; application of zinc and heat to Terrestrial Model Ecosystems from heavy metal polluted grassland
    Kools, S.A.E. ; Berg, M.P. ; Boivin, M.E.Y. ; Wurff, A.W.G. van der; Gestel, C.A.M. van; Straalen, N.M. van; Kuenen, F.J.A. - \ 2008
    Science of the Total Environment 406 (2008)3. - ISSN 0048-9697 - p. 462 - 468.
    potentially harmful substances - field-validation - stability - biodiversity - instrument - complexity - soils - tme
    This study tested the hypothesis that soils with a deprived biodiversity due to metal pollution are less stable than non-polluted soils, containing a more diverse community. For this, soils were sampled from specific grasslands in the Netherlands that contain elevated heavy metal concentrations (Cu, Pb and Zn). Soils that showed the largest differences in metal concentrations were incubated in the laboratory using Terrestrial Model Ecosystems (TMEs). This approach enabled simultaneous measurement of structural (bacteria, nematodes, enchytraeids, earthworms) and functional parameters (nitrogen leaching, feeding activity, CO2 production, plant growth). The highest polluted soils showed a lower bacterial growth, and decreased enchytraeid and nematode biomass and diversity, hence a deprived community. More nitrate leached from high polluted soils, while all other functional endpoints did not differ. Additional stress application of zinc and heat was used to test the stability. Zinc treatment caused effects only in the higher polluted soils, observed at several moments in time for enchytraeids, CO2 fluxes and plant growth. Heat stress caused a large reduction in enchytraeid and earthworm biomass. Ammonium leaching was decreased by heat treatments in the most polluted soils, while CO2 was increased by heat in less polluted soils. Most effects were seen in the most polluted systems and it was concluded that they seem less stable.
    Quantitative analysis of SCIAMACHY carbon monoxide total column measurements
    Laat, A.T.J. de; Gloudemans, A.M.S. ; Schrijver, H. ; Broek, M.M.P. van den; Meirink, J.F. ; Aben, I. ; Krol, M.C. - \ 2006
    Geophysical Research Letters 33 (2006). - ISSN 0094-8276 - 5 p.
    co - instrument - resolution - retrieval - emissions - mopitt - trends - impact - ch4
    Global tropospheric ozone distributions, budgets, and radiative forcings from an ensemble of 26 state-of-the-art atmospheric chemistry models have been intercompared and synthesized as part of a wider study into both the air quality and climate roles of ozone. Results from three 2030 emissions scenarios, broadly representing “optimistic,” “likely,” and “pessimistic” options, are compared to a base year 2000 simulation. This base case realistically represents the current global distribution of tropospheric ozone. A further set of simulations considers the influence of climate change over the same time period by forcing the central emissions scenario with a surface warming of around 0.7K. The use of a large multimodel ensemble allows us to identify key areas of uncertainty and improves the robustness of the results. Ensemble mean changes in tropospheric ozone burden between 2000 and 2030 for the 3 scenarios range from a 5% decrease, through a 6% increase, to a 15% increase. The intermodel uncertainty (±1 standard deviation) associated with these values is about ±25%. Model outliers have no significant influence on the ensemble mean results. Combining ozone and methane changes, the three scenarios produce radiative forcings of -50, 180, and 300 mW m-2, compared to a CO2 forcing over the same time period of 800–1100 mW m-2. These values indicate the importance of air pollution emissions in short- to medium-term climate forcing and the potential for stringent/lax control measures to improve/worsen future climate forcing. The model sensitivity of ozone to imposed climate change varies between models but modulates zonal mean mixing ratios by ±5 ppbv via a variety of feedback mechanisms, in particular those involving water vapor and stratosphere-troposphere exchange. This level of climate change also reduces the methane lifetime by around 4%. The ensemble mean year 2000 tropospheric ozone budget indicates chemical production, chemical destruction, dry deposition and stratospheric input fluxes of 5100, 4650, 1000, and 550 Tg(O3) yr-1, respectively. These values are significantly different to the mean budget documented by the Intergovernmental Panel on Climate Change (IPCC) Third Assessment Report (TAR). The mean ozone burden (340 Tg(O3)) is 10% larger than the IPCC TAR estimate, while the mean ozone lifetime (22 days) is 10% shorter. Results from individual models show a correlation between ozone burden and lifetime, and each model's ozone burden and lifetime respond in similar ways across the emissions scenarios. The response to climate change is much less consistent. Models show more variability in the tropics compared to midlatitudes. Some of the most uncertain areas of the models include treatments of deep tropical convection, including lightning NO x production; isoprene emissions from vegetation and isoprene's degradation chemistry; stratosphere-troposphere exchange; biomass burning; and water vapor concentrations.
    Evidence for long-range transport of Carbon Monoxide in the Southern Hemisphere from SCIAMACHY observations
    Gloudemans, A.M.S. ; Krol, M.C. ; Meirink, J.F. ; Laat, A.T.J. de; Werf, G.R. van der; Schrijver, H. ; Broek, M.M.P. van den; Aben, I. - \ 2006
    Geophysical Research Letters 33 (2006). - ISSN 0094-8276 - 5 p.
    wfm-doas - total columns - data set - co - retrieval - ch4 - calibration - instrument - emissions - pacific
    The SCIAMACHY satellite instrument shows enhanced carbon monoxide (CO) columns in the Southern Hemisphere during the local Spring. Chemistry-transport model simulations using the new GFEDv2 biomass-burning emission database show a similar temporal and spatial CO distribution, indicating that the observed enhancements are mainly due to biomass burning (BB). Large differences between the year 2003 and 2004 are observed in both the measurements and the model for South America and Australia. This study analyzes the origin of these observed enhancements in the Southern Hemisphere. The fact that SCIAMACHY is sensitive to surface CO allows for the observation of enhanced CO columns in both emission areas and in areas that are affected by long-range transport of CO. Model results show a large contribution of South American BB CO over Australian BB regions during the 2004 BB season of up to similar to 30-35% and up to 55% further south, with smaller contributions for 2003. BB CO transported from southern Africa contributes up to similar to 40% in 2003 and similar to 30% in 2004. The results indicate that differences between SCIAMACHY CO and the model simulations over Australian BB areas are probably not only caused by uncertainties in local emissions but also in overseas emissions.
    Pervasive developmental disorder, behavior problems, and psychotropic drug use in children and adolescents with mental retardation.
    Bildt, A. de; Mulder, E.J. ; Scheers, T. ; Minderaa, R.B. ; Tobi, H. - \ 2006
    Pediatrics 118 (2006)6. - ISSN 0031-4005 - p. e1860 - e1866.
    autism spectrum disorders - intellectual disability - psychiatric-disorders - risperidone - scales - psychopharmacology - population - prevalence - instrument - medication
    OBJECTIVE. This study investigated the interrelationship between psychopharmacotherapy in general and the use of specific psychotropic drugs and pervasive developmental disorder and other behavior problems in children and adolescents with mental retardation. METHODS. A total of 862 participants 4 to 18 years of age, including all levels of mental retardation, were recruited through facilities for children with mental retardation in Friesland, the Netherlands. Information on medication was collected through parent interviews. Behavior problems were investigated with a standardized parent questionnaire (Developmental Behavior Checklist). A pervasive developmental disorder classification was based on the Pervasive Developmental Disorder in Mental Retardation Scale, completed by psychologists or teachers. Logistic regression analysis was used to investigate the relationship between the use of psychotropic drugs and pervasive developmental disorder and other behavioral problems, in the presence of possible confounders. RESULTS. One of 10 participants used psychotropic medication. The main factors associated with psychotropic drug use were pervasive developmental disorder and disruptive behavior. The level of functioning was also associated. Self-absorbed behavior was statistically significantly associated with clonidine use and disruptive behavior with stimulant use. Pervasive developmental disorder and communication problems were the main factors associated with the use of antipsychotic drugs. Age also played a role, whereas gender, living situation, and level of mental retardation did not. CONCLUSIONS. Antipsychotic drugs were associated with pervasive developmental disorder, whereas clonidine and stimulants were associated with self-absorbed and disruptive behavior, respectively. Although clonidine and risperidone are not registered for the problems reported and the other nonstimulants were only sometimes used on-label, their use was associated with specific psychiatric or behavioral problems
    Evaluation of Spectrodirectional Alfalfa Canopy Data Acquired During Daisex'99
    Strub, G. ; Schaepman, M.E. ; Knyazikhin, Y. ; Itten, K.I. - \ 2003
    IEEE Transactions on Geoscience and Remote Sensing 41 (2003)5. - ISSN 0196-2892 - p. 1034 - 1042.
    solar tracking - leaf-area - brdf data - vegetation - radiation - model - architecture - calibration - instrument - morphology
    Field goniometer measurements are a tool to generate a priori bidirectional reflectance distribution function (BRDF) knowledge for correction and validation of directional reflectance data acquired by air- and spaceborne sensors. This study analyzes the diurnal hemispherical.-directional reflectance factor data of an Alfalfa canopy measured during the Digital Airborne Imaging Spectrometer Experiment 1999 (DAISEX'99). We analyze the variation (if measured and modeled spectrodirectional vegetation data, revealing that measurement noise is negligible compared to the variation due to the canopy's anisotropy. The deviations of the spectral albedo (bihemispherical reflectance) and of field spectrometer nadir measurements throughout a day prove to be larger than modeled deviations. Calculated anisotropy factors quantify the spectral-dependent effects of the vegetation reflectance anisotropy. This paper is a contribution toward the generation of a reliable BRDF database by suggesting methods to preprocess and analyze observed directional vegetation reflectance data, with special emphasis on the spectral dimension.
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