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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Behaviour of migrating toads under artificial lights differs from other phases of their life cycle
Grunsven, Roy H.A. Van; Creemers, Raymond ; Joosten, Kris ; Donners, Maurice ; Veenendaal, Elmar M. - \ 2017
Amphibia-Reptilia 38 (2017)1. - ISSN 0173-5373 - p. 49 - 55.
Amphibian - Anura - fragmentation - light pollution - mitigation - phototaxis - spectra
During annual spring migration in Western Europe many amphibians are killed by traffic when they cross roads moving to reproduction sites. Especially in urban settings these roads are often equipped with street lighting. The response of amphibians to this light during migration is however poorly known. Street lighting may attract migrating amphibians increasing the risk of being struck by traffic. Using experimental illumination we tested whether light affected the migration and if adjustment of the spectral composition could mitigate effects. Barriers used to catch toads and help them cross roads safely were divided in 25 meter long sections and these were illuminated with white, green or red light or kept dark. The number of toads caught in each section was counted. Common toads avoided sections of roads that were illuminated with white or green light but not red light. Street light thus affects migrating toads but not as expected and red light with low levels of short wavelength can be used to mitigate effects.
Spectrofotometer VWR
Bom, Jesse ; Dijksman, J.A. ; Lageschaar, Luuk ; Galen, Martijn van; Hoogendam, C.W. ; Wegh, R.A.J. - \ 2016
Wageningen : Wageningen UR
absorptiegraad - meetinstrumenten - instrumenten (meters) - optische instrumenten - spectra - absorbance - indicating instruments - instruments - optical instruments
Instructievideo over het gebruik van de VWR spectofotometer
Spectrofotometer LKB
Bom, Jesse ; Dijksman, J.A. ; Lageschaar, Luuk ; Galen, Martijn van; Hoogendam, C.W. ; Wegh, R.A.J. - \ 2016
Wageningen : Wageningen UR
spectra - absorptiegraad - instrumenten (meters) - meetinstrumenten - absorbance - instruments - indicating instruments
Instructievideo over het gebruik van de LKB Spectofotometer
Unified Formulation of Single- and Multimoment Normalizations of the Raindrop Size Distribution Based on the Gamma Probability Density Function
Yu, N. ; Delrieu, G. ; Boudevillain, Brice ; Hazenberg, P. ; Uijlenhoet, R. - \ 2014
Journal of Applied Meteorology and Climatology 53 (2014)1. - ISSN 1558-8424 - p. 166 - 179.
slope-shape relation - rainfall estimation - spectra - precipitation - variability - france - snow
This study offers a unified formulation of single- and multimoment normalizations of the raindrop size distribution (DSD), which have been proposed in the framework of scaling analyses in the literature. The key point is to consider a well-defined “general distribution” g(x) as the probability density function (pdf) of the raindrop diameter scaled by a characteristic diameter Dc. The two-parameter gamma pdf is used to model the g(x) function. This theory is illustrated with a 3-yr DSD time series collected in the Cévennes region, France. It is shown that three DSD moments (M2, M3, and M4) make it possible to satisfactorily model the DSDs, both for individual spectra and for time series of spectra. The formulation is then extended to the one- and two-moment normalization by introducing single and dual power-law models. As compared with previous scaling formulations, this approach explicitly accounts for the prefactors of the power-law models to yield a unique and dimensionless g(x), whatever the scaling moment(s) considered. A parameter estimation procedure, based on the analysis of power-law regressions and the self-consistency relationships, is proposed for those normalizations. The implementation of this method with different scaling DSD moments (rain rate and/or radar reflectivity) yields g(x) functions similar to the one obtained with the three-moment normalization. For a particular rain event, highly consistent g(x) functions can be obtained during homogeneous rain phases, whatever the scaling moments used. However, the g(x) functions may present contrasting shapes from one phase to another. This supports the idea that the g(x) function is process dependent and not “unique” as hypothesized in the scaling theory.
The (un)certainty of selectivity in liquid chromatography tandem mass spectrometry
Berendsen, B.J.A. ; Stolker, A.A.M. ; Nielen, M.W.F. - \ 2013
Journal of the American Society for Mass Spectrometry 24 (2013). - ISSN 1044-0305 - p. 154 - 163.
drug residues - lc-ms - identification - confirmation - spectra - library - fragmentation - system - food
We developed a procedure to determine the "identification power" of an LC-MS/MS method operated in the MRM acquisition mode, which is related to its selectivity. The probability of any compound showing the same precursor ion, product ions, and retention time as the compound of interest is used as a measure of selectivity. This is calculated based upon empirical models constructed from three very large compound databases. Based upon the final probability estimation, additional measures to assure unambiguous identification can be taken, like the selection of different or additional product ions. The reported procedure in combination with criteria for relative ion abundances results in a powerful technique to determine the (un)certainty of the selectivity of any LC-MS/MS analysis and thus the risk of false positive results. Furthermore, the procedure is very useful as a tool to validate method selectivity. Figure
Simulation of Sentinel-3 images by four stream surface atmosphere radiative transfer modeling in the optical and thermal domains
Verhoef, W. ; Bach, H. - \ 2012
Remote Sensing of Environment 120 (2012). - ISSN 0034-4257 - p. 197 - 207.
reflectance - resolution - spectra - canopy - soil - tool
Simulation of future satellite images can be applied in order to validate the general mission concept and to test the performance of advanced multi-sensor algorithms for the retrieval of surface parameters. This paper describes the radiative transfer modeling part of a so-called Land Scene Generator (LSG) that was developed to simulate images of the sensors OLCI (Ocean and Land Colour Instrument) and SLSTR (Sea and Land Surface Temperature Radiometer) on board of the Sentinel-3 mission. Features of this mission are its wide spectral coverage (optical and thermal domains) and its wide imaging swath, which imposes particular requirements on the simulator in dealing with atmospheric effects over both spectral domains and with angular effects caused by variations in surface bi-directional reflectance distribution function (BRDF) and atmospheric scattering. In the simulator, radiative transfer models for the combination vegetation-soil and for water are coupled to atmospheric parameters derived from MODTRAN runs in order to calculate top-of-atmosphere radiances. For this, four-stream radiative transfer theory is applied to allow simulation of BRDF effects, topography effects, adjacency effects, as well as its uniform application over the optical and thermal spectral domains.
Identification and age estimation of blood stains on colored backgrounds by near infrared spectroscopy
Edelman, G. ; Manti, V. ; Ruth, S.M. van; Leeuwen, T. van; Aalders, M. - \ 2012
Forensic Science International 220 (2012)1-3. - ISSN 0379-0738 - p. 239 - 244.
least-squares regression - transmission spectroscopy - human serum - bloodstains - glucose - hemoglobin - resonance - proteins - spectra - albumin
Non-destructive identification and subsequent age estimation of blood stains are significant steps in forensic casework. The latter can provide important information on the temporal aspects of a crime. As previously shown, visible spectroscopy of blood stains on white backgrounds can successfully be used for their identification and age estimation. The use of this technique however, is hampered by dark backgrounds. In the present study the feasibility to use near infrared (NIR) spectroscopy was evaluated for blood stain identification and age estimation on dark backgrounds. Using NIR reflectance spectroscopy, blood stains were distinguished from other substances with 100% sensitivity and 100% specificity. In addition, Partial Least Squares Regression analysis was applied to estimate the age of blood stains on colored backgrounds. The age of blood stains up to 1 month old was estimated successfully with a root mean squared error of prediction of 8.9%. These findings are an important step toward the practical implementation of blood stain identification and age estimation in forensic casework, where a large variety of backgrounds can be encountered.
Prediction of pork quality with near infrared spectroscopy (NIRS): 1. Feasibility and robustness of NIRS measurements at laboratory scale
Kapper, C. ; Klont, R.E. ; Verdonk, J.M.A.J. ; Urlings, H.A.P. - \ 2012
Meat Science 91 (2012)3. - ISSN 0309-1740 - p. 294 - 299.
water-holding capacity - early post-mortem - reflectance spectroscopy - intramuscular fat - drip loss - meat - spectra - beef - attributes - carcass
The objective was to study prediction of pork quality by near infrared spectroscopy (NIRS) technology in the laboratory. A total of 131 commercial pork loin samples were measured with NIRS. Predictive equations were developed for drip loss %, colour L*, a*, b* and pH ultimate (pHu). Equations with R2 > 0.70 and residual prediction deviation (RPD) = 1.9 were considered as applicable to predict pork quality. For drip loss% the prediction equation was developed (R2 0.73, RPD 1.9) and 76% of those grouped superior and inferior samples were predicted within the groups. For colour L*, test-set samples were predicted with R2 0.75, RPD 2.0, colour a* R2 0.51, RPD 1.4, colour b* R2 0.55, RPD 1.5 and pHu R2 0.36, RPD 1.3. It is concluded that NIRS prediction equations could be developed to predict drip loss% and L*, of pork samples. NIRS equations for colour a*, b* and pHu were not applicable for the prediction of pork quality on commercially slaughtered pigs.
Prediction of pork quality with near infrared spectroscopy (NIRS) 2. Feasibility and robustness of NIRS measurements under production plant conditions
Kapper, C. ; Klont, R.E. ; Verdonk, J.M.A.J. ; Williams, P.C. ; Urlings, H.A.P. - \ 2012
Meat Science 91 (2012)3. - ISSN 0309-1740 - p. 300 - 305.
water-holding capacity - early post-mortem - reflectance spectroscopy - intramuscular fat - drip loss - meat - spectra - beef - attributes - carcass
Longissimus dorsi samples (685) collected at four processing plants were used to develop prediction equations for meat quality with near infrared spectroscopy. Equations with R2 > 0.70 and residual prediction deviation (RPD) = 2.0 were considered as applicable for screening. One production plant showed R2 0.76 and RPD 2.05, other plants showed R2 <0.70 and RPD <2.0 for drip loss %. RPD values were = 2.05 for drip loss%, for colour L* = 1.82 and pH ultimate (pHu) = 1.57. Samples were grouped for drip loss%; superior (<2.0%), moderate (2–4%), inferior (> 4.0%). 64% from the superior group and 56% from the inferior group were predicted correctly. One equation could be used for screening drip loss %. Best prediction equation for L* did not meet the requirements (R2 0.70 and RPD 1.82). pHu equation could not be used. Results suggest that prediction equations can be used for screening drip loss %.
Authentication of Organic Feed by Near-Infrared Spectroscopy Combined with Chemometrics A Feasibilily Study
Tres, A. ; Veer, J.C. van der; Perez-Marin, M.D. ; Ruth, S.M. van; Garrido-Varo, A. - \ 2012
Journal of Agricultural and Food Chemistry 60 (2012)33. - ISSN 0021-8561 - p. 8129 - 8133.
orthogonal signal correction - reflectance spectroscopy - compound feedingstuffs - ingredient composition - products - spectra - classification - samples - meat - oil
Organic products tend to retail at a higher price than their conventional counterparts, which makes them susceptible to fraud. In this study we evaluate the application of near-infrared spectroscopy (NIRS) as a rapid, cost-effective method to verify the organic identity of feed for laying hens. For this purpose a total of 36 organic and 60 conventional feed samples from The Netherlands were measured by NIRS. A binary classification model (organic vs conventional feed) was developed using partial least squares discriminant analysis. Models were developed using five different data preprocessing techniques, which were externally validated by a stratified random resampling strategy using 1000 realizations. Spectral regions related to the protein and fat content were among the most important ones for the classification model. The models based on data preprocessed using direct orthogonal signal correction (DOSC), standard normal variate (SNV), and first and second derivatives provided the most successful results in terms of median sensitivity (0.91 in external validation) and median specificity (1.00 for external validation of SNV models and 0.94 for DOSC and first and second derivative models). A previously developed model, which was based on fatty acid fingerprinting of the same set of feed samples, provided a higher sensitivity (1.00). This shows that the NIRS-based approach provides a rapid and low-cost screening tool, whereas the fatty acid fingerprinting model can be used for further confirmation of the organic identity of feed samples for laying hens. These methods provide additional assurance to the administrative controls currently conducted in the organic feed sector
Estimation of rain kinetic energy from radar reflectivity and/or rain rate based on a scaling formulation of the raindrop size distribution
Yu, N. ; Boudevillain, B. ; Delrieu, G. ; Uijlenhoet, R. - \ 2012
Water Resources Research 48 (2012)4. - ISSN 0043-1397 - 13 p.
soil-erosion - spectra - model - intensity - cloud - precipitation - france
This study offers an approach to estimate the rainfall kinetic energy (KE) by rain intensity (R) and radar reflectivity factor (Z) separately or jointly on the basis of a one- or two-moment scaled raindrop size distribution (DSD) formulation, which contains (1) R and/or Z observations and (2) the dimensionless probability density function (pdf) of a scaled raindrop diameter. The key point is to explain all variability of the DSD by the evolution of the explaining moments (R and Z); hence the pdf is considered as constant. A robust method is proposed to estimate the climatological values of the parameters with a 28 month DSD data set collected in the Cévennes-Vivarais region of France. Three relationships (KE-R, KE-Z, and KE-RZ), which link the observations (R and/or Z) to rainfall kinetic energy (KE), are established. As expected, the assessment using the disdrometer data indicates that (1) because of the proximity of the moment orders, the KE-Z relationship exhibits less variability than the KE-R relationship and (2) the combination of R and Z yields a significant improvement of the estimation of KE compared to the single-moment formulations. Subsequently, a first attempt to spatialize the kinetic energy using radar and rain gauge measurements is presented for a convective event, showing a promising potential for erosion process studies. Different from the application with the disdrometer data, the performance of the KE-Z relationship degrades compared to the KE-R relationship as a result of a bias and/or the sampling characteristics of the radar data
Scaling of raindrop size distributions and classification of radar reflectivity-rain rate relations in intense Mediterranean precipitation
Hazenberg, P. ; yu, Nan ; Boudevillain, Brice ; Delrieu, Guy ; Uijlenhoet, R. - \ 2011
Journal of Hydrology 402 (2011)3-4. - ISSN 0022-1694 - p. 179 - 192.
z-r relations - drop-size - microphysical evolution - florida cumulonimbus - convective clouds - terminal velocity - weather radar - bright band - spectra - variability
In radar hydrology the relationship between the reflectivity factor (Z) and the rainfall intensity (R) is generally assumed to follow a power law of which the parameters change both in space and time and depend on the drop size distribution (DSD). Based on disdrometer data, this study tries to improve our understanding of the temporal variability of the power-law relationship between Z and R using a scaling-law formalism for the raindrop size distribution proposed in previous contributions. In particular, this study focuses on the inter-event variability of Z–R coefficients and associated DSD-parameters and their relationship to the type of precipitation. This is crucial for developing improved quantitative precipitation estimation algorithms for extreme, flash flood triggering rainfall. Within the DSD scaling-law framework a new normalized parameter estimation method is presented, which calculates significantly faster than the original method and leads to bulk event estimates of the DSD-parameters and associated Z–R coefficients. Based on a 2.5-year disdrometer dataset collected in the Cévennes-Vivarais region in the south of France, comprising a total of 70 events, it is shown that the quality of the resulting Z–R relationships obtained by the new method compares well to two standard least-squares fitting techniques. A major benefit of the new implementation, as compared to such purely statistical methods, is that it also provides information concerning the properties of the DSD. For each of the 70 events this study also estimates the convective activity based on a threshold technique. Results show that convective events generally tend to have smaller Z–R exponents, which is assumed to result from an increased amount of drop interaction. For stratiform events, a much larger range in exponents is obtained, which is thought to depend on differences in meteorological origin (snow vs. ice). For the types of precipitation events observed in the Cévennes region, for a given value of the exponent, the prefactor of the Z–R relation tends to be larger for the more convective type of events. This emphasizes the different meteorological origin of the heavy rainfall observed in the south of France as compared to other regions of the world.
An HflX-type GTPase from Sulfolobus solfataricus binds to the 50S ribosomal subunit in all nucleotide-bound states
Blombach, F. ; Swarts, D.C. ; Oost, J. van der - \ 2011
Journal of Bacteriology 193 (2011)11. - ISSN 0021-9193 - p. 2861 - 2867.
bacillus-subtilis - escherichia-coli - crystal-structure - protein - interacts - family - ylqf - obg - biogenesis - spectra
HflX GTPases are found in all three domains of life, the Bacteria, Archaea, and Eukarya. HflX from Escherichia coli has been shown to bind to the 50S ribosomal subunit in a nucleotide-dependent manner, and this interaction strongly stimulates its GTPase activity. We recently determined the structure of an HflX ortholog from the archaeon Sulfolobus solfataricus (SsoHflX). It revealed the presence of a novel HflX domain that might function in RNA binding and is linked to a canonical G domain. This domain arrangement is common to all archaeal, bacterial, and eukaryotic HflX GTPases. This paper shows that the archaeal SsoHflX, like its bacterial orthologs, binds to the 50S ribosomal subunit. This interaction does not depend on the presence of guanine nucleotides. The HflX domain is sufficient for ribosome interaction. Binding appears to be restricted to free 50S ribosomal subunits and does not occur with 70S ribosomes engaged in translation. The fingerprint 1H-15N heteronuclear correlation nuclear magnetic resonance (NMR) spectrum of SsoHflX reveals a large number of well-resolved resonances that are broadened upon binding to the 50S ribosomal subunit. The GTPase activity of SsoHflX is stimulated by crude fractions of 50S ribosomal subunits, but this effect is lost with further high-salt purification of the 50S ribosomal subunits, suggesting that the stimulation depends on an extrinsic factor bound to the 50S ribosomal subunit. Our results reveal common properties but also marked differences between archaeal and bacterial HflX proteins
Mapping soil clay contents in Dutch marine districts using gamma-ray spectrometry
Klooster, E. van der; Egmond, F.M. van; Sonneveld, M.P.W. - \ 2011
European Journal of Soil Science 62 (2011)5. - ISSN 1351-0754 - p. 743 - 753.
plant-available potassium - radiometric data - water-content - topsoil - netherlands - sediments - spectra - models - part
Conventional soil sampling methods to obtain high-resolution soil data are labour intensive and costly. Recently, gamma ray spectrometry has emerged as a promising technique to overcome these obstacles. The objective of our study was to investigate the prediction of soil clay contents using gamma-ray spectrometry in three marine clay districts in the Netherlands: the southwestern marine district (SMD), the IJsselmeerpolder district (IJPD) and the northern marine district (NMD). The performance of linear regression models was investigated at field (1000 km2) scales and for all the Dutch marine districts together. For this study, a database was available with 1371 gamma-ray spectra measured on arable fields in marine clay districts during the period 2005–2008 and these were all linked to laboratory analyses of clay contents. At the field scale, linear regression models based on 40K, 232Th, or a combination of these revealed much smaller root mean squared error (RMSE) values (2–3%) compared with a model based on the field mean (8–10%). At the district scale, the regression models for the SMD and IJPD, which have comparable sediments, performed better than for the NMD. This indicates that the prediction of clay contents in late Holocene marine sediments may be made with gamma-ray spectrometry provided that the origin of the parent material results in a unique fingerprint. Because of the heterogeneous parent material of all marine districts taken together, our study shows that no unique and precise fingerprint exists, and the RMSE of 6% between clay contents and gamma-ray spectra is not much different from the RMSE of 7% when using the overall mean as a predictor.
Development of the EcoQO for the North Sea fish community
Greenstreet, S.P.R. ; Rogers, S.I. ; Rice, J.C. ; Piet, G.J. ; Guirey, E. - \ 2011
ICES Journal of Marine Science 68 (2011)1. - ISSN 1054-3139 - p. 1 - 11.
size-based indicators - ecosystem approach - transfer efficiencies - reference points - food webs - body-mass - model - management - fisheries - spectra
Development of the Ecological Quality Objective (EcoQO) for the North Sea demersal fish community is described. Size-based metrics were identified as the most effective indicators of the state of the community, but such metrics are also sensitive to environmental influence. Redefining the large fish indicator (LFI) produced a metric more sensitive to fishing-induced change and therefore more useful to managers. Fish stocks were thought to be exploited at a sustainable rate in the early 1980s, so in a process echoing the precautionary approach to fish stock management, this was considered the reference period for the LFI, suggesting a value of 0.3 as the appropriate EcoQO. The LFI declined from around 0.3 in 1983 to 0.05 in 2001, followed by a recovery to 0.22 in 2008. However, analyses of the longer-term groundfish survey data suggest that, even were fishing pressure to be reduced to early 20th century levels, the LFI would be unlikely to rise much above a value of 0.3. The response of the LFI to variation in fishing pressure suggested a more complex relationship than anticipated, underscoring the need for operational theoretical size-resolved multispecies fish community models to support management towards broader ecosystem objectives.
Geostatistical simulation of two-dimensional fields of raindrop size distributions at the meso-¿ scale
Schleiss, M.A. ; Berne, A. ; Uijlenhoet, R. - \ 2009
Water Resources Research 45 (2009). - ISSN 0043-1397 - 10 p.
prediction model - rainfall fields - time - precipitation - variability - space - resolution - variables - spectra - matrix
The large variability of the raindrop size distribution (DSD) in space and time must be taken into account to improve remote sensing of precipitation. The ability to simulate a large number of 2-D fields of DSDs sharing the same statistical properties provides a very useful simulation framework that nicely complements experimental approaches based on DSD ground measurements. These simulations can be used to investigate radar beam propagation through rain and to evaluate different radar retrieval techniques. The proposed approach uses geostatistical methods to provide structural analysis and stochastic simulation of DSD fields. First, the DSD is assumed to follow a Gamma distribution with three parameters. As a consequence, 2-D fields of DSDs can be described as a multivariate random function. The parameters are normalized using a Gaussian anamorphosis and simulated by taking advantage of fast Gaussian simulation algorithms. Variograms are used to characterize the spatial structure of the DSD fields. The generated fields have identical spatial structure and are consistent with the observations. Because intermittency cannot be simulated using this technique, the size of the simulation domain is limited to the meso-¿ scale (2-20 km). To assess the proposed approach, the method is applied to data collected during intense Mediterranean rainfall. Taylor's hypothesis is invoked to convert time series into 1-D range profiles. The anisotropy of the fields is derived from radar measurements. Simulated and measured reflectivity fields are in good agreement with respect to the mean, the standard deviation, and the spatial structure, demonstrating the promising potential of the proposed stochastic model of DSD fields
Prediction of Molar Extinction Coefficients of Proteins and Peptides Using UV Absorption of the Constituent Amino Acids at 214 nm To Enable Quantitative Reverse Phase High-Performance Liquid Chromatography-Mass Spectrometry Analysis
Kuipers, B.J.H. ; Gruppen, H. - \ 2007
Journal of Agricultural and Food Chemistry 55 (2007)14. - ISSN 0021-8561 - p. 5445 - 5451.
beta-lactoglobulin hydrolysis - enzyme inhibitory peptides - bioactive peptides - spectra - identification - polypeptide - conglycinin
The molar extinction coefficients of 20 amino acids and the peptide bond were measured at 214 nm in the presence of acetonitrile and formic acid to enable quantitative comparison of peptides eluting from reversed-phase high-performance liquid chromatography, once identified with mass spectrometry (RP-HPLC-MS). The peptide bond has a molar extinction coefficient of 923 M-1 cm-1. Tryptophan has a molar extinction coefficient that is ~30 times higher than that of the peptide bond, whereas the molar extinction coefficients of phenylalanine, tyrosine, and histidine are ~six times higher than that of the peptide bond. Proline, as an individual amino acid, has a negligible molar extinction coefficient. However, when present in the peptide chain (except at the N terminus), it absorbs ~three times more than a peptide bond. Methionine has a similar molar extinction coefficient as the peptide bond, while all other amino acids have much lower molar extinction coefficients. The predictability of the molar extinction coefficients of proteins and peptides, calculated by the amino acid composition and the number of peptide bonds present, was validated using several proteins and peptides. Most of the measured and calculated molar extinction coefficients were in good agreement, which shows that it is possible to compare peptides analyzed by RP-HPLC-MS in a quantitative way. This method enables a quantitative analysis of all peptides present in hydrolysates once identified with RP-HPLC-MS. Keywords: Molar extinction coefficient; molar absorption coefficient; UV absorbance; proteins; peptides; amino acids
Coupled soil-leaf-canopy and atmosphere radiative transfer modeling to simulate hyperspectral multi-angular surface reflectance and TOA radiance data
Verhoef, W. ; Bach, H. - \ 2007
Remote Sensing of Environment 109 (2007)2. - ISSN 0034-4257 - p. 166 - 182.
photosynthetically active radiation - light interaction-model - vegetation canopies - plant-canopy - sail model - scattering - inversion - prospect - spectra - indexes
Coupling radiative transfer models for the soil background and vegetation canopy layers is facilitated by means of the four-stream flux interaction concept and use of the adding method. Also the coupling to a state-of-the-art atmospheric radiative transfer model like MODTRAN4 can be established in this way, thus enabling the realistic simulation of top-of-atmosphere radiances detected by space-borne remote sensing instruments. Possible applications of coupled modeling vary from mission design to parameter retrieval and data assimilation. This paper introduces a modified Hapke soil BRDF model, a robust version of the PROSPECT leaf model, and a modernized canopy radiative transfer model called 4SAIL2. The latter is a hybrid two-layer version of SAIL accommodating horizontal and vertical heterogeneities, featuring improved modeling of the hot spot effect and output of canopy absorptances. The integrated model is simply called SLC (soil¿leaf-canopy) and has been implemented as a speed-optimized Windows DLL which allows efficient use of computer resources even when simulating massive amounts of hyperspectral multi-angular observations. In this paper various examples of possible model output are shown, including simulated satellite image products. First validation results have been obtained from atmospherically corrected hyperspectral multi-angular CHRIS-PROBA data of the Upper Rhine Valley in Germany.
Modelling an exploited marine fish community with 15 parameters - results from a simple size-based model
Pope, J.G. ; Rice, J.C. ; Daan, N. ; Jennings, S. ; Gislason, H. - \ 2006
ICES Journal of Marine Science 63 (2006)6. - ISSN 1054-3139 - p. 1029 - 1044.
north-sea - fisheries - spectra - indicators - diversity - assemblages - management - predation - biomass - ecology
To measure and predict the response of fish communities to exploitation, it is necessary to understand how the direct and indirect effects of fishing interact. Because fishing and predation are size-selective processes, the potential response can be explored with size-based models. We use a simulation approach to describe the relationship between size spectrum slope and overall fishing mortality and to try to understand how a linear spectrum might be maintained. The model uses 15 parameters to describe a 13 `species¿ fish community, where species are defined by their maximum body size and the general relationship between size and life history characteristics. The simulations allow us to assess the role of changes in the strength and type of density dependence in controlling the response to fishing and to investigate the tradeoffs between catches and the status of the different species. The outputs showed that the linear slope of the size spectrum was a function of community exploitation rate. Density dependent controls, specifically predation mortality and the extent of compensation in the stock-recruitment relationship, were key mechanisms in maintaining a linear spectrum. Compensation caused by the dependence of predation mortality on predator abundance can linearise the spectrum even when the compensation caused by the dependence of recruitment on spawning stock biomass is weak. However, as compensation in the stock-recruit relationship was increased, the effects of changes in fishing mortality dominated those of the dynamic changes in predation mortality. The approach allows us to explore the effects of different fishing mortality schedules on properties of the fish community, to assess how fishing affects species with different life histories in mixed fisheries and to assess the effects of selectively fishing different size classes. The simulations indicate that the size classes to be included when developing and interpreting sized-based metrics must be carefully considered in relation to the trophic structure and likely strength of predatory interactions in the community. Runs with differential fishing mortality by size suggest that the dynamics of predation cannot compensate fully for changing rates and patterns of exploitation, implying that the effects of selectively fishing different size classes should be assessed on a case by case basis.
Consideration of smoothing techniques for hyperspectral remote sensing
Vaiphasa, C. - \ 2006
ISPRS Journal of Photogrammetry and Remote Sensing 60 (2006)2. - ISSN 0924-2716 - p. 91 - 99.
feature-selection - derivative analysis - vegetation - spectra - model - differentiation - discrimination - inversion - canopies - accuracy
Spectral smoothing filters are popularly used in a large number of modern hyperspectral remote sensing studies for removing noise from the data. However, most of these studies subjectively apply ad hoc measures to select filter types and their parameters. We argue that this subjectively minded approach is not appropriate for choosing smoothing methods for hyperspectral applications. In our case study, it is proved that smoothing filters can cause undesirable changes to statistical characteristics of the spectral data; thereby, affecting the results of the analyses that are based on statistical class models. If preserving statistical properties of the original hyperspectral data is desired, smoothing filters should then be used, if necessary, after careful consideration of which smoothing techniques will minimize disturbances to the statistical properties of the original data. A comparative t-test is proposed as a method for choosing a smoothing filter suitable for hyperspectral data at hand.
Relating Eulerian and Lagrangian Statistics for the Turbulent Dispersion in the Atmospheric Convective Boundary Layer
Dosio, A. ; Vilà-Guerau de Arellano, J. ; Holtslag, A.A.M. ; Builtjes, P.J.H. - \ 2005
Journal of the Atmospheric Sciences 62 (2005)4. - ISSN 0022-4928 - p. 1175 - 1191.
large-eddy simulation - direct numerical simulations - laboratory model - time-scale - plume dispersion - buoyancy-driven - diffusion - shear - field - spectra
Eulerian and Lagrangian statistics in the atmospheric convective boundary layer (CBL) are studied by means of large eddy simulation (LES). Spectra analysis is performed in both the Eulerian and Lagrangian frameworks, autocorrelations are calculated, and the integral length and time scales are derived. Eulerian statistics are calculated by means of spatial and temporal analysis in order to derive characteristic length and time scales. Taylor's hypothesis of frozen turbulence is investigated, and it is found to be satisfied in the simulated flow. Lagrangian statistics are derived by tracking the trajectories of numerous particles released at different heights in the turbulent flow. The relationship between Lagrangian properties (autocorrelation functions) and dispersion characteristics (particles' displacement) is studied through Taylor's diffusion relationship, with special emphasis on the difference between horizontal and vertical motion. Results show that for the horizontal motion, Taylor's relationship is satisfied. The vertical motion, however, is influenced by the inhomogeneity of the flow and limited by the ground and the capping inversion at the top of the CBL. The Lagrangian autocorrelation function, therefore, does not have an exponential shape, and consequently, the integral time scale is zero. If distinction is made between free and bounded motion, a better agreement between Taylor's relationship and the particles' vertical displacement is found. Relationships between Eulerian and Lagrangian fr ameworks are analyzed by calculating the ratio ß between Lagrangian and Eulerian time scales. Results show that the integral time scales are mainly constant with height for z/zi <0.7. In the upper part of the CBL, the capping inversion transforms vertical motion into horizontal motion. As a result, the horizontal time scale increases with height, whereas the vertical one is reduced. Current parameterizations for the ratio between the Eulerian and Lagrangian time scales have been tested against the LES results showing satisfactory agreement at heights z/zi <0.7.
Multiple glass transitions in the plastic crystal phase of triphenylene derivates
Yildirim, Z. ; Wubbenhorst, M. ; Mendes, E. ; Picken, S.J. ; Paraschiv, I. ; Marcelis, A.T.M. ; Zuilhof, H. ; Sudhölter, E.J.R. - \ 2005
Journal of Non-Crystalline Solids 351 (2005)33-36. - ISSN 0022-3093 - p. 2622 - 2628.
dielectric-relaxation spectroscopy - molecular-dynamics - liquid-crystal - nematic-columnar - separation - viscosity - polymers - mesogens - spectra - probes
The dynamics and phase behavior of the discotic liquid crystalline compound hexahexyloxytriphenylene (HAT6) and a derivative were studied by broad-band dielectric spectroscopy, differential scanning calorimetry, X-ray diffraction and optical microscopy. While the pristine compound HAT6 forms both a columnar mesophase (Colh) and a plastic crystal phase, no liquid crystallinity was observed for the highly asymmetric compound HAT6-C10Br. This paper focuses on the dielectric relaxations in the plastic crystal phase. For HAT6-C10Br, a `high temperature¿ glass transition, manifested by a Vogel¿Fulcher¿Tammann (VFT) type ¿2-process, was found at ¿31 °C that was assigned to the columnar glass transition in accordance with previous literature. The main result of our study is the observation of a second, low-temperature VFT process (¿1) for both compounds, which indicates co-operative liquid dynamics within the framework of the plastic crystal order at temperatures as low as ¿100 °C. Comparison of these fast dynamics with relaxation data from polyethylene and polymer series with long alkyl groups identifies this process as a `hindered¿ polyethylene-like dynamic glass transition that originates from the nanophase-separated, spatially confined fraction of aliphatic tails.
Detection and classification of latent defects and diseases on raw French fries with multispectral imaging
Noordam, J.C. ; Broek, W.H.A.M. van den; Buydens, L.M.C. - \ 2005
Journal of the Science of Food and Agriculture 85 (2005)13. - ISSN 0022-5142 - p. 2249 - 2259.
pattern-recognition - vision system - inspection - potatoes - spectroscopy - reflectance - spectra - images
This paper describes an application of both multispectral imaging and red/green/blue (RGB) colour imaging for the discrimination between different defect and diseases on raw French fries. Four different potato cultivars generally used for French fries production are selected from which fries are cut. Both multispectral images and RGB colour images are classified with parametric and non-parametric classifiers. The effect of applying different preprocessing techniques on the spectra was also investigated. The best classification results in terms of accuracy, yield and purity are obtained with a modified version of standard normal variate (snv_mod) preprocessing for different classifiers and potato cultivars. The classification results of the multispectral images are compared with RGB images. The results show that the support vector classifier gives the best classification performance for the snv_mod preprocessed multispectral images and k-nearest neighbours classifier gives the best classification performance for raw RGB images. The detection of the latent greening defect in French fries with the exploration of multispectral images shows the additional value of multispectral imaging for French fries. A comparison between the multispectral images and the RGB colour images confirms this since this type of defect is not visible in the colour images
Changes in the North Sea fish community: evidence of indirect effects of fishing?
Daan, N. ; Gislason, H. ; Pope, J.G. ; Rice, J.C. - \ 2005
ICES Journal of Marine Science 62 (2005). - ISSN 1054-3139 - p. 177 - 188.
coastal waters - fisheries - size - diversity - impact - exploitation - assemblages - patterns - spectra - ecology
We investigate changes in the North Sea fish community with particular reference to possible indirect effects of fishing, mediated through the ecosystem. In the past, long-term changes in the slope of size spectra of research vessel catches have been related to changes in fishing effort, but such changes may simply reflect the cumulative, direct effects of fishing through selective removal of large individuals. If there is resilience in a fish community towards fishing, we may expect increases in specific components, for instance as a consequence of an associated reduction in predation and/or competition. We show on the basis of three long-term trawl surveys that abundance of small fish (all species) as well as abundance of demersal species with a low maximum length (Lmax) have steadily and significantly increased in absolute numbers over large parts of the North Sea during the last 30 years. Taking average fishing mortality of assessed commercial species as an index of exploitation rate of the fish community, it appears that fishing effort reached its maximum in the mid-1980s and has declined slightly since. If the observed changes in the community are caused by indirect effects of fishing, there must be a considerable delay in response time, because the observed changes generally proceed up to recent years, although both size and Lmax spectra suggest some levelling off, or even recovery in one of the surveys. Indeed, significant correlations between all community metrics and exploitation rate were obtained only if time lags >=6 years were introduced
Modification of beta-lactoglobulin by oligofructose: Impact on protein adsorption at the air-water interface
Trofimova, D. ; Jongh, H.H.J. de - \ 2004
Langmuir 20 (2004)13. - ISSN 0743-7463 - p. 5544 - 5552.
air/water interface - functional-properties - maillard reaction - stability - ovalbumin - thermostability - glycation - spectra
Maillard products of -lactoglobulin (Lg) and fructose oligosaccharide (FOS) were obtained in different degrees of modification depending on incubation time and pH. By use of a variety of biochemical and spectroscopic tools, it was demonstrated that the modification at limited degrees does not significantly affect the secondary, tertiary, and quaternary structure of Lg. The consequence of the modification on the thermodynamics of the protein was studied using differential scanning calorimetry, circular dichroism, and by monitoring the fluorescence intensity of protein samples with different concentrations of guanidine-HCl. The modification leads to lowering of the denaturation temperature by 5 C and a reduction of the free energy of stabilization of about 30%. Ellipsometry and drop tensiometry demonstrated that upon adsorption to air-water interfaces in equilibrium modified Lg exerts a lower surface pressure than native Lg (16 versus 22 mN/m). Moreover, the surface elastic modulus increased with increasing surface pressure but reached significantly smaller values in the case of FOS-Lg. Compared to native Lg, modification of the protein with oligofructose moieties results in higher surface loads and thicker surface layers. The consequences of these altered surface rheological properties are discussed in view of the functional behavior in technological applications.
Transformations in occluded light fraction organic matter in a clayey oxisol; evidence from 13C-CCPMAS-NMR and &13C signature
Roscoe, R. ; Buurman, P. ; Lagen, B. van; Velthorst, E.J. - \ 2004
Revista Brasileira de Ciência do Solo 28 (2004). - ISSN 0100-0683 - p. 811 - 818.
particle-size fractions - c-13 nmr-spectroscopy - soil - decomposition - spectra - density - carbon
We hypothesised that, during occlusion inside granular aggregates of oxide-rich soils, the light fraction organic matter would Undergo a strong process of decomposition, either due to the slow process of aggregate formation and stabilisation or due to digestion in the macro- and meso-fauna guts. This process would favour the accumulation of recalcitrant materials inside aggregates. The aim of this study was to compare the dynamics and the chemical composition, of free and occluded light fraction organic matter in a natural cerrado vegetation (woodland savannah) and a nearby pasture (Brachiaria spp.) to elucidate the transformations during occlusion of light fraction in aggregates of a clayey Oxisol. Nuclear Magnetic Resonance of the C-13, with Cross Polarisation and Magic Angle Spinning (C-13-CPMAS-NMR), and C-13/C-12 isotopic ratio were combined to study organic matter composition and changes in carbon dynamics, respectively. The occluded light fraction had a slower turnover than. the free light fraction and the heavy fraction. Organic matter in the occluded fraction also showed a higher degree of decomposition. The results confirm that processes of soil organic matter occlusion in the typical "very fine strong granular" structure of the studied oxide-rich soil led to an intense transformation, selectively preserving stable organic matter. The small amount of organic material stored as occluded light faction, as well as its stability, suggests that this is not an important or manageable sink for sequestration of atmospheric CO2.
Changes in soil organic matter compositrion after introduction of riparian vegetation on shores of hydroelectric reservoires (Southeast of Brazil)
Alcantara, F.A. de; Buurman, P. ; Curi, N. ; Furtini Neto, A.E. ; Lagen, B. van; Meijer, E.M. - \ 2004
Soil Biology and Biochemistry 36 (2004)9. - ISSN 0038-0717 - p. 1497 - 1508.
humic substances - c-13 nmr - pyrolysis - systems - recognition - cuticles - spectra - state
This work is part of a research program with the general objective of evaluating soil sustainability in areas surrounding hydroelectric reservoirs, which have been planted with riparian forest. The specific aims were: (i) to assess if and how the soil organic matter (SOM) chemical composition has changed in such areas, and (ii) to contribute to the knowledge of SOM chemistry in Brazil. To this end, we sampled litter and soil (Anionic Acrustox) in two adjacent areas: one under native vegetation and another forested with riparian species in 1992. The native vegetation was Brazilian savannah orcerrado. In this case, it was a 'grassy cerrado', dominated by grasses with few shrubs. Litter was collected and humic substances were extracted from soil by an alkaline solution. Both were characterised by a combination of cross-polarisation-magic angle spinning (CPMAS) solid state C-13 nuclear magnetic resonance (NMR) spectroscopy and pyrolysis-gas-chromatography/mass-spectrometry (Py-GC/MS). Eight years after forestation, the addition of the forest litter had changed SOM chemical composition. The C input pattern exerted a key role on the observed alterations. In the grassy cerrado, litter addition is predominantly belowground and the litter is richer in carbohydrate-derived compounds and poorer in lignin moieties. In the forested area, C input is largely aboveground and grass litter has been partially replaced by a relatively more recalcitrant material. As a result, topsoil under forest was chemically strongly different from that under cerrado. Factor analysis indicated that the largest differences were between topsoil under forest and deepest subsoil under cerrado, where there is influence of remaining cerrado-derived C. Both semi-quantification and factor analysis of pyrolysis data gave further insight on the extent of alterations, but more research on such a quantitative approach should be developed to detail its application in SOM studies. (C) 2004 Elsevier Ltd. All rights reserved.
Characteristic Length Scales of Reactive Species in a Convective Boundary Layer
Jonker, H.J.J. ; Vilà-Guerau de Arellano, J. ; Duynkerke, P.G. - \ 2004
Journal of the Atmospheric Sciences 61 (2004). - ISSN 0022-4928 - p. 41 - 56.
large-eddy simulation - aircraft measurements - turbulence - scalars - fluxes - ozone - plume - diffusion - spectra - clouds
In this paper variance spectra of chemically active species in a dry convective boundary layer are studied by means of large-eddy simulations (LESs). The aim is to quantify the impact of chemistry on the spatial fluctuations in the concentration fields. The computational domain has a large aspect ratio ( width/height 5 16) in order to encompass all relevant scales (mesoscale to microscale). Variance spectra are used to calculate a characteristic length scale of the species' concentration variability. By locating the peak in the spectrum, a "variance dominating length scale'' is derived. For a simple first-order reaction, this length scale demonstrates a clear dependence on the reaction rate: an increase in the reaction rate leads to a significant decrease of the length scale of the species. For a chemical cycle composed of a second-order reaction and first-order backreaction, the length scales turn out to depend much less on the reaction rate. The value of the length scales of the species involved appears to lie well in the mesoscale range, rather than the microscale range, demonstrating that concentration fluctuations are driven predominantly by scales much larger than the depth of the boundary layer. External perturbation of the chemical balance can have a direct impact on the variance spectra. For the case where a ( hypothetical) passing cloud switches off the chemical backreaction for a while, a dramatic drop in the length scale of the nonabundant species is observed. Once the feedback has been restored, a rapid increase of the length scale is observed. To better understand these results, a spectral model is developed that incorporates turbulent production and dissipation of variance, chemistry, and spectral transfer. The model gives valuable insight into the relative importance of these processes at each scale separately, and enables one to predict the value of the variance dominating length scale in the limiting cases of very slow and very fast chemistry.
Conformational aspects of proteins at the air/water interface studied by infrared reflection-adsorption spectroscopy
Martin, A.H. ; Meinders, M.B.J. ; Bos, M.A. ; Cohen Stuart, M.A. ; Vliet, T. van - \ 2003
Langmuir 19 (2003)7. - ISSN 0743-7463 - p. 2922 - 2928.
air-water-interface - x-ray reflectivity - beta-lactoglobulin - rheological properties - neutron reflectivity - hydrophobin sc3 - soy glycinin - adsorption - monolayers - spectra
From absorption spectra obtained with infrared reflection-absorption spectroscopy (IRRAS), it is possible to obtain information on conformational changes at a secondary folding level of proteins adsorbed at the air/water interface. In addition, information on protein concentration at the interface can be retrieved by means of spectral simulation. In this paper, we studied the adsorption behavior of -casein, -lactoglobulin, and (soy) glycinin at the air/water interface and the conformational changes that may take place during adsorption. The adsorbed amount was determined as a function of time, and the values found for the three proteins agree well with ellipsometry data. Only limited conformational changes in terms of secondary structure were found. Upon adsorption at the air/water interface, loss of -sheet structure was observed for -lactoglobulin whereas the amount of unordered structure increased. For glycinin (pH 3), aggregation at the interface was observed by the appearance of an absorption band at 1630 cm-1, which involves the formation of -sheet structures. For -casein, no conformational changes were observed at all. By comparison of IRRAS spectra of adsorbed and spread protein layers, it was found that spreading of protein at an air/water interface leads to a conformational state that is somewhat different from that when adsorbed from solution
Improving Quantification of 13C CP-MAS NMR by steady state and well-defined data processing in variable contact time experiments
Lagen, B. van; Jager, P.A. de - \ 2003
Fressenius Environmental Bulletin 12 (2003)10. - ISSN 1018-4619 - p. 1211 - 1217.
natural organic-matter - linear prediction - humic substances - determining quantitation - peat bog - ft nmr - spectra - spectroscopy - soils - deposition
C-13 CP-MAS NMR is used as a non-destructive technique to measure the distribution of carbon types in humic substances. Although it is well-known that quantification of CP-MAS is problematic because different parts of the spectrum have different optimal contact times, a single contact time is used in most studies and in such cases C-13 CP-MAS NMR is only qualitative. Using Variable Contact Time experiments and back-extrapolating the signals for the various chemical shift regions to t=0 significantly improves quantification. Because signals decrease markedly during the beginning of an experiment, samples need a steady-state condition before acquisition of the Free Induction Decay (FID). Well-defined processing of the raw data significantly improves data quality. The effect of these various treatments on overall accuracy is shown.
Variability of raindrop size distributions in a squall line and implications for radar rainfall estimation
Uijlenhoet, R. ; Steiner, M. ; Smith, J.A. - \ 2003
Journal of Hydrometeorology 4 (2003). - ISSN 1525-755X - p. 43 - 61.
differential reflectivity - microwave attenuation - catastrophic rainfall - conceptual-model - r relationships - gauge data - stratiform - spectra - precipitation - clouds
The intrastorm variability of raindrop size distributions as a source of uncertainty in single-parameter and dual-parameter radar rainfall estimates is studied using time series analyses of disdrometer observations. Two rain-rate (R) estimators are considered: the traditional single-parameter estimator using only the radar reflectivity factor (Z) and a dual-polarization estimator using a combination of radar reflectivity at horizontal polarization (Z(H)) and differential reflectivity (Z(DR)). A case study for a squall-line system passing over the Goodwin Creek experimental watershed in northern Mississippi is presented. Microphysically, the leading convective line is characterized by large raindrop concentrations (>500 drops per cubic meter), large mean raindrop sizes (>1 mm), and wide raindrop size distributions (standard deviations >0.5 mm), as compared to the transition region and the trailing stratiform rain. The transition and stratiform phases have similar raindrop concentrations and mean raindrop sizes. Their main difference is that the distributions are wider in the latter. A scaling-law analysis reveals that the shapes of the scaled spectra are bent downward for small raindrop sizes in the leading convective line, slightly bent upward in the transition zone, and strongly bent upward in the trailing stratiform rain. The exponents of the resulting Z-R relationships are roughly the same for the leading convective line and the trailing stratiform rain (approximate to1.4) and slightly larger for the transition region (approximate to1.5), with prefactors increasing in this order: transition (approximate to200), convective (approximate to300), stratiform (approximate to450). In terms of rainfall estimation bias, the best-fit mean R(Z(H), Z(DR)) relationship outperforms the best-fit mean R( Z) relationship, both for each storm phase separately and for the event as a whole.
Imaging spectroscopy for early detection of nitrogen deficiency in grass swards
Schut, A.G.T. ; Ketelaars, J.J.M.H. - \ 2003
NJAS Wageningen Journal of Life Sciences 51 (2003)3. - ISSN 1573-5214 - p. 297 - 317.
grasveld - lolium perenne - mineraaltekorten - stikstof - spectroscopie - stress - reflectiefactor - grass sward - mineral deficiencies - nitrogen - spectroscopy - reflectance - red edge - canopy reflectance - thylakoid proteins - leaf reflectance - corn leaves - chlorophyll - carotenoids - spectra - growth - plants
The potential of an experimental imaging spectroscopy system with high spatial (0.16–0.28 mm²) ) and spectral resolution (5–13 nm) was explored for early detection of nitrogen (N) stress. From June through October 2000, a greenhouse experiment was conducted with 15 Lolium perenne L. mini-swards and 5 N treatments. Images were recorded twice a week. With the experimental system, spectra of grass leaves in the canopy can be obtained. Treatment effects on ground cover (GC) and changes in leaf spectral characteristics were studied separately. Leaf pixels with similar reflection intensity were grouped in intensity classes (IC). An index of reflection intensity (IRI) indicates the percentages of strongly reflecting grass pixels. Blue edge, green edge and red edge positions were calculated for each IC. Both GC and IRI increased until harvest, with largest increases for liberal N treatments. The width of the chlorophylldominated absorption band around 680 nm (CAW) increased up to a maximum of 133 nm for both liberal and limited N in the first two weeks after harvesting. CAW decreased for limited N in the second half of the growth period in contrast to liberal N. At harvest CAW explained 95% of the variation in relative dry matter (DM) yield between treatments. Principal component analyses showed an intertwined response of the principal components to both DM yield and N content. Edge positions changed strongly with IC. Possible effects of sensor characteristics, canopy geometry, leaf angle and changes in leaf characteristics with canopy position on the observed relation between IC and edge position are discussed.
Scale variability of atmospheric surface layer fluxes of energy and carbon over a tropical rain forest in southwest Amazonia; 1 diurnal conditions
Randow, C. von; Sá, L.D.A. ; Gannabathula, P.S.S.D. ; Manzi, A.O. ; Arlino, P.R.A. ; Kruijt, B. - \ 2002
Journal of Geophysical Research: Atmospheres 107 (2002)020. - ISSN 2169-897X - p. 8062 - 8062.
boundary-layer - wavelet analysis - turbulence - temperature - decomposition - similarity - modulation - canopies - aircraft - spectra
The aim of this study is to investigate the low-frequency characteristics of diurnal turbulent scalar spectra and cospectra near the Amazonian rain forest during the wet and dry seasons. This is because the available turbulent data are often nonstationary and there is no clear spectral gap to separate data into "mean" and "turbulent" parts. Daubechies-8 orthogonal wavelet is used to scale project turbulent signals in order to provide scale variance and covariance estimations. Based on the characteristics of the scale dependence of the scalar fluxes, some classification criteria of this scale dependence are investigated. The total scalar covariance of each 4-hour data run is partitioned in categories of scale covariance contributions. This permits the study of some statistical characteristics of the scalar turbulent fields in each one of these classes and, thus, to give an insight and a possible explanation of the origin of the variability of the scalar fields close to the Amazonian forest. The results have shown that a two-category classification is the most appropriate to describe the kind of observed fluctuations: "turbulent" and "mesoscale" contributions. The largest contribution of the sensible heat, latent heat, and CO2 covariance contributions occurs in the "turbulent" length scales. Mesoscale eddy motions, however, can contribute up to 30% of the total covariances under weak wind conditions. Analysis of scale correlation coefficient [r(Tvq)] between virtual temperature (Tv) and humidity (q) signals shows that the scale patterns of Tv and q variability are not similar and r(Tvq) <1 for all analyzed scales. Scale humidity skewness calculations are negative during the dry season and positive during the wet season. This suggests that different boundary layer moisture regimes occur during the dry and wet seasons.
Multispectrale luchtfotografie van de akkerbouwproefboerderij Vredepeel
Bakker, J.G.M. ; Boer, R.J. de - \ 1991
Lelystad : PAGV - 46
luchtfotografie - monitoring - bodemkarteringen - gewassen - bladoppervlakte-index - nederland - spectra - landbouwkundig onderzoek - aerial photography - soil surveys - crops - leaf area index - netherlands - agricultural research
Some factors influencing the shape of the near - infrared absorption spectrum of Chromatium, strain D
Kronenberg, G.H.M. - \ 1969
Wageningen : Veenman (Mededelingen / Landbouwhogeschool Wageningen 69-10) - 15
bacteriën - fotosynthese - absorptie - ultraviolette straling - licht - optica - spectra - bacteria - photosynthesis - absorption - ultraviolet radiation - light - optics
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