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.
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