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| Petitgas, Pierre; Woillez, Mathieu; Doray, Mathieu; Rivoirard, Jacques. |
| Marine research survey data on fish stocks often show a small proportion of very high-density values, as for many environmental data. This makes the estimation of second-order statistics, such as the variance and the variogram, non-robust. The high fish density values are generated by fish aggregative behaviour, which may vary greatly at small scale in time and space. The high values are thus imprecisely known, both in their spatial occurrence and order of magnitude. To map such data, three indicator-based geostatistical methods were considered, the top-cut model, min–max autocorrelation factors (MAF) of indicators, and multiple indicator kriging. In the top-cut and MAF approaches, the variable is decomposed into components and the most continuous ones... |
| Tipo: Text |
Palavras-chave: Top-cut; MAF; Indicators; Co-kriging; Skewed distribution; Anchovy; Bay of Biscay; Fisheries survey data; Aggregation. |
| Ano: 2018 |
URL: https://archimer.ifremer.fr/doc/00429/54021/55339.pdf |
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| Petitgas, Pierre; Doray, Mathieu; Masse, Jacques; Grellier, Patrick. |
| Fish length frequency histograms from research surveys are of prime importance for identifying habitats of different life stages, as well as for stock assessment. However, no method has thus far been available for mapping these histograms as spatially varying curves. Here, a procedure is applied to map spatially connected curves, and detail is given on how it can be applied to map the length frequency histograms. At each sample location, a fish length frequency histogram is given as a vector of non-independent values. The histogram is first modelled as a polynomial expansion on the basis of orthogonal polynomials. Then, the polynomial coefficients are mapped by co-kriging, after fitting a model of co-regionalization. The length frequency map is finally... |
| Tipo: Text |
Palavras-chave: Co-kriging; European anchovy; Fish length; Functional kriging; Habitat; Mapping curves. |
| Ano: 2011 |
URL: http://archimer.ifremer.fr/doc/00049/16042/13581.pdf |
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| Schaffrath,Valter Roberto; Gonçalves,Antônio Carlos Andrade; Sousa,António Jorge; Tormena,Cássio Antonio. |
| The spatial correlation between soil properties and weeds is relevant in agronomic and environmental terms. The analysis of this correlation is crucial for the interpretation of its meaning, for influencing factors such as dispersal mechanisms, seed production and survival, and the range of influence of soil management techniques. This study aimed to evaluate the spatial correlation between the physical properties of soil and weeds in no-tillage (NT) and conventional tillage (CT) systems. The following physical properties of soil and weeds were analyzed: soil bulk density, macroporosity, microporosity, total porosity, aeration capacity of soil matrix, soil water content at field capacity, weed shoot biomass, weed density, Commelina benghalensis density,... |
| Tipo: Info:eu-repo/semantics/article |
Palavras-chave: Cross-variogram; Co-kriging; Physical and biological meanings. |
| Ano: 2015 |
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-06832015000100279 |
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