Éditeur(s) : HAL CCSD Elsevier
Résumé : Vegetation phenology is the study of the timing of seasonal events that are considered to be the result of adaptive responses to climate variations on short and long time scales. In the field of remote sensing of vegetation phenology, phenological metrics are derived from time series of optical data. For that purpose, considerable effort has been specifically focused on developing noise reduction and cloud-contaminated data removal techniques to improve the quality of remotely-sensed time series. Comparative studies between time series composed of satellite data acquired under clear and cloudy conditions and from radiometric data obtained with high accuracy from ground-based measurements constitute a direct and effective way to assess the operational use and limitations of remote sensing for predicting the main plant phenological events. In the present paper, we sought to explicitly evaluate the potential use of MODerate resolution Imaging Spectroradiometer (MODIS) remote sensing data for monitoring the seasonal dynamics of different types of vegetation cover that are representative of the major terrestrial biomes, including temperate deciduous forests, evergreen forests, African savannah, and crops. After cloud screening and filtering, we compared the temporal patterns and phenological metrics derived from in situ NDVI time series and from MODIS daily and 16-composite products. We also evaluated the effects of residual noise and the influence of data gaps in MODIS NDVI time series on the identification of the most relevant metrics for vegetation phenology monitoring. The results show that the inflexion points of a model fitted to a MODIS NDVI time series allow accurate estimates of the onset of greenness in the spring and the onset of yellowing in the autumn in deciduous forests (RMSE <= one week). Phenological metrics identical to those provided with the MODIS Global Vegetation Phenology product (MDC12Q2) are less robust to data gaps, and they can be subject to large biases of approximately two weeks or more during the autumn phenological transitions. In the evergreen forests, in situ NDVI time series describe the phenology with high fidelity despite small temporal changes in the canopy foliage. However, MODIS is unable to provide consistent phenological patterns. In crops and savannah, MODIS NDVI time series reproduce the general temporal patterns of phenology, but significant discrepancies appear between MODIS and ground-based NDVI time series during very localized periods of time depending on the weather conditions and spatial heterogeneity within the MODIS pixel. In the rainforest, the temporal pattern exhibited by a MODIS 16-day composite NDVI time series is more likely due to a pattern of noise in the NDVI data structure according to both rainy and dry seasons rather than to phenological changes. More investigations are needed, but in all cases, this result leads us to conclude that MODIS time series in tropical rainforests should be interpreted with great caution. (C) 2013 Elsevier Inc. All rights reserved.
ISSN: 0034-4257

hal-01032407
https://hal.archives-ouvertes.fr/hal-01032407
DOI : 10.1016/j.rse.2013.01.010

Éditeur(s) : Blackwell science
Résumé : This paper deals with the design of modelling tools suitable for investigating the consequences of alternative policies on the dynamics of resources and fisheries, such as the evaluation of marine protected areas (MPA). We first review the numerous models that have been developed for this purpose, and compare them from several standpoints: population modelling, exploitation modelling and management measure modelling. We then present a generic fisheries simulation model, Integration of Spatial Information for FISHeries simulation (ISIS-Fish). This spatially explicit model allows quantitative policy screening for fisheries with mixed-species harvests. It may be used to investigate the effects of combined management scenarios including a variety of policies: total allowable catch (TAC), licenses, gear restrictions, MPA, etc. Fisher's response to management may be accounted for by means of decision rules conditioned on population and exploitation parameters. An application to a simple example illustrates the relevance of this kind of tool for policy screening, particularly in the case of mixed fisheries. Finally, the reviewed models and ISIS-Fish are discussed and confronted in the light of the underlying assumptions and model objectives. In the light of this discussion, we identify desirable features for fisheries simulation models aimed at policy evaluation, and particularly MPA evaluation.
Fish and Fisheries (1467-2960) (Blackwell science), 2005-12 , Vol. 6 , N. 4 , P. 307-349

Droits : 2005 Blackwell Publishing, Inc
http://archimer.ifremer.fr/doc/2005/publication-1031.pdf
DOI:10.1111/j.1467-2979.2005.00199.x
http://archimer.ifremer.fr/doc/00000/1031/

Éditeur(s) : Canadian Science Publishing, Nrc Research Press
Résumé : We develop a spatially and seasonally explicit bioeconomic model with three fleet dynamics processes built in endogenously. The model has been applied to the large French trawlers harvesting a medium-depth demersal stock, North Sea saithe (i.e., pollock, Pollachius virens), and a mix of deepwater species over a 10-year period (1999-2008), and the predictions have been contrasted with observations. The best overall fit was achieved where effort allocation was determined to be 80% by traditions and 20% by economic opportunism and where harvest efficiency increased by 8% a year. With this fleet dynamics parameterization, annual trends in fishing effort and profit were well reproduced by the model over the whole time period. Time series of the observed fishing effort by metier were generally well fitted by the model over the period 1999-2003, but less so over 2004-2008. The model also reasonably reproduced the catches by species over most of the time series, except for black scabbardfish (Aphanopus carbo).
Nous développons un modèle bio-économique spatial et saisonnier dans lequel trois processus caractérisant la dynamique des flottilles sont décrits de manière explicite. Ce modèle a été appliqué aux grands chalutiers français exploitant le lieu noir de mer du Nord (Pollachius virens) et une variété d'espèces profondes au cours d'une période de 10 ans (1999–2008), et les prévisions ont été contrastées avec les observations. Le meilleur ajustement est obtenu lorsque l'allocation de l'effort de pêche est déterminée a` hauteur de 80% par les traditions et 20% par l'opportunisme économique, et lorsque l'augmentation de l'efficacité de pêche est d'environ 8% par an. En paramétrant ainsi le module de dynamique des flottilles, les tendances annuelles de l'effort de pêche et du profit sont bien reproduites par le modèle sur l'ensemble de la période. Les variations temporelles de l'effort de pêche par métier sont généralement bien prises en compte sur la période 1999–2003, mais non sur la période 2004–2008. Le modèle ajuste les captures raisonnablement sur la plus grande partie de la période d'étude, pour toutes les espèces sauf le sabre noir (Aphanopus carbo).
Canadian Journal Of Fisheries And Aquatic Sciences (0706-652X) (Canadian Science Publishing, Nrc Research Press), 2013-07 , Vol. 70 , N. 7 , P. 992-1010

Droits : 2013 NRC Research Press
http://archimer.ifremer.fr/doc/00151/26227/24329.pdf
DOI:10.1139/cjfas-2012-0326
http://archimer.ifremer.fr/doc/00151/26227/

Éditeur(s) : Elsevier
Résumé : In order to provide reliable scientific advice and support for fisheries management, it is necessary to evaluate the biological and economic sustainability of complex fisheries, such as multi-species multi-fleet fisheries. Existing policy-screening modelling tools are not fully suitable in this purpose due to either an over-simplified description of population dynamics, or due to the lack of consideration of economic aspects. In this paper, we present a package that enables quantitative bioeconomic assessment of management scenarios. Population dynamics is described through spatially- and seasonally-explicit models. Exploitation dynamics is characterized by several fishing activities with specific spatial and seasonal features, and practiced by several kinds of vessels with specific technical characteristics. Exploitation costs and revenues are considered at several levels: the fishing trip, the fishing unit (vessel and crew), and the vessel owner. The model is generic and can be used for different types of fisheries. A database is attached to the software for the storage and updating of information for each fishery. This includes the specification of model dimensions and of the parameters describing populations and exploitation. Several model assumptions regarding either population or exploitation may be adapted to suit a specific fishery. Both policies and corresponding fishers' response may be interactively specified through JAVA (TM) scripts. This version of ISIS-Fish allows for the calculation of biological and economic consequences of a range of policies, including conventional ones like catch and effort controls, and alternative policies such as marine protected areas. To facilitate policy-screening in a high-dimension parameter space, the software includes features, like interfaces for sensitivity analysis and simulation queues. (C) 2009 Elsevier B.V. All rights reserved.
Ecological Modelling (0304-3800) (Elsevier), 2009-04 , Vol. 220 , N. 7 , P. 1013-1033

Droits : 2009 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/2009/publication-6782.pdf
DOI:10.1016/j.ecolmodel.2009.01.007
http://archimer.ifremer.fr/doc/00000/6782/

Éditeur(s) : Oxford Univ Press
Résumé : Spatio-seasonal explicit simulation models can predict the impact of spatial management measures on marine fish populations and fishing activities. As fisheries are complex systems, fisheries simulation models are often complex, with many uncertain parameters. Here, the methodology is provided to deliver fishery diagnostics within an uncertainty context using a complex simulation tool. A sensitivity analysis of the model is performed on model outputs using partial least-squares to identify the most sensitive parameters. The impact of several management measures is then simulated using a statistical simulation design taking into account the uncertainty of the selected sensitive parameters. This approach was applied to the Bay of Biscay anchovy stock using the ISIS-Fish (Integration of Spatial Information for Simulation of Fisheries) model to assess the impact of imposing marine protected areas (MPAs) conditionally on parameter uncertainty. The diagnostic appeared to be highly sensitive to the mortality of larvae and juveniles, growth, and reproduction. The uncertainty of the values of these parameters did not permit any of the simulated MPA designs to be proposed. However, according to anchovy catch and biomass, the simulations allowed the low impact of closure duration to be shown and underscored the utility of protecting such key processes as spawning.
Ices Journal Of Marine Science (1054-3139) (Oxford Univ Press), 2010-07 , Vol. 67 , N. 5 , P. 1063-1075

Droits : 2010 ICES/CIEM. Oxford journals
http://archimer.ifremer.fr/doc/00011/12234/9281.pdf
DOI:10.1093/icesjms/fsq002
http://archimer.ifremer.fr/doc/00011/12234/