Ragweed, Ambrosia artemisiifolia, is an annual plant, the pollen of which is responsible for respiratory allergies. In 2005, these allergies affected up to 20% of the population in parts of the department of Rhne. This is a major health problem for six of the eight departments of the Rhne-Alpes region (Ain, Ardche, Drme, Isre, Loire and Rhne). Our objective was to validate a method to map ragweed infestation in a village and then to extend this experiment to a department. Using methods developed by Auda et al. (2002a), we undertook a survey of ragweed infestation at the end of July 2005 in the village of Estrablin (Isre). Plots of land were registered in a Geographical Information System, with indications of crop type and ragweed infestation included in each plot. The sample area covered 3650km2 and constituted 30% of the total area of the village. The data were used to validate a SPOT 5 multispectral satellite image captured on 16 August 2005. Analysis of the ground data confirmed the extent of the ragweed infestation. More than 90% of the sample area was found to be infested. The image processing was based on crossing the crop type with the degree of infestation, using maximum likelihood classification. The accuracy of the method of detection used was demonstrated by the percentage of correctly classified pixels (45%), the reasons for confusion and the clarity of the visual representations. The success of our approach is highly influenced by the availability of high-quality images. Its feasibility, which is linked therefore to technical constraints, is examined in relation to space agency programmes.

P-138 Abstract: The control of invasive plants proliferation requires: their identification for an adequate detection, the mapping of their areas, implementation policies aiming at controlling their spread. Remote sensing technology is probably the most efficient tool for solving points 1 and 2 especially as large geographical areas can be surveyed in a relatively short time. Since 2001, thanks to a cooperation between a ragweed research association and the “Centre National de la Recherche Scientifique” (CNRS), new methods have been developed for the detection from space of the short ragweed, Ambrosia artemisiifolia L. Its spectral signature was identified for the first time in the world. In 2003, ground experiments took place during July and August around Lyon and satellite analysis were carried out. This experiment demonstrates that areas of 100 square meters are detectable from space. This result is mainly due to an extreme heatwave during this summer. Short ragweed continued to develop green leaves during this long period of dryness, this characteristic preventing to mix up it with other plants. In 2005, our experiments cover only some thousand square meters, nevertheless, it appears that this weed can be well differentiated from other species. A participation of “Communauté d'Agglomération du Pays Viennois≫ allowed to have an important ground survey in a small town and its surroundings (Estrablin, Isère, France) and so to validate methodology. For each studied parcel, informations concerning shape, farming type (corn, maize, sunflower…) and infestation degrees are registered by the mean of a Geographic Information System (SIG) on a cadastral map. In the same time, a multispectral Spot 5 Image (10m/pixel) is acquired on the 2005/August/16 and the both are compared. The performance of the method is linked to acquiring images at a convenient date. The method is limited by technical constraints which must be examined in the context of the future programs of Spaces Agencies. However all the previous observations and the 2005 study, with a very precise ground inquiry, do show that, at a commune scale, it is possible to give a cartography of the short ragweed infested zones using remote sensing.

Numerous methods exist for the analysis of changes applied to time series of satellite images. After a quick review of these methods, a new approach is proposed. This approach is based on residuals computed from PCA (Principal Component Analysis) on a NDVI table. It consists of: computing the NDVI variable for each date; building a space x time table which joins NDVI variables; carrying out a PCA on this table; choosing the number, k , of factors of PCA which explain time invariant landscape structures; and computing residuals between NDVI table and the table computed from the k factors. This method applied to the analysis of a series of three Landsat TM scenes acquired in 1983, 1984 and 1993 on the Camargue region (France) allows separation of the permanent land use structure from its annual variations. The specificity of the so called 'island Camargue' is clearly shown; control of water exchanges by man alters the land use every year.

This study is an attempt to produce an assessment of the impact of shrimp aquaculture in the Mekong Delta (Viet Nam) on mangrove ecosystems. For this exercise we selected two sub-areas (Ca Mau and Tra Vinh provinces) encompassing a variety of land uses and ecological conditions. Twenty stations in Tra Vinh and 15 stations in Ca Mau have been surveyed several times from September 2000 to March 2002. Field investigations included mangrove soils studies, measurements of pH and salinity of the water, analysis of mangrove flora, and density and structure of the vegetation. Four Syst@me Probatoire de l'Observation de la Terre (SPOT) scenes were used for the discrimination of mangrove types and for the delineation of landscape units. For the first time, five ecologically distinct landscape classes were identified and delineated. Their possible links with the farming and yields of high valued species of shrimps, especially the giant tiger shrimp (Penaeus monodon) destined for export markets, need further studies. Since 1965, about 30% of mangrove ecosystems have been lost in Ca Mau Province and more than 30% of present mangroves are replanted monospecific stands. To the best of our knowledge, this is the first study which demonstrates that, in spite of deep and ancient man interactions in the Mekong Delta, five ecologically distinct classes of land use can be defined. Satellite surveys confirm a clear distribution of landscape units with possible links with shrimp aquaculture potentialities.

Over the last twenty years, extensive shrimp aquaculture has dramatically expanded in the coastal fringe of the Mekong Delta. This occurred primarily at the expense of the mangrove, already severely affected by the Vietnam war. More recently, paddy land has been reclaimed for shrimp aquaculture, a higher currency earner. However, production collapses have frequently occurred and the overall yield has remained far below the expectations for traditional farming. A number of parameters enter into play in the success of this activity, summarized in two questions: i) is the Mekong deltaic environment - under high continental pressure - suitable to shrimp farming, ii) if not, is it possible to adapt the low technicity of rural poor farmers to reach economic sustainability? This paper is based on the analysis of two full sets of data. Ecological data are composed of hydrobiological, hydrodynamical and land cover data. The former were collected at a number of stations encompassing the local variability, the latter were derived from processing Spot imagery. Surveys of farms zootechniques and management were conducted over a network of shrimp farms, with the objective of determining the part played by these data in farming efficiency, with respect to the environmental conditions. Statistical methods, i.e. PCA for continuous variables and MCA (Multiple Correspondance Analysis) for qualitative ones respectively provided a zonation of the stations and a classification of the farms. GIS illustrated the distribution of the latter within the former. Summarizing yields per ecological zone revealed a production pattern that might lead to review present land use planning policy and in particular the widespread "integrated mangrove-shrimp" system.

The detection of dense populations of ragweed (Ambrosia artemisiifolia L.) using spatial remote sensing methods seems possible. A sufficiently accurate map of-parcels of land infested with ragweed could offer new possibilities to engage in weeding campaigns and to appreciate the space-time evolution of this plant, Obviously, the main difficulties in this approach are related to the heterogeneous floral composition of herbaceous stands and to the risk of confusion of the spectral composition of ragweed with that of other species. On 21 July 2001, we carried out field surveys in zones with abundant ragweed near Lyon (Department of the Rhone), and we used the resulting data in connection with two images of the same area obtained by the Terra ASTER 1B. satellite on 26 June and 13 August 2001. A measurement was made in the laboratory on a sample of the plant obtained from the same area to determine its reflectance spectrum. On analysis of the,spatial images, we were able to localize herbaceous patches in which ragweed is dominant. When the density of this plant decreases, the reflectance signals of the populations become multiform, requiring further studies. Further progressin be expected when sensors such as the spatial tel IKONOS (operating at a resolution in the order of I to 5 m) or the future SPOT 5 (operating at a resolution of 2 to 3 m in the panchromatic mode or at 10 m in a multispectral mode) will be used, allowing us to work at a resolution on the order of one meter. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.

DART (Discrete Anisotropic Radiative Transfer) model simulates 3-D radiative transfer in the "Earth - Atmosphere" system from the visible to the thermal infrared domains (0.3µm - 15µm), for natural (e.g., forests with different tree species) and urban landscapes, with / without topography and atmosphere. Its two major outputs are: - remote sensing images (directional reflectance and temperature) for any sun/view direction, altitude and spatial resolution. Data bases specify atmosphere and earth material parameters. - 3-D radiation budget. This is used for simulating photosynthesis, energy and mass fluxes. DART simulates landscapes as 3-D cell matrices with scene elements optical properties (reflectance, emissivity) either isotropic (lambertian) or not (specular,...). It is coupled with PROSPECT leaf model. It uses a friendly Graphic User Interface (GUI) to input parameters, to create/resample DEMs, to run multiple simulations, to display results,... Its accuracy was validated by the European Research Center (RAMI experiment). It was patented in 2003 and professionalized by CNES with Magellium. It is nowadays a useful tool for conducting remote sensing studies of Earth surfaces. Paul Sabatier University delivers free licenses to scientists.