Spécial Erosion

Les publications sur le thème de la télédétection spatiale appliquée à l'étude de l'érosion des sols sont relativement récentes, puisque les premières remontent aux années 1973-1974. L'étude bibliographique présentée ici, qui ne prétend pas à une exhaustivité totale, vise à établir un inventaire des différents travaux, des méthodologies et des résultats obtenus. Trois préoccupations majeures apparaissent : la cartographie des zones dégradées : cartographie de l'érosion à petite échelle et carte F.A.O. au 1/5 000 000 ; la quantification de l'érosion : modèles d'érosion des sols et modèles hydrologiques ; le suivi de l'érosion : analyses multitemporelles fondées sur des variations de luminance ou d'albédo. Toutes les publications examinées, sauf deux, ont pour objet l'étude de l'érosion des sols dans un domaine spectral allant du visible au proche infrarouge. L'analyse des résultats obtenus et des expérimentations met en valeur les possibilités offertes par la télédétection spatiale de même que ses limites. Les nouveaux capteurs nous permettent d'envisager une nouvelle approche des milieux dégradés et d'obtenir de précieuses informations complémentaires à la planification agricole. (Résumé d'auteur

Spécial Erosion

Les publications sur le thème de la télédétection spatiale appliquée à l'étude de l'érosion des sols sont relativement récentes, puisque les premières remontent aux années 1973-1974. L'étude bibliographique présentée ici, qui ne prétend pas à une exhaustivité totale, vise à établir un inventaire des différents travaux, des méthodologies et des résultats obtenus. Trois préoccupations majeures apparaissent : la cartographie des zones dégradées : cartographie de l'érosion à petite échelle et carte F.A.O. au 1/5 000 000 ; la quantification de l'érosion : modèles d'érosion des sols et modèles hydrologiques ; le suivi de l'érosion : analyses multitemporelles fondées sur des variations de luminance ou d'albédo. Toutes les publications examinées, sauf deux, ont pour objet l'étude de l'érosion des sols dans un domaine spectral allant du visible au proche infrarouge. L'analyse des résultats obtenus et des expérimentations met en valeur les possibilités offertes par la télédétection spatiale de même que ses limites. Les nouveaux capteurs nous permettent d'envisager une nouvelle approche des milieux dégradés et d'obtenir de précieuses informations complémentaires à la planification agricole. (Résumé d'auteur

ESTIMATION OF THE THICKNESS AND EMULSION RATE OF OIL SPILLED AT SEA USING HYPERSPECTRAL REMOTE SENSING IMAGERY IN THE SWIR DOMAIN

The thickness and the emulsion rate of an oil spill are two key parameters allowing to design a tailored response to an oil discharge. If estimated on per pixel basis at a high spatial resolution, the estimation of the oil thickness allows the volume of pollutant to be estimated, and that volume is needed in order to evaluate the magnitude of the pollution, and to determine the most adapted recovering means to use. The estimation of the spatial distribution of the thicknesses also allows the guidance of the recovering means at sea. The emulsion rate can guide the strategy to adopt in order to deal with an offshore oil spill: efficiency of dispersants is for example not identical on a pure oil or on an emulsion. Moreover, the thickness and emulsion rate allow the amount of the oil that has been discharged to be estimated. It appears that the shape of the reflectance spectrum of oil in the SWIR range (1000–2500nm) varies according to the emulsion rate and to the layer thickness. That shape still varies when the oil layer reaches a few millimetres, which is not the case in the visible range (400–700nm), where the spectral variation saturates around 200 μm (the upper limit of the Bonn agreement oil appearance code). In that context, hyperspectral imagery in the SWIR range shows a high potential to describe and characterize oil spills. Previous methods which intend to estimate those two parameters are based on the use of a spectral library. In that paper, we will present a method based on the inversion of a simple radiative transfer model in the oil layer. We will show that the proposed method is robust against another parameter that affects the reflectance spectrum: the size of water droplets in the emulsion. The method shows relevant results using measurements made in laboratory, equivalent to the ones obtained using methods based on the use of a spectral library. The method has the advantage to release the need of a spectral library, and to provide maps of thickness and emulsion rate values per pixel. The maps obtained are not composed of regions of thickness ranges, such as the ones obtained using discretized levels of measurements in the spectral library, or maps made from visual observations following the Bonn agreement oil appearance code

DETECTION AND DISCRIMINATION OF THE THICK OIL PATCHES ON THE SEA SURFACE

Detection of natural or accidental oil slick at sea surface is important both for exploration purposes and for environment protection. Radar imagery, either satellite or airborne is the prime tool to detect those slicks. Radar is widely used by the national agencies to monitor their maritime areas for accidental pollutions or boat discharges. Radar images can detect oil slick even in the presence of clouds. However the sea surface back scattered energy is rather insensitive to oil thickness. On the contrary several studies tend to prove that optical data may be used to estimate the oil thickness. These data may be in the form of hyperspectral data or thermal infrared data. The objective of this study is to show that SWIR satellite data which are more widely available than hyperspectral data, better resolved than thermal data and available at a very limited cost, can be used to detect and qualitatively assess the thickness of oil slicks. This is important to assess volumes of naturally release oil in the oceans and in case of a crisis to send intervention teams where oil is thickest

The roles of calcium and manganese ions in the in vitro conversion of 1-aminocyclopropane-1-carboxylic acid to ethylene by lentil root membranes

Ca2+ and Mn2+ activate the conversion of 1-aminocyclopropane-1-carboxylic acid (ACC) by root microsomes of Vicia lens as they do in other similar systems. The preparation of microsomes in the presence of Mn2+ greatly increases their ability to convert ACC into ethylene, without addition of Mn2+ in the reaction mixture. Ca2+ does not have this property. The effect could not be attributed to Mn2+ entrapping into membrane vesicles (sonication followed by repelleting had no effect) but, possibly, in part to Mn2+-mediated binding to microsomes of a soluble factor favouring the conversion of ACC to C2H4. Although no direct correlation could be established in vitro between ethylene-forming-enzyme (EFE) and peroxidase activities, some soluble peroxidases might be this soluble factor. Mn2+ favoured attachment to membranes of some peroxidase activity from the soluble fraction and from commercial HRP and lipoxygenase. This binding effect of Mn2+ cannot be readily distinguished from its role in the generation of a chain of free radicals and in redox mechanisms