DETECTION OF CRESCENT SAND DUNES CONTOURS IN SATELLITE IMAGES USING AN ACTIVE SHAPE MODEL WITH A CASCADE CLASSIFIER

Crescent sand dunes called barchans are the fastest moving sand dunes in the desert, causing disturbance for infrastructure and threatening human settlements. Their study is of great interest for urban planners and geologists interested in desertification (Hugenholtz et al., 2012). In order to study them at a large scale, the use of remote sensing is necessary. Indeed, barchans can be part of barchan fields which can be composed of thousands of dunes (Elbelrhiti et al.2008). Our region of interest is located in the south of Morocco, near the city of Laayoune, where barchans are stretching over a 400&thinsp;km corridor of sand dunes. We used image processing techniques based on machine learning approaches to detect both the location and the outlines of barchan dunes. The process we developed combined two main parts: The first one consists of the detection of crescent shaped dunes in satellite images using a supervised learning method and the second one is the mapping of barchans contours (windward, brink and leeward) defining their 2D pattern. For the detection, we started by image enhancement techniques using contrast adjustment by histogram equalization along with noise reduction filters. We then used a supervised learning method: We annotated the samples and trained a hierarchical cascade classifier that we tested with both Haar and LBP features (Viola et Jones, 2001; Liao et al., 2007). Then, we merged positive bounding boxes exceeding a defined overlapping ratio. The positive examples were then qualified to the second part of our approach, where the exact contours were mapped using an image processing algorithm: We trained an ASM (Active Shape Model) (Cootes et al., 1995) to recognize the contours of barchans. We started by selecting a sample with 100 barchan dunes with 30 landmarks (10 landmarks for each one of the 3 outlines). We then aligned the shapes using Procrustes analysis, before proceeding to reduce the dimensionality using PCA. Finally, we tested different descriptors for the profiles matching: HOG features were used to construct a multivariate Gaussian model, and then SURF descriptors were fed an SVM. The result was a recursive model that successfully mapped the contours of barchans dunes. We experimented with IKONOS high resolution satellite images. The use of IKONOS high resolution satellite images proved useful not only to have a good accuracy, but also allowed to map the contours of barchans sand dunes with a high precision. Overall, the execution time of the combined methods was very satisfying.</p

Temperature dependencies of the relaxation, order, and segregation at a ?= 5 (210) [001] tilt grain boundary in Cu3Au

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A Monte Carlo study of the thermal properties of Cu3Au low index surfaces

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Thermal disordering near a ?=3{111} twin boundary in Cu3Au

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Détermination et spéciation chimique du plomb et du chrome dans les sédiments superficiels du Sebou, Maroc

Total concentration of lead and chromium and the spéciation of these metals in sediments of the River Sebou are studied to establish the extent to wich they are polluted and their capacity of remobilitation. Triacid attaque (HT-HNO3-HClO4) was used for the determination of total trace metal. The result show a highly polluted area (Cr, Pb) in the oued Fès area, for metal spéciation, a combination of two sequential schems was used (Tessier & al., 1979 ; Luoma & Bryan, 1979). From the results obtained, it can be concluded that Pb is mainly bonded to Fe-Mn hydroxides (in the lowest water period) and to the carbonate phase (in growing water period) and to the carbonate phase (in growing water period). Cr was also bonded to the hydroxide phase in the lowest water period, but in the growing water, this association caracterise only the riches sites (F, Rl, SI). In the other sections of the river, Cr was specially bonded to the residual phase.Des échantillons de sédiments superficiels prélevés le long du Sebou et dans ses affluents ont fait l'objet d'une étude par fractionnement chimique du chrome et du plomb. L'analyse du métal total met en exergue la forte contamination de l'oued Fès aussi bien en crue qu'en étiage. L'analyse par fractionnement chimique de ces deux métaux associée à un traitement statistique (SAS) montre que la distribution du plomb est contrôlée essentiellement par les sulfures et les silicates en période d'étiage, et par les carbonates en période de crue. La répartition du chrome est régie par les hydroxydes et la matière organique en étiage. En crue, le métal est surtout répartit sous la dépendance des hydroxydes. Ces types d'associations soulignent ainsi la grande mobilité du chrome par rapport au plomb.Azzaoui S., El Hanbali M., Leblanc Marc, El Boukhari A., Srhiri A. Détermination et spéciation chimique du plomb et du chrome dans les sédiments superficiels du Sebou, Maroc. In: Géologie Méditerranéenne. Tome 26, numéro 1-2, 1999. pp. 113-119

DETECTION OF BARCHAN DUNES IN HIGH RESOLUTION SATELLITE IMAGES

Barchan dunes are the fastest moving sand dunes in the desert. We developed a process to detect barchans dunes on High resolution satellite images. It consisted of three steps, we first enhanced the image using histogram equalization and noise reduction filters. Then, the second step proceeds to eliminate the parts of the image having a texture different from that of the barchans dunes. Using supervised learning, we tested a coarse to fine textural analysis based on Kolomogorov Smirnov test and Youden’s J-statistic on co-occurrence matrix. As an output we obtained a mask that we used in the next step to reduce the search area. In the third step we used a gliding window on the mask and check SURF features with SVM to get barchans dunes candidates. Detected barchans dunes were considered as the fusion of overlapping candidates. The results of this approach were very satisfying in processing time and precision

Growth and lattice dynamics of Co nanoparticles embedded in Ag: A combined molecular-dynamics simulation and Mössbauer study

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Lattice dynamics of Co nanoparticles in Ag

A comparison is made between the lattice dynamics of cobalt embedded in silver, studied by Mossbauer spectroscopy and by classical molecular dynamics (MD). The MD is achieved in the NPT ensemble by means of the Rahman Parrinello technique which accounts for the temporal fluctuations of all the components of the stress tensor. Atomic interactions are described within an empirical embedded atom model. The mean square thermal vibration amplitude of substitutional Co is calculated and found to compare well with experimental value extracted from Mossbauer spectroscopy. Mossbauer spectroscopy shows the Debye temperature to be cluster size dependent and a comparison with MD suggests the possibility of quantitative cluster size estimates.info:eu-repo/semantics/publishe

Co nanoprecipitates formed in Ag upon ion implantation: their lattice dynamical properties

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