Terrain

... JPEG - 104.3 ko Image 2 DVD de Wa'azin Kassa. ... Dans les cas des deux femmes qui voulaient se procurer le dernier album d'AbdulAziz, on peut lire à travers leur attachement un besoin de rester en relation avec un discours qu'elles ne trouvent pas toujours à leurs nouveaux ...

This paper revisits several aspects of defining and computing the anomalous gravity data for purposes of gravimetric inversion/interpretation. Attention is paid to evaluation of a refined global topographic correction to the gravity disturbance based on the reference ellipsoid (RE) and constant reference density for solid topography onshore and sea water density for liquid topography offshore. The global bathymetric correction is discussed. Two issues associated with compilation and inversion of bathymetrically and topographically corrected gravity disturbances in regions of negative ellipsoidal (geodetic) heights are pointed out: the evaluation of normal gravity and the harmonic continuation of the gravity data. Stripping, the removal of an effect of a known density contrast, is considered also for additional geological elements such as lakes, glaciers, sedimentary basins, isostatic mountain roots, etc. The stripping corrections are discussed in the context of the gravimetric inverse problem.

A new global elevation dataset known as G-DEM, based on the ASTER satellite imagery, will be released in late 2008. G-DEM will be the best freely available global digital elevation model (DEM) at a horizontal resolution of 1 arc second. We assess the quality of G-DEM in ...

This paper presents a method to forecast terrain trafficability from visual appearance. During training, the system identifies a set of image chips (or exemplars) that span the range of terrain appearance. Each chip is assigned a vector tag of vehicle-terrain interaction characteristics that are obtained from on-board sensors and simple performance models, as the vehicle traverses the terrain. The system uses the exemplars to segment images into regions, based on visual similarity to the terrain patches observed during training, and assigns the appropriate vehicle-terrain interaction tag to them. This methodology will therefore allow the online forecasting of vehicle performance on upcoming terrain. Currently, we are using fuzzy c-means clustering and exploring a number of different features for characterizing the visual appearance of the terrain.

Evaluation of soil erodibility is an important task for Mediterranean lands, in which fertility and crop yield are significantly affected by soil erosion. The soil physicochemical parameters affecting soil erodibility are highly variable in space and, as for many other environmental variables, sample measurements are generally not enough for assessing its spatial variability with an acceptable level of uncertainty at the scales of practical interest. This study illustrates the procedure applied for estimating the pattern of soil erodibility across the Sele Basin (Southern Italy), where soil properties have been measured on a limited number of sparse samples. Sampled data were integrated with other sparse data estimated by local regression functions, which relate soil erodibility to auxiliary variables, such as terrain attributes and land system class memberships. Sampled and estimated data were merged in a composed data set to assess the spatial pattern of soil erodibility by ordinary kriging. The proposed approach offers effective spatial predictions, and it is exportable to regions where financial costs for soil sampling are not feasible.

A new dynamic, scale-dependent subgrid model based on Lagrangian time averaging is proposed. The model is tested in large eddy simulations (LES) of high-Reynolds number boundary layer flows over homogeneous and heterogeneous rough surfaces. The model computes averages over time, following fluid trajectories of the resolved velocity field. The model allows for scale-dependence of the coefficient by including a second test-filtering operation to determine how the coefficient changes as a function of scale. Validation tests in LES of high Reynolds number boundary layer flow over homogeneous surfaces are performed at various resolutions. The model is also tested against detailed atmospheric boundary layer data that include measurements of the response of the flow to abrupt transitions in wall roughness. Results show that the dynamic Smagorinsky coefficient close to the wall is very sensitive to the underlying local surface roughness, thus justifying the use of the Lagrangian formulation. It also reproduces experimental data more accurately than the planar-averaged formulation in simulations over heterogeneous rough surfaces.

Complete polarimetric signatures of a layer of random, nonspherical discrete scatterers overlying a homogeneous half space are studied with the first- and second-order solutions of the vector radiative transfer theory. The vector radiative transfer equation contains a general nondiagonal extinction matrix and a phase matrix that are averaged over particle orientations. The nondiagonal extinction matrix accounts for the difference in propagation constants and the difference in attenuation rates between the two characteristic polarisations. The Mueller matrix based on the first-order and second-order multiple scattering solutions of the vector radiative transfer equation is calculated. The copolarized and depolarized returns are also calculated

SummaryFlow simulation in ungauged catchments is presently regarded as one of the most challenging tasks in surface water hydrology. Many of the ungauged catchments are located in the headwaters of rivers in mountainous regions of the world having enormous potential for sustainable water resource development. However, due to inaccessibility, rugged and inhospitable terrain, and historical lack of foresight concerning the need to have these headwaters adequately gauged, their potential is not readily realizable. Many downstream sites also suffer from non-availability of site-specific data as even in countries having extensive networks of gauged stations data may not be available at sites where these are most needed. As predictive tools for water resources, water quality, natural hazard mitigation and water availability assessment are generally data-driven, the lack of adequate hydrometric records poses difficult problems for planners, engineers, managers, and stake-holders alike. In this study, a methodology is developed for flow simulation in ungauged catchments using a regionalisation and multi-model approach involving a suite of rainfall-runoff models and combination techniques. Daily observed hydrometeorological data for 12 French catchments are used for illustrating the procedures. Following a preliminary investigation of the regional homogeneity of that group of catchments, three regional flow simulation techniques are applied. Although all 12 catchments are gauged, initially each catchment is successively considered as being ungauged for the purpose of flow simulation in that catchment, their actual discharges being subsequently used for evaluating the performance of the flow estimation procedures for the catchment. The Nash-Sutcliffe efficiency index ( R2) is used for assessing and ranking the relative performances of the regionalisation-model couples to identify the most appropriate couple for the region. The final step of applying that couple to a truly ungauged (13th) catchment in the region is described. Results are presented and conclusions drawn on the efficacy of the regional-multi-model approach. Of the couples considered, the pooling method of regionalisation coupled with the conceptual soil moisture accounting and routing (SMAR) model is deemed to be the best for simulating flow in an ungauged catchment in the region.

Chlorophyll fluorescence and landscape-level reflectance imagery were used to evaluate spatial variations in stress in Myrica cerifera and Iva frutescens during a severe drought and compared to an extremely wet year. Measurements of relative water content and the water band index (WBI970) indicated that the water stress did not vary across the island. In contrast, there were significant differences in tissue chlorides across sites for both species. Using the physiological reflectance index (PRI), we were able to detect salinity stress across the landscape. For M. cerifera, PRI did not differ between wet and dry years, while for I. frutescens, there were differences in PRI during the 2 years, possibly related to flooding during the wet year. There was a positive relationship between PRI and $$ \Updelta F/F_{\text{m}}^{\prime } $$ for M. cerifera (r 2 = 0.79) and I. frutescens (r 2 = 0.72). The normalized difference vegetation index (NDVI), the chlorophyll index (CI), and WBI970 were higher during the wet summer for M. cerifera, but varied little across the island. CI and WBI970 were higher during 2004 for I. frutescens, while there were no differences in NDVI during the 2 years. PRI was not significantly related to NDVI, suggesting that the indices are spatially independent. These results suggest that PRI may be used for early identification of salt stress that may lead to changes in plant distributions at the landscape level, as a result of rising sea level. Comparsions between the two species indicate that variations in PRI and other indices may be species specific.

ABSTRACT Images of evil or evil images ?Popular images of Devil in Ghanaian ChristianityFocusing on images of evil, this paper explores differences between the modes of looking induced by the exposition All About Evil in the Royal Tropical Museum in Amsterdam, on the one hand, and the Christian setting in which the items on display feature in Ghana, on the other. While images of evil are more or less harmless depictions in the context of the exposition, in the Ghanaian setting they may easily slip into evil images that render present the very force that they depict. Tracing the genesis of Christian attitudes towards images of evil in Ghana, the paper focuses on the continued importance of the image of Satan in popular Ghanaian Christianity. It is argued that Christianity propounds a religious aesthetics that induces particular “looking acts” and attitudes towards evil through which images of evil achieve a reality of themselves.