Bernard Cervelle

A combined algorithm for automated drainage network extraction

Based on existing principles of automated drainage network extraction we have developed two methodological algorithms, the “profile scan” and “hydrological flow modeling,” and used them to extract networks from digital elevation models (DEMs). The “hydrological flow modeling” algorithm specializes in the extraction of well-connected hierarchically arranged skeletal channel networks. On the other hand, the channels extracted by the “profile scan” algorithm lack adequate connectivity, but this algorithm is suitable for the extraction of wide valley bottoms and other flat areas. A combination of the two algorithms gives a more versatile algorithm capable of yielding networks which are not only well connected but also portray the surface character of the drainage network thus generated. The good functioning of our algorithm is not inhibited by the presence of pits in the DEM. There is therefore no preprocessing of the DEM prior to drainage extraction. Rather, at the end of extraction, isolated spots are eliminated since these are the ones most probably representing artifacts.

Visible spectrometric indices of hematite (Hm) and goethite (Gt) content in lateritic soils: The application of a Thematic Mapper (TM) image for soil-mapping in Brasilia, Brazil

Abstract Data on mineralogy and diffuse reflectance spectra, obtained from 56 samples of Brazilian lateritic soils, were used to establish quantitative relationships between spectral parameters and iron oxides contents (hematite and goethite). A redness index RI H calculated from Helmholtz chromatic co-ordinates ( lambda d, P e, Y) and correlated to hematite content is found. A good estimate of the ratio Hematite/ (Hematite + Goethite) is given by the dominant wavelength lambda which takes into account a large proportion of the tint detected on the soil sample. Based on these laboratory results, radiometric indices were elaborated by combining only those parts of the visible spectrum that correspond to Thematic Mapper (TM) channels: (i) a hematite index I Hm to estimate hematite concentration; and (ii) a ferric index I Fe to estimate the ratio hematite/(hematite goethite). The hematite index, applied to a TM image of the area around Brasilia, allowed hematite contents in the surface horizons of lateritic ...

Mn2+-activated luminescence in dolomite, calcite and magnesite: quantitative determination of manganese and site distribution by EPR and CL spectroscopy

Abstract Dolomite, calcite and magnesite were studied by EPR and CL spectroscopy. Mn2+-activated luminescence in calcite and magnesite is characterized by single Gaussian peaks at 16,250 cm−1 (615 nm) and at 15,300 cm−1 (654 nm), respectively. In calcite the Mn2+ content and the normalized EPR area are linearly correlated when the Mn2+ content is Deconvolution of corrected CL spectra from dolomite shows two overlapping peaks at 17,315 cm−1 (578 nm) and 15,270 cm−1 (655 nm). In rare cases only the 15,270 cm−1 (655 nm) Gaussian peak is present. The CL peak at 17,315 cm−1 (578 nm, Ia) is due to Mn2+ in the Ca site and the peak at 15,270 cm−1 (655 nm, Ib) to Mn2+ in the Mg position. The Mn2+ content in dolomite is linearly correlated with the normalized EPR areas of the two sites. The distribution ratio (KD) of Mn2+ in the two sites of dolomite, i.e. the Ca and the Mg position, was determined by EPR and CL spectroscopy. A linear correlation exists between KD from EPR and the intensity ratio ( I b I a from CL. CL spectroscopy is thus an appropriate method to determine KD in dolomite. Evaporitic dolomites may be differentiated from non-evaporitic dolomites by their KD-values.

Moisture effects on visible spectral characteristics of lateritic soils

Samples from ferralitic soils of similar texture were immersed in water, placed in a pressure chamber and subjected to different soil suction pressures (pF: 2.0, 2.5, 2.8, 3.0, and 4.2). The Cie color values (intensity, hue and saturation) were taken as the spectral signatures of these soils and calculated from the diffuse reflectance spectra. The dominant wavelength Λd (hue) increases with moisture content; as the soil becomes more “colored” by iron oxi-hydroxides, this increase becomes more pronounced. The purity Pe (saturation) decreases systematically with increasing moisture content. When the moisture content increases, i.e., from oven-dried to airdried and then to moist samples, there is a change of the refractive index, N, of the immersion medium from N = 1 (air) to N = 1.33 (water). This change causes an increase in the volumetric reflectance, especially in the weak absorption regions, and a decrease in the specular reflectance. Contrary to the generally accepted assumption, diffuse reflectance spectra of soils at different moisture contents undergo nonlinear changes leading to displacements in the spectral extrema of the absorption bands. Therefore, spectral signatures of moist soils cannot be derived simply from those of their dry equivalents.

Light scattering by spherical particles with hematite and goethitelike optical properties: Effect of water impregnation

The interpretation of reflectance spectra (through remote sensing or laboratory research) requires spectral reflectance models that can be inversed to determine the more fundamental physical properties of these surfaces. One of the main hypotheses in reflectance models is that a soil or a powder are generally considered as a collection of particles or aggregates with averaged optical properties. Verification of this hypothesis is of great interest. This paper deals with the study of the scattering and absorption of light by a single mineral particle where diameter ranges from 0.01 to 50 μm. The particles are assumed to be spherical, and their complex refractive index is assumed to be equal to that of hematite or goethite (ordinary indices). These two minerals are responsible for the nonlinear and wavelength-dependent behavior of lateritic soils reflectance spectra upon moistening. The absorption and scattering efficiencies, single scattering albedo, scattering diagram, and opening angle were computed for a single sphere. Different scenarios were considered: first, a sphere in the air, second, a sphere in water, and third, a sphere surrounded by a water layer of different thickness. All the computed spectra (400–700 nm) are classified into three diameter groups (0.01–0.1, 0.1–2, and 2–50 μm). The behavior of the calculated spectra (second and third scenarios) depends both on the particle diameter and the wavelength. A simplified Hapkes model was then used to simulate the reflectance spectra of powders of hematite and goethite. The main result is the existence of an optical elementary arrangement cell which is for the soil what a unit cell is for a crystal.

Reflectance spectrophotometry extended to u.v. for terrestrial, lunar and meteoritic samples

Extension of remote sensing of planetary bodies to the ultraviolet is now feasiable up to 2000 A from earth-orbiting telescopes and spacecraft. The benefits of this extension is analysed on the basis of laboratory spectra taken on a large variety of terrestrial, lunar and meteoritic samples. Knowledge of the albedo for two wavelengths at 2300 and 6500 A permits classification of a surface into one of the following types: lunar, carbonaceous chondrites, ordinary chondrites, achondrites or acidic rocks, basaltic rocks, irons. For lunar-type surfaces, a simple albedo measurement at 6500 A can be converted into quantitative abundance determinations of silicate, aluminium oxide and iron; a large amount of telescopic lunar photometry data is available for mapping these abundances. Extension of the photometry to 2300 A permits quantitative measurement of TiO2 abundances. For asteroids and non-icy satellites, rock-type classification and constraints in chemical abundances of Si, Al, Fe and Ti can be derived from photometry at 2300 and 6500 A. The IUE telescope already orbiting the earth, the Space Telescope to come, the lunar polar orbiter and other spacecraft under prospect are potentially available to provide the photometric observations at 6500 and 2300 A required.

Evaluation of the spatial Dynamics of Great Oran (Algeria) using spatial Imagery and GIS

The last decade has been characterised by a transfer of demographic growth from the city of Oran (Algeria) to its immediate peripheral areas, especially towards Bir El Djir and Sidi Chahmi to the east and towards Es Senia to the south. This paper attempts to evaluate this spatial growth over the period from 1991 to 2003 by characterising and quantifying the spaces that have become urbanised over this time frame. To achieve this, we have used panchromatic Spot images from 1991, 1998 and 2003 to measure this spatial dynamic and GIS to evaluate the built surfaces and their locations. This methodology has proven itself efficient for evaluating and monitoring spatial dynamics in a regional metropolis such as Oran, Algeria’s second largest city after the capital (Algiers), which is subject to strong land development pressure.