Real-time sea-state surveillance with Skywave Radar

To extract sea-state information from the ionospherically distorted echoes received by a skywave radar, we use a signal-processing strategy that permits real-time decisions about the quality of incoming data. This paper explains the need for an on-line processor and describes some of its engineering details. We use an array processor to quickly compute all the spectra required to display ocean waveheight, as well as some indices of data quality, while the radar interrogates an ocean cell. The results are shown in a test using an experimental radar that mapped waveheight over its North Pacific coverage area. Coverage efficiency was 85 percent, and the radar's waveheight estimates averaged 2ft(0.6 m) higher than those forecast by a numerical model.     

Rôle de la végétation dans la protection contre l'érosion hydrique de surface

This paper is a review on the current knowledge concerning the role of vegetation in protection against surface hydric erosion. It first explains the mechanisms of vegetation action in relation to processes of erosion and sedimentation. Secondly, it presents the results of researches carried out on the efficiency of different vegetation structures and the significance of the rate of vegetation cover for combating gully erosion. To cite this article: F. Rey et al., C. R. Geoscience 336 (2004).     

Gradual Deformation and Iterative Calibration of Sequential Stochastic Simulations

Based on the algorithm for gradual deformation of Gaussian stochastic models, we propose, in this paper, an extension of this method to gradually deforming realizations generated by sequential, not necessarily Gaussian, simulation. As in the Gaussian case, gradual deformation of a sequential simulation preserves spatial variability of the stochastic model and yields in general a regular objective function that can be minimized by an efficient optimization algorithm (e.g., a gradient-based algorithm). Furthermore, we discuss the local gradual deformation and the gradual deformation with respect to the structural parameters (mean, variance, and variogram range, etc.) of realizations generated by sequential simulation. Local gradual deformation may significantly improve calibration speed in the case where observations are scattered in different zones of a field. Gradual deformation with respect to structural parameters is necessary when these parameters cannot be inferred a priori and need to be determined using an inverse procedure. A synthetic example inspired from a real oil field is presented to illustrate different aspects of this approach. Results from this case study demonstrate the efficiency of the gradual deformation approach for constraining facies models generated by sequential indicator simulation. They also show the potential applicability of the proposed approach to complex real cases.     

Color centers,associated rare-earth ions and the origin of coloration in natural fluorites

Natural colored fluorites were studied by means of optical absorption and electron paramagnetic resonance (EPR). Complex centers involving rare-earth ions and/or oxygen give rise to the various colors observed. These include yttrium-associated F centers (blue), coexisting yttrium and cerium-associated F centers (yellowish-green), the (YO₂) center (rose) and the O ₃ ^? molecule ion (yellow). Divalent rare-earth ions also contribute to the colorations, as for instance Sm³⁺ (green fluorites), or they are at the origin of strong fluorescence observed (Eu²⁺). Strong irradiation of the crystals with ionizing radiation leads to coagulation of color centers, and to precipitation of metallic calcium colloids. There is probably no simple relation connecting the coloration and the growth process of the crystal. Thermal stability studies, however, have allowed to partially classify the colors as being of primary or secondary origin.     

Radon daughters and sulfur output from Erebus volcano, Antarctica

The 1977–1978 French New-Zealand summer campaign at Mount Erebus took place during a period of rather low activity. In such conditions, we could measure an output of 3 Ci of ²¹⁰Pb, 100 Ci of ²¹⁰Po and 10¹⁰ tons of sulfate per year.The ²¹⁰Po seems to be the only element emitted by Mount Erebus whose contribution to the Antarctic atmosphere is significant: sulfur compounds as well as radon emitted by Mount Erebus during a period of quiescent activity, have a negligible contribution to the overall Antarctic budgets.The presence of long-lived radon daughters in volcanic gases, highly enriched in volatile elements, seems to be a characteristic of gases emitted directly from the magma at high temperature.     

A note on adjustment of free networks

The present paper deals with the least-squares adjustment where the design matrix (A) is rank-deficient. The adjusted parameters \(\hat x\) as well as their variance-covariance matrix ( \(\sum _{\hat x} \) ) can be obtained as in the “standard” adjustment whereA has the full column rank, supplemented with constraints, \(C\hat x = w\) , whereC is the constraint matrix andw is sometimes called the “constant vector”. In this analysis only the inner adjustment constraints are considered, whereC has the full row rank equal to the rank deficiency ofA, andAC ^T =0. Perhaps the most important outcome points to the three kinds of results

1. A general least-squares solution where both \(\hat x\) and \(\sum _{\hat x} \) are indeterminate corresponds tow=arbitrary random vector.
2. The minimum trace (least-squares) solution where \(\hat x\) is indeterminate but \(\sum _{\hat x} \) is detemined (and trace \(\sum _{\hat x} \) corresponds tow=arbitrary constant vector.
3. The minimum norm (least-squares) solution where both \(\hat x\) and \(\sum _{\hat x} \) are determined (and norm \(\hat x\) , trace \(\sum _{\hat x} \) corresponds tow?0

     

Modal base forces in structures having a straight-line mode of vibration

The modal base forces in structures having a straight-line mode of vibration are investigated. Making use of the orthogonality relationship between the different modes, a relation between the modal base shears and base moments is found in all but the straight-line mode. This relation states that the contribution of the inertia forces to the modal overturning moments referred to the centre of rotation of the straight-line mode is identically null. The contributions of the vertical forces and lateral constraints must, however, be accounted for. For the special case of the straight-line mode being proportional to the height of each storey, the centre of rotation coincides with the base of the structure. For the case of the straight-line mode being a uniform displacement, the centre of rotation is at infinity and the contribution of the inertia forces to the modal base shears identically disappears in all but the straight-line mode.     

Paleomagnetic study of Sicily: consequences for the deformation of Italian and African margins over the last 100 million years

Paleomagnetic analysis of Cenozoic sediments from the Iblean platform (12 sites, 100 samples) has provided four new poles. These data are combined with those available from volcanic series to yield a new apparent polar wander path for “stable” Sicily since the Upper Cretaceous. This curve, when compared to a revised curve for Africa (using a selection of available data points), demonstrates a 15° rotation of Sicily with respect to Africa during the Plio-Pleistocene. This rotation accounts for the extensional tectonic regime that prevails in the Pelagian Sea and which is evidenced by “en relais” rifts (Malta, Pantelleria, Linosa), associated with alkaline volcanism of Pliocene and Quaternary age. Paleomagnetic directions from various areas of the Italian Peninsula also indicate anticlockwise rotations with diverse amplitudes. The chronology of these rotations is consistent with a deformation of the western Italian margin during progressive suturation from north to south of the Corsican-Sardinian block since the end of the Oligocene.     

Magma and hydrothermally driven sector collapses: The 3100 and 11,500 y. B.P. eruptions of la Grande Decouverte (la Soufrière) volcano, Guadeloupe, French West Indies

We recently reported (Boudon et al., 1984) on an eruption similar to that of May 18, 1980 at Mount St. Helens, that took place about 3100 years ago at la Soufrière, Guadeloupe. During the course of detailed geological mapping of the deposits of this event, older debris flow and blast deposits were recognized in the northern sector of the mapped area. Uncarbonized wood fragments in the debris flow have yielded ages ca. 11,500 y. B.P. The deposits extend from an amphitheater crater westward to the caribbean shore about 10 km downslope from the volcano. The deposits and crater structure suggest that they are the result of catastrophic flank failure like the event 3100 years ago. Unlike the latter activity, however, no magmatic component is found in the deposits.