A simulation study of multi-beam altimetry for lunar reconnaissance orbiter and other planetary missions   总被引：4，自引：4，他引：0  

D. D. Rowlands  F. G. Lemoine  D. S. Chinn  S. B. Luthcke 《Journal of Geodesy》2009,83(8):709-721

The combined use of altimetry, Earth-based Doppler and Earth-based range measurements in the lunar reconnaissance orbiter (LRO) mission (Chin et al. in Space Sci Rev 129:391–419, 2007) has been examined in a simulation study. It is found that in the initial phases of the mission orbit and altimeter geolocation accuracies should be better than 10 m in the radial component and 60 m overall. It is demonstrated that LRO’s precise 1-way laser range measurement from Earth-based stations (Smith et al. in Proceedings of the 15th International Laser Ranging Workshop, Canberra, Australia, October 15–20, 2006) will be useful for gravity recovery. The advantages of multiple laser beams are demonstrated for altimeter calibration, orbit determination and gravity recovery in general planetary settings as well as for LRO.  相似文献   

Testing the survival of microfossils in artificial martian sedimentary meteorites during entry into Earth’s atmosphere: The STONE 6 experiment     

Frédéric Foucher  Frances Westall  Franz Brandstätter  René Demets  John Parnell  Charles S. Cockell  Howell G.M. Edwards  Jean-Michel Bény  André Brack 《Icarus》2010,207(2):616-279

If life ever appeared on Mars, could we find traces of primitive life embedded in sedimentary meteorites? To answer this question, a 3.5-byr-old volcanic sediment containing microfossils was embedded in the heat shield of a space capsule in order to test survival of the rock and the microfossils during entry into the Earth’s atmosphere (the STONE 6 experiment). The silicified volcanic sediment from the Kitty’s Gap Chert (Pilbara, Australia) is considered to be an excellent analogue for Noachian-age volcanic sediments. The microfossils in the chert are also analogues for potential martian life. An additional goal was to investigate the survival of living microorganisms (Chroococcidiopsis) protected by a 2-cm thick layer of rock in order to test whether living endolithic organisms could survive atmospheric entry when protected by a rocky coating.Mineralogical alteration of the sediment due to shock heating was manifested by the formation of a fusion crust, cracks in the chert due to prograde and retrograde changes of α quartz to β quartz, increase in the size of the fluid inclusions, and dewatering of the hydromuscovite-replaced volcanic protoliths. The carbonaceous microfossils embedded in the chert matrix survived in the rock away from the fusion crust but there was an increase in the maturity index of the kerogen towards the crust. We conclude that this kind of sediment can survive atmospheric entry and, if it contains microfossils, they could also survive. The living microorganisms were, however, completely carbonised by flame leakage to the back of the sample and therefore non-viable. However, using an analytical model to estimate the temperature reached within the sample thickness, we conclude that, even without flame leakage, the living organisms probably need to be protected by at least 5 cm of rock in order to be shielded from the intense heat of entry.  相似文献   

The fresnel interferometric imager     

Laurent Koechlin  Denis Serre  Paul Deba  Roser Pelló  Christelle Peillon  Paul Duchon  Ana Ines Gomez de Castro  Margarita Karovska  Jean-Michel Désert  David Ehrenreich  Guillaume Hebrard  Alain Lecavelier des Etangs  Roger Ferlet  David Sing  Alfred Vidal-Madjar 《Experimental Astronomy》2009,23(1):379-402

The Fresnel Interferometric Imager has been proposed to the European Space Agency (ESA) Cosmic Vision plan as a class L mission. This mission addresses several themes of the CV Plan: Exoplanet study, Matter in extreme conditions, and The Universe taking shape. This paper is an abridged version of the original ESA proposal. We have removed most of the technical and financial issues, to concentrate on the instrumental design and astrophysical missions. The instrument proposed is an ultra-lightweight telescope, featuring a novel optical concept based on diffraction focussing. It yields high dynamic range images, while releasing constraints on positioning and manufacturing of the main optical elements. This concept should open the way to very large apertures in space. In this two spacecraft formation-flying instrument, one spacecraft holds the focussing element: the Fresnel interferometric array; the other spacecraft holds the field optics, focal instrumentation, and detectors. The Fresnel array proposed here is a 3.6 ×3.6 m square opaque foil punched with 10⁵ to 10⁶ void “subapertures”. Focusing is achieved with no other optical element: the shape and positioning of the subapertures (holes in the foil) is responsible for beam combining by diffraction, and 5% to 10% of the total incident light ends up into a sharp focus. The consequence of this high number of subapertures is high dynamic range images. In addition, as it uses only a combination of vacuum and opaque material, this focussing method is potentially efficient over a very broad wavelength domain. The focal length of such diffractive focussing devices is wavelength dependent. However, this can be corrected. We have tested optically the efficiency of the chromatism correction on artificial sources (500 < λ < 750 nm): the images are diffraction limited, and the dynamic range measured on an artificial double source reaches 6.2 10^− 6. We have also validated numerical simulation algorithms for larger Fresnel interferometric arrays. These simulations yield a dynamic range (rejection factor) close to 10^− 8 for arrays such as the 3.6 m one we propose. A dynamic range of 10^− 8 allows detection of objects at contrasts as high as than 10^− 9 in most of the field. The astrophysical applications cover many objects in the IR, visible an UV domains. Examples are presented, taking advantage of the high angular resolution and dynamic range capabilities of this concept.  相似文献   

The Algodões amphibolite–tonalite gneiss sequence,Borborema Province,NE Brazil: Geochemical and geochronological evidence for Palaeoproterozoic accretion of oceanic plateau/back-arc basalts and adakitic plutons     

Guttenberg Martins  Elson P. Oliveira  Jean-Michel Lafon 《Gondwana Research》2009,15(1):71-85

Field relationships, geochemistry and U–Pb zircon and Sm–Nd whole-rock geochronology are used to constrain the genesis of Palaeoproterozoic massive amphibolites and orthogneisses of the Algodões Sequence, Central Ceará Domain, Northeastern Brazil. The 2236 ± 55 Ma-old Algodões amphibolites show trace element geochemical signature and positive εNd(t) values similar to Phanaerozoic oceanic plateau basalts and less often to back-arc basalts. The amphibolites are intruded by tonalitic to quartz-dioritic gneisses of the Cipó unit which were dated at 2160–2170 Ma and 2130 Ma. Neodimium isotope data and whole-rock geochemistry for these gneisses show they are akin to juvenile arc plutonics of the adakitic suite. The likely occurrence of Palaeoproterozoic plateau basalts and arc plutonics in this part of northeastearn Brazil render comparisons with similar terranes elsewhere in South America and Africa, which in turn indicate a significant contribution of accretionary orogens in the early assembly of the Columbia Supercontinent.  相似文献   

A combined modelling and geochemical study of the fate of terrigenous inputs from mixed natural and mining sources in a coral reef lagoon (New Caledonia)   总被引：1，自引：0，他引：1  

Fernandez JM  Ouillon S  Chevillon C  Douillet P  Fichez R  Le Gendre R 《Marine pollution bulletin》2006,52(3):320-331

Open-cast mining for Ni, Cr and Co was conducted in the south-west part of New Caledonia during the 20th century. Abandoned mining and prospecting sites were severely affected by erosion, resulting in an increase in the load of terrigenous particles transported to the coral reef lagoon. This article assesses the impact of a typical small catchment area (La Coulée River, 85 km2 watershed) on two bays (Boulari and Sainte Marie) located near Noumea, New Caledonia's main city. This multi-disciplinary study combines geochemical, sedimentological, and hydrodynamic approaches. Ni and Cr concentrations contained in the geochemical matrix phase of the pelitic fraction were determined. The study of the geochemical signatures together with sedimentological data and 3D numerical simulations of the transport of non-settling particles throughout the lagoon demonstrated that terrigenous inputs from the Coulée River were mainly transported and deposited along the shoreline, reaching areas as distant as Sainte Marie Bay. Although quantitatively low (about 3% of the pelite mass of the bay sediments), the terrigenous inputs in Sainte Marie Bay originating from the Coulée River could be traced. The metal content in suspended matter was over 7000 mg kg(-1) for Ni and 4200 mg kg(-1) for Cr.  相似文献   

Super-parameterization in ocean modeling: Application to deep convection     

Jean-Michel Campin  Chris Hill  Helen Jones  John Marshall 《Ocean Modelling》2011,36(1-2):90-101

We explore the efficacy of “super parameterization” (SP) in ocean modeling in which local 2-d non-hydrostatic plume-resolving fine-grained (FG) models are embedded at each vertical column of a coarse-grained (CG) hydrostatic model. A general multi-scale algorithm is described in which tendencies from the FG models are projected onto the CG model which in turn constrains the average state of the FG models, coupling the two models together. The approach is tested in the context of models of open ocean deep convection and compared with a pure hydrostatic, coarse resolution model using convective adjustment (HYD) and a full 3-d non-hydrostatic plume-resolving simulation (NH). The SP model is found to be greatly superior to HYD at much less computational cost than the fully non-hydrostatic calculation.  相似文献   

Structure and metamorphism of the Karakorum gneisses in the Braldu-Baltoro Valley (North Pakistan)     

Jean-Michel Bertrand  Jean-Robert Kienast  Jean-Luc Pinardon 《Geodinamica Acta》2013,26(3):135-150

Abstract

The Karakorum gneisses outcrop north of the complex suture separating the Indian-Pakistan plate from the Europe-Asia block; they grade to deformed earlier members of the Karakorum batholith ranging in age from Cretaceous to Miocene and are cross-cut by its later members. The main interest of the region lies in the fact that very young high-grade gneisses (Miocene), outline the southern edge of the Europe-Asia Plate. The tectonic and metamorpic evolution of the Braldu-Baltoro region is interpreted here as resulting from a poly phased history. The following structural sequence has been defined : - (1) A Dl isoclinal folding was accompanied by subparallel healed shear zones and by intense boudinage, and cross-cut by a dense net of post-Dl hetero-geneous leucogranitic veins and stocks; - (2) a major phase of EW trending recumbent folds (D2), is followed by (3) large open D3 folds generating EW trending domai structures (Dassu and Panmah domes); and (4) a late set of brittle to locally more ductile structures such as the southern thrust contact of the Karakorum gneisses with the Shyok suture zone. The sequence proposed here differs from other interpretations (Rex et al. 1988). We consider that the Dl event only may be attributed to the main India-Asia collision and that the D2-D3 events, interpreted as having occurred in a continuum, correspond to a late reactivation of the major thrusts and sutures related to continuing continental subduction.

A Dl-related intermediate pressure assemblage is preserved (Grt-St-Ky) in the upper levels of the tectonic pile; the estimated PT conditions determined are 10-4 Kb and 700°--525°C. In the core of the large D3 domes, late granoblastic recrystallization is widespread together with almost complete S1-S2 transposition, incipient melting and development of a low-pressure sillimanite-bearing assemblage where relicts of higher pressure minerals are locally preserved. Corresponding PT conditions are 650°-550°C and a lower pressure (5.5 to 2.5 Kb). As most of the observed structures at the lower levels (mineral lineations, boudinage) are clearly associated with (or reworked by) D2 and accentuated by D3 which was accompagnied by partial melting, D2 and D3 are interpreted as representing a continuum developed in the same PT field. It can be assumed also that the Baltoro granite was emplaced by the end of this combined D2-D3 event. From the Miocene ages published for the Baltoro granite (20 Ma to 8 Ma), the low-pressure evolution of the Karakorum gneisses may represent a very young high-grade assemblage. The age of Dl is less defined but at least older than 36 Ma old leucogranites.

The sharp contact along the Shyok Suture zone, interpreted as a large thrust (Main Karakorum Thrust - MKT) of this young high-grade metamorphic terrene against the older (older than 30-45 Ma from late undeformed intrusives) Kohistan-Ladakh island-arc domain, is interpreted, following Mattauer (1985), as resulting from the interaction between the still-ongoing northward movement of the Indo-Pakistan plate and an opposite southward continental subduction, seismically active, operating in Pamir.  相似文献   

Chemical and dynamical evolution of spiral galaxies     

Sébastien Poirier  Pascale Jablonka  Jean-Michel Alimi 《Astrophysics and Space Science》2003,284(2):849-852

We investigate the consequences of the hypothesis of the secular evolution (growth of the bulge from disc material via a bar and temporal evolution of the Hubble sequence) on the chemical evolution of a galaxy. We present the first dynamical and chemical results of our 3D tree-SPH simulations. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Groundwater occurrence in cold environments: examples from Nunavik,Canada     

Jean-Michel Lemieux  Richard Fortier  Marie-Catherine Talbot-Poulin  John Molson  René Therrien  Michel Ouellet  David Banville  Marion Cochand  Renaud Murray 《Hydrogeology Journal》2016,24(6):1497-1513

Water availability and management issues related to the supply of drinking water in northern communities are problematic in Canada. While rivers and lakes are abundant, they are vulnerable to contamination and may become dry in winter due to freezing. Groundwater can often provide a more secure and sustainable water source, however its availability is limited in northern Canada due to the presence of permafrost. Moreover, the exploitation of northern aquifers poses a dual challenge of identifying not only permafrost-free areas, but also permeable areas which will allow groundwater recharge and exploitation. Suitable aquifers are not as common in northern Canada since the shallow subsurface is mostly composed of low-permeability crystalline rocks or unconsolidated sediments of glacial origin that are highly heterogeneous. In order to investigate groundwater occurrence and associated geological contexts in Nunavik (northern Quebec, Canada), along with exploring how these resources will evolve in response to climate change, field and compilation work were conducted in the surroundings of the four villages of Salluit, Kuujjuaq, Umiujaq and Whapmagoostui-Kuujjuarapik. These villages are located in different permafrost zones, ranging from continuous to discontinuous, as well as in different geological environments. It was found that despite the ubiquitous presence of permafrost, unfrozen aquifers could be identified, which suggests that groundwater may be available as a source of drinking water for small communities. Expected climate change, with predicted permafrost thawing and increases in temperature and precipitation, should enhance groundwater availability and may contribute to a more secure source of drinking water for northern communities.  相似文献