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ABSTRACT The current heterogeneity of the existing global collection of measuring assets, satellite and surface based, is a major obstacle to creating a truly integrated, globally uniform information system. Many [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.07.018 Byline: Dirk Elbeshausen (a), Kai Wunnemann (a), Gareth S. Collins (b) Keywords: Cratering; Impact processes; Geologic processes; Earth; Meteorites Abstract: Almost every meteorite impact occurs at an oblique angle of incidence, yet the effect of impact angle on crater size or formation mechanism is only poorly understood. This is, in large part, due to the difficulty of inferring impactor properties, such as size, velocity and trajectory, from observations of natural craters, and the expense and complexity of simulating oblique impacts using numerical models. Laboratory oblique impact experiments and previous numerical models have shown that the portion of the projectile's kinetic energy that is involved in crater excavation decreases significantly with impact angle. However, a thorough quantification of planetary-scale oblique impact cratering does not exist and the effect of impact angle on crater size is not considered by current scaling laws. To address this gap in understanding, we developed iSALE-3D, a three-dimensional multi-rheology hydrocode, which is efficient enough to perform a large number of well-resolved oblique impact simulations within a reasonable time. Here we present the results of a comprehensive numerical study containing more than 200 three-dimensional hydrocode-simulations covering a broad range of projectile sizes, impact angles and friction coefficients. We show that existing scaling laws in principle describe oblique planetary-scale impact events at angles greater than 30[degrees] measured from horizontal. The displaced mass of a crater decreases with impact angle in a sinusoidal manner. However, our results indicate that the assumption that crater size scales with the vertical component of the impact velocity does not hold for materials with a friction coefficient significantly lower than 0.7 (sand). We found that increasing coefficients of friction result in smaller craters and a formation process more controlled by impactor momentum than by energy. Author Affiliation: (a) Museum fur Naturkunde, Leibniz-Institute at the Humboldt-University of Berlin, D-10115 Berlin, Germany (b) Impacts and Astromaterials Research Centre, Department of Earth Science and Engineering, Imperial College London, London SW7 2AZ, UK Article History: Received 16 February 2009; Revised 27 June 2009; Accepted 14 July 2009

This paper deals with an inverse problem arising in infrared (IR) thermography for buried landmine detection. It is aimed at using a thermal model and measured IR images to detect the presence of buried objects and characterize them in terms of thermal and geometrical properties. The inverse problem is mathematically stated as an optimization one using the well-known least-square approach. The main difficulty in solving this problem comes from the fact that it is severely ill posed due to lack of information in measured data. A two-step algorithm is proposed for solving it. The performance of the algorithm is illustrated using some simulated and real experimental data. The sensitivity of the proposed algorithm to various factors is analyzed. A data processing chain including anomaly detection and characterization is also introduced and discussed. Index Terms--Adjoint technique, classification, infrared (IR) thermography, inverse problem, landmine detection, optimization.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2008.03.008 Byline: G. Tobie (a)(b), O. Aadek (c), C. Sotin (a)(b)(d) Keywords: Enceladus; Ices; Infrared observations; Interiors; Tides; solid body Abstract: Earth, Jupiter's moon Io and Saturn's tiny moon Enceladus are the only solid objects in the Solar System to be sufficiently geologically active for their internal heat to be detected by remote sensing. Interestingly, the endogenic activity on Enceladus is only located on a specific region at the south pole, from which jets of water vapor and ice particles have been observed [Spencer, J.R., and 9 colleagues, 2006. Science 311, 1401-1405; Porco, C.C., and 24 colleagues, 2006. Science 311, 1393-1401]. The current polar location of the thermal anomaly can possibly be explained by diapir-induced reorientation of the satellite [Nimmo, F., Pappalardo, R.T., 2006. Nature 441, 614-616], but the thermal anomaly triggering and the heat power required to sustain it over geological timescales remain problematic. Using a three-dimensional viscoelastic numerical model simulating the response of Enceladus to tidal forcing, we explore the effect of a low-viscosity anomaly in the ice shell, localized to the south polar region, on the tidal dissipation patterns. We demonstrate that only interior models with a liquid water layer at depth can explain the observed magnitude of dissipation rate and its particular location at the south pole. Moreover, we show that tidally-induced heat must be generated over a relatively broad region in the southern hemisphere, and it is then transferred toward the south pole where it is episodically released during relatively short resurfacing events. As large tidal dissipation and internal melting cannot be induced in the south polar region in the absence of a pre-existing liquid decoupling layer, we propose that liquid water must have been present in the interior for a very long period of time, and possibly since the satellite formation. Owing to the orbital equilibrium requirement [Meyer, J., Wisdom, J., 2007. Icarus 188, 535-539], sustaining some liquid water at depth is impossible if heat is continuously emitted at a rate of 4-8 GW at the south pole. Based on that requirement, we propose that the current thermal emission is not in equilibrium with the heat production, and that the thermal emission rate is abnormally high at present time. Alternatively, continuous dissipation at a rate of 1-2 GW in the ice shell at the south pole should be sufficient to induce internal melting and it could sustain a layer of liquid water at depth over geologic timescales. Author Affiliation: (a) Laboratoire de Planetologie et Geodynamique de Nantes, Universite Nantes Atlantique, 2, rue de la Houssiniere, 44322 Nantes cedex 03, France (b) CNRS, UMR-6112, 2, rue de la Houssiniere, 44322 Nantes cedex 03, France (c) Department of Geophysics, Faculty of Mathematics and Physics, Charles University, V Holesovickach 2, 180 00 Prague 8, Czech Republic (d) JPL-Caltech, 4800 Oak Grove Drive, Pasadena, CA 91109, USA Article History: Received 26 September 2007; Revised 27 February 2008

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.earscirev.2006.01.002 Byline: W.P. Schellart (a)(b), G.S. Lister (a), V.G. Toy (a)(c) Keywords: subduction; slab; rollback; hinge-retreat; backarc; extension; spreading; Southwest Pacific; tectonics; geodynamics; reconstruction; Cretaceous; Cenozoic Abstract: A Cenozoic tectonic reconstruction is presented for the Southwest Pacific region located east of Australia. The reconstruction is constrained by large geological and geophysical datasets and recalculated rotation parameters for Pacific-Australia and Lord Howe Rise-Pacific relative plate motion. The reconstruction is based on a conceptual tectonic model in which the large-scale structures of the region are manifestations of slab rollback and backarc extension processes. The current paradigm proclaims that the southwestern Pacific plate boundary was a west-dipping subduction boundary only since the Middle Eocene. The new reconstruction provides kinematic evidence that this configuration was already established in the Late Cretaceous and Early Paleogene. From [approximately equal to]82 to [approximately equal to]52Ma, subduction was primarily accomplished by east and northeast-directed rollback of the Pacific slab, accommodating opening of the New Caledonia, South Loyalty, Coral Sea and Pocklington backarc basins and partly accommodating spreading in the Tasman Sea. The total amount of east-directed rollback of the Pacific slab that took place from [approximately equal to]82Ma to [approximately equal to]52Ma is estimated to be at least 1200km. A large percentage of this rollback accommodated opening of the South Loyalty Basin, a north-south trending backarc basin. It is estimated from kinematic and geological constraints that the east-west width of the basin was at least [approximately equal to]750km. The South Loyalty and Pocklington backarc basins were subducted in the Eocene to earliest Miocene along the newly formed New Caledonia and Pocklington subduction zones. This culminated in southwestward and southward obduction of ophiolites in New Caledonia, Northland and New Guinea in the latest Eocene to earliest Miocene. It is suggested that the formation of these new subduction zones was triggered by a change in Pacific-Australia relative motion at [approximately equal to]50Ma. Two additional phases of eastward rollback of the Pacific slab followed, one during opening of the South Fiji Basin and Norfolk Basin in the Oligocene to Early Miocene (up to [approximately equal to]650km of rollback), and one during opening of the Lau Basin in the latest Miocene to Present (up to [approximately equal to]400km of rollback). Two new subduction zones formed in the Miocene, the south-dipping Trobriand subduction zone along which the Solomon Sea backarc Basin subducted and the north-dipping New Britain-San Cristobal-New Hebrides subduction zone, along which the Solomon Sea backarc Basin subducted in the west and the North Loyalty-South Fiji backarc Basin and remnants of the South Loyalty-Santa Cruz backarc Basin subducted in the east. Clockwise rollback of the New Hebrides section resulted in formation of the North Fiji Basin. The reconstruction provides explanations for the formation of new subduction zones and for the initiation and termination of opening of the marginal basins by either initiation of subduction of buoyant lithosphere, a change in plate kinematics or slab-mantle interaction. Author Affiliation: (a) Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia (b) School of Geosciences, Monash University, Melbourne, VIC 3800, Australia (c) Department of Geology, University of Otago, Dunedin, New Zealand Article History: Received 21 July 2005; Accepted 18 January 2006

Source-receptor relationships for mercury (Hg) and other trace elements wet deposited in southeastern Florida were investigated using daily event precipitation samples collected over a 1-yr period in 1995-96. Data collected in Davie, Florida, showed significantly higher (2.2 times) volume-weighted mean (VWM) Hg concentrations during the spring and summer seasons relative to winter. A meteorological tracer analysis, utilizing the ratio of trace elements lanthanum (La) to cerium (Ce), determined that 'feed' air to precipitation cells arriving at the site incorporated local urban emissions more frequently during the spring and summer seasons. Using Weather Surveillance Radar-1988 Doppler (WSR-88D) data, analysis of precipitation-cell path histories for events collected at 17 sites in southeastern Florida over 1 month in the summer of 1995 showed significantly higher (2.0 times) VWM Hg concentrations in events with easterly cell paths than in those with westerly paths for storms arriving at Everglades sites. Significantly higher VWM concentrations for known anthropogenic elements vanadium (V) and nickel (Ni) (oil combustion) and lead (Pb) and antimony (Sb) (waste incineration) were also observed in events with easterly paths. In addition, events arriving from the east (offshore) that impacted the coastal sites were significantly lower in Hg (a factor of 2.6) than were events from the east that impacted the urban sites (after events moved inland over emission sources). This study demonstrates that source-receptor relationships can be established by analyzing the meteorological conditions corresponding to each precipitation event, and it supports the previous finding that local anthropogenic sources played the dominant role in the wet deposition of Hg to southern Florida and the Everglades during the study period.

The making and use of Nature in Enlightenment accounts of the soil are explored. The enlightened notion of nature as perceived by the English society is discussed.