Analysis of a cryolava flow-like feature on Titan     

L. Le Corre  S. Le Mouélic  J.-P. Combe  J.W. Barnes  B.J. Buratti  J. Soderblom  R. Clark  P.D. Nicholson 《Planetary and Space Science》2009,57(7):870-879

This paper reports on the analysis of the highest spatial resolution hyperspectral images acquired by the Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft during its prime mission. A bright area matches a flow-like feature coming out of a caldera-like feature observed in Synthetic Aperture Radar (SAR) data recorded by the Cassini radar experiment [Lopes et al., 2007. Cryovolcanic features on Titan's surface as revealed by the Cassini Titan Radar Mapper. Icarus 186, 395-412, doi:10.1016/j.icarus.2006.09.006]. In this SAR image, the flow extends about 160 km east of the caldera. The contrast in brightness between the flow and the surroundings progressively vanishes, suggesting alteration or evolution of the composition of the cryolava during the lifetime of the eruptions. Dunes seem to cover part of this flow on its eastern end. We analyze the different terrains using the Spectral Mixing Analysis (SMA) approach of the Multiple-Endmember Linear Unmixing Model (MELSUM, Combe et al., 2008). The study area can be fully modeled by using only two types of terrains. Then, the VIMS spectra are compared with laboratory spectra of known materials in the relevant atmospheric windows (from 1 to 2.78 μm). We considered simple molecules that could be produced during cryovolcanic events, including H₂O, CO₂ (using two different grain sizes), CH₄ and NH₃. We find that the mean spectrum of the cryoflow-like feature is not consistent with pure water ice. It can be best fitted by linear combinations of spectra of the candidate materials, showing that its composition is compatible with a mixture of H₂O, CH₄ and CO_2.  相似文献   

Geology of the Selk crater region on Titan from Cassini VIMS observations     

Jason M. Soderblom  Robert H. Brown  Jason W. Barnes  Stéphane Le Mouélic  Katrin Stephan  Bonnie J. Buratti  Philip D. Nicholson 《Icarus》2010,208(2):905-912

Observations of Titan obtained by the Cassini Visual and Infrared Mapping Spectrometer (VIMS) have revealed Selk crater, a geologically young, bright-rimmed, impact crater located ∼800 km north-northwest of the Huygens landing site. The crater rim-crest diameter is ∼90 km; its floor diameter is ∼60 km. A central pit/peak, 20-30 km in diameter, is seen; the ratio of the size of this feature to the crater diameter is consistent with similarly sized craters on Ganymede and Callisto, all of which are dome craters. The VIMS data, unfortunately, are not of sufficient resolution to detect such a dome. The inner rim of Selk crater is fluted, probably by eolian erosion, while the outer flank and presumed ejecta blanket appear dissected by drainages (particularly to the east), likely the result of fluvial erosion. Terracing is observed on the northern and western walls of Selk crater within a 10-15 km wide terrace zone identified in VIMS data; the terrace zone is bright in SAR data, consistent with it being a rough surface. The terrace zone is slightly wider than those observed on Ganymede and Callisto and may reflect differences in thermal structure and/or composition of the lithosphere. The polygonal appearance of the crater likely results from two preexisting planes of weakness (oriented at azimuths of 21° and 122° east of north). A unit of generally bright terrain that exhibits similar infrared-color variation and contrast to Selk crater extends east-southeast from the crater several hundred kilometers. We informally refer to this terrain as the Selk “bench.” Both Selk and the bench are surrounded by the infrared-dark Belet dune field. Hypotheses for the genesis of the optically bright terrain of the bench include: wind shadowing in the lee of Selk crater preventing the encroachment of dunes, impact-induced cryovolcanism, flow of a fluidized-ejecta blanket (similar to the bright crater outflows observed on Venus), and erosion of a streamlined upland formed in the lee of Selk crater by fluid flow. Vestigial circular outlines in this feature just east of Selk’s ejecta blanket suggest that this might be a remnant of an ancient, cratered crust. Evidently the southern margin of the feature has sufficient relief to prevent the encroachment of dunes from the Belet dune field. We conclude that this feature either represents a relatively high-viscosity, fluidized-ejecta flow (a class intermediate to ejecta blankets and long venusian-style ejecta flows) or a streamlined upland remnant that formed downstream from the crater by erosive fluid flow from the west-northwest.  相似文献   

Influence of antecedent soil moisture on hydraulic conductivity in a series of texture‐contrast soils     

Marcus A. Hardie  Richard B. Doyle  William E. Cotching  Kathrin Mattern  Shaun Lisson 《水文研究》2012,26(20):3079-3091

Antecedent soil moisture significantly influenced the hydraulic conductivity of the A1, A2e and B21 horizons in a series of strong texture‐contrast soils. Tension infiltration at six supply potentials demonstrated that in the A1 horizon, hydraulic conductivity was significantly lower in the ‘wet’ treatment than in the ‘dry’ treatment. However in the A2e horizon, micropore and mesopore hydraulic conductivity was lower in the ‘dry’ treatment than the ‘wet’ treatment, which was attributed to the precipitation of soluble amorphous silica. In the B21 horizon, desiccation of vertic clays resulted in the formation of shrinkage cracks which significantly increased near‐saturated hydraulic conductivity and prevented the development of subsurface lateral flow in the ‘dry’ treatment. In the ‘wet’ treatment, the difference between the hydraulic conductivity of the A1 and B21 horizons was reduced; however, lateral flow still occurred in the A1 horizon due to difficulty displacing existing soil water further down the soil profile. Results demonstrate the need to account for temporal variation in soil porosity and hydraulic conductivity in soil‐water model conceptualisation and parameterisation. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Saturn's icy satellites investigated by Cassini-VIMS: I. Full-disk properties: 350-5100 nm reflectance spectra and phase curves     

G. Filacchione  F. Capaccioni  A. Coradini  P. Cerroni  F. Tosi  V. Formisano  K.H. Baines  B.J. Buratti  M. Combes  P. Drossart  Y. Langevin  V. Mennella  P.D. Nicholson  C. Sotin  K. Hibbitts  S. Newman 《Icarus》2007,186(1):259-290

Saturn's icy satellites are among the main scientific objectives of the Cassini-VIMS (Visual and Infrared Mapping Spectrometer) experiment. This paper contains a first systematic and comparative analysis of the full-disk spectral properties of Dione, Enceladus, Epimetheus, Hyperion, Iapetus, Mimas, Phoebe, Rhea and Tethys as observed by VIMS from July 2004 to June 2005. The disk integrated properties (350-5100 nm reflectance spectra and phase curves at 550-2232 nm) and images of satellites are reported and discussed in detail together with the observed geometry. In general, the spectra in the visible spectral range are almost featureless and can be classified according to the spectral slopes: from the bluish Enceladus and Phoebe to the redder Iapetus, Hyperion and Epimetheus. In the 1000-1300 nm range the spectra of Enceladus, Tethys, Mimas and Rhea are characterized by a negative slope, consistent with a surface largely dominated by water ice, while the spectra of Iapetus, Hyperion and Phoebe show a considerable reddening pointing out the relevant role played by darkening materials present on the surface. In between these two classes are Dione and Epimetheus, which have a flat spectrum in this range. The main absorption bands identified in the infrared are the 1520, 2020, 3000 nm H₂O/OH bands (for all satellites), although Iapetus dark terrains show mostly a deep 3000 nm band while the 1520 and 2020 nm bands are very faint. In this spectral range, the Iapetus spectrum is characterized by a strong reddening. The CO₂ band at 4260 nm and the Fresnel ice peak around 3100 nm are evident only on Hyperion, Phoebe and Iapetus. The phase curves at 550 and at 2232 nm are reported for all the available observations in the 0°-144° range; Rhea shows an opposition surge at visible wavelengths in the 0.5°-1.17° interval. The improvement on the retrieval of the full-disk reflectance spectra can be appreciated by a direct comparison with ground-based telescopic data available from literature. Finally, data processing strategies and recent upgrades introduced in the VIMS-V calibration pipeline (flat-field and destriping-despiking algorithm) are discussed in appendices.  相似文献   

Towards accurate modelling of the integrated Sachs–Wolfe effect: the non-linear contribution     

Yan-Chuan Cai  Shaun Cole  Adrian Jenkins  Carlos Frenk 《Monthly notices of the Royal Astronomical Society》2009,396(2):772-778

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Seeing how it was?: childhood geographies and memories in home movies     

Heather Norris Nicholson 《Area》2001,33(2):128-140

Home movies provided valuable insights into childhood experiences during much of the twentieth century. Contrasting footage of children in rural and urban setting in Northern England between c.1937 and 1970, viewed through the cinematic gaze of two male amateur film-makers underpins this discussion of childhood geographies in the past. Issues explored in the paper include the social construction of childhood, power relations and visual representation of children, and the role of home movie-making in shaping memories and constituting ideas and ideologies about family and children.  相似文献   

Movements and population structure of Atlantic menhaden indicated by tag returns     

William R. Nicholson 《Estuaries and Coasts》1978,1(3):141-150

Over 968,000 adult Atlantic menhaden,Brevoortia tyrannus, were tagged from 1967 to 1969 and over 85,000 juvenile menhaden were tagged from 1969 to 1973. Recoveries of these tagged fish through 1975 provide direct evidence that Atlantic menhaden consist of a single population that over-winters in offshore waters off the southeastern coast of the United States, moves northward in spring and stratifies along the coast by age and size during summer, and moves southward in late autumn.  相似文献   

At home and abroad with cine enthusiasts: Regional amateur filmmaking and visualizing the Mediterranean, ca. 1928–1962.     

Heather Norris Nicholson 《GeoJournal》2004,59(4):323-333

After the appearance of a portable Kodak cine camera in 1923, home moving making grew steadily in popularity in the years leading up to and following World War II. Cine enthusiasts, particularly in the pre-war period, tended to be male, white and middle class, although exceptions exist, and they tended to travel with their cameras much as earlier generations had documented their experiences in written and artistic form. Despite their amateur status, they were often very professional in their approach to cinematography and they produced material for a range of domestic and public audiences on varied topics and in different genres. Specialist publications and the rapid growth of local amateur film societies fostered the rise of an active non-professional film movement; the result is a highly distinctive although neglected component of film history. With reference to materials held at the North West Film Archives in Manchester, England, this discussion considers the rise of non-professional filmmaking at the regional level during the decades before and after the second world war. Making and showing home movies is placed within various socio-cultural contexts. The imagery discloses much about visual practice, including filmmakers' perceptions and their relationships with different kinds of subject matter. The making of holiday footage, in Mediterranean settings, and its subsequent screening in domestic or public places, connects with broader issues of visualization, social practice and leisure-related consumption. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Three-dimensional empirical traveltimes: construction and applications     

T. Nicholson  M. Sambridge  Ó. Gudmundsson 《Geophysical Journal International》2004,156(2):307-328

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Constraints on earthquake epicentres independent of seismic velocity models   总被引：1，自引：0，他引：1  

T. Nicholson  Ó. Gudmundsson  M. Sambridge 《Geophysical Journal International》2004,156(3):648-654

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