High spectral resolution infrared studies of Titan: Winds, temperature, and composition     

Theodor Kostiuk  Tilak Hewagama  Kelly E. Fast  John Annen  Guido Sonnabend  Juan D. Delgado  Richard Achterberg 《Planetary and Space Science》2010,58(13):1715-1723

The Cassini Huygens mission provides a unique opportunity to combine ground-based and spacecraft investigations to increase our understanding of chemical and dynamical processes in Titan’s atmosphere. Spectroscopic measurements from both vantage points enable retrieving global wind structure, temperature structure, and atmospheric composition. An updated analysis of Titan data obtained with the NASA Goddard Space Flight Center’s Infrared Heterodyne Spectrometer (IRHS) and Heterodyne Instrument for Planetary Wind and Composition (HIPWAC) prior to and during the Cassini Huygens mission is compared to retrievals from measurements with the Cassini Composite Infrared Spectrometer (CIRS). IRHS/HIPWAC results include the first direct stratospheric wind measurements on Titan, constraints on stratospheric temperature, and the study of atmospheric molecular composition. These results are compared to CIRS retrievals of wind and temperature profile from thermal mapping data and ethane abundance at 10-15° South latitude, near the equatorial region. IRHS/HIPWAC wind results are combined with other direct techniques, stellar occultation measurements, and CIRS results to explore seasonal variability over nearly one Titan year and to provide an empirical altitude profile of stratospheric winds, varying from ∼50 to 210 m/s prograde. The advantage of fully resolved line spectra in species abundance measurements is illustrated by comparing the possible effect on retrieved ethane abundance by blended spectral features of other molecular constituents, e.g., acetylene (C₂H₂), ethylene (C₂H₄), allene (C₃H₄), and propane (C₃H₈), which overlap the ν₉ band of ethane, and are not resolved at lower spectral resolution. IR heterodyne spectral resolution can discriminate weak spectral features that overlap the ν₉ band of ethane, enabling ethane lines alone to be used to retrieve abundance. Titan’s stratospheric mean ethane mole fraction (8.6±3 ppmv) retrieved from IRHS/HIPWAC emission line profiles (resolving power λ?Δλ∼10⁶) is compared to past values obtained from lower resolution spectra and from CIRS measurements (resolving power λ?Δλ∼2×10³) and more compatible recent analysis. Results illustrate how high spectral resolution ground-based studies complement the spectral and spatial coverage and resolution of moderate spectral resolution space-borne spectrometers.  相似文献   

Matching INSPIRE Quality of Service Requirements with Hybrid Clouds     

Bastian Baranski  Theodor Foerster  Bastian Schäffer  Kristof Lange 《Transactions in GIS》2011,15(Z1):125-142

A lot of effort has been invested in Spatial Data Infrastructures (SDIs) during the last decade regarding interoperable standards for services and data. But still the scalability and performance of SDI services is reported to be crucial especially if they are accessed concurrently by a high number of users. Furthermore, laws and provisions such as the INSPIRE directive specify challenging requirements regarding the performance, availability and scalability of SDI services. This article presents a Hybrid Cloud architecture for matching INSPIRE‐related Quality of Service (QoS) requirements, without investing in rarely used hardware in advance, by occupying external third‐party resources on a pay‐as‐you‐go basis. The presented Hybrid Cloud is a composition of a local IT‐infrastructure (Private Cloud) and the computational resources of third‐party vendors (Public Cloud). The local infrastructure is laid out to handle the average main load of a service and in lasting peak times additional resources of external providers are allocated and integrated on demand into the local infrastructure to provide sufficient service quality automatically. A proof‐of‐concept implementation of the proposed Hybrid Cloud approach is evaluated and benchmarked with respect to INSPIRE‐related QoS requirements.  相似文献   

Thermospheric/mesospheric temperatures on Venus: Results from ground-based high-resolution spectroscopy of CO2 in 1990/1991 and comparison to results from 2009 and between other techniques     

Guido Sonnabend  Peter Krötz  Frank Schmülling  Theodor Kostiuk  Jeff Goldstein  Manuela Sornig  Dušan Stupar  Timothy Livengood  Tilak Hewagama  Kelly Fast  Arnaud Mahieux 《Icarus》2012,217(2):856-862

We report temperatures in Venus’ upper mesosphere/lower thermosphere, deduced from reanalyzing very high resolution infrared spectroscopy of CO₂ emission lines acquired in 1990 and 1991. Kinetic temperatures at ～110 km altitude (0.15 Pa) are derived from the Doppler width of fully-resolved single line profiles measured near 10.4 μm wavelength using the NASA GSFC Infrared Heterodyne Spectrometer (IRHS) at the NASA IRTF on Mauna Kea, HI, close to Venus inferior conjunction and two Venus solstices. Measured temperatures range from ～200 to 240 K with uncertainty typically less than 10 K. Temperatures retrieved from similar measurement in 2009 using the Cologne Tuneable Heterodyne Infrared Spectrometer (THIS) at the NOAO McMath Telescope at Kitt Peak, AZ are 10–20 K lower. Temperatures retrieved more recently from the SOIR instrument on Venus EXpress are consistent with these results when the geometry of observation is accounted for. It is difficult to compare ground-based sub-mm retrievals extrapolated to 110 km due to their much larger field of view, which includes the night side regions not accessible to infrared heterodyne observations. Temperature variability appears to be high on day-to-day as well as longer timescales. Observed short term and long term variability may be attributed to atmospheric dynamics, diurnal variability and changes over solar activity and seasons. The Venus International Reference Atmosphere (VIRA) model predicts cooler temperatures at the sampled altitudes in the lower thermosphere/upper mesosphere and is not consistent with these measurements.  相似文献   

Strength enhancement in particulate solids under high loading rates     

Dipankar Chandra  Theodor Krauthammer 《地震工程与结构动力学》1995,24(12):1609-1622

The so-called ‘strain-rate effect’ in any material has been investigated here from a structural dynamics point of view. Starting with lumped-mass models (SDOF and 2-DOF) and assuming a rate-independent failure criterion, it is shown here how a high loading rate produces an effect of strength enhancement in any massive elastic material and how failure takes place in a stronger component of a system as the loading rate increases. Extrapolating the concept of an equivalent elastic modulus as introduced in lumped-mass models and extending the analysis to a semi-infinite elastic continuum, an algorithm has been schematized to evaluate an overall equivalent elastic modulus of a concrete body under the influence of high loading rate treating the concrete as a two-component solid mixture consisting of cement paste matrix and aggregates.  相似文献   

Temporal and Spatial Variabilities of Chemical and Physical Parameters on the Heron Island Coral Reef Platform     

Kekuewa  Samuel A. H.  Courtney  Travis A.  Cyronak  Tyler  Kindeberg  Theodor  Eyre  Bradley D.  Stoltenberg  Laura  Andersson  Andreas J. 《Aquatic Geochemistry》2021,27(4):241-268

Globally, coral reefs are threatened by ocean warming and acidification. The degree to which acidification will impact reefs is dependent on the local hydrodynamics, benthic community composition, and biogeochemical processes, all of which vary on different temporal and spatial scales. Characterizing the natural spatiotemporal variability of seawater carbonate chemistry across different reefs is critical for elucidating future impacts on coral reefs. To date, most studies have focused on select habitats, whereas fewer studies have focused on reef scale variability. Here, we investigate the temporal and spatial seawater physicochemical variability across the entire Heron Island coral reef platform, Great Barrier Reef, Australia, for a limited duration of six days. Autonomous sensor measurements at three sites across the platform were complemented by reef-wide boat surveys and discrete sampling of seawater carbonate chemistry during the morning and evening. Variability in both temporal and spatial physicochemical properties were predominantly driven by solar irradiance (and its effect on biological activity) and the semidiurnal tidal cycles but were influenced by the local geomorphology resulting in isolation of the platform during low tide and rapid flooding during rising tides. As a result, seawater from previous tidal cycles was sometimes trapped in different parts of the reef leading to unexpected biogeochemical trends in space and time. This study illustrates the differences and limitations of data obtained from high-frequency measurements in a few locations compared to low-frequency measurements at high spatial resolution and coverage, showing the need for a combined approach to develop predictive capability of seawater physicochemical properties on coral reefs.

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Using the SDIlight Approach in Teaching a Geoinformatics Master     

Barend Köbben  Rolf De By  Theodor Foerster  Otto Huisman  Rob Lemmens  Javier Morales 《Transactions in GIS》2010,14(Z1):25-37

ITC, the Faculty of Geo–Information Science and Earth Observation of the University of Twente, is an institute that aims at capacity building and institutional development, specifically in developing countries. In our Geoinformatics curriculum, we emphasise two principles. The first addresses the systematics of purposeful spatial data production and uptake into computerised systems; the second addresses the methodical construction of these computerised systems, applying principles of model – driven architecture, formal specification and transformational design of SDI nodes. The term Spatial Data Infrastructure (SDI) usually denotes large, complex systems, but its principles can also be applied in simple and cost–effective ways. This approach we have called SDI^light and it is of particular interest to our students that come from developing countries. We work with and build a software stack consisting of free and open source components. To achieve interoperability, we emphasise the use of open standards from the Open Geospatial Consortium and others. In this paper, we explain how our students apply the SDI^light approach in the GeoinformaticsMaster degree course. An important part of that course is a Case Study Application Building & Programming, in which students apply their knowledge in a ‘real–world’ project, with a focus on geo–information engineering skills. We conclude with a section that evaluates the effectiveness of using the SDI^light concept in teaching our Geoinformatics Master, and on the more general applicability of the methodology.  相似文献   

Relativistic Rotational Darkening of Lightlike Radiation and Von Zeipel's Theorem for Radially Emitting Spheroids     

Andreas de Vries  Theodor Schmidt-Kaler 《Astrophysics and Space Science》1999,266(3):371-378

It is shown that an outgoing null radiation field in the outer space of a Kerr-Newman black hole is darkened by the rotation of the black hole. This rotational darkening is calculated for a spheroid emitting null radiation normally to its surface, yielding the von Zeipel-like effectthat the equatorial region is darkened more strongly than the polar regions.This effect is not confined to the case of black holes but is also observable for relativistically rotating fluid spheroids such as atmospheres of pulsars or neutron stars. Moreover, application to Hawking radiation suggests that the black hole cannot be viewed as a classical black body but that the Hawking radiationis a global geometric effect. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Dust-Corrected Star Formation Rates in Galaxies with Outer Rings     

I. Kostiuk  O. Silchenko 《Astrophysics》2018,61(1):1-8

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Comparison of HIPWAC and Mars Express SPICAM observations of ozone on Mars 2006-2008 and variation from 1993 IRHS observations     

Kelly E. Fast  Theodor Kostiuk  Franck Lefèvre  Timothy A. Livengood  Juan D. Delgado  John Annen  Guido Sonnabend 《Icarus》2009,203(1):20-27

Ozone is a tracer of photochemistry in the atmosphere of Mars and an observable used to test predictions of photochemical models. We present a comparison of retrieved ozone abundances on Mars using ground-based infrared heterodyne measurements by NASA Goddard Space Flight Center’s Heterodyne Instrument for Planetary Wind And Composition (HIPWAC) and space-based Mars Express Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars (SPICAM) ultraviolet measurements. Ozone retrievals from simultaneous measurements in February 2008 were very consistent (0.8 μm-atm), as were measurements made close in time (ranging from <1 to >8 μm-atm) during this period and during opportunities in October 2006 and February 2007. The consistency of retrievals from the two different observational techniques supports combining the measurements for testing photochemistry-coupled general circulation models and for investigating variability over the long-term between spacecraft missions. Quantitative comparison with ground-based measurements by NASA/GSFC’s Infrared Heterodyne Spectrometer (IRHS) in 1993 reveals 2-4 times more ozone at low latitudes than in 2008 at the same season, and such variability was not evident over the shorter period of the Mars Express mission. This variability may be due to cloud activity.  相似文献   

Time Analysis of the CO+ COMA OF COMET P/HALLEY BY IMAGE PROCESSING TECHNIQUES     

Voelzke  Marcos Rincon  Schlosser  Wolfgang  Schmidt-Kaler  Theodor 《Astrophysics and Space Science》1997,250(1):35-51

Photographic and photoelectric observations of comet P/Halley's ion gas coma from CO⁺ at 4250 ? were part of the Bochum Halley Monitoring Program, conducted from 1986 February 17, to April 17 at the European Southern Observatory on La Silla (Chile). In this spectral range it is possible to watch the continuous formation, motion and expansion of plasma structures. To observe the morphology of these structures 32CO⁺ photos (glass plates) from P/Halley's comet have been analysed. They have a field of view of 28°.6× 28°.6 and were obtained from 1986 March 29, to April 17 with exposure times between 20 and120 minutes. All photos were digitized with a PDS 2020 GM (Photometric Data System) microdensitometer at the Astronomisches Institut derWestf?lischen Wilhelms-Universit?t in Münster (one pixel= 25 μm × 25 μm ≈ 46′.88×46′.88). After digitization the data were reduced to relative intensities, and the part with proper calibrations were also converted to absolute intensities, expressed in terms of column densities using the image data systems MIDAS (Munich Image Data Analysis System; ESO – Image Processing Group, 1988) and IHAP (Image Handling And Processing; Middleburg, 1983). With the help of the Stellingwerf-Theta-Minimum-Method (Stellingwerf, 1978) a period of (2.22 ± 0.09) days results from analysis of structures in the plasma-coma by subtracting subsequent images. This method is also compared with the Fourier method. There may be a second cycle with a period of about 3.6 days. The idea behind subtracting subsequent images is that rotation effects are only 10% phenomena on gas distribution. Difference images are than used to suppress the static component of the gas cloud. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献