Improving the computation of the gravitational terrain effect close to ground stations in the GTE software     

Martina Capponi  Ahmed H. Mansi  Daniele Sampietro 《Studia Geophysica et Geodaetica》2018,62(2):206-222

The precise computation of the vertical gravitational attraction of the topographic masses (terrain correction) is still being studied both for geodetic and geophysical applications. In fact, it is essential in high precision geoid estimation by means of the well-known remove-compute-restore technique, which is used to isolate the gravitational effects of anomalous masses in exploration geophysics. The terrain correction can be evaluated exploiting a Digital Terrain Model (DTM) in different ways, such as classical numerical integration, prisms, tesseroids, polyhedrons, and/or Fast Fourier Transform techniques. The increasing resolution of recently developed DTMs, the increasing number of observation points, and the increasing accuracy of gravity data represent, nowadays, major challenges for the terrain correction computation. Classical point mass approximation and prism based-algorithms are indeed too slow, while Fourier-based algorithms are usually too much approximate when compared to the required accuracy. In this work, we improve the Gravity Terrain Effects (GTE) algorithm, the innovative tool that exploits a combined prism-Fast Fourier Transform approach especially developed for airborne gravimetry, to compute the terrain correction on the surface of the DTM (i.e. corresponding to the ground stations and/or its vicinity). This required development of a proper adjustment of the algorithms implemented within the GTE software and also to define and implement a procedure to overcome the problems of the computation of the gravitational effects due to the actual slope of the terrain close to the stations. The latter problem is thoroughly discussed and solved by testing different solutions like concentric cylindrical rings, triangulated polyhedrons, or ultra-high resolution squared prisms. Finally, numerical tests to prove the temporal efficiency and the computational performances of the improved GTE software to compute terrain correction for ground stations are also presented.  相似文献   

Hyper‐resolution global hydrological modelling: what is next?          下载免费PDF全文

Marc F. P. Bierkens  Victoria A. Bell  Peter Burek  Nathaniel Chaney  Laura E. Condon  Cédric H. David  Ad de Roo  Petra Döll  Niels Drost  James S. Famiglietti  Martina Flörke  David J. Gochis  Paul Houser  Rolf Hut  Jessica Keune  Stefan Kollet  Reed M. Maxwell  John T. Reager  Luis Samaniego  Edward Sudicky  Edwin H. Sutanudjaja  Nick van de Giesen  Hessel Winsemius  Eric F. Wood 《水文研究》2015,29(2):310-320

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Opening a new window to other worlds with spectropolarimetry     

Maren Mohler  Johannes Bühl  Stephen Doherty  Siegfried Eggl  Vera Theresa Eybl  François Farago  Aleksandar Jaćimović  Lars Hunger  Nynne L. B. Lauritsen  David Ludena  Martina Meisnar  Alexander Reissner  Nicolas Sarda  Benjamin Toullec  Meritxell Viñas Tió 《Experimental Astronomy》2010,28(2-3):101-135

A high level of diversity has already been observed among the planets of our own Solar System. As such, one expects extrasolar planets to present a wide range of distinctive features, therefore the characterisation of Earth- and super Earth-like planets is becoming of key importance in scientific research. The Search (Spectropolarimetric Exoplanet AtmospheRe CHaracerisation) mission proposal of this paper represents one possible approach to realising these objectives. The mission goals of Search include the detailed characterisation of a wide variety of exoplanets, ranging from terrestrial planets to gas giants. More specifically, Search will determine atmospheric properties such as cloud coverage, surface pressure and atmospheric composition, and may also be capable of identifying basic surface features. To resolve a planet with a semi major axis of down to 1.4 AU and 30 pc distant Search will have a mirror system consisting of two segments, with elliptical rim, cut out of a parabolic mirror. This will yield an effective diameter of 9 m along one axis. A phase mask coronagraph along with an integral spectrograph will be used to overcome the contrast ratio of star to planet light. Such a mission would provide invaluable data on the diversity present in extrasolar planetary systems and much more could be learned from the similarities and differences compared to our own Solar System. This would allow our theories of planetary formation, atmospheric accretion and evolution to be tested, and our understanding of regions such as the outer limit of the Habitable Zone to be further improved.  相似文献   

Assessing organizational resilience to climate and weather extremes: complexities and methodological pathways     

Martina K. Linnenluecke  Andrew Griffiths 《Climatic change》2012,113(3-4):933-947

This paper offers insights for assessing organizational resilience to the effects of climate change, specifically to climate and weather extremes. The assessment of organizational resilience to climate and weather extremes brings about several challenges due to (1) uncertainties about future climate change outcomes across temporal and spatial scales and (2) a lack of insight into what lead to organizational resilience, or which variables should be measured in a given study. We suggest methodological pathways for organizational managers to identify properties of future climate and weather extremes and to include them in resilience assessments. We also suggest approaches to identify factors that promote organizational resilience to selected climate and weather extremes. Findings are intended to help managers to understand how organizational resilience to climate and weather extremes can be enhanced.  相似文献   

Aspects of CO2 advection measurements     

Lukas Siebicke  Martina Hunner  Thomas Foken 《Theoretical and Applied Climatology》2012,109(1-2):109-131

Observations of vegetation–atmosphere exchange of carbon dioxide (CO₂) by the eddy covariance (EC) technique are limited by difficult conditions such as nighttime and heterogeneous terrain. Thus, advective flux components are included into the net ecosystem exchange (NEE) budget. However, advection measurements are experimentally challenging and do not always help to solve the night flux problem of the EC technique. This study investigates alternative methods for the observation of horizontal advection, in particular horizontal concentration gradients, as well as different approaches to coordinate rotation and vertical advection. Continuous high-frequency measurements of the horizontal CO₂ concentration field are employed and compared to the often used discontinuous sequential sampling. Significant differences were found in the case of 30-min mean concentration values between the conventional discontinuous sampling approach and the complete observation of the time series by continuous sampling. Estimates of vertical advection rely on accurate estimates of vertical wind velocity ( $\emph{w}$ ). Therefore, different approaches to the planar fit coordinate rotation have been investigated. Sector-wise rotation was able to eliminate directional dependencies of mean $\emph{w}$ . Furthermore, the effect of the data set length used for rotation (window length) was investigated and was found to have significant impact on estimates of vertical advection, with larger window lengths yielding about 50% larger vertical advection. A sequential planar fit with controlled window length is proposed to give reproducible results. The different approaches to the measurement and calculation of horizontal and vertical advection presented are applied to data obtained during the exchange processes in mountainous region experiment at the FLUXNET site Waldstein–Weidenbrunnen (DE-Bay). Estimates of NEE including advection are compared to NEE from turbulent and storage flux alone without advection. NEE including vertical advection with sector-wise planar fit rotation and controlled window length and including horizontal advection from continuous gradient measurements, which were comprehensively bias corrected by a new approach, did compare well with the expected night flux error, with meteorological drivers of the fluxes and with soil chamber measurements. Unrealistically large and noisy values of horizontal advection from the conventional discontinuous sampling approach, which lead to unrealistic values of NEE, could be eliminated by the alternative approaches presented. We therefore suggest the further testing of those approaches at other sites in order to improve the accuracy of advection measurements and, subsequently, estimates of NEE.  相似文献   

Late Pleistocene spread of (cool-)temperate forests in Northeast China and climate changes synchronous with the North Atlantic region   总被引：1，自引：0，他引：1  

Martina Stebich  Jens Mingram  Jingtai Han  Jiaqi Liu 《Global and Planetary Change》2009,65(1-2):56-70

The results presented here from the annually laminated sedimentary sequence of Sihailongwan lake provide the first comprehensive palaeoecological record covering the Late Pleniglacial to the Early Holocene (16,700–10,600 cal yrs. BP) from Northeast China. High-resolution pollen analyses have enabled the vegetational and climatic changes of the last glacial-interglacial transition to be reconstructed in more detail than has been previously possible. Moreover, a reliable chronology has been provided by both varve counting and 40 calibrated AMS ¹⁴C age determinations.Palaeobotanical evidence indicates predominantly steppe and open taiga-like woodland communities, with abundant Betula, Larix, Alnus fruticosa, Artemisia, grasses and sedges, which are typical of cold and dry conditions between 16,700 and 14,450 cal yrs. BP. The beginning expansion of Ulmus and Fraxinus marks the onset of the Late-glacial climatic amelioration at 14,450 cal yrs. BP. Dense deciduous forests, predominantly consisting of thermophilous broadleaf taxa, become established and widespread during the Early Holocene.Two short-term climatic reversals to colder and/or dryer conditions are recorded in the proxy data between 13,900 and 13,800 cal yrs. BP and 13,100 and 12,900 cal yrs. BP, correlating with the Oldest Dryas/Greenland Interstadial (GI) 1d event and the Gerzensee/Killarney/GI-1b oscillation, respectively. The prominent reappearance of Picea and Larix, coupled with a marked decrease in broadleaved trees, prior to the start of the Holocene, implies a climatic reversal compatible with the Younger Dryas event in the circum-Atlantic region. The evident synchroneity of climate changes in the North Atlantic region and East Asia supports the theory of strong atmospheric coupling between both regions.  相似文献   

Geochemical modelling of a Zn–Pb skarn: Constraints from LA–ICP–MS analysis of fluid inclusions     

Martina Bertelli  Timothy Baker  James S. Cleverley  Thomas Ulrich 《Journal of Geochemical Exploration》2009

The Bismark deposit (northern Chihuahua, Mexico) is one of several base metal-rich high-temperature, carbonate-replacement deposits hosted in northern Mexico. Previous fluid inclusion studies based on microthermometry and PIXE have shown that the Zn-rich, Pb-poor Bismark deposit formed from a moderate salinity magmatic fluid [Baker, T. and Lang, J.R., 2003. Reconciling fluid inclusion types, fluid processes, and fluid sources in skarns: an example from the Bismark Deposit, Mexico. Mineralium Deposita 38(4), 474–495; Baker, T., van Achterberg, E., Ryan, C.G. and Lang, J.R., 2004. Composition and evolution of ore fluids in a magmatic-hydrothermal skarn deposit. Geology 32(2), 117–120]. The exact precipitation mechanisms are unclear and may have due to cooling, salinity decrease and wall rock reaction. Furthermore, PIXE data suggested that Pb and Zn concentrations were comparable and inconsistent with the Zn-rich nature of the ore. However, Pb was commonly below the limit of detection for PIXE and the data presented by Baker et al. [Baker, T., van Achterberg, E., Ryan, C.G. and Lang, J.R., 2004. Composition and evolution of ore fluids in a magmatic-hydrothermal skarn deposit. Geology 32(2), 117–120] are regarded as the maximum concentrations of Pb in the fluid. In this study new LA ICP MS analysis was carried out on the same fluid inclusion population to compare with the PIXE data in order to constrain the uncertainty related to the Pb data and the new results are used to model possible ore deposition mechanisms. The new laser ablation data reveal overall lower concentrations of Pb in the ore fluid (average value ~ 285 ppm) than previously indicated by PIXE analysis (average value ~ 713 ppm). Chemical modelling using the new laser ablation data tested the following ore deposition processes: 1) cooling; 2) fluid–rock reaction at constant temperature; 3) cooling and simultaneous fluid–rock interaction. Modelling results show that the gangue and ore minerals observed at Bismark are best reproduced by fluid–rock interaction and simultaneous cooling. Results from the simulations strongly indicate that ore deposition was mainly driven by a pH increase due to the neutralization of the acidic ore fluid (pH = 3.9) as the result of the reaction with the limestone. Modelling results also suggest that the deposit likely formed under cooling conditions, but do not support the hypothesis of a temperature decrease as the principal ore-forming process.  相似文献   

An evaluation of the potential of using Raman spectroscopy to determine the carbon isotope composition of CO₂ inclusions     

Martina Menneken  Thorsten Geisler 《Journal of Geochemical Exploration》2009

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Impact of horizontal diffusion, radiation and cloudiness parameterization schemes on fog forecasting in valleys     

Martina Tudor 《Meteorology and Atmospheric Physics》2010,108(1-2):57-70

Fog and low stratus forecasting experiments have been carried out with the numerical weather prediction model ALADIN on a case of long lasting fog. The model has been used with different radiation, cloud diagnosing and horizontal diffusion schemes, different representation of orography, increased vertical resolution and with or without prognostic condensates and turbulent kinetic energy (TKE). Some of the numerical set-ups are able to reproduce the fog (low stratus) field as seen in the satellite images as well as the measured 2m temperature and relative humidity diurnal cycles. The results show that cloud diagnosing schemes and overlap assumptions play a more important role than a more sophisticated radiation scheme, or introduction of prognostic cloud water, ice, rain, snow or TKE. More realistic orography representation and a more physical horizontal diffusion scheme significantly improve the modelled low stratus and 2m temperature in the areas with variable orography.  相似文献   

Firm relocation as adaptive response to climate change and weather extremes   总被引：1，自引：0，他引：1  

Martina K. Linnenluecke  Alexander Stathakis  Andrew Griffiths   《Global Environmental Change》2011,21(1):123-133

Growing scientific evidence suggests that human-induced climate change will bring about large-scale environmental changes such as sea-level rise and coastal flooding, extreme weather events and agricultural disruptions. The speed and extent of these changes and the expected impacts on social and corresponding economic and industrial systems are now moving to the forefront of debates. In this paper, we argue that climate change will lead to significant disruptions to firms which might ultimately create the necessity of a geographical shift of firm and industrial activities away from regions highly affected by climate change. Such a shift might become necessary due to (1) direct disruptions through climate change impacts on firm operations, for instance through droughts, floods, or sea level rise, and due to (2) disruptions in a firm's supplier, buyer or resource base that lead to flow-on effects and adverse consequences for a firm. We propose a framework for integrating firm relocation decisions into firm adaptive responses to climate change. The framework consists of three assessment steps: the level of risk from climate change impacts at a firm's location, the feasibility of relocation, and associated costs and benefits. We apply the framework to two case examples. The first case of electricity distribution firms in Victoria/Australia illustrates how the relocation (undergrounding) of cables could decrease the vulnerability of distribution networks to bushfires and the risk of electricity-caused fires, but would require significant investments. The second case of firms in the Australian pastoral industry points to geographic diversification of pastoral land holdings as possible adaptation option, but also to constraints in form of availability of suitable properties, ties to local communities, and adverse impacts on biodiversity. Implications for adaptation research and practice are outlined.  相似文献