FFT-based high-performance spherical harmonic transformation   总被引：6，自引：0，他引：6  

Christian Gruber  Pavel Nov��k  Josef Sebera 《Studia Geophysica et Geodaetica》2011,55(3):489-500

Spherical harmonic transformation is of practical interest in geodesy for transformation of globally distributed quantities such as gravity between space and frequency domains. The increasing spatial resolution of the latest and forthcoming gravitational models pose true computational challenges for classical algorithms since serious numerical instabilities arise during the computation of the respective base functions of the spherical harmonic expansion. A possible solution is the evaluation of the associated Legendre functions in the Fourier domain where numerical instabilities can be circumvented by an independent frequency-wise scaling of numerical coefficients into a numerically suitable double precision range. It is then rather straightforward to commit global fast data transformation into the Fourier domain and to evaluate subsequently spherical harmonic coefficients. For the inverse, the computation of respective Fourier coefficients from a given spherical harmonic model is performed as an inverse Fast Fourier Transform into globally distributed data points. The two-step formulation turns out to be stable even for very high resolutions as well as efficient when using state-of-the-art shared memory/multi-core architectures. In principle, any functional of the geopotential can be computed in this way. To give an example for the overall performance of the algorithm, we transformed an equiangular 1 arcmin grid of terrain elevation data corresponding to spherical harmonic degree and order 10800.  相似文献   

Timing of rockfalls in the Mont Blanc massif (Western Alps): evidence from surface exposure dating with cosmogenic <Superscript>10</Superscript>Be     

Xavi Gallach  Ludovic Ravanel  Markus Egli  Dagmar Brandova  Michael Schaepman  Marcus Christl  Stephan Gruber  Philip Deline  Julien Carcaillet  François Pallandre 《Landslides》2018,15(10):1991-2000

Rockfalls and rock avalanches are a recurrent process in high mountain areas like the Mont Blanc massif. These processes are surveyed due to the hazard they present for infrastructure and alpinists. While rockfalls and rock avalanches have been documented for the last 150 years, we know very little about their frequency since the Last Glacial Maximum (LGM). In order to improve our understanding, it is imperative to date them on a longer timescale. A pilot campaign using Terrestrial Cosmogenic Nuclide (TCN) dating of five samples was carried out in 2006 at the Aiguille du Midi (3842 m a.s.l.). In 2011, a larger scale study (20 samples) was carried out in five other test sites in the Mont Blanc massif. This paper presents the exposure ages of the 2011 TCN study as well as the updated exposure ages of the 2006 study using newer TCN dating parameters. Most of these exposure ages lie within the Holocene but three ages are Pleistocene (59.87?±?6.10 ka for the oldest). A comparison of these ages with air temperature and glacier cover proxies explored the possible relationship between the most active rockfall periods and the warmest periods of the Holocene: two clusters of exposure ages have been detected, corresponding to the Middle Holocene (8.2–4.2 ka) and the Roman Warm Period (c. 2 ka) climate periods. Some recent rockfalls have also been dated (<?0.56 ka).  相似文献   

Short note: the experimental geopotential model XGM2016     

R. Pail  T. Fecher  D. Barnes  J. F. Factor  S. A. Holmes  T. Gruber  P. Zingerle 《Journal of Geodesy》2018,92(4):443-451

As a precursor study for the upcoming combined Earth Gravitational Model 2020 (EGM2020), the Experimental Gravity Field Model XGM2016, parameterized as a spherical harmonic series up to degree and order 719, is computed. XGM2016 shares the same combination methodology as its predecessor model GOCO05c (Fecher et al. in Surv Geophys 38(3): 571–590, 2017. doi: 10.1007/s10712-016-9406-y). The main difference between these models is that XGM2016 is supported by an improved terrestrial data set of \(15^\prime \times 15^\prime \) gravity anomaly area-means provided by the United States National Geospatial-Intelligence Agency (NGA), resulting in significant upgrades compared to existing combined gravity field models, especially in continental areas such as South America, Africa, parts of Asia, and Antarctica. A combination strategy of relative regional weighting provides for improved performance in near-coastal ocean regions, including regions where the altimetric data are mostly unchanged from previous models. Comparing cumulative height anomalies, from both EGM2008 and XGM2016 at degree/order 719, yields differences of 26 cm in Africa and 40 cm in South America. These differences result from including additional information of satellite data, as well as from the improved ground data in these regions. XGM2016 also yields a smoother Mean Dynamic Topography with significantly reduced artifacts, which indicates an improved modeling of the ocean areas.  相似文献   

MSS93A: A new stationary sea surface combining one year upgraded ERS-1 fast delivery data and 1987 GEOSAT altimeter data     

M. Anzenhofer  Th. Gruber 《Journal of Geodesy》1995,69(3):157-163

Summary At the German Processing and Archiving Facility (D-PAF) an off-line altimeter data processing system has been developed with the capability to handle different satellite missions. For combining data from different missions an algorithm has been implemented that processes a reference sea surface from altimeter data of one mission while other mission data is taken to improve the spatial resolution of this reference model. In this way a stationary sea surface (MSS93A) was computed by compiling upgraded ERS-1 fast delivery data of the first year of the 35 day repeat cycle together with Geosat T2 GDRs of 1987.MSS93A was validated by means of comparisons to external models, gradient method and visualization techniques.  相似文献   

The role of biogeochemical cycling for the formation and preservation of varved sediments in Soppensee (Switzerland)   总被引：3，自引：0，他引：3  

N. Gruber  B. Wehrli  A. Wüest 《Journal of Paleolimnology》2000,24(3):277-291

We analyzed seasonally aggregated observations of temperature, conductivity, dissolved oxygen and dissolved inorganic carbon from Soppensee (District of Lucerne, Switzerland) for the yrs 1980 to 1993. Holomictic Soppensee is characterized by a strong summer stratification with a thin epilimnion separated from an anoxic hypolimnion by a strong pycnocline formed by thermal and chemical gradients. A vertical one-dimensional model was developed to simulate the observed seasonal cycles of carbon and oxygen. The processes of net community production, mineralization of organic matter, precipitation and dissolution of calcite, gas exchange, in- and outflow, sedimentation and vertical eddy diffusion are included. According to the model, the annual net community production is estimated to about 110 g C m^-2 yr^-1 and the annual net primary production to about 330 to 440 g C m^-2 yr^-1, which is a typical value for eutrophic lakes. A mass balance of the carbon cycle indicates that most of the inflow comes from groundwater which is super-saturated with respect to atmospheric CO₂. Therefore the surface waters exhibit a large capacity for calcite precipitation. The results of the model are used to constrain the conditions that favor the formation of varved sediments in Soppensee during thousands of yrs. Model calculations show that the deep waters would still turn anoxic even if the sedimentation rate of organic matter were decreased to 25%. Several physical factors such as biogenic stabilization of the deep waters due to calcite dissolution and low input of wind energy are responsible for the long term anoxia in Soppensee.  相似文献   

High-resolution gravity field modeling with full variance–covariance matrices     

T. Gruber 《Journal of Geodesy》2001,75(9-10):505-514

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Avalanche Hazard Mitigation Strategies Assessed by Cost Effectiveness Analyses and Cost Benefit Analyses—evidence from Davos,Switzerland     

Sven Fuchs  Magdalena Thöni  Maria Christina McAlpin  Urs Gruber  Michael Bründl 《Natural Hazards》2007,41(1):113-129

This paper demonstrates the application of cost effectiveness analysis and cost benefit analysis to alternative avalanche risk reduction strategies in Davos, Switzerland. The advantages as well as limitations of such analysis for natural hazards planning are discussed with respect to 16 avalanche risk reduction strategies. Scenarios include risk reduction measures that represent the main approaches to natural hazards planning in Switzerland, such as technical, organisational, and land use planning measures. The methodologies used outline how concepts and techniques from risk analysis, hazard mapping, Geographic Information System, and economics can be interdisciplinary combined. The results suggest important considerations, such as possible sources of uncertainty due to different choices in the calculation of cost effectiveness ratio and net present value. Given the parameters and assumptions, it seems as if the current approach to avalanche risk reduction in the study area approximates to economic and cost efficiency and serves the aim of reducing risk to human fatalities.  相似文献   

Occurrence of shallow cold flows in the winter atmospheric boundary layer of interior of Alaska     

Gilberto J. Fochesatto  John A. Mayfield  Derek P. Starkenburg  Matthew A. Gruber  James Conner 《Meteorology and Atmospheric Physics》2015,127(4):369-382

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GOCO05c: A New Combined Gravity Field Model Based on Full Normal Equations and Regionally Varying Weighting   总被引：1，自引：0，他引：1  

T. Fecher  R. Pail  T. Gruber  the GOCO Consortium 《Surveys in Geophysics》2017,38(3):571-590

GOCO05c is a gravity field model computed as a combined solution of a satellite-only model and a global data set of gravity anomalies. It is resolved up to degree and order 720. It is the first model applying regionally varying weighting. Since this causes strong correlations among all gravity field parameters, the resulting full normal equation system with a size of 2 TB had to be solved rigorously by applying high-performance computing. GOCO05c is the first combined gravity field model independent of EGM2008 that contains GOCE data of the whole mission period. The performance of GOCO05c is externally validated by GNSS–levelling comparisons, orbit tests, and computation of the mean dynamic topography, achieving at least the quality of existing high-resolution models. Results show that the additional GOCE information is highly beneficial in insufficiently observed areas, and that due to the weighting scheme of individual data the spectral and spatial consistency of the model is significantly improved. Due to usage of fill-in data in specific regions, the model cannot be used for physical interpretations in these regions.  相似文献