On the probability distribution of GNSS carrier phase observations   总被引：1，自引：0，他引：1  

Xiaoguang Luo  Michael Mayer  Bernhard Heck 《GPS Solutions》2011,15(4):369-379

When processing observational data from global navigation satellite systems (GNSS), the carrier phase measurements are generally assumed to follow a normal distribution. Although full knowledge of the probability distribution of the observables is not required for parameter estimation, for example when using the least-squares method, the distributional properties of GNSS observations play a key role in quality control procedures, such as outlier and cycle-slip detection, in ambiguity resolution, as well as in the reliability assessment of estimation results. In addition, when applying GNSS positioning under critical observation conditions with respect to multipath and atmospheric effects, the validity of the normal distribution assumption of GNSS observables certainly comes into doubt. This paper illustrates the discrepancies between the normal distribution assumption and reality, based on a large and representative data set of GPS phase measurements covering a range of factors, including multipath impact, baseline length, and atmospheric conditions. The statistical inferences are made using the first through fourth sample moments, hypothesis tests, and graphical tools such as histograms and quantile–quantile plots. The results show clearly that multipath effects, in particular the near-field component, produce the dominant influence on the distributional characteristics of GNSS observables. Additionally, using surface meteorological data, considerable correlations between distributional deviations from normality on the one hand and atmospheric relative humidity on the other are detected.  相似文献   

Verification of ARMA identification for modelling temporal correlations of GNSS observations using the ARMASA toolbox   总被引：1，自引：0，他引：1  

Xiaoguang Luo  Michael Mayer  Bernhard Heck 《Studia Geophysica et Geodaetica》2011,55(3):537-556

The classical least-squares (LS) algorithm is widely applied in practice of processing observations from Global Satellite Navigation Systems (GNSS). However, this approach provides reliable estimates of unknown parameters and realistic accuracy measures only if both the functional and stochastic models are appropriately specified. One essential deficiency of the stochastic model implemented in many available GNSS software products consists in neglecting temporal correlations of GNSS observations. Analysing time series of observation residuals resulting from the LS evaluation, the temporal correlation behaviour of GNSS measurements can be efficiently described by means of socalled autoregressive moving average (ARMA) processes. For a given noise realisation, a well-fitting ARMA model can be automatically estimated and identified using the ARMASA toolbox available free of charge in MATLAB® Central.In the preliminary stage of applying the ARMASA toolbox to residual-based modelling of temporal correlations of GNSS observations, this paper presents an empirical performance analysis of the automatic ARMA estimation tool using a large amount of simulated noise time series with representative temporal correlation properties comparable to the GNSS residuals. The results show that the rate of unbiased model estimates increases with data length and decreases with model complexity. For large samples, more than 80% of the identified ARMA models are unbiased. Additionally, the model error representing the deviation between the true data-generating process and the model estimate converges rapidly to the associated asymptotical value for a sufficiently large sample size with respect to the correlation length.  相似文献   

预料之外的安第斯地震     

韩立波 《国际地震动态》2011,(10):12-14

沿南美安第斯山脉西缘的俯冲带边界预期会发生大地震。而沿东边界的地表运动测量表明,曾预期不会发生大地震的安第斯山脉东缘也具有发生同等规模大地震的潜在可能。  相似文献   

Fall,classification, and exposure history of the Mifflin L5 chondrite     

Noriko T. Kita  Kees C. Welten  John W. Valley  Michael J. Spicuzza  Daisuke Nakashima  Travis J. Tenner  Takayuki Ushikubo  Glenn J. MacPherson  Linda Welzenbach  Philipp R. Heck  Andrew M. Davis  Matthias M. M. Meier  Rainer Wieler  Marc W. Caffee  Matthias Laubenstein  Kunihiko Nishiizumi 《Meteoritics & planetary science》2013,48(4):641-655

The Mifflin meteorite fell on the night of April 14, 2010, in southwestern Wisconsin. A bright fireball was observed throughout a wide area of the midwestern United States. The petrography, mineral compositions, and oxygen isotope ratios indicate that the meteorite is a L5 chondrite fragmental breccia with light/dark structure. The meteorite shows a low shock stage of S2, although some shock‐melted veins are present. The U,Th‐He age is 0.7 Ga, and the K‐Ar age is 1.8 Ga, indicating that Mifflin might have been heated at the time of the 470 Ma L‐chondrite parent body breakup and that U, Th‐He, and K‐Ar ages were partially reset. The cosmogenic radionuclide data indicate that Mifflin was exposed to cosmic rays while its radius was 30–65 cm. Assuming this exposure geometry, a cosmic‐ray exposure age of 25 ± 3 Ma is calculated from cosmogenic noble gas concentrations. The low ²²Ne/²¹Ne ratio may, however, indicate a two‐stage exposure with a longer first‐stage exposure at high shielding. Mifflin is unusual in having a low radiogenic gas content combined with a low shock stage and no evidence of late stage annealing; this inconsistency remains unexplained.  相似文献   

Style for the Zeitgeist: The Stealthy Revival of Historicist Housing Since the Late 1960s     

Nadine Dostrovsky  Richard Harris 《The Professional geographer》2013,65(3):314-332

A revival has occurred in the use of historical architectural styles for modern suburban houses but this has attracted little attention from journalists and academics. Those who have noted it disagree about when it began and gathered momentum. Newspaper and trade journal evidence for Canadian cities indicates that the revival began in the late 1960s; that it has reached market saturation; and that Victorian and neo-classical styles became dominant after 1980. Coinciding with the beginnings of inner-city gentrification, the historicist revival in suburban dwellings preceded the recent interest in neotraditional urban design. Not a fringe taste, it says something about the zeitgeist.  相似文献   

Tweet Me Your Talk: Geographical Learning and Knowledge Production 2.0   总被引：1，自引：0，他引：1  

Nadine Schuurman 《The Professional geographer》2013,65(3):369-377

We are in a Gutenberg moment in which we are migrating from book reading to Internet browsing. We are subtly shifting to more ephemeral, summary methods of learning and producing knowledge, shaped by how we consume information on the Web. Thus, a strong determinant of learning might be the very technology that hosts the information, such that technology is both the arbiter of our understanding of the world and how we come to gain that understanding. Based on recent evidence that the Internet is reshaping our learning processes, I argue that geographical knowledge production and translation are not so much products of individualism but rather shaped by rapidly changing work styles that favor concise and highly accessible methods of academic production. I offer examples of changes in journal formats, academic social networking, and academic reviewing to reveal that we are catering to shorter attention spans that prefer to browse.  相似文献   

Heliophysics Event Knowledgebase for?the?Solar Dynamics Observatory (SDO) and Beyond     

N. Hurlburt  M. Cheung  C. Schrijver  L. Chang  S. Freeland  S. Green  C. Heck  A. Jaffey  A. Kobashi  D. Schiff  J. Serafin  R. Seguin  G. Slater  A. Somani  R. Timmons 《Solar physics》2012,275(1-2):67-78

The immense volume of data generated by the suite of instruments on the Solar Dynamics Observatory (SDO) requires new tools for efficient identifying and accessing data that is most relevant for research. We have developed the Heliophysics Events Knowledgebase (HEK) to fill this need. The HEK system combines automated data mining using feature-detection methods and high-performance visualization systems for data markup. In addition, web services and clients are provided for searching the resulting metadata, reviewing results, and efficiently accessing the data. We review these components and present examples of their use with SDO data.  相似文献   

Corrections to “A comparison of the tesseroid,prism and point-mass approaches for mass reductions in gravity field modelling” (Heck and Seitz, 2007) and “Optimized formulas for the gravitational field of a tesseroid” (Grombein et al., 2013)     

Xiao-Le Deng  Thomas Grombein  Wen-Bin Shen  Bernhard Heck  Kurt Seitz 《Journal of Geodesy》2016,90(6):585-587

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Storage,mixing, and fluxes of water in the critical zone across northern environments inferred by stable isotopes of soil water          下载免费PDF全文

Matthias Sprenger  Doerthe Tetzlaff  Jim Buttle  Sean K. Carey  James P. McNamara  Hjalmar Laudon  Nadine J. Shatilla  Chris Soulsby 《水文研究》2018,32(12):1720-1737

Quantifying soil water storage, mixing, and release via recharge, transpiration, and evaporation is essential for a better understanding of critical zone processes. Here, we integrate stable isotope (²H and ¹⁸O of soil water, precipitation, and groundwater) and hydrometric (soil moisture) data from 5 long‐term experimental catchments along a hydroclimatic gradient across northern latitudes: Dry Creek (USA), Bruntland Burn (Scotland), Dorset (Canada), Krycklan (Sweden), and Wolf Creek (Canada). Within each catchment, 6 to 11 isotope sampling campaigns occurred at 2 to 4 sampling locations over at least 1 year. Analysis for ²H and ¹⁸O in the bulk pore water was done for >2,500 soil samples either by cryogenic extraction (Dry Creek) or by direct equilibration (other sites). The results showed a similar general pattern that soil water isotope variability reflected the seasonality of the precipitation input signal. However, pronounced differences among sampling locations occurred regarding the isotopic fractionation due to evaporation. We found that antecedent precipitation volumes mainly governed the fractionation signal, temperature and evaporation rates were of secondary importance, and soil moisture played only a minor role in the variability of soil water evaporation fractionation across the hydroclimatic gradient. We further observed that soil waters beneath conifer trees were more fractionated than beneath heather shrubs or red oak trees, indicating higher soil evaporation rates in coniferous forests. Sampling locations closer to streams were more damped and depleted in their stable isotopic composition than hillslope sites, revealing increased subsurface mixing towards the saturated zone and a preferential recharge of winter precipitation. Bulk soil waters generally comprised a high share of waters older than 14 days, which indicates that the water in soil pores are usually not fully replaced by recent infiltration events. The presented stable isotope data of soil water were, thus, a useful tool to track the spatial variability of water fluxes within and from the critical zone. Such data provide invaluable information to improve the representation of critical zone processes in spatially distributed hydrological models.  相似文献   

The Rock–Water–Ice Topographic Gravity Field Model RWI_TOPO_2015 and Its Comparison to a Conventional Rock-Equivalent Version     

Thomas Grombein  Kurt Seitz  Bernhard Heck 《Surveys in Geophysics》2016,37(5):937-976

RWI_TOPO_2015 is a new high-resolution spherical harmonic representation of the Earth’s topographic gravitational potential that is based on a refined Rock–Water–Ice (RWI) approach. This method is characterized by a three-layer decomposition of the Earth’s topography with respect to its rock, water, and ice masses. To allow a rigorous separate modeling of these masses with variable density values, gravity forward modeling is performed in the space domain using tesseroid mass bodies arranged on an ellipsoidal reference surface. While the predecessor model RWI_TOPO_2012 was based on the \(5'\times 5'\) global topographic database DTM2006.0 (Digital Topographic Model 2006.0), the new RWI model uses updated height information of the \(1'\times 1'\) Earth2014 topography suite. Moreover, in the case of RWI_TOPO_2015, the representation in spherical harmonics is extended to degree and order 2190 (formerly 1800). Beside a presentation of the used formalism, the processing for RWI_TOPO_2015 is described in detail, and the characteristics of the resulting spherical harmonic coefficients are analyzed in the space and frequency domain. Furthermore, this paper focuses on a comparison of the RWI approach to the conventionally used rock-equivalent method. For this purpose, a consistent rock-equivalent version REQ_TOPO_2015 is generated, in which the heights of water and ice masses are condensed to the constant rock density. When evaluated on the surface of the GRS80 ellipsoid (Geodetic Reference System 1980), the differences of RWI_TOPO_2015 and REQ_TOPO_2015 reach maximum amplitudes of about 1 m, 50 mGal, and 20 mE in terms of height anomaly, gravity disturbance, and the radial–radial gravity gradient, respectively. Although these differences are attenuated with increasing height above the ellipsoid, significant magnitudes can even be detected in the case of the satellite altitudes of current gravity field missions. In order to assess their performance, RWI_TOPO_2015, REQ_TOPO_2015, and RWI_TOPO_2012 are validated against independent gravity information of current global geopotential models, clearly demonstrating the attained improvements in the case of the new RWI model.  相似文献