Seismic interferometry,intrinsic losses and Q‐estimation*     

Deyan Draganov  Ranajit Ghose  Elmer Ruigrok  Jan Thorbecke  Kees Wapenaar 《Geophysical Prospecting》2010,58(3):361-373

Seismic interferometry is the process of generating new seismic traces from the cross‐correlation, convolution or deconvolution of existing traces. One of the starting assumptions for deriving the representations for seismic interferometry by cross‐correlation is that there is no intrinsic loss in the medium where the recordings are performed. In practice, this condition is not always met. Here, we investigate the effect of intrinsic losses in the medium on the results retrieved from seismic interferometry by cross‐correlation. First, we show results from a laboratory experiment in a homogeneous sand chamber with strong losses. Then, using numerical modelling results, we show that in the case of a lossy medium ghost reflections will appear in the cross‐correlation result when internal multiple scattering occurs. We also show that if a loss compensation is applied to the traces to be correlated, these ghosts in the retrieved result can be weakened, can disappear, or can reverse their polarity. This compensation process can be used to estimate the quality factor in the medium.  相似文献   

Spatio-temporal relationships between habitat types and microbial function of an upland floodplain     

Pascal Bodmer  Remo Freimann  Stefanie von Fumetti  Christopher T. Robinson  Michael Doering 《Aquatic Sciences - Research Across Boundaries》2016,78(2):241-254

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Shifts in isotopic signatures of animals with complex life-cycles can complicate conclusions on cross-boundary trophic links     

Maria Alp  Barbara L. Peckarsky  Stefano M. Bernasconi  Christopher T. Robinson 《Aquatic Sciences - Research Across Boundaries》2013,75(4):595-606

Stable isotopes (¹³C and ¹⁵N) are widely applied in studies of trophic links. We used this method to investigate the contribution of aquatic and terrestrial prey to the diet of riparian predatory arthropods in two mountain headwater streams in Colorado, USA. Aquatic and terrestrial prey and riparian predators were collected during summer 2009. To evaluate the reliability of conclusions based on stable isotope ratios, we compared the isotopic signatures of aquatic larval and terrestrial adult stages of three abundant stream insect species and assessed variation in mixing model estimates for spider diet composition under varying assumptions for trophic fractionation. Adult isotopic signatures of some aquatic prey species were indistinguishable from those of prey species with exclusively terrestrial life histories (stoneflies: ¹³C and ¹⁵N, chironomids: ¹³C). Other prey had distinctly aquatic isotopic signatures as both larvae and adults (a mayfly and a caddisfly). There was no evidence that prey with aquatic isotopic signatures contributed to the diet of the spiders near one stream. For the other stream, mixing model analysis suggested that chironomids were included in the diets of lycosid, linyphiid and liocranid spiders. Reliable estimates of the contributions of prey sources were compromised by the sensitivity of mixing models to assumptions on trophic fractionation and the presence of “isotopically cryptic” prey. This study emphasizes the importance of supporting isotope-based studies on cross-boundary trophic links with data on isotopic shifts in prey with complex life cycles and assessment of fractionation rates specific to the study system.  相似文献   

Maximizing Net Extraction Using an Injection‐Extraction Well Pair in a Coastal Aquifer     

Chunhui Lu  Adrian D. Werner  Craig T. Simmons  Neville I. Robinson  Jian Luo 《Ground water》2013,51(2):219-228

In this study, we examine the maximum net extraction rate from the novel arrangement of an injection‐extraction well pair in a coastal aquifer, where fresh groundwater is reinjected through the injection well located between the interface toe and extraction well. Complex potential theory is employed to derive a new analytical solution for the maximum net extraction rate and corresponding stagnation‐point locations and recirculation ratio, assuming steady‐state, sharp‐interface conditions. The injection‐extraction well‐pair system outperforms a traditional single extraction well in terms of net extraction rate for a broad range of well placement and pumping rates, which is up to 50% higher for an aquifer with a thickness of 20 m, hydraulic conductivity of 10 m/d, and fresh water influx of 0.24 m²/d. Sensitivity analyses show that for a given fresh water discharge from an inland aquifer, a larger maximum net extraction is expected in cases with a smaller hydraulic conductivity or a smaller aquifer thickness, notwithstanding physical limits to drawdown at the pumping well that are not considered here. For an extraction well with a fixed location, the optimal net extraction rate linearly increases with the distance between the injection well and the sea, and the corresponding injection rate and recirculation ratio also increase. The analytical analysis in this study provides initial guidance for the design of well‐pair systems in coastal aquifers, and is therefore an extension beyond previous applications of analytical solutions of coastal pumping that apply only to extraction or injection wells.  相似文献   

DEVELOPING SCENARIOS OF TEMPERATURE THRESHOLDS     

Peter J. Robinson 《自然地理学》2013,34(1):14-30

Scenarios of future climates must be made so that the potential impacts of climatic change can be assessed. A simple method is presented for developing regional scenarios of the number of days per month above a selected temperature. The method uses the observational record of daily maximum temperatures to develop linear regressions between monthly average temperature and the number of days above the threshold. The relationships are then extrapolated to the average temperature conditions estimated by General Circulation Models (GCMs) and the new number of days determined. The method is demonstrated by developing a set of scenarios for the United States for a 90° F threshold. The validity of the approach, including consideration of the linearity of the relationships and the amount of extrapolation needed, is discussed. The regional variability of the results can be explained in climatological terms while local variations are associated with topographic and hydrologic effects. The results are in general agreement with estimates obtained directly from GCM results.  相似文献   

Elements of viral cartography     

Anthony C. Robinson 《制图学和地理信息科学》2013,40(4):293-310

ABSTRACT

Making and sharing maps is easier than ever, and social media platforms make it possible for maps to rapidly attain widespread visibility and engagement. Such maps can be considered examples of viral cartography – maps that reach rapid popularity via social media dissemination. In this research we propose a framework for evaluating the design and social dissemination characteristics of viral maps. We apply this framework in two case studies using maps that reached wide audiences on Twitter. We then analyze collections of maps derived from and inspired by viral maps using image analysis and machine learning to characterize their design elements. Based on our initial work to conceptualize and analyze virality in cartography, we propose a set of new research challenges to better understand viral mapmaking and leverage its social affordances.  相似文献   

Association Between <Emphasis Type="BoldItalic">Fusarium</Emphasis> spp. on <Emphasis Type="BoldItalic">Spartina alterniflora</Emphasis> and Dieback Sites in Connecticut and Massachusetts     

Wade H. Elmer  James A. LaMondia  Frank L. Caruso 《Estuaries and Coasts》2012,35(2):436-444

Sudden vegetation dieback (SVD) is defined as the loss and lack of recovery of smooth cordgrass (Spartina alterniflora) in salt marshes. A new species of a moderately pathogenic fungus called Fusarium palustre is consistently found in SVD sites, but greenhouse tests revealed that it is not capable of causing mortality of healthy plants. Similarly, root-knot nematodes (Meloidogyne spartinae) are also found in SVD sites, but their incidence in marshes affected by SVD is not known. To understand more about the ecology of F. palustre and M. spartinae, salt marshes along Connecticut’s Long Island Sound and Massachusetts’ Cape Cod that exhibited SVD and those that did not, were visited during the summers of 2007, 2008, and 2009. Belowground and aboveground tissues of smooth cordgrass plants from 18 marshes were removed, washed, and assayed for Fusarium spp. to determine if patterns between the incidence of the different species of Fusarium, their virulence on S. alterniflora, root-knot nematodes (M. spartinae), and the health of the marsh could be revealed. There were significantly more colonies of Fusarium growing from plants in SVD sites (6.1%) than in healthy marshes where no SVD was present (<1.0%). The incidence of Fusarium spp. from plants at the perimeter of the SVD site was not statistically different from asymptomatic plants 10–20 m from the SVD edge. The majority of isolates could be assigned to one of two species, F. palustre or another slightly pathogenic group called Fusarium cf. incarnatum (88% in 2007, 62% in 2008, and 96% in 2009). The ratio of F. palustre to F. cf. incarnatum was 6.7, 2.7, or 2.1 for 2007, 2008, or 2009, respectively. Greenhouse tests on healthy S. alterniflora revealed that isolates of F. palustre were more virulent than F. cf. incarnatum, regardless of whether they were recovered from plants in healthy marshes or in SVD sites. Root-knot nematodes were found sporadically and could not be associated with SVD. Factorial greenhouse experiments did not demonstrate any interaction between F. palustre and M. spartinae providing no experimental evidence that combining Fusarium and root-knot nematodes could cause mortality. The presence of Fusarium on S. alterniflora in healthy marshes also suggests an endophytic relationship that may subsequently function in the breakdown of tissue when plants are compromised.  相似文献   

The Stanford Climate Change Behavior Survey (SCCBS): assessing greenhouse gas emissions-related behaviors in individuals and populations     

K. Carrie Armel  Katy Yan  Annika Todd  Thomas N. Robinson 《Climatic change》2011,109(3-4):671-694

Many individual-level behaviors are associated with greenhouse gas (GHG) emissions. Reliable and valid assessment instruments are needed to (1) identify behaviors and populations to target with emissions-reduction programs and policies, (2) evaluate the effectiveness of such programs, (3) link self-reported and objective measures of GHG emissions to establish the impact of specific behaviors, and (4) estimate frequencies of behaviors and their changes over time to aid policy makers in understanding energy consumption trends. The self-administered Stanford Climate Change Behavior Survey (SCCBS) is shown to be a reliable and valid instrument that can be used for these purposes in college students, and we anticipate that it will also be useful for assessing these behaviors in other adolescent or adult populations in developed countries. Questions included behaviors likely to be within the control of most individuals and did not include behaviors specific to home owners (e.g. appliance purchases). Ten indices were identified: Energy Use, No-, Low-, and High-GHG Transportation, Waste, Food Packaging, High- and Low-GHG Food, Food Purchasing, and GHG Credits use. A Total GHG Behavior score was calculated. Test–retest reliabilities of individual items ranged from .64 to .91. Internal consistency reliabilities for each of the indices ranged from .51 to .89. Most indices were statistically significantly correlated with one another. Correlational validity of the SCCBS was demonstrated with statistically significant associations between behavior scores and perceived importance of environmental sustainability and membership in an environmental organization. The use of the SCCBS to identify potential target sub-populations and behaviors was demonstrated.  相似文献   

Block removal and step backwearing as erosion processes on rock shore platforms: a preliminary case study of the chalk shore platforms of south‐east England     

U. Dornbusch  D.A. Robinson 《地球表面变化过程与地形》2011,36(5):661-671

Shore platforms frequently exhibit steps or risers facing seaward, landwards or obliquely across‐shore. A combination of soft copy photogrammetry, ortho‐rectification, geo referencing and field measurement of step height are linked in a GIS environment to measure step retreat on chalk shore platforms at sample sites in the south of England over two periods, 1973–2001, 2001–2007. The methods used allow for the identification, delineation and measurement of historic change at high spatial resolution. The results suggest that while erosion of chalk shore platforms by step backwearing is highly variable, it appears to be of similar magnitude to surface downwearing of the same platforms measured by micro‐erosion meters (MEMs) and laser scanning, in a range equivalent to 0·0006 – 0·0050 m y^?1 of surface downwearing. This equates to annual chalk volume loss from the platforms, by the two erosion processes combined, of between 0·0012 m³ m^?2 and 0·0100 m³ m^?2. Results from the more recent years' data suggests that step retreat has variability in both space and time which does not relate solely to climatic variability. The results must be viewed with caution until much larger numbers of measurements have been made of both downwearing and step erosion at higher spatial and temporal resolution. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

The Regional Ocean Modeling System (ROMS) 4-dimensional variational data assimilation systems: Part II - Performance and application to the California Current System     

Andrew M. Moore  Hernan G. ArangoGregoire Broquet  Chris EdwardsMilena Veneziani  Brian PowellDave Foley  James D. DoyleDan Costa  Patrick Robinson 《Progress in Oceanography》2011,91(1):50-73

The Regional Ocean Modeling System (ROMS) 4-dimensional variational (4D-Var) data assimilation systems have been systematically applied to the mesoscale circulation environment of the California Current to demonstrate the performance and practical utility of the various components of ROMS 4D-Var. In particular, we present a comparison of three approaches to 4D-Var, namely: the primal formulation of the incremental strong constraint approach; the dual formulation “physical-space statistical analysis system”; and the dual formulation indirect representer approach. In agreement with theoretical considerations all three approaches converge to the same ocean circulation estimate when using the same observations and prior information. However, the rate of convergence of the dual formulation was found to be inferior to that of the primal formulation. Other aspects of the 4D-Var performance that relate to the use of multiple outer-loops, preconditioning, and the weak constraint are also explored. A systematic evaluation of the impact of the various components of the 4D-Var control vector (i.e. the initial conditions, surface forcing and open boundary conditions) is also presented. It is shown that correcting for uncertainties in the model initial conditions exerts the largest influence on the ability of the model to fit the available observations. Various important diagnostics of 4D-Var are also examined, including estimates of the posterior error, the information content of the observation array, and innovation-based consistency checks on the prior error assumptions. Using these diagnostic tools, we find that more than 90% of the observations assimilated into the model provide redundant information. This is a symptom of the large percentage of satellite data that are used and to some extent the nature of the data processing employed. This is the second in a series of three papers describing the ROMS 4D-Var systems.  相似文献