Application of DInSAR-GPS optimization for derivation of fine-scale surface motion maps of Southern California

A method based on random field theory and Gibbs-Markov random fields equivalency within Bayesian statistical framework is used to derive 3-D surface motion maps from sparse global positioning system (GPS) measurements and differential interferometric synthetic aperture radar (DInSAR) interferogram in the southern California region. The minimization of the Gibbs energy function is performed analytically, which is possible in the case when neighboring pixels are considered independent. The problem is well posed and the solution is unique and stable and not biased by the continuity condition. The technique produces a 3-D field containing estimates of surface motion on the spatial scale of the DInSAR image, over a given time period, complete with error estimates. Significant improvement in the accuracy of the vertical component and moderate improvement in the accuracy of the horizontal components of velocity are achieved in comparison with the GPS data alone. The method can be expanded to account for other available data sets, such as additional interferograms, lidar, or leveling data, in order to achieve even higher accuracy

Some aspects of the glaciology of the mars ice piedmont, Anvers Island, Antarctica

The results of a comprehensive three-year study of the Harr Ice Piedmont, Anvers Island, Antarctica are presented. The piedmont stands on a low coastal platform ranging from slightly below sea level to 200 m. a.s.l. Ice thickness ranges from 60 to 80 m. at the coastal cliffs to more than 600 m. inland. Annual accumulation is high. There is a strong relationship between elevation and accumulation rates and a marked variation of accumulation rates from year to year. Surface ice velocities range from 14 m/year to 218 m/year and there is considerable ice streaming as a result of the subglacial topography. The mass balance of a representative part of the piedmont is considered to be in equilibrium or possibly, slightly positive. A study of a peripheral ramp shows annual fluctuations of balance and it is hypothesised that there may be a long-term tendency towards a positive regime. Ice core studies indicate that there is no dry snow facies but all other facies are identified. The saturation line lies at approximately 600 m. a.s.l. and the equilibrium line ranges from 60 to 120 m. a.s.l. Englacial ten-metre temperatures range from -0.8 ºC near the coast to -4.9 ºC inland. Deformation velocities have been calculated and basal sliding velocities inferred. It is hypothesised that basal conditions are not everywhere the same and that parts of the piedmont are frozen to bedrock. It is suggested that basal sliding and erosion are related and that the piedmont is selectively eroding its bed and accentuating the subglacial topography. Evidence of erosion, debris-rich ice, exists in the piedmont but is below sea level at the coastal cliff. The piedmont is not a "Strandflat Glacier" which is cutting a planed surface at a level controlled by the sea

Some aspects of the glaciology of the marr ice piedmont, Anvers Island, Antarctica

The results of a comprehensive three-year study of the Marr Ice Piedmont, Anvers Island, Antarctica are presented. The piedmont stands on a low coastal platform ranging from slightly below sea level to 200 m. a.s.l. Ice thickness ranges from 60 to 80 m, at the coastal cliffs to more than 600 m. inland. Annual accumulation is high. There is a strong relationship between elevation and accumulation rates and a marked variation of accumulation rates from year to year. Surface ice velocities range from 14 m/year to 218 m/year and there is considerable ice streaming as a result of the subglacial topography. The mass balance of a representative part of the piedmont is considered to be in equilibrium or possibly, slightly positive. A study of a peripheral ramp shows annual fluctuations of balance and it is hypothesised that there may be a long-term tendency towards a positive regime. Ice core studies indicate that there is no dry snow fades but all other fades are identified. The saturation line lies at approximately 600 m. a.s.l. and the equilibrium line ranges from 60 to 120 m. a.s.l. Englacial ten-metre temperatures range from -0.8ºC near the coast to -4.9ºC inland. Deformation velocities have been calculated and basal sliding velocities inferred. It is hypothesised that basal conditions are not everywhere the same and that parts of the piedmont are frozen to bedrock. It is suggested that basal sliding and erosion are related and that the piedmont is selectively eroding its bed and accentuating the subglacial topo,j;raphy. Evidence of erosion, debris-rich ice, exists in the piedmont but is below sea level at the coastal cliff. The piedmont is not a "Strandflat Glacier" which is cutting a planed surface at a level controlled by the sea

Simulated Dynamical Weakening and Abelian Avalanches in Mean-Field Driven Threshold Models

Mean-field coupled lattice maps are used to approximate the physics of driven threshold systems with long range interactions. However, they are incapable of modeling specific features of the dynamic instability responsible for generating avalanches. Here we present a method of simulating specific frictional weakening effects in a mean field slider block model. This provides a means of exploring dynamical effects previously inaccessible to discrete time simulations. This formulation also results in Abelian avalanches, where rupture propagation is independent of the failure sequence. The resulting event size distribution is shown to be generated by the boundary crossings of a stochastic process. This is applied to typical models to explain some commonly observed features.Comment: 27 pages, 9 figure

Comparing Complex Fitness Surfaces: Among-Population Variation in Mutual Sexual Selection in Drosophila serrata

The problem of synchronization of metacommunities is investigated in this article with reference to a rather general model composed of a chaotic environmental compartment driving a biological compartment. Synchronization in the absence of dispersal (i.e., the so-called Moran effect) is first discussed and shown to occur only when there is no biochaos. In other words, if the biological compartment is reinforcing environmental chaos, dispersal must be strictly above a specified threshold in order to synchronize population dynamics. Moreover, this threshold can be easily determined from the model by computing a special Lyapunov exponent. The application to prey-predator metacommunities points out the influence of frequency and coherence of the environmental noise on synchronization and agrees with all experimental studies performed on the subject

Genetic Constraints and the Evolution of Display Trait Sexual Dimorphism by Natural and Sexual Selection.

The evolution of sexual dimorphism involves an interaction between sex-specific selection and a breakdown of genetic constraints that arise because the two sexes share a genome. We examined genetic constraints and the effect of sex-specific selection on a suite of sexually dimorphic display traits in Drosophila serrata. Sexual dimorphism varied among nine natural populations covering a substantial portion of the species range. Quantitative genetic analyses showed that intersexual genetic correlations were high because of autosomal genetic variance but that the inclusion of X-linked effects reduced genetic correlations substantially, indicating that sex linkage may be an important mechanism by which intersexual genetic constraints are reduced in this species. We then explored the potential for both natural and sexual selection to influence these traits, using a 12-generation laboratory experiment in which we altered the opportunities for each process as flies adapted to a novel environment. Sexual dimorphism evolved, with natural selection reducing sexual dimorphism, whereas sexual selection tended to increase it overall. To this extent, our results are consistent with the hypothesis that sexual selection favors evolutionary divergence of the sexes. However, sex-specific responses to natural and sexual selection contrasted with the classic model because sexual selection affected females rather than males