Incorporating Information About Edge Effects When Simulating Lithofacies

Some years ago, earth scientists came to realize that knowing more about the geology of an orebody or an oil reservoir makes it easier to make the appropriate decisions concerning mine planning or reservoir exploitation. Geostatistical techniques for simulating lithofacies—that is, the geometry of the geology—were developed as a result of this. These methods should be able to produce geological images that respect not only the anisotropies of the different lithofacies but also their spatial layout relative to one another. While indicator variograms ensure that anisotropies are respected, another tool needs to be incorporated in the simulation technique to reflect the relative spatial layout of the different lithofacies. We propose to use the concept of edge effects that define the position of one lithofacies relative to another. Simple tests using direct and cross indicator variograms confirm the presence or absence of edge effects. We investigate if and how edge effect information can be incorporated in the different indicator simulation techniques—sequential indicator simulations, simulated annealing, the truncated Gaussian method and plurigaussian simulations. Results show that the choice of simulation method must be guided by the edge effect characteristics of the experimental lithologic data.     

Quantitative models of sedimentary basin filling

Quantitative modelling of the filling of sedimentary basins was begun in earnest in the 1960s. Dozens of themes and variations have been proposed since then, and have yielded an abundance of idealized stratigraphic patterns as functions of both imposed changes and basin properties. Post‐plate‐tectonic modelling began with ‘rigid‐lid' models, which show the stratigraphic signature of subsidence variation. This work introduced the connection between stratigraphy and the rheology of the lithosphere. Rigid‐lid models are the simplest type of geometric model, in which the sediment surface is assigned prescribed geometries, usually corresponding to different depositional environments. These can reproduce many aspects of overall stratal geometry but are formally restricted to relatively long timescales, for which quasi‐steady surface topography can be assumed. So‐called dynamic models attempt to represent the morphodynamics of the sediment surface by abstracting and averaging short‐term transport processes. Most of the dynamic models proposed to date can be seen as special cases of a single general morpho‐dynamic equation. The most important result of the first wave of quantitative basin‐filling models is that even relatively simple models can produce reasonable stratal patterns. We now have a wide array of tools for exploring scenarios, searching for general behaviours and effects, and making initial quantitative predictions. We have also learned that basin response to external forcing as recorded in stratigraphy can be as sensitive to the characteristics of the basin as to the forcing. The main brake on the development of basin modelling is not computing power but lack of methods and data for testing the models we have already developed. Physical experiments, which are only just beginning, are one means of doing this. Experimental stratigraphy is a bridge to quantitative field tests, which will require collaboration among academic researchers from a wide range of areas, and between academia and industry, on projects of greater scale and degree of integration than we have seen so far. The advancement of quantitative sedimentary geology will also require significant changes in the way the subject is taught, at all levels.     

Carrier phase-based integrity monitoring for high-accuracy positioning

Pseudorange-based integrity monitoring, for example receiver autonomous integrity monitoring (RAIM), has been investigated for many years and is used in various applications such as non-precision approach phase of flight. However, for high-accuracy applications, carrier phase-based RAIM (CRAIM), an extension of pseudorange-based RAIM (PRAIM) must be used. Existing CRAIM algorithms are a direct extension of PRAIM in which the carrier phase ambiguities are estimated together with the estimation of the position solution. The main issues with the existing algorithms are reliability and robustness, which are dominated by the correctness of the ambiguity resolution, ambiguity validation and error sources such as multipath, cycle slips and noise correlation. This paper proposes a new carrier phase-based integrity monitoring algorithm for high-accuracy positioning, using a Kalman filter. The ambiguities are estimated together with other states in the Kalman filter. The double differenced pseudorange, widelane and carrier phase observations are used as measurements in the Kalman filter. This configuration makes the positioning solution both robust and reliable. The integrity monitoring is based on a number of test statistics and error propagation for the determination of the protection levels. The measurement noise and covariance matrices in the Kalman filter are used to account for the correlation due to differencing of measurements and in the construction of the test statistics. The coefficient used to project the test statistic to the position domain is derived and the synthesis of correlated noise errors is used to determine the protection level. Results from four cases based on limited real data injected with simulated cycle slips show that residual cycle slips have a negative impact on positioning accuracy and that the integrity monitoring algorithm proposed can be effective in detecting and isolating such occurrences if their effects violate the integrity requirements. The CRAIM algorithm proposed is suitable for use within Kalman filter-based integrated navigation systems.

In-situ estimates of net sediment flux per swash: Reply to discussion by TE Baldock of “Measurement of wave-by-wave bed-levels in the swash zone”

This paper replies to TE Baldock's discussion [Coastal Eng. 56 (2009) 380–381] of ‘Measurement of wave-by-wave bed-levels in the swash zone’ by Turner et al. [Coastal Eng. 55 (2008) 1237–1242]. We address and extend the comparison and discussion of ultrasonic bed-level sensors and buried pressure transducers to obtain estimates of the beach face elevation within the swash zone. We demonstrate the use of the former method to obtain many and continuous (every time the beach face is exposed) in-situ estimates of net sediment flux per swash.     

Field and laboratory measurements of mean overtopping discharges and spatial distributions at vertical seawalls

Within the CLASH project, wave overtopping at the vertical seawall at Samphire Hoe was measured by HR Wallingford (HRW), and compared laboratory tests in 2 & 3 dimensions carried out at the University of Edinburgh and HRW. At Samphire Hoe, overtopping volumes were captured in three volumetric tanks capable of measuring wave-by-wave and total overtopping volumes. The three tanks were placed progressively farther back from the seawall edge so that the spatial distribution of the overtopping discharges could be determined. The field measurement equipment was successfully deployed on three occasions, and measured overtopping discharges ranged from that barely considered to be hazardous to the public to over q = 3.0 l/s/m. The 2d testing at Edinburgh was modelled at a scale of 1:40, and the 3d model at HRW was modelled at 1:20. For both sets of laboratory tests, a range of conditions, representative of the storm wave conditions and water levels, was reproduced in addition to a set of parametric conditions. The storm conditions allowed a direct comparison between the field and laboratory measurements, and the parametric conditions were used to test the generic overtopping behaviour of the structure. For both sets of laboratory tests, mean overtopping discharges and the spatial distribution were measured separately. Analysis of the distribution data relates the proportion of the discharge that has landed as a function of (x / L_o); where x is the distance behind the crest, and L_o is the offshore wavelength. Analysis of the field, 2d & 3d laboratory data, and empirical prediction methods have not identified any scale effects for overtopping discharges at vertical and near-vertical seawalls.     

A revision of soft proton scattering at grazing incidence and its implementation in the <Emphasis Type="SmallCaps">geant</Emphasis>4 toolkit

The scattering of soft protons inside the Wolter-type optics of X-ray observatories has been proven to concentrate these particles onto the focal plane instruments. The funneling of these protons increases the instrumental background and can also contribute to the degrading of the detectors. The instrumental background and degradation of the detector’s performance experienced by Chandra and XMM-Newton is significantly larger than what was expected on the basis of previous Monte Carlo simulations. For Chandra the main issue is the degradation of the energy resolution due to lattice displacements in the detectors. For XMM the contribution to the instrumental background is more significant. In between, new laboratory measurements as well as a revision of the theory are needed to correctly assess the impact of the environmental radiation for future missions. In this publication we present a Geant4 class that will allow future users to select between either theoretical models or measured data to simulate the scattering of soft protons at grazing angles. To develop this method, we revisit the theory of elastic scattering of protons on polished surfaces and implement these approaches into Geant4. We also implemented recently performed measurements using parts of eROSITA (extended ROentgen Survey with an Imaging Telescope Array) mirror shells as scattering targets as another scattering model to be used within the Geant4 toolkit.     

Hyper-velocity impact risk assessment and mitigation strategies in the context of future X-ray astronomy missions

Future X-ray astronomy missions will be based on instruments with apertures much larger than those used up to now. Therefore, the risk posed by hyper-velocity dust grains in the space environment to the onboard instrumentation will increase, especially when a larger aperture is combined with a longer focal length. Starting from the lessons learned from the XMM and Swift satellites, we review the question of hyper-velocity impacts and discuss the expected impact-rate, risk of damage and possible mitigation strategies in the context of LOFT, eROSITA and ATHENA.     

Evidence and Implications of Recent Climate Change in Northern Alaska and Other Arctic Regions

The Arctic climate is changing. Permafrost is warming, hydrological processes are changing and biological and social systems are also evolving in response to these changing conditions. Knowing how the structure and function of arctic terrestrial ecosystems are responding to recent and persistent climate change is paramount to understanding the future state of the Earth system and how humans will need to adapt. Our holistic review presents a broad array of evidence that illustrates convincingly; the Arctic is undergoing a system-wide response to an altered climatic state. New extreme and seasonal surface climatic conditions are being experienced, a range of biophysical states and processes influenced by the threshold and phase change of freezing point are being altered, hydrological and biogeochemical cycles are shifting, and more regularly human sub-systems are being affected. Importantly, the patterns, magnitude and mechanisms of change have sometimes been unpredictable or difficult to isolate due to compounding factors. In almost every discipline represented, we show how the biocomplexity of the Arctic system has highlighted and challenged a paucity of integrated scientific knowledge, the lack of sustained observational and experimental time series, and the technical and logistic constraints of researching the Arctic environment. This study supports ongoing efforts to strengthen the interdisciplinarity of arctic system science and improve the coupling of large scale experimental manipulation with sustained time series observations by incorporating and integrating novel technologies, remote sensing and modeling.