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371.
Karl Thomas Hjelmervik Jan Kristian Jensen Petter ?stenstad Atle Ommundsen 《Ocean Dynamics》2012,62(2):253-264
Sonar performance modeling is crucial for submarine and anti–submarine operations. The validity of sonar performance models
is generally limited by environmental uncertainty, and particularly uncertainty in the vertical sound speed profile (SSP).
Rapid environmental assessment (REA) products, such as oceanographic surveys and ocean models may be used to reduce this uncertainty
prior to sonar operations. Empirical orthogonal functions (EOF) applied on the SSPs inherently take into account the vertical
gradients and therefore the acoustic properties. We present a method that employs EOFs and a grouping algorithm to divide
a large group of SSPs from an ocean model simulation into smaller groups with similar SSP characteristics. Such groups are
henceforth called acoustically stable groups. Each group represents a subset in space and time within the ocean model domain.
Regions with low acoustic variability contain large and geographically contiguous acoustically stable groups. In contrast,
small or fragmented acoustically stable groups are found in regions with high acoustic variability. The main output is a map
of the group distribution. This is a REA product in itself, but the map may also be used as a planning aid for REA survey
missions. 相似文献
372.
373.
Karl W. Bandilla Michael A. Celia Jens T. Birkholzer Abdullah Cihan Evan C. Leister 《Ground water》2015,53(3):362-377
Geologic carbon sequestration (GCS) is being considered as a climate change mitigation option in many future energy scenarios. Mathematical modeling is routinely used to predict subsurface CO2 and resident brine migration for the design of injection operations, to demonstrate the permanence of CO2 storage, and to show that other subsurface resources will not be degraded. Many processes impact the migration of CO2 and brine, including multiphase flow dynamics, geochemistry, and geomechanics, along with the spatial distribution of parameters such as porosity and permeability. In this article, we review a set of multiphase modeling approaches with different levels of conceptual complexity that have been used to model GCS. Model complexity ranges from coupled multiprocess models to simplified vertical equilibrium (VE) models and macroscopic invasion percolation models. The goal of this article is to give a framework of conceptual model complexity, and to show the types of modeling approaches that have been used to address specific GCS questions. Application of the modeling approaches is shown using five ongoing or proposed CO2 injection sites. For the selected sites, the majority of GCS models follow a simplified multiphase approach, especially for questions related to injection and local‐scale heterogeneity. Coupled multiprocess models are only applied in one case where geomechanics have a strong impact on the flow. Owing to their computational efficiency, VE models tend to be applied at large scales. A macroscopic invasion percolation approach was used to predict the CO2 migration at one site to examine details of CO2 migration under the caprock. 相似文献
374.
Shikha Sharma Michon L. Mulder Andrea Sack Karl Schroeder Richard Hammack 《Ground water》2014,52(3):424-433
Water and gas samples were collected from (1) nine shallow groundwater aquifers overlying Marcellus Shale in north‐central West Virginia before active shale gas drilling, (2) wells producing gas from Upper Devonian sands and Middle Devonian Marcellus Shale in southwestern Pennsylvania, (3) coal‐mine water discharges in southwestern Pennsylvania, and (4) streams in southwestern Pennsylvania and north‐central West Virginia. Our preliminary results demonstrate that the oxygen and hydrogen isotope composition of water, carbon isotope composition of dissolved inorganic carbon, and carbon and hydrogen isotope compositions of methane in Upper Devonian sands and Marcellus Shale are very different compared with shallow groundwater aquifers, coal‐mine waters, and stream waters of the region. Therefore, spatiotemporal stable isotope monitoring of the different sources of water before, during, and after hydraulic fracturing can be used to identify migrations of fluids and gas from deep formations that are coincident with shale gas drilling. 相似文献
375.
Karl Killian 《Marine Geodesy》2013,36(4):323-335
Let A,B,C denote three mainland‐stations whose positions are unknown. Let D,E,F denote the positions of a moving ship at three different moments of time. At any of the locations D,E,F, the three azimuths to the target‐stations A,B,C are measured. The problem is to determine from these nine measurements the mutual positions of all stations A,B,C,D,E,F up to a common shift and a change of scale. The problem was formulated by J. H. Lambert in 1765. He also specified a mathematical solution. In this paper so‐called “critical configurations”; are investigated. It is shown that there are nontrivial configurations of the six stations A to F, such that solution of the problem is not unique (critical configuration of the first kind). There is a larger set of configurations, such that the linearized problem admits of an infinity of solutions (critical configurations of the second kind). In the latter case, the original nonlinear problem may be solvable, but the solution is highly unstable with respect to perturbations of the measurements. The main result obtained is as follows. If all stations A to F are located on a second degree curve, i.e., on a conic section, then the configuration is critical, at least of the second kind. The configuration continues to be critical if arbitrarily many observations and target‐points are added which are all situated on the second‐degree curve. 相似文献
376.
Microbial decomposition experiments were used to characterize changes in the amino acid and amino sugar yields and compositions of natural marine substrates during early diagenesis in seawater. On average, 63% of added carbon and 68% of added nitrogen were removed within the first 30 days of decomposition. In all cases, amino acid utilization accounted for a substantial fraction of the removed C and N. Carbon-normalized amino acid yields decreased to less than 50% of their starting values and most of this change occurred within the first 10 days of decomposition. Increases in the concentrations of amino sugars and decreases in the GlcN:GalN ratio in particulate organic matter (POM) illustrated the significance of microbial production during the decomposition of added substrates. Changes in the mol % composition of amino acids during early diagenesis were substantial but highly variable with substrate. Previous survey data collected from the same region were used in conjunction with the experimental data to investigate the utility of several established amino acid-based indices of organic matter diagenesis. This comparison showed that a combination of these degradation indexes is most effective for describing the diagenetic state of dissolved organic matter (DOM). Carbon-normalized amino acid yields were found to be the most effective indicator for early diagenesis. Relative abundances of amino acids were effective indicators of intermediate stages of diagenesis and the mol % composition of the non-protein amino acid γ-Aba (γ-aminobutyric acid) was an effective indicator of advanced DOM diagenesis. 相似文献
377.
Alicia Fantasia Karl B. Fllmi Thierry Adatte Jorge E. Spangenberg Emanuela Mattioli 《Sedimentology》2019,66(1):262-284
A sedimentological, biostratigraphical and geochemical (stable isotopes and Rock‐Eval parameters) analysis was performed on four Swiss successions, in order to examine the expression of the Toarcian Oceanic Anoxic Event along a north–south transect, from the Jura through the Alpine Tethys (Sub‐Briançonnais and Lombardian basins). The locations were selected to represent a range of palaeoceanographic positions from an epicontinental sea to a more open marine setting. The Toarcian Oceanic Anoxic Event was recognized by the presence of the characteristic negative carbon‐isotope excursion in carbonate (ca 2 to 4‰) and organic matter (ca 4 to 5‰) at the base of the falciferum ammonite Zone (NJT6 nannofossil Zone). The sedimentary expression of the Toarcian Oceanic Anoxic Event varies along the transect from laminated mudstone rich in total organic carbon (≤11 wt.%) in the Jura, to thin‐bedded marl (≤5 wt.% total organic carbon) in the Sub‐Briançonnais Basin and to hemipelagic reddish marly limestone (total organic carbon <0·05 wt.%) in equivalent levels from the Lombardian Basin. The carbon‐isotope excursion is thus independent of facies and palaeoceanographic position. The low nannofossil abundance and the peak in Calyculaceae in the Jura and the Sub‐Briançonnais Basin indicate low salinity surface waters and stratified water masses in general. Sedimentological observations (for example, obliquely‐bedded laminae and homogeneous mud layers containing rip‐up clasts) indicate the presence of dynamic conditions, suggesting that water mass stratification was episodically disrupted during the Toarcian Oceanic Anoxic Event. The proposed correlation highlights a stratigraphic gap and/or condensed interval between the Pliensbachian–Toarcian boundary and the Toarcian Oceanic Anoxic Event interval (most of the tenuicostatum ammonite Zone is missing), which is also observed in coeval European sections and points to the influence of sea‐level change and current dynamics. This transect shows that the sedimentary expression of the Toarcian Oceanic Anoxic Event is not uniform across the Alpine Tethys, supporting the importance of local conditions in determining how this event is recorded across different palaeoceanographic settings. 相似文献
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