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561.
A number of statistic Global Positioning System (GPS) measurement campaigns have been made on a floating Antarctic ice shelf, the Amery Ice Shelf, as part of ongoing glaciological studies designed to investigate the ice shelf dynamics, grounding zone definition, and ice shelf strain. Such studies ar fundamental to improving out knowledge of the Antarctic ice-sheet mass balance and dynamical models of ice sheet/ocean interaction. This article describes two techniques used to process the statistic GPS data. One approach uses a segmented version of the classical static methodology, and the other approach adopts a new sequential processing technique. Both approaches yield similar results for the station coordinates and demonstrate the potential of GPS for extracting the tidal signal on the ice shelves and giving information on the dynamical motion of the ice sheet. To verify our results for the vertical component, we compare the ice shelf GPS tidal signal with a tidal model derived from tide gauge measurements at nearby Beaver Lake. Comparison of the GPS results with the tide model give good agreement in amplitude at the few cm level (GPS results always larger) but clearly shows evidence of phase propagation of the ocean tidal wave under the ice shelf. Improving the resolution of the tides over the ice shelves will be of tremendous benefit for future satellite missions, such as Ice, Cloud and Land Elevation Satellite (ICESAT), and the integrated use of GPS and satellite data will be fundamental for any on-going Antarctic ice sheet mass balance studies. ? 2000 John Wiley & Sons, Inc.  相似文献   
562.
A near-inertial oscillation (NIO) burst event in the west South China Sea (SCS) was observed by an upward-looking mooring Acoustic Doppler Current Profiler (ADCP) in summer 2004. The mooring station was located at 13.99°N, 110.52°E. The spectral analysis reveals that typhoon Chanchu is a major mechanism in triggering the NIO burst event. Before typhoon Chanchu passed over, the NIO signals were quite weak. The NIO band becomes the most energetic constituent of the circulation during the typhoon-wake period. The average peak power density (PD) reaches (5.3 ± 2.6) × 102 cms−2 (cycles per hour, cph)−1 with a maximum value of 9.0 × 102 cms−2 cph−1, i.e., 3.1 times higher than that of diurnal tide (DT), (1.7 ± 0.5) × 102 cms−2 cph−1. At the upper (80 m) and sub-upper (208 m) layers, the central frequency of the NIO band is 0.022 cph with a blueshift of about 9% above the inertial frequency f (0.02015 cph). At the lower layer (400 m), the central frequency of the NIO band is 0.021 cph with a blueshift of about 4% above the inertial frequency. The blueshifts are explained partially by the Doppler shift induced by the vorticity of mesoscale eddies. During the after-typhoon period, a resonance-like process between NIO and DT is observed in the upper layer. As the NIO frequency approaches the DT subharmonic frequency (0.5K1), the PD of the NIO band rises sharply accompanied by a sharp drop of the PD of the DT band. The PD ratio of the two bands increases from 4.5 during the typhoon-wake period to 8 during the after-typhoon period, indicating the effect of the parametric subharmonic instability (PSI) mechanism.  相似文献   
563.
Knowledge of the in situ, or contemporary stress field is vital for planning optimum orientations of deviated and horizontal wells, reservoir characterization and a better understanding of geodynamic processes and their effects on basin evolution.This study provides the first documented analysis of in situ stress and pore pressure fields in the sedimentary formations of the Cuu Long and Nam Con Son Basins, offshore Vietnam, based on data from petroleum exploration and production wells.In the Cuu Long Basin, the maximum horizontal stress is mainly oriented in NNW–SSE to N–S in the northern part and central high. In the Nam Con Son Basin, the maximum horizontal stress is mainly oriented in NE–SW in the northern part and to N–S in the central part of the basin.The magnitude of the vertical stress has a gradient of approximately 22.2 MPa/km at 3500 m depth. Minimum horizontal stress magnitude is approximately 61% of the vertical stress magnitude in normally pressured sequences.The effect of pore pressure change on horizontal stress magnitudes was estimated from pore pressure and fracture tests data in depleted zone caused by fluid production, and an average pore pressure–stress coupling ratio (ΔShPp) obtained was 0.66. The minimum horizontal stress magnitude approaches the vertical stress magnitude in overpressured zones of the Nam Con Son Basin, suggesting that an isotropic or strike-slip faulting stress regime may exist in the deeper overpressured sequences.  相似文献   
564.
A series of narrowband acoustic transmissions may be combined into an equivalent broadband signal - with a corresponding increase in resolution in the time domain. This procedure is called synthetic bandwidth processing. If ray methods are used in combination with inverse theory to determine the otacoustic properties of bottom sediments, the increased time resolution aids in the identification of arrivals which are closely spaced in time. This, in turn, permits improved estimates of the spatial distribution of properties and more accurate otacoustic models. Signal processing techniques and guidelines for synthesizing multioctave broadband pulse-like signals are presented. Also described is the instrumentation used to implement the technique in real ocean environments  相似文献   
565.
566.
567.
The reproducing kernel functions and the integral formulae involving the solutions of the fixed gravimetric boundary value problems for the earth's ellipsoid are investigated in a suitable polar coordinate system defined on the boundary ellipsoid. The infinite series expressions of the reproducing kernel functions are represented explicitly up to the square of the first excentricity of the boundary surface. The obtained results show that the reproducing kernel functions for the earth's ellipsoid are, in contrast to the case of the spherical boundary, inhomogeneous and anisotropic. Moreover, the anisotropy is stronger near the pole. Subsequently the kernel functions are regularized in order to overcome the weak singularity of the integrals.  相似文献   
568.
Abstract. The ophiuroid Amphiiodia urtica L yman is presently under study as a potential wastewater discharge indicator species from ocean outfalls in the Southern California Bight. On the San Pedro Shelf, the maximum abundance of A. urtica was found at depths from 30 to 100 m, and in sediment with a median grain size of 0.085 nim, 60–80% sand. 15–30% silt, 0–37% clay, and 0.2–0.5% TOC. The mean abundance of A. urtica fluctuated annually with a slight increase from 1977 through 1993.
The hypothesis was posed that the distribution and abundance of A. urtica is not influenced by an ocean outfall and its operation on the San Pedro Shelf. Based on long-term (1977–1994) and intensive (2860 samples) sampling. the hypothesis was rejected. However, the effect of the outfall is not clear because sediment bioassays from test stations and controls produced no significant differences in survivorship and growth of juveniles. Amphiodia presently occupies areas within the Zone of Initial Dilution (ZID) where it was not found during the mid-1970s and early 1980s. While recognizing that A. urtica abundance responds to proximity to the outfall, the mechanism for this response is still unclear. The application of a single species as a bioindicator is not recommended, and most certainly not without fully essing its role in community structure and function.  相似文献   
569.
Abstract

This study conducted a series of laboratory experiments and established numerical models on selected undisturbed soil samples in the Red River Delta (RRD) to determine the effect of change in soils intruded by saline water. The variation in the technical parameters of soils was verified in soils fully saturated by solution of four salt concentrations, that is, 0.0, 9.9, 19.8, and 33.0?g/L. Results show that the content and composition of clay minerals in cohesive soils before and after saline intrusion are unchanged. The same finding is obtained for clay after removing absorbed water layer by using a centrifuge apparatus. The zeta potential and settlement velocity of soils in the RRD increase when salt is added to the saturated solution. Similarly, the deformation of soils increases proportionally with the salt concentrations of that solution. This result is attributed to the linear decrease in deformation modulus. The decrease in modulus versus salinities is nearly consistent for pressure stages from 100 to 400?kPa. The safety factor of bearing capacity also decreases linearly with salinities. The decrease reaches 12.5–16.3% when soils are in the maximum saline solution. All these changes are considered as the degradation of soils in saline media.  相似文献   
570.
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