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521.
Reflection profiling in a region of anomalous topography and structure in the Bay of Bengal off Burma has revealed the presence of a large submarine slide (olistostrome) at the base of the continental slope off the Bassein River. The slide overlies a thick section of Bengal Deep-Sea Fan turbidites and has a complex internal structure consisting of two primary elements. The lower element is pervasively disturbed and is interpreted as a mudflow generated at the time of the slide which spread over a large area to as much as 35 km beyond the topographic toe. This mudflow poured into a distributary channel on the Bengal Fan and virtually filled it for 145 km along its length. The upper element comprises a series of relatively coherent blocks of stratified sediments (olistoliths) bounded by curved fault planes. The blocks have been transported as much as 55 km from the original Sunda Trench wall. Their dimensions, up to 360 m thick and 2.8 km between faults, are similar to olistoliths of the slide terrain in the Apennines. The blocks are blanketed by younger slope strata. The total area covered by the slide, including the mudflow, is almost 4,000 km2, and total volume of the slide is over 900 km3. Material of the slide consists of Bengal Fan turbidites offscraped above the Sunda Subduction zone and blanketed by rapidly deposited slope sediments from a western Irrawaddy River distributary (the Bassein River) during Late Quaternary glacial low sea level. This rapid loading, probably coupled with a large earthquake, triggered the slide. 相似文献
522.
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.
相似文献
Shaojun FengEmail: |
523.
The rate of regrowth of Limaria hians nest material, following a simulated dredging impact, was examined on an extensive L. hians bed off the west coast of Scotland. Within an area of complete coverage of the sea bed by a turf of L. hians nest material, the turf was cleared by diver from 10 × 0.25 m2 plots and the sediment subsequently raked to simulate the passage of a scallop dredge. The areal extent and pattern of nest regrowth were recorded after 6 and 12 months. Control plots showed no significant change in 100% nest cover over the year. In the treated plots regrowth generally occurred from extension of peripheral nest material. Over the initial 6 autumn and winter months treatment plots displayed a mean regrowth of 9.2% of the cleared area, increasing to 15% in the second 6-month spring and summer period. However, no significant difference in growth was found between these periods. After 12 months half the treatment plots exhibited <25% nest cover and none of them contained nest of a thickness comparable to the surrounding bed. Conversion of regrowth rates within the treated plots to the rate of nest advance along a linear front, gave a value of 3.2 cm per year, highlighting the susceptibility of this species-rich biotope to scallop dredging. 相似文献
524.
Jia-Zhong Zhang Christopher R. Kelble Charles J. Fischer Lloyd Moore 《Estuarine, Coastal and Shelf Science》2009
Water quality surveys conducted in Biscayne Bay, Florida, indicated enhanced nutrient input coupled with increased runoff as a result of precipitation associated with Hurricane Katrina. Nutrient concentrations before Katrina ranged from 0.06–24.2 μM (mean 3.3 μM) for nitrate and 0.01–0.18 μM (mean 0.1 μM) for soluble reactive phosphate. Five days after Katrina, nitrate concentrations ranged from 0.87–80.0 μM (mean 17.0 μM), with a bay-wide mean increase of 5.2-fold over pre-hurricane levels. Soluble reactive phosphate concentrations ranged from 0.07–0.62 μM (mean 0.2 μM), with a bay-wide mean increase of 2-fold over pre-hurricane levels. The maximum concentrations for both nitrate and soluble reactive phosphate were found at a water quality monitoring station near the mouth of Mowry Canal, which drains an agricultural area in the southern Biscayne Bay watershed near Homestead, Florida. At this station, nitrate and soluble reactive phosphate concentrations increased 7- and 10-fold, respectively. Storm-induced fertilizer runoff from this agricultural area caused a bay-wide increase in nutrient concentrations after Hurricane Katrina. Nutrient concentrations in the bay returned to pre-hurricane levels within three months after Hurricane Katrina, showing the resiliency of the Biscayne Bay ecosystem. 相似文献
525.
William C. Burnett Richard Peterson Willard S. Moore Joselene de Oliveira 《Estuarine, Coastal and Shelf Science》2008
We determined groundwater flow rates shortly after the wet season into an embayment near Ubatuba, Brazil as part of an international intercomparison experiment for submarine groundwater discharge (SGD) assessment techniques. Our estimated rates were determined by the combined use of continuous radon measurements and assessment of radium isotope patterns. The spatial distribution of the short-lived radium isotopes (223Ra and 224Ra) provided the means for independent evaluations of radon losses by mixing and atmospheric evasion. We were thus able to construct a well-constrained mass balance for radon that included a groundwater flux term. Our results showed that the groundwater discharge into this embayment from the fractured crystalline rock aquifer is not steady-state but varies with tidal modulation and rain-induced forcing. Tidally modulated and rain-induced flow rates were comparable during this period. The SGD rates estimated from radon ranged from 1 cm/day to 29 cm/day (cm3/cm2 day) with a mean and standard deviation of 13 ± 6 cm/day. These estimates were mostly similar to a dye-dilution automatic seepage meter (15 ± 19 cm/day) and were within the broad ranges estimated by manual and continuous heat seepage meters but lower than indicated by an artificial tracer test performed nearshore. 相似文献
526.
The RaDeCC™ system has proved to be a robust method of measuring 223Ra and 224Ra extracted from natural waters. Samples ranging in size from < 1 to > 1000 L are first concentrated onto Mn-fiber. The Mn-fiber is partially dried and placed into a circulation system with helium as the carrier gas. Alpha decays of the radon daughters of 223Ra and 224Ra are recorded in a scintillation cell. These data are used to activate electronic gates in the delayed coincidence system, which separate events due to 223Ra from those due to 224Ra. The system combines a high detection efficiency with low background to accurately measure 223Ra and 224Ra at concentrations on the order of 5 atoms per liter. Since this system was first deployed, numerous improvements in electronics and technique have occurred. In this paper I present tests we have conducted to confirm certain assumptions and improve the overall technique of sample collection and measurement. 相似文献
527.
George W. Luther III Brian T. Glazer Shufen Ma Robert E. Trouwborst Tommy S. Moore Edouard Metzger Chareonkwan Kraiya Tim J. Waite Gregory Druschel Bjrn Sundby Martial Taillefert Donald B. Nuzzio Timothy M. Shank Brent L. Lewis Paul J. Brendel 《Marine Chemistry》2008,108(3-4):221-235
Solid-state voltammetric (micro)electrodes have been used in a variety of environments to study biogeochemical processes. Here we show the wealth of information that has been obtained in the study of sediments, microbial mats, cultures and the water column including hydrothermal vents. Voltammetric analyzers have been developed to function with operator guidance and in unattended mode for temporal studies with an in situ electrochemical analyzer (ISEA). The electrodes can detect the presence (or absence) of a host of redox species and trace metals simultaneously. The multi-species capacity of the voltammetric electrode can be used to examine complex heterogeneous environments such as the root zone of salt marsh sediments. The data obtained with these systems clearly show that O2 and Mn2+ profiles in marine sedimentary porewaters and in microbial biofilms on metal surfaces rarely overlap indicating that O2 is not a direct oxidant for Mn2+. This lack of overlap was suggested originally by Joris Gieskes' group. In waters emanating from hydrothermal vents, Fe2+, H2S and soluble molecular FeS clusters (FeSaq) are detected indicating that the reactants for the pyrite formation reaction are H2S and soluble molecular FeS clusters. Using the ISEA with electrodes at fixed positions, data collected continuously over three days near a Riftia pachyptila tubeworm field generally show that O2 and H2S anti-correlate and that H2S and temperature generally correlate. Unlike sedimentary environments, the data clearly show that Riftia live in areas where both O2 and H2S co-exist so that its endosymbiont bacteria can perform chemosynthesis. However, physical mixing of diffuse flow vent waters with oceanic bottom waters above or to the side of the tubeworm field can dampen these correlations or even reverse them. Voltammetry is a powerful technique because it provides chemical speciation data (e.g.; oxidation state and different elemental compounds/ions) as well as quantitative data. Because (micro)organisms occupy environmental niches due to the system's chemistry, it is necessary to know chemical speciation. Voltammetric methods allow us to study how chemistry drives biology and how biology can affect chemistry for its own benefit. 相似文献
528.
Zuohao Cao G.W.K. Moore Department of Physics University of Toronto Toronto Ontario Canada MS A 《大气科学进展》1998,(2)
ADiagnosticStudyofMoistPotentialVorticityGenerationinanExtratropicalCyclone①ZuohaoCaoandG.W.K.MoreDepartmentofPhysics,Univers... 相似文献
529.
Edgar L. Andreas Reginald J. Hill James R. Gosz Douglas I. Moore William D. Otto Achanta D. Sarma 《Boundary-Layer Meteorology》1998,86(3):409-420
From a set of turbulence data collected with a three-axis sonic anemometer/thermometer and described in a companion paper, we simulate the eddy-accumulation process for sensible heat and momentum fluxes. The resulting eddy-accumulation coefficient for momentum clearly depends on surface-layer stability; at neutral stability, its value is 0.63. On supplementing the scalar eddy-accumulation coefficients that we derive from our sensible heat flux data with values of sensible and latent heat flux coefficients reported by Businger and Oncley, we also find that scalar eddy-accumulation coefficients depend on stability, though more weakly than does the momentum coefficient. The coefficients for sensible and latent heat show no significant difference; we, thus, fit them with one function of stability whose value is 0.52 for neutral stratification. 相似文献
530.
Eighty samples of submarine basaltic lava were sampled from an 8 km segment of the floor and walls of the inner rift valley of the Mid-Atlantic Ridge during the French American Mid-Ocean Undersea Study (project Famous). The samples were collected from outcrops and talus slopes by the three submersibles: Alvin, Archimede, and Cyana at water depths of about 2600 meters.The early formed mineral content of the pillow lavas' glassy margins enables classification of the rocks into 5 types: (1) olivine basalt, (2) picritic basalt, (3) plagioclase-olivine-pyroxene basalt, (4) aphyric basalt, and (5) plagioclase-rich basalt. Chemical and mineralogical study indicates that at least 4 types are directly interrelated and that types (1) and (2) are higher-temperature, primitive lavas, and types (3) and (4) are lower-temperature, differentiated lavas derived from the primitive ones by crystal-liquid differentiation. The plagioclase-rich basalts also have a chemical composition of their glass comparable to that of the most differentiated basalts (types 3 and 4) but they differ in their greater amount of early formed plagioclase (12–35%).In general, the mineralogical variation across the rift valley shows an assymetrical distribution of the major basalt types. Despite the mineralogical diversity of the early formed crystals, the chemistry of the basalt glasses indicates a symmetrical and a gradual compositional change across the rift valley. Based primarily on their chemistry, the rock types 1 and 2 occupy an axial zone 1.1 km wide and make up the central volcanic hills. Differentiated lavas (types 3, 4) occupy the margins and walls of the inner rift valley and also occur near the center of the rift valley between the central hills.FeO/MgO ratios of olivine and coexisting melt indicate that the average temperature of eruption was 40 ° C higher for the primitive melts (types 1 and 2). Aside from major elements trends, the higher temperature character of the primitive basalts is shown by their common content of chrome spinel.The thickness of manganese oxide and palagonite on glassy lava provide an estimate of age. In a general fashion the relative age of the various volcanic events follow the compositional zoning observed in the explored area. Most of the youngest samples are olivine basalt of the axial hills. Most older samples occur in the margins of the rift valley (West and N.E. part of explored area) but are significantly younger than the spreading age of the crust on which they are erupted. Intermediate lava types occur mainly east of the rift valley axis and in other areas where plagioclase—olivine—pyroxene basalt and aphyric basalt are present.The above relations indicate that the diverse lava types were erupted from a shallow, zoned magma chamber from fissures distributed over the width of the inner rift valley and elongate parallel to it. Differentiation was accomplished by cooling and crystallization of plagioclase, olivine, and clinopyroxene toward the margins of the chamber. The centrally located hills were built by the piling up of frequent eruption of mainly primitive lavas which also are the youngest flows. In contrast smaller and less frequent eruptions of more differentiated lavas were exposed on both sides of the rift valley axis.Contribution n ° 480 du Départment Scientifique, Centre Océanologique de Bretagne 相似文献