Velocity-Aided Underwater Navigation System Using Receding Horizon Kalman Filter

This paper discusses the problems related to constructing a receding horizon filter for underwater inertial navigation systems which are subject to external disturbances. Noises are assumed to be bounded, additive, and contained in both state and measurement equations. An estimator is designed according to the sliding-window strategy to minimize the receding horizon estimation cost function. The derived filter is applied to a velocity-aided inertial navigation system. Simulations show that the derived filter is more accurate than the standard Kalman filter (KF) for underwater navigation systems subject to temporary unknown disturbances     

Evidence of temperature depression and hydrological variations in the eastern Sierra Nevada during the Younger Dryas stade

Sediment records from two lakes in the east-central Sierra Nevada, California, provide evidence of cooling and hydrological shifts during the Younger Dryas stade (YD; ~ 12,900-11,500 cal yr BP). A chironomid transfer function suggests that lake-water temperatures were depressed by 2°C to 4°C relative to maximum temperatures during the preceding Bølling-Allerød interstade (BA; ~ 14,500-12,900 cal yr BP). Diatom and stable isotope records suggest dry conditions during the latter part of the BA interstade and development of relatively moist conditions during the initiation of the YD stade, with a reversion to drier conditions later in the YD. These paleohydrological inferences correlate with similar timed changes detected in the adjacent Great Basin. Vegetation response during the YD stade includes the development of more open and xeric vegetation toward the end of the YD. The new records support linkages between the North Atlantic, the North Pacific, and widespread YD cooling in western North America, but they also suggest complex hydrological influences. Shifting hydrological conditions and relatively muted vegetation changes may explain the previous lack of evidence for the YD stade in the Sierra Nevada and the discordance in some paleohydrological and glacial records of the YD stade from the western United States.     

Lateral terrestrial water flow contribution to summer precipitation at continental scale – A comparison between Europe and West Africa with WRF-Hydro-tag ensembles

It is well accepted that summer precipitation can be altered by soil moisture condition. Coupled land surface – atmospheric models have been routinely used to quantify soil moisture – precipitation feedback processes. However, most of the land surface models (LSMs) assume a vertical soil water transport and neglect lateral terrestrial water flow at the surface and in the subsurface, which potentially reduces the realism of the simulated soil moisture – precipitation feedback. In this study, the contribution of lateral terrestrial water flow to summer precipitation is assessed in two different climatic regions, Europe and West Africa, for the period June–September 2008. A version of the coupled atmospheric-hydrological model WRF-Hydro with an option to tag and trace land surface evaporation in the modelled atmosphere, named WRF-Hydro-tag, is employed. An ensemble of 30 simulations with terrestrial routing and 30 simulations without terrestrial routing is generated with random realizations of turbulent energy with the stochastic kinetic energy backscatter scheme, for both Europe and West Africa. The ensemble size allows to extract random noise from continental-scale averaged modelled precipitation. It is found that lateral terrestrial water flow increases the relative contribution of land surface evaporation to precipitation by 3.6% in Europe and 5.6% in West Africa, which enhances a positive soil moisture – precipitation feedback and generates more uncertainty in modelled precipitation, as diagnosed by a slight increase in normalized ensemble spread. This study demonstrates the small but non-negligible contribution of lateral terrestrial water flow to precipitation at continental scale.     

Lithospheric mantle signatures as revealed by zircon Hf isotopes of Late Triassic post‐collisional plutons from the central Korean peninsula,and their tectonic implications

The Mesozoic tectonic architecture of the Korean peninsula is largely governed by the continental collision between the North and South China blocks. Zircon Hf isotopic compositions presented in this study and whole‐rock geochemical and Sr‐Nd isotope data in the literature collectively suggest that the lithophile‐elements‐enriched signature of the Late Triassic post‐collisional plutons from the Gyeonggi massif in central Korea is a primary feature inherited from the metasomatized mantle lithosphere. Highly negative zircon ε_Hf (t) values (?23 to ?19) of plutons from the middle and eastern parts of the massif indicate an ancient metasomatism of their mantle source. Distinctly higher zircon ε_Hf (t) values (?15 to ?12) from the southwestern plutons are ascribed to a contribution from an accreted component of the South China‐like block. The involvement of asthenospheric mantle is not recognized in zircons from either group. The implications of these isotopic features are discussed in the context of Mesozoic collisional tectonics.     

Analytical evaluation of structural component limit state probabilities

Probabilistic seismic assessment requires extensive computational effort resulting from variability both in input ground motions and mechanical properties. Nonetheless, such methodologies are of considerable importance, namely for pre-earthquake disaster planning or development of retrofitting programs. A framework for the analytical definition of closed form expressions for exceedance probabilities of structural component limit states, defined by limit values of structural response parameters, is proposed herein. The definition of these expressions is based on the probabilistic representation of the ground motion intensity and on the establishment of suitable expressions characterizing the evolution of structural demand with increasing earthquake intensity. Distinction is made between deformation-based and force-based structural parameters in the definition of such relations. Within the proposed framework, the limit states are defined by single deterministic thresholds of structural response quantities at the component level, as defined in structural codes. Different approaches are also discussed to account for the randomness of the mechanical properties and ground motion input within the proposed methodology. An application of the assessment of different limit state probabilities of members from a reinforced concrete building is presented, for which limit states and limit state capacities are defined according to the upcoming Part 3 of the Eurocode 8. Although the presented application only deals with member chord rotation and shear force limit state probabilities, the proposed methodology can be generalized to other deformation-based and force-based structural parameters.     

Tidal circulation and buoyancy effects in the St. Lawrence Estuary

Abstract

The action of tides on density‐driven circulation, internal gravity waves, and mixing was investigated in the St. Lawrence Estuary between Rimouski and Québec City. Time‐varying fields of water level, currents and density were computed under typical summer conditions using a three‐dimensional hydrostatic coastal ocean model that incorporates a second order turbulence closure submodel. These results are compared with current meter records and other observations. The model and the observations reveal buoyancy effects produced by tidal forcing. The semi‐diurnal tide raises the isopycnals over the sills at the head of the Laurentian Trough and English Bank, producing internal tides radiating seaward. Relatively dense intermediate waters rise from below 75‐m depth to the near surface over the sills, setting up gravity currents on the inner slopes. Internal hydraulic controls develop over the outer sills; during flood, surface flow separation occurs at the entrances of the Saguenay Fjord and the upper estuary west of Ilet Rouge Bank. Early during ebb flow (restratification), the surface layer deepens to encompass the tops of the sills. As the ebb current intensifies, the model predicts the formation of seaward internal jumps over the outer sills, which were confirmed from acoustic reflection observations. As the internal Froude number increases further, flow separation migrates up to sill height. As a result of these transitions, internal bores emanate from the head region one to two hours before low water. We find that the mixing of oceanic and surface waters near the sills is driven by the vertical shear produced during ebb in the channel south of Ilet Rouge, the shear produced in the bottom gravity flood currents, and, to a lesser extent, the processes over the sills.