Satellite clock bias estimation for iGPS

The High Integrity GPS program seeks to provide enhanced navigation performance by combining conventional GPS with a communications and ranging broadcast from the Iridium^® Communications System. Through clock and message aiding, it would enable existing GPS receivers to acquire and track in more challenging environments. As is the case for standard GPS, accurate and precise timing is key to performance. An approach is presented for estimating the bias of each Iridium satellite clock using satellite-to-ground and satellite-to-satellite measurements. The satellite clock bias estimates are based on a Kalman filter that incorporates code-type observations from the measurements at 10 s intervals. Filter parameters are set based on the expected behavior of the clocks, allowing for discontinuous bias and frequency adjustments due to ground commands. Typical results show the current filter to be accurate to within 200 ns while always meeting the initial system specification of half a microsecond.     

Experimentation of structured light and stereo vision for underwater 3D reconstruction

Current research on underwater 3D imaging methods is mainly addressing long range applications like seafloor mapping or surveys of archeological sites and shipwrecks. Recently, there is an increasing need for more accessible and precise close-range 3D acquisition technologies in some application fields like, for example, monitoring the growth of coral reefs or reconstructing underwater archaeological pieces that in most cases cannot be recovered from the seabed. This paper presents the first results of a research project that aims to investigate the possibility of using active optical techniques for the whole-field 3D reconstructions in an underwater environment. In this work we have tested an optical technique, frequently used for in air acquisition, based on the projection of structured lighting patterns acquired by a stereo vision system. We describe the experimental setup used for the underwater tests, which were conducted in a water tank with different turbidity conditions. The tests have evidenced that the quality of 3D reconstruction is acceptable even with high turbidity values, despite the heavy presence of scattering and absorption effects.     

粤北晚泥盆世天子岭组遗迹组构及其环境解释

遗迹组构是由生物成因改造的沉积岩组构,它是物理过程和生物过程相互作用的产物。本文在广东韶关晚泥盆世天子岭组碳酸盐岩沉积中建立了4个遗迹组构,即反映局限台地或封闭海湾环境的Planolies montanus遗迹组构,反映台地潮下低能环境的Thalassinoides—Planolites遗迹组构,反映潮上-潮间环境的．Skolithos遗迹组构和受固底底质控制的Thalassinoides遗迹组构。对遗迹化石和生物扰动构造进行阶层分析,从中识别出受固底底质控制的遗迹化石Thalassinoides.sp,这类遗迹化石常常代表层序地层学中的重要界面。     

Rates of generation and growth of the continental crust

Models for when and how the continental crust was formed are constrained by estimates in the rates o crustal growth. The record of events preserved in the continental crust is heterogeneous in time with distinctive peaks and troughs of ages for igneous crystallisation, metamorphism, continental margin and mineralisation. For the most part these are global signatures, and the peaks of ages tend to b associated with periods of increased reworking of pre-existing crust, reflected in the Hf isotope ratios o zircons and their elevated oxygen isotope ratios. Increased crustal reworking is attributed to periods o crustal thickening associated with compressional tectonics and the development of supercontinents Magma types similar to those from recent within-plate and subduction related settings appear to hav been generated in different areas at broadly similar times before ~3.0 Ga. It can be difficult to put th results of such detailed case studies into a more global context, but one approach is to consider when plate tectonics became the dominant mechanism involved in the generation of juvenile continental crust The development of crustal growth models for the continental crust are discussed, and a number o models based on different data sets indicate that 65%-70% of the present volume of the continental crus was generated by 3 Ga. Such estimates may represent minimum values, but since ~3 Ga there has been reduction in the rates of growth of the continental crust. This reduction is linked to an increase in th rates at which continental crust is recycled back into the mantle, and not to a reduction in the rates a which continental crust was generated. Plate tectonics results in both the generation of new crust and it destruction along destructive plate margins. Thus, the reduction in the rate of continental crustal growth at ~3 Ga is taken to reflect the period in which plate tectonics became the dominant mechanism b which new continental crust was generated.     

Evidence of a shallow magma intrusion beneath the NE Rift system of Mt. Etna during 2013

Continuous GPS (CGPS) data, collected at Mt. Etna between April 2012 and October 2013, clearly define inflation/deflation processes typically observed before/after an eruption onset. During the inflationary process from May to October 2013, a particular deformation pattern localised in the upper North Eastern sector of the volcano suggests that a magma intrusion had occurred a few km away from the axis of the summit craters, beneath the NE Rift system. This is the first time that this pattern has been recorded by CGPS data at Mt. Etna. We believe that this inflation process might have taken place periodically at Mt. Etna and might be associated with the intrusion of batches of magma that are separate from the main feeding system. We provide a model to explain this unusual behaviour and the eruptive regime of this rift zone, which is characterised by long periods of quiescence followed by often dangerous eruptions in which vents can open at low elevation and thus threaten the villages in this sector of the volcano.     

Experimental constraints on pre-eruption conditions of pantelleritic magmas: Evidence from the Eburru complex, Kenya Rift

The phase relationships and compositions of a pantellerite from the Eburru complex in the Kenya Rift Valley have been determined at 150 MPa and under reducing conditions, 2 log units below the Ni–NiO solid buffer. The effects of temperature and melt water content on phase relationships have been explored. Alkali feldspar and quartz crystallise alone at temperatures above 700 °C, irrespective of melt water content. Below 700 °C, sodic amphibole and clinopyroxene also crystallise; the amphibole being the liquidus phase under water-rich conditions. The coexistence of amphibole phenocrysts with alkali feldspar and quartz in a crystal-poor pantellerite implies temperatures below 700 °C and melt water contents higher than 4 wt.%, possibly up to 5–6 wt.%. Pantellerites have lower liquidus temperatures than associated comendites, which supports a parent–daughter relationship between the two magma types. The melts produced in the experiments extend the compositional trend displayed by the natural rock series, and reproduce some extreme compositions occasionally observed in alkaline volcanic series, with FeO contents above 12 wt.% and Na₂O contents approaching 10 wt.%. Pantellerites are therefore the true near-minimum melt compositions of alkaline oversaturated magma series.     

Unusual variations of dissolved As, Sb and Ni in the Rhône River during flood events

Dissolved major and trace element concentrations were determined from November 2000 to December 2003 in the lower Rhône River (France). Subsurface water samples were collected about twice a month and more regularly during flood events. An unusual trend was observed for As, Sb, Ni and Ba concentrations which increased with river discharge at the beginning of the floods, in contrast with other elements. Variations of Sb/Na and As/Na molar ratios show that it is related to higher contributions of waters from western tributaries of the Rhône River enriched in As, Sb, Ni and Ba due to ancient mining activities. These unusual variations of dissolved element concentrations are thus interpreted as mark of a water mass origin within the watershed.