Sea ice ridges and keels (hummocks and bummocks) are important in sea ice research for both scientific and practical reasons. A long-term objective is to make quantitative measurements of sea ice ridges using synthetic aperture radar (SAR) images. The preliminary results of a scattering model for sea ice ridge are reported. The approach is through the ridge height variance spectrum Psi(K), where K is the spatial wavenumber, and the two-scale scattering model. The height spectrum model is constructed to mimic height statistics observed with an airborne optical laser. The spectrum model is used to drive a two-scale scattering model. Model results for ridges observed at C- and X-band yield normalized radar cross sections that are 10 to 15 dB larger than the observed cross sections of multiyear ice over the range of angles of incidence from 10 to 70 deg.
This memoir describes the geology of the district around Bridgend, largely situated to the south of the South Wales Coalfield and forming the western part of the Vale of Glamorgan. It explains the sequences of rocks and superficial deposits, encompassing a geological history of some 395 million years. The rocks comprise limestones, sandstones and mudstones of Devonian and Carboniferous age, disposed in a major fold, the Cardiff-Cowbridge Anticline. They are overlain by mostly red to green marls and sandstones of Triassic age and thinly interbedded limestones and shales of the Lower Jurassic. The latter form the spectacular cliffline of the Glamorgan Heritage Coast. The superficial deposits of the last glaciation, which are preserved in the north and east of the district, are also described, together with those developed in the river valleys and along the coast during the postglacial period. A chapter on the tectonic evolution and mineralisation of the district is included, together with an economic geology chapter dealing with the main resources, including water supply. A reference list, summary logs of key boreholes and an excursion guide to the coast near Ogmore-by-Sea are also provided. 115 refs., 30 figs., 2 tabs.
Image-processing techniques for extracting the characteristics of lead and pressure ridge features in SAR images of sea ice are reported. The methods are applied to a SAR image of the Beaufort Sea collected from the Seasat satellite on October 3, 1978. Estimates of lead and ridge statistics are made, e.g., lead and ridge density (number of lead or ridge pixels per unit area of image) and the distribution of lead area and orientation as well as ridge length and orientation. The information derived is useful in both ice science and polar operations for such applications as albedo and heat and momentum transfer estimates, as well as ship routing and offshore engineering.
GPS and low-cost INS sensors are widely used for positioning and attitude determination applications. Low-cost inertial sensors exhibit large errors that can be compensated using position and velocity updates from GPS. Combining both sensors using a Kalman filter provides high-accuracy, real-time navigation. A conventional Kalman filter relies on the correct definition of the measurement and process noise matrices, which are generally defined a priori and remain fixed throughout the processing run. Adaptive Kalman filtering techniques use the residual sequences to adapt the stochastic properties of the filter on line to correspond to the temporal dependence of the errors involved. This paper examines the use of three adaptive filtering techniques. These are artificially scaling the predicted Kalman filter covariance, the Adaptive Kalman Filter and Multiple Model Adaptive Estimation. The algorithms are tested with the GPS and inertial data simulation software. A trajectory taken from a real marine trial is used to test the dynamic alignment of the inertial sensor errors. Results show that on line estimation of the stochastic properties of the inertial system can significantly improve the speed of the dynamic alignment and potentially improve the overall navigation accuracy and integrity.
Increasingly greater numbers of wells are being drilled below 25,000 ft, and considerations of methane stability in the deep subsurface are becoming more important. The authors have calculated equilibrium gas compositions corresponding to conditions down to 40,000 ft for low, average, and high geothermal gradients, for hydrostatic and lithostatic pressures, and with and without graphite. Calculations have been made for sandstone reservoirs with various amounts and combinations of feldspars, clays, carbonate cements, and iron oxides with and without graphite, and for limestone and dolomite reservoirs with various combinations of clays, iron minerals, anhydrite, and sulfur, again with and without graphite. Natural gas shows considerable stability in sandstone reservoirs under most conditions, but its concentration in deep carbonates is much more variable and tends to a H/sub 2/S-CO/sub 2/ mixture except when an appreciable concentration of iron is present.The thermodynamic predictions can (in principle) be checked by direct analysis down to the depth limit of available gas samples. In practice, considerable problems exist due to partial gas loss during sample retrieval. The analysis of gases trapped in fluid inclusions in late-stage cements offers one solution to this problem. This gas is being analyzed by thermally rupturing inclusions in the inlet systemmore » of a fast-scanning, computer-controlled mass spectrometer. Each bursting inclusion is analyzed separately, and several hundred individual inclusions can be analyzed using only 10 mg of sample. A wide variety of compositions, including water-rich, methane-rich, and H/sub 2/S-rich, is found in samples from below 20,000 ft.« less
Abstract Sulfur-bearing monazite-(Ce) occurs in silicified carbonatite at Eureka, Namibia, forming rims up to ~0.5 mm thick on earlier-formed monazite-(Ce) megacrysts. We present X-ray photoelectron spectroscopy data demonstrating that sulfur is accommodated predominantly in monazite-(Ce) as sulfate, via a clino-anhydrite-type coupled substitution mechanism. Minor sulfide and sulfite peaks in the X-ray photoelectron spectra, however, also indicate that more complex substitution mechanisms incorporating S 2– and S 4+ are possible. Incorporation of S 6+ through clino-anhydrite-type substitution results in an excess of M 2+ cations, which previous workers have suggested is accommodated by auxiliary substitution of OH – for O 2– . However, Raman data show no indication of OH – , and instead we suggest charge imbalance is accommodated through F – substituting for O 2– . The accommodation of S in the monazite-(Ce) results in considerable structural distortion that may account for relatively high contents of ions with radii beyond those normally found in monazite-(Ce), such as the heavy rare earth elements, Mo, Zr and V. In contrast to S-bearing monazite-(Ce) in other carbonatites, S-bearing monazite-(Ce) at Eureka formed via a dissolution–precipitation mechanism during prolonged weathering, with S derived from an aeolian source. While large S-bearing monazite-(Ce) grains are likely to be rare in the geological record, formation of secondary S-bearing monazite-(Ce) in these conditions may be a feasible mineral for dating palaeo-weathering horizons.
The rare earth elements (REE), and in particular neodymium and dysprosium, are essential for the development of renewable energy. At present the REE are sourced from either low concentration weathered granitoid (ion adsorption clay) deposits in southern China, or from high concentration carbonatite-related deposits [1], especially the World’s dominant REE mine at Bayan Obo, China, but also including the Mt Weld weathered carbonatite, Australia. Weathered carbonatites (e.g. Tomtor, Russia; Mount Weld, Australia) are some of the world’s highest grade REE deposits. As part of the NERC Global Partnerships Seedcorn fund project WREED, we have carried out preliminary investigations in weathering products from carbonatite hosted REE deposits. Three end member deposit styles can be identified – in situ residual deposits, where carbonate dissolution has generated primary REE mineral enrichment on palaeosurfaces or in karst; supergene enrichment from dissolution and reprecipitation of REE phosphates and fluorcarbonates forming hydrated phosphates or authigenic carbonate minerals; clay and oxide caps (either from in situ weathering or from soil transport from surrounding rocks) that may hold the REE adsorbed to mineral surfaces (c.f. the ion adsorption deposits). High grade weathered carbonatite deposits typically consist of supergene horizons, that may be phosphate-rich due to dissolution and re-precipitation of apatite and monazite during the weathering process (Mount Weld [2][3]), overlain by later sediments that may be REE enriched by accumulation of residual minerals (e.g. Tomtor [4]). The mineralogy of the ore zone is linked to, but distinct from, the unweathered carbonatite rock, and includes phosphates, crandallite-group minerals, carbonates and fluorcarbonates and oxides. We have carried out leaching studies, SEM examination and XPS characterisation of soil and weathered rock samples from a range of deposits. Residual and supergene processes can result in enrichments up to 100x times bedrock concentrations, with residual enrichments in particular hosted in monazite and bastnäsite. Supergene enrichment results in more complex mineralogy which may present processing challenges. Clay-rich soils have much lower REE concentrations. However, sequential leaching studies demonstrate that a significant proportion of REE are present at trace levels in the oxide fraction in residual and supergene deposits. In clay caps the easily leachable fraction of REE matches that of ion adsorption deposits and may represent a potentially easily extractable resource. References[1] Wall and Chakhmouradian, 2012, Elements 8, 333-340;[2] Duncan and Willett, 1990, Geology of Mineral Deposits of Australia pp. 591-597;[3] Lottermoser, 1990, Lithos 24, 151-167;[4] Kravchenko and Pokrovsky, 1995, Econ. Geol. 90, 676-689
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