Geometrical aspects of a sonar-based navigation system for underwater vehicles     

N. McLaren  C. Kuo 《Ocean Engineering》1996,23(2):201-217

A novel self-contained navigation system has been devised for underwater vehicles operating in and around offshore installations. This system matches data from a sector-scanning sonar device to a computer model of the installation. The paper begins by highlighting the existing approaches to subsea navigation before outlining the main features of the proposed system. It then concentrates on a key component of this system which is a method for calculating the position and heading of an underwater vehicle navigating in the vincinity of tubular steel structures. An iterative solution method is presented which incorporates six degree of freedom vehicle motions and this is verified in a series of laboratory experiments with various arrangements of structural members and using a commercial sonar device. The key features, applications and performance of this method are discussed. The main conclusion is that the proposed method for calculating the position and heading of an underwater vehicle contributes towards achieving an accurate and reliable subsea navigation capability.  相似文献   

MODELLING FOR DIGITAL TERRAIN AND LANDSCAPE VISUALISATION     

T. J. M. Kennie  R. A. McLaren   《The Photogrammetric Record》1988,12(72):711-745

Methods of creating digital terrain and landscape models for regional and site specific visualisations are described. A number of alternative approaches are discussed and their relative accuracies are considered. This is followed by a review of the computer graphics procedures which can be used to render such models. Particular attention is directed towards methods for depth cueing, hidden surface removal, shading and texturing. The effects of the atmosphere and methods of producing shadows are also examined. The paper then presents varied applications of such visualisations, including small scale, regional examples and large scale, site specific applications. In conclusion, the role of photogrammetry in the process of visualisation is assessed and possible future developments in this field are identified.  相似文献   

The relations between modulus of elasticity and temperature in the context of the experimental simulation of rock weathering by fire     

A. S. Goudie  R. J. Allison  S. J. McLaren 《地球表面变化过程与地形》1992,17(6):605-615

Fires occur frequently in many biomes and generate high temperatures on the ground surface. There are many field examples of fire causing rock disintegration. The simulation of fire in the laboratory (using a furnace) and the monitoring of changes in rock modulus of elasticity (with a Grindosonic apparatus), reveal that different rocks respond differently to heating. Significant decreases in elasticity occur at temperatures as low as 200°C and granites display particularly marked reductions. Extended periods of heating are not required for significant reductions to occur. It is postulated that the degree of change in elasticity as a result of simulated fire is such that rock outcrops subjected to real fires are likely to be sufficiently modified as to increase their susceptibility to erosion and weathering processes.  相似文献   

Multiple phases of North African humidity recorded in lacustrine sediments from the Fazzan Basin, Libyan Sahara     

S.J. Armitage  N.A. Drake  S. Stokes  A. El-Hawat  M.J. Salem  K. White  P. Turner  S.J. McLaren 《Quaternary Geochronology》2007,2(1-4):181-186

The Fazzan Basin of south-west Libya is at present arid with less than 20 mm of rainfall per annum. However, regionally extensive limestones, lacustrine sands and coquina (fossiliferous carbonate rock) deposits show that the Fazzan Basin previously contained a large palaeolake, indicating that the climate in the past was more humid. Optically stimulated luminescence (OSL) dating techniques have been applied to key lacustrine deposits within the basin in an attempt to provide an internally consistent chronology for this humidity record. Results indicate that palaeolake sediments within the Fazzan Basin record a very long history of palaeohydrological change, ranging from present day arid conditions to humidity capable of sustaining a lake with an approximate area of 76,250 km². The existence of humid periods in mid oxygen isotope stage 5 and the early Holocene is confirmed. An older lacustrine event, tentatively correlated to oxygen isotope stage 11, is also recognized. In addition, evidence is presented for at least two humid phases beyond the age range over which the conventional OSL dating technique is applicable. This study demonstrates that OSL dating of palaeolake sediments within the Fazzan Basin offers the potential to provide a detailed record of North African humidity spanning several glacial–interglacial cycles.  相似文献   

Coarsening kinetics of the exsolution microstructure in alkali feldspar     

R. A. Yund  A. C. McLaren  B. E. Hobbs 《Contributions to Mineralogy and Petrology》1974,44(1):45-55

Actinolite, hornblende and biotite coexisting in greenschist mafic metagreywackes have been analysed with the electron microprobe to obtain information on their chemical relationship during metamorphism. As in some other parts of the world, the two calcic amphiboles coexist in the greenschist facies because of a miscibility gap between them which is observed under conditions of low-pressure regional metamorphism; it is thought that the two amphiboles are in equilibrium, or at least that the actinolite participated in hornblendeforming reactions. Contact metamorphism by granitic intrusives of these metagreywackes has converted them to hornblende hornfelses with the assemblage hornblende, andesine, quartz, biotite±cummingtonite; the hornblendes of the hornfelses are found to have compositions between actinolite and hornblende of the greenschists, and frequently show fine exsolution lamellae of cummingtonite as a result of oversaturation in this component. The distribution of Fe-Mg between hornblende and biotite changes from the greenschist to the hornblende hornfels facies, and the K _D is probably dependent on Al^VI in the hornblende.  相似文献   

Transmission electron microscope study of the domain structures associated with the b-, c-, d-, e- and f-reflections in plagioclase feldspars     

A. C. McLaren  D. B. Marshall 《Contributions to Mineralogy and Petrology》1974,44(3):237-249

Ten specimens of plagioclase feldspars (An₁₀₀ to An₂₅) have been examined by transmission electron microscopy using dark field and direct lattice imaging. The specimens are classified into two groups: (i) those that have been quenched from the melt (synthetic An₁₀₀, An₉₅, An₆₆ and An₅₀) and (ii) those that have been cooled relatively slowly (An₉₄, An₇₇, An₇₅, An₅₂, An₃₂ and An₂₆). The observed contrast is interpreted in detail using the two-beam dynamical theory of electron diffraction contrast. The fault vectors of the antiphase boundaries (APBs) observed in An₁₀₀ and An₇₇ are determined. Direct resolution of the sublattice and superlattice in specimens of intermediate composition (An₇₅ to An₂₅) indicates that the superlattice is not a regular array of out-of-step faults and is probably due to a simple sinusoidal distortion of the structure. Only three specimens (An₁₀₀, An₇₇ and An₅₀) exhibited a single structural type. All the remaining specimens consisted of intergrowths of two structural types. The structural type present in any particular specimen depends upon its An-content and thermal history. The rate of transformation from any structural type to a lower-temperature structural type appears to decrease with decreasing An-content.  相似文献   

A review of the assessments of the major fisheries resources in South Africa     

CL de Moor  SJ Johnston  A Brandão  RA Rademeyer  JP Glazer  LB Furman 《African Journal of Marine Science》2015,37(3):285-311

The waters off South Africa's coastline boast a rich mix of commercially fished species. Quantitative assessments of these marine resources have developed from simple methods first applied in the 1970s, to models that encompass a wide range of methodologies. The more valuable resources have undergone regular assessments in recent decades, with frequencies closely related to the management approach employed for each fishery. Many of these assessments form the operating models used to simulation-test candidate management procedures. This paper provides a comprehensive review of the assessments of 11 of the most important fisheries resources in South Africa. Some assessments use simple biomass dynamics models, whereas others are a hybrid of age- and length-based models, each designed to model the specific characteristics of the resource and fishery concerned. Many of the assessments have been disaggregated by species/stock and/or area as related multispecies/stock/ distribution hypotheses have arisen. This paper explores the similarities and differences in the data available and the methods applied. The review indicates that, whereas the status of three of these resources cannot be estimated reliably at present, the status of six resources is considered to be reasonable to good, whereas that of abalone Haliotis midae and West Coast rock lobster Jasus lalandii remains poor.  相似文献   

Proposal to Use MAGDAS/CPMN to Study the Equatorial Electrojet: A Philippine Contribution to the International Heliophysical Year     

R. E. S. Otadoy  D. McNamara SJ  K. Yumoto 《Earth, Moon, and Planets》2009,104(1-4):167-172

As a Philippine contribution to the International Heliophysical Year, we propose to use the MAGnetic Data Acquisition System/Circum Pan-Pacific Magnetometer Network (MAGDAS/CPMN), installed by the Space Environment Research Center (SERC), Kyushu University along the 210° magnetic meridian and the magnetic equator, to study the equatorial electrojet (EEJ) and counter electrojet (CEJ). Through this installation, it is made possible to observe geomagnetic field variations in real time. By utilizing this network of ground-based instruments, we hope to elucidate their regular day-to-day and seasonal variabilities and variations during magnetic storms and substorms. We also want to study the behavior of this ionospheric current system before, during, and after the occurrence of an earthquake.  相似文献   

The astrobiological landscape,Milan M. Ćirković. Cambridge,UK: Cambridge University Press, 2012, ISBN:9780521197755, hardback, $110, 274 p.     

SJ Guy Consolmagno 《Meteoritics & planetary science》2013,48(2):316-317

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Analysis of sediment distribution and transport for mitigation of sand deposition hazard in Tam Quan estuary,Vietnam     

Do Minh Duc  Dinh Xuan Thanh  Dinh Thi Quynh  Patrick McLaren 《Environmental Earth Sciences》2016,75(9):741

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