Theory of satellite ground-track crossovers

The fundamental geometry of satellite ground tracks and their crossover problem are investigated. For idealized nominal ground tracks, the geometry is governed by a few constant parameters whose variations lead to qualitative changes in the crossover solutions. On the basis that the theory to locate crossovers has not been studied in sufficient detail, such changes are described in regard to the number of crossover solutions in conjunction with their bifurcations. Employing the spinor algebra as a tool for establishing the ground-track crossing condition, numerical methodologies to locate crossovers appearing in general dual-satellite ground-track configurations are also presented. The methodologies are applied to precisely determined orbital ephemerides of the GEOSAT, ERS-1, and TOPEX/POSEIDON altimeter satellites. Received: 19 November 1996 / Accepted: 12 May 1997     

The origin and response of zircon in eclogite to metamorphism during the multi-stage evolution of the Huwan Shear Zone,China: Insights from Lu–Hf and U–Pb isotopic and trace element geochemistry

The Huwan Shear Zone (HSZ) is an eclogite bearing transpressive wrench zone located along the Shangdan Suture that juxtaposes the Paleozoic Qinling and Mesozoic Hong'an–Dabie orogenic terrains. The region preserves a complex history that bridges the gap between adjacent orogenic terrains. Simultaneous in-situ trace element, U–Th–Pb and Lu–Hf‐isotope analysis of zircon grains from samples of the Xiongdian and Sujiahe eclogite identify a late Carboniferous to early Permian period of high pressure metamorphism, ca. 283 to 306 Ma. Zircon grains are observed to respond to metamorphic overprint via a two stage process: (1) An initial prograde stage of fluid catalyzed interface coupled dissolution–reprecipitation, involving exsolution of a non-ideal solid solution thorite (ThSiO₄) end member and loss of highly incompatible components (LREE and Pb), (2) A second stage of coupled zircon dissolution, coarsening, and new rim growth in equilibrium with garnet at high pressure conditions.We identify Proterozoic whole rock Sm–Nd and zircon grain Lu–Hf isotopic evidence which challenges the traditional interpretation that the Xiongdian and Sujiahe eclogite formed in response to early Paleozoic mantle melting and oceanic crust generation. We argue the Huwan Shear Zone contains no conclusive evidence of early/middle Paleozoic oceanic crust, but rather Proterozoic crustal components analogous to those found in the Northern Qinling Terrain and associated with formation of the Shangdan Suture. We present a simpler geodynamic model involving continuous convergence and accretion of terrains onto the southern margin of the North China Block during the Paleozoic Qinling and Mesozoic Dabie orogenies.     

A redox profile of the Slave mantle and oxygen fugacity control in the cratonic mantle

The authors report a redox profile based on Mössbauer data of spinel and garnet to a depth of 210 km from mantle xenoliths of the northern (N) and southeastern (SE) Slave craton (northern Canada). The profile transects three depth facies of peridotites that form segments of different bulk composition, represented by spinel peridotite, spinel–garnet peridotite, low-temperature garnet peridotite, high-temperature garnet peridotite, and pyroxenite. The shallow, more depleted N Slave spinel peridotite records lower oxygen fugacities compared to the deeper, less depleted N Slave spinel–garnet peridotite, consistent with their different spinel Fe³⁺ concentrations. Garnet peridotites show a general reduction in log fO₂ (FMQ)s with depth, where values for garnet peridotites are lower than those for spinel–garnet peridotites. There is a strong correlation between depletion and oxygen fugacity in the spinel peridotite facies, but little correlation in the garnet peridotite facies. The strong decrease in log fO₂ (FMQ) with depth that arises from the smaller partial molar volume of Fe³⁺ in garnet, and the observation of distinct slopes of log fO₂ (FMQ) with depth for spinel peridotite compared to spinel–garnet peridotite strongly suggest that oxygen fugacity in the cratonic peridotitic mantle is intrinsically controlled by iron equilibria involving garnet and spinel.

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The multiresolution character of collocation

 An interesting theoretical connection between the statistical (non-stochastic) collocation principle and the multiresolution/wavelet framework of signal approximation is presented. The rapid developments in multiresolution analysis theory over the past few years have provided very useful (theoretical and practical) tools for approximation and spectral studies of irregularly varying signals, thus opening new possibilities for `non-stationary' gravity field modeling. It is demonstrated that the classic multiresolution formalism according to Mallat's pioneering work lies at the very core of some of the general approximation principles traditionally used in physical geodesy problems. In particular, it is shown that the use of a spatio-statistical (non-probabilistic) minimum mean-square-error criterion for optimal linear estimation of deterministic signals, in conjunction with regularly gridded data, always gives rise to a generalized multiresolution analysis in the Hilbert space L <sup>2</sup>(R), under some mild constraints on the spatial covariance function and the power spectrum of the unknown field under consideration. Using the theory and the actual approximation algorithms associated with statistical collocation, a new constructive framework for building generalized multiresolution analyses in L <sup>2</sup>(R) is presented, without the need for the usual dyadic restriction that exists in classic wavelet theory. The multiresolution and `non-stationary' aspects of the statistical collocation approximation procedure are also discussed, and finally some conclusions and recommendations for future work are given. Received: 26 January 1999 / Accepted: 16 August 1999     

Landsat mss data for land use and land cover inventory and mapping: A case study of Andhra Pradesh

This study deals with the technique of remote sensing and how far it helps in the rapid study of geographical phenomena especially land use within a very short time and accurate manner. It evaluates how well data from the Landsat - Multispectral Scanner (MSS) could be used to detect, identify and delineate land use features within the Andhra Pradesh State. The main objective was to prepare a small scale land use map from satellite imagery showing the broad distribution of land use patterns to serve as a base for monitoring land use change.     

Selenium content in soils from Murcia Region (SE,Spain)

The objective of this study was to determine the selenium content in soils from the Region of Murcia (SE, Spain) and to study the possible relationship between mineralogical composition, soil properties and selenium content. In addition, generic reference level (GRL) for selenium was determined according to Spanish legislation. For this study, 490 samples were selected in areas subjected to agricultural activity or abandoned agricultural soils with natural vegetation. Five different zones were established in order to study selenium variability. Four different mineralogical groups were established, based on significant relationship with the mineralogical composition, and each sample was included in one mineralogical group. The results showed that the concentration of selenium is correlated with the electrical conductivity, sulphate content and with the mineralogical composition, particularly positively with quartz and in a negative way with calcite percentage. In addition, selenium level was positively correlated with the phyllosilicate content. Established GRL for selenium varies with the mineralogical group, having a great transcendence from the legal and economic points of view.