Dual-satellite crossover latitude-lumped coefficients, their use in geodesy and oceanography

Latitude-lumped coefficients (LLC) are defined, representing geopotential-orbit variations for dual-satellite crossovers (DSC). Formulae are derived for their standard errors from the covariances of geopotential field models. Numerical examples are presented for pairs of the altimeter-bearing satellites TOPEX/Poseidon, ERS 1, and Geosat, using the error matrices of recent gravity models. The DSC, connecting separate missions, will play an increasingly important role in oceanography spanning decades only when its nonoceanographic signals are thoroughly understood. In general, the content of even the long-term averaged DSC is more complex then their single satellite crossover (SSC) counterpart. The LLC, as the spatial spectra for the geopotential-caused crossover effects, discriminate these source-differences sharply. Thus, the zero-order LLC in DSC data contains zonal gravity information not present in SSC data. In addition, zero- and first-order LLC of DSC data can reveal a geocenter discrepancy between the orbit tracking of the separate satellite missions. For example, DSC analysis from orbits computed with JGM 2 show that the y-axis of the geocenter for Geosat in 1986–1988 is shifted with respect to T/P by 6–9 cm towards the eastern Pacific. Also, where the time-gap is necessarily large (as between, say, Geosat and T/P missions) oceanographic (sea-level) differences in DSC may corrupt the geopotential interpretation of the data. Most importantly, as we illustrate, media delays for the altimeter (from the ionosphere, wet troposphere and sea-state bias) are more likely sources of contamination across two missions than in SSC analyses. Again, the LLC of zero order best shows this contrast. Using the higher-order LLC of DSC for both Geosat-T/P and ERS 1-T/P as likely representation of geopotential-only error, we show by comparison with the predicted standard errors of JGM 2 that the latter's previously calibrated covariance matrix is generally valid. Received: 14 February 1996 / Accepted: 27 March 1997     

A thin film approach for producing mineral diffusion couples

Few diffusion coefficient values have been measured for silicate minerals at pertinent geologic conditions because of experimental restrictions. Until recently, analysis of diffusion couples was conducted principally with electron microprobes which have rather poor spatial resolution (micrometer scale). Ion microprobe analyses, however, eliminate many of the previous experimental restrictions; in depth profile mode they have excellent spatial resolution (tens of angstroms) and diffusion couples can be analyzed normal to the interface. Diffusion couples analyzed by ion microprobe must be well-defined and uniform; previous methods using solution precipitates to form the diffusion couples were heterogeneous and had limited success. A new approach, the thermal evaporation of²⁵MgO under high vacuum onto a crystalline substrate (oxide, silicate), produces a 1000 Å thick²⁵MgO _x (x<1) thin film. This method yields an excellent diffusion couple for low-temperature diffusion experiments. Diffusion anneal experiments using this approach for garnet provide a Mg self-diffusion coefficient ofD=0.60±0.09×10^–21 m²/s at 1000°C (logFO₂=–11.3,P=1 atm,X _Almandine=0.24).     

地形图高程精度的估计方法

本文针对缺少野外检测资料情况提出了两图对照检测法;探讨了高程误差分布规律;并在此基础上,提出不等权逐步回归法答解科佩系数。理论研究和实例均证明了这种方法的可取性。     

安徽省山丘区匹配开发综合评价

安徽省山地丘陵区区域开发中存在区域开发方式与区域特征，人口数量、质量与土地承载力，经济发展与环境保护不匹配的问题。在制定区域匹配开发评价指标的基础上，通过环境指标、经济指标、社会指标的定量分析，获得不同类型区的匹配系数（Ｃ＿ｃ），根据匹配系数所揭示的问题，提出区域开发措施。     

Quantum yields for the photodissociation of acetone in air and an estimate for the life time of acetone in the lower troposphere

The room-temperature photodecomposition of acetone diluted with synthetic air was studied at nine wavelengths in the spectral region 250–330 nm. The quantum yields for the products CO₂ and CO indicated that it was not possible to suppress secondary reactions sufficiently, even with acetone/air mixing ratios as low as 150 ppmv, to derive from these data primary acetone photodissociation quantum yields. The behavior of CO₂ and CO formation nevertheless provides some insight into the mechanism of acetone photodecomposition. When small amounts of NO₂ are added to acetone/air mixtures, peroxyacetyl nitrate (PAN) is formed. Quantum yields for PAN are reported. They are better suited to represent primary quantum yields for acetone photodissociation, because PAN is a direct indicator for the formation of acetyl radicals. The data were combined with absorption cross-sections for acetone measured at wavelengths up to 360 nm to calculate photodissociation coefficients applicable to the ground-level atmosphere at 40° northern latitude. Comparison with the rates for the reaction of acetone with OH radicals shows that both processes contribute almost equally to the total acetone losses in the lower atmosphere. The resulting atmospheric life time at 40° northern latitude is 32 days, on average. This value must be considered an upper limit, since it does not take into account acetone losses due to the reaction of excited triplet acetone with oxygen.     

Ultraviolet absorption spectrum of trifluoro-bromo-methane,difluoro-dibromo-methane and difluoro-bromo-chloro-methane in the vapor phase

Ultraviolet absorption cross-sections of trifluoro-bromo-methane (CF₃Br-Halon 1301), difluoro-dibromo-methane (CF₂Br₂-Halon 1202) and of difluoro-bromo-chloro-methane (CF₂BrCl-Halon 1211) are measured in the wavelength interval 172–304 nm for temperatures ranging from 210 to 295 K with uncertainties of between 2 and 4%. They are compared with previous measurements available at room temperature. Temperature effects are discussed and parametrical formulae are proposed to compute the absorption cross-sections for wavelengths and temperatures useful in atmospheric modelling calculations. Photodissociation coefficients are presented and their temperature dependence is discussed.     

Characterization and Quantification of Uncertainty in?Coregionalization Analysis

Coregionalization analysis has been presented as a method of multi-scale analysis for multivariate spatial data. Despite an increasing use of this method in environmental and earth sciences, the uncertainty associated with the estimation of parameters in coregionalization analysis (e.g., sills and functions of sills) is potentially high and has not yet been characterized. This article aims to discuss the theory underlying coregionalization analysis and assess the robustness and limits of the method. A theoretical framework is developed to calculate the ergodic and fluctuation variance-covariance matrices of least-squares estimators of sills in the linear model of coregionalization. To adjust for the positive semidefiniteness constraint on estimated coregionalization matrices, a confidence interval estimation procedure for sills and functions of sills is presented. Thereafter, the relative importance of uncertainty measures (bias and variance) for sills and structural coefficients of correlation and determination is assessed under different scenarios to identify factors controlling their uncertainty. Our results show that the sampling grid density, the choice of the least-squares estimator of sills, the positive semidefiniteness constraint, the presence of scale dependence in the correlations, and the number and range of variogram models, all affect the level of uncertainty, sometimes through multiple interactions. The asymptotic properties of variogram model parameter estimators in a bounded sampling domain impose a theoretical limit to their accuracy and precision. Because of this limit, the uncertainty was found to be high for several scenarios, especially with three variogram models, and was often more dependent on the ratio of variogram range to domain extent than on the sampling grid density. In practice, in the coregionalization analysis of a real dataset, the circular requirement for sill estimates in the calculation of uncertainty measures makes the quantification of uncertainty very problematic, if not impossible. The use of coregionalization analysis must be made with due knowledge of the uncertainty levels and limits of the method.     

Water partitioning between mantle minerals from peridotite xenoliths

The speciation and amount of water dissolved in nominally anhydrous silicates comprising eight different mantle xenoliths has been quantified using synchrotron micro-FTIR spectroscopy. Samples studied are from six geographic localities and represent a cross-section of the major upper mantle lithologies from a variety of tectonic settings. Clinopyroxene contains between 342 and 413 ppm H₂O. Orthopyroxene, olivine and garnet contain 169–201, 3–54 and 0 to <3 ppm H₂O, respectively. Pyroxenes water contents and the distribution of water between ortho- and clinopyroxene is identical regardless of sample mineralogy (D _water^cpx/opx = 2.1 ± 0.1). The total water contents of each xenolith are remarkably similar (113 ± 14 ppm H₂O). High-resolution spectroscopic traverses show that the concentration and speciation of hydrous defects dissolved in each phase are spatially homogeneous within individual crystals and identical in different crystals interspersed throughout the xenolith. These results suggest that the amount of water dissolved in the silicate phases is in partial equilibrium with the transporting melt. Other features indicate that xenoliths have also preserved OH signatures of equilibrium with the mantle source region: Hydroxyl stretching modes in clinopyroxene show that garnet lherzolites re-equilibrated under more reducing conditions than spinel lherzolites. The distribution of water between pyroxenes and olivine differs according to xenolith mineralogy. The distribution of water between clinopyroxene and olivine from garnet peridotites (D _water^cpx/oliv(gnt) = 22.2 ± 24.1) is a factor of four greater than mineral pairs from spinel-bearing xenoliths (D _water^cpx/oliv(sp) = 88.1 ± 47.8). Such an increase in olivine water contents at the spinel to garnet transition is likely a global phenomenon and this discontinuity could lead to a reduction of the upper mantle viscosity by 0.2–0.7 log units and a reduction of its electrical resistivity by a factor of 0.5–0.8 log units.