GPS signal diffraction modelling: the stochastic SIGMA-δ model

The SIGMA-Δ model has been developed for stochastic modelling of global positioning system (GPS) signal diffraction errors in high precision GPS surveys. The basic information used in the SIGMA-Δ model is the measured carrier-to-noise power-density ratio (C/N0). Using the C/N0 data and a template technique, the proper variances are derived for all phase observations. Thus the quality of the measured phase is automatically assessed and if phase observations are suspected to be contaminated by diffraction effects they are weighted down in the least-squares adjustment. The ability of the SIGMA-Δ model to reduce signal diffraction effects is demonstrated on two static GPS surveys as well as on a kinematic high-precision GPS railway survey. In cases of severe signal diffraction the accuracy of the GPS positions is improved by more than 50% compared to standard GPS processing techniques. Received: 27 July 1998 / Accepted: 1 March 1999     

广东省邮电通信业发展空间差异变动

利用基尼系数,分析广东省邮电通信业务量1980～2006年的变化趋势,在此基础上,选取1985年、1995年和2005年3个时间断面,利用因子分析剖析邮电业务水平的空间分布格局,并在GIS软件中表达出来,进而构建邮电通信发展指数P,反映各市的邮电通信发展速度.研究表明:广东省邮电通信业务量的分布经历了20世纪80年代的广州单中心,90年代初的广州、深圳双中心,90年代中以来的广州、深圳、佛山、东莞两主两副四中心,朝着多极化方向发展.邮电通信水平的空间格局则经历了"均衡-不均衡-均衡"的发展过程,变异系数从1985年的1.574到1995年的1.870,2005年变为1.115.邮电通信发展速度1985年开始呈现出珠三角城市明显高于外围城市的格局,且高于平均水平的城市数量不断增加,范围不断扩大.通过多元回归分析得出,除政策因素以外,外商投资作用和第三产业、城市化发展水平是1980年以来影响广东省邮电通信业发展最主要的3个因素,而人口密度、交通发展水平、固定资产投资水平等对邮电通信发展的影响不显著.     

台湾-阿尔泰地学断面阿尔金-龙门山剖面的地壳纵波速度结构

通过分析阿尔金—龙门山地学断面的地震资料,建立了该剖面的地壳纵波速度结构。研究结果表明,阿尔金北侧的塔里木盆地地区莫霍面为50km,而在其南侧的祁连地块莫霍面突然加深至73km,在柴达木盆地莫霍面又抬升至58km左右,然后,在松潘甘孜地块莫霍面降至70km,并呈现为台阶状向龙门山方向抬升到60km左右,最低速层,而在其南部地区则没有低速层出现,推测低速层为地壳中部的局部熔融物质,阿尔金—龙门山剖面上的两个莫霍面坳陷区分别与祁连地块和松潘—甘孜地块上的两个莫霍面坳陷区相对应,指示出这个两个地块具有较深的山根,青藏高原北部的巨厚地壳很可能是由于中生代以来发生的印度板块与亚洲板块碰撞时受到来自东西及南北方向的挤压,使地壳缩短所致。     

Reassessing the invasion of South African waters by the European shore-crab Carcinus maenas

The European shore-crab Carcinus maenas has been present in South Africa since 1983. Despite this species’ international reputation as a biological invader, its distribution in this region has only been considered by three outdated ‘snapshot surveys.’ The present study is the most comprehensive to date, providing an update on the species’ range and the first temporal assessment of its abundance and demographics. Along South Africa's Cape Peninsula and surrounding areas, C. maenas was absent from 12 intertidal sites surveyed, except for Sea Point, and no crabs were found during subtidal surveys along the open coastline. Subtidal harbour populations were recorded in the Cape Town harbours of Table Bay and Hout Bay (previously estimated as comprising approximately 164 200 and 6 500 individuals, respectively). Table Bay was surveyed monthly for one year, using baited traps, crab condos and postlarvae settlement collectors, to assess size distributions and reproductive seasonality of the crab. Reproductive females were recorded throughout most of the year. These results suggest that the harbour populations could be targeted by control programmes, but provide no strong evidence to support the initiation of management action during a particular season. The lack of detection of postlarval settlement, even among well-established populations, suggests this will not be a useful monitoring tool for detecting incursions.     

ASTER遥感影像数据在土壤盐渍化评价中的应用

本文通过运用ASTER遥感影像数据，对不同地物进行光谱分析，根据不同地物在不同波段的光谱特征曲线，分别提取植被和水体信息，然后进行非监督分类。并结合物探试验和土样分析结果，进行聚类分析，定性和定量的评价了焉耆盆地内土壤盐渍化程度分布状况。评价结果为：在焉耆盆地的平原区内，非盐渍化土壤，457．65km^2；轻度盐渍化土壤，335．61km^2；中度-重度盐渍化土壤，580．93km^2；盐土，41．11km^2。根据野外实际调查，评价结果的精度达到了85％以上。     

Using on‐nadir spectral reflectance to detect soil surface changes induced by simulated rainfall and wind tunnel abrasion

The surface susceptibility to erosion (erodibility) is an important component of soil erosion models. Many studies of wind erosion have shown that even relatively small changes in surface conditions can have a considerable effect on the temporal and spatial variability of dust emissions. One of the main difficulties in measuring erodibility is that it is controlled by a number of highly variable soil factors. Collection of these data is often limited in scale because in situ measurements are labour‐intensive and very time‐consuming. To improve wind erosion model predictions over several spatial and temporal scales simultaneously, there is a requirement for a non‐invasive approach that can be used to rapidly assess changes in the compositional and structural nature of a soil surface in time and space. Spectral reflectance of the soil surface appears to meet these desirable requirements and it is controlled by properties that affect the soil erodibility. Three soil surfaces were modified using rainfall simulation and wind tunnel abrasion experiments. Observations of those changes were made and recorded using digital images and on‐nadir spectral reflectance. The results showed clear evidence of the information content in the spectral domain that was otherwise difficult to interpret given the complicated interrelationships between soil composition and structure. Changes detected at the soil surface included the presence of a crust produced by rainsplash, the production of loose erodible material covering a rain crust and the selective erosion of the soil surface. The effect of rainsplash and aeolian abrasion was different for each soil tested and crust abrasion was shown to decrease as rainfall intensity increased. The relative contributions of the eroded material from each soil surface to trapped mixtures of material assisted the erodibility assessment. Ordination analyses within each of two important soil types explained significant amounts of the variation in the reflectance of all wavebands by treatments of the soil and hence changes in the soil surface. The results show that soil surface conditions within a soil type are an underestimated source of variation in the characterization of soil surface erodibility and in the remote sensing of soil. Copyright © 2005 John Wiley & Sons, Ltd.     

A revised isotope fractionation model for dissimilatory sulfate reduction in sulfate reducing bacteria

Sulfur isotope fractionation during dissimilatory sulfate reduction has been conceptually described by the widely accepted Rees model as related to the stepwise reduction of sulfate to sulfide within the cells of bacteria. The magnitude of isotope fractionation is determined by the interplay between different reduction steps in a chain of reactions. Here we present a revision of Rees’ model for bacterial sulfate reduction that includes revised fractionation factors for the sulfite-sulfide step and incorporates new forward and reverse steps in the reduction of sulfite to sulfide, as well as exchange of sulfide between the cell and ambient water. With this model we show that in contrast to the Rees model, isotope fractionations well in excess of −46‰ are possible. Therefore, some of the large sulfur isotope fractionations observed in nature can be explained without the need of alternate pathways involving the oxidative sulfur cycle. We use this model to predict that large fractionations should occur under hypersulfidic conditions and where electron acceptor concentrations are limiting.