A NEW PARAMETER FOR AEROMAGNETIC SURVEYING*     

STEPHEN THYSSEN-BORNEMISZA 《Geophysical Prospecting》1967,15(2):204-207

The author proposes the parameter Δ²/ΔT¹ for possible application in aeromagnetic surveying making use of already available gradiometer systems equipped with sensors separated vertically.  相似文献   

Three modelling approaches for seasonal streamflow droughts in southern Africa: the use of censored data     

EMMA L. TATE  STEPHEN N. FREEMAN 《水文科学杂志》2013,58(1):27-42

Abstract

Three approaches to modelling the duration of streamflow droughts at eight southern African sites are considered; a non-parametric method (that of Kaplan-Meier) is compared with the fitting of two simple parametric models: the exponential and Weibull. All techniques allow the instantaneous probability of a drought coming to an end to differ between wet and dry seasons, using the concept of censored data. Model-fitting is discussed, and the Kaplan-Meier estimates permit an assessment of the fit of the parametric models, with the aim of finding a parsimonious model for the data, which can be used for predictive purposes. In most cases considered herein, either the exponential or Weibull approach is found to be adequate.  相似文献   

Using Contents Addressable Filestore for rapid access to a large cartographic data set†     

STEPHEN WISE 《International journal of geographical information science》2013,27(2):111-120

Abstract

The need for rapid access to large amounts of data is one of the central problems in the field of geographical information systems. This paper describes the use of a hardware solution to this problem, in the particular case of selecting digitized boundary data from a very large file. The hardware is International Computers'(ICL's) award winning Contents Addressable Filestore (CAFS) which is a special unit fitted to ICL disc drives allowing the fast selection of records from large files. By reformatting the boundary data, it was possible to perform searches using CAFS. A command-driven package was written to allow users to select the boundaries for any named zone or zones, display them on a graphics terminal and write them out in a format suitable for input to the GIMMS package. This package was tested on a file containing the boundaries of all the wards of Great Britain. After reformatting, this file was 6 Mbytes in size, but by means of CAFS could be searched interactively with response times of the order of 5-10 seconds.  相似文献   

Modelling the temporal element in land information systems     

STEPHEN PRICE 《International journal of geographical information science》2013,27(3):233-243

Abstract

This paper considers the use of a modern programming language (Modula-2) to develop a data model for a lot-based land information system. The emphasis is on the importance of maintaining the history of the lots, and a data model is developed which incorporates the history of each lot.  相似文献   

The role of landscape setting in minimizing hydrogeomorphic impacts of flow regulation     

H.E.REID  G.J.BRIERLEY  K.MCFARLANE  S.E.COLEMAN  S.TROWSDALE 《国际泥沙研究》2013,28(2):149-161

The Tongariro Power Development Scheme (TPDS) is used to regulate flow in the headwaters of the largest catchment on the North Island of New Zealand (the Waikato). Two small dams, the Rangipo Dam and the Poutu Intake Dam, were constructed in 1973 and 1983. The flow regime of the river is managed to divert freshes into the power scheme, but allows flows larger than 100 m³ s^?1 to be released, to rework and transport sediment through the catchment. Analysis of aerial photos and maps spanning 1928 to 2007, alongside field measurements, show that there have been few hydrogeomorphic adjustments since dam construction. This includes limited changes to channel geometry, channel planform and bed material organization immediately downstream of the dams. In addition, offsite effects are minimal, both 500 m downstream of each dam, and in the more sensitive, less confined reaches in the lower catchment (11 km downstream of the Poutu Intake dam). The limited changes can be attributed to the locations of the dams within reaches characterised by bedrock gorges and confined within terraces. These locations act to flush sediments and impose margins that allow minimal adjustment of the channel. Bed material within this reach is characterised by the presence of a boulder lag. This is sourced from long-term incision into lahar deposits, and acts to limit the rate of incision, creating a steep and stable base upon which active fractions are transported. Just as importantly, significant storage in the low-relief volcanic plateau located in the upper catchment acts to disconnect and store the high sediment yields generated by active volcanic cones in the western sub-catchment upstream of the dams. This limits the rate of sediment supply to regulated reaches. Findings from this study show that analysis of reach-scale controls is essential in framing dam site locations in relation to the distribution of reaches and landscape units across the catchment. In this instance, tributary inputs downstream of the dams do not replenish the sediment and flow removed at the dam locations, as has been observed in other regulated systems. Rather, the river itself is resilient to change and flow variability is well managed allowing geomorphically effective floods to occur. Landscape setting is a key consideration in determining the hydrogeomorphic impact of flow regulation.  相似文献   

CONSTRUCTING,VISUALIZING, AND ANALYZING A DIGITAL FOOTPRINT*   总被引：1，自引：0，他引：1  

STEPHEN D. WEAVER  MARK GAHEGAN 《Geographical review》2007,97(3):324-350

ABSTRACT. Herein, we discuss the desire for new technology, the need for security, and the right to privacy; in doing so, we argue that each of these concerns comprises an important, tripartite debate. To highlight the complexities in this problem, we define our notion of a “digital footprint” and introduce Big Foot—specialized software created for the research described here to facilitate visualization and exploration of the data that comprise Stephen Weaver's personal digital footprint. Using Big Foot we demonstrate how multiple digital personae can be created from the data that constitute one unique digital footprint and provide a methodology for understanding the good and bad impacts that new technologies may have on future societies. One of the primary arguments of this work is that the debate—though not formally recognized—is currently before contemporary society and must receive sufficient attention.  相似文献   

The Range of Spinel Compositions in Terrestrial Mafic and Ultramafic Rocks   总被引：33，自引：10，他引：33  

BARNES  STEPHEN J.; ROEDER  PETER L. 《Journal of Petrology》2001,42(12):2279-2302

Compositional fields for spinels from a wide variety of mafic–ultramaficigneous rock types and tectonic environments have been determinedfrom a global database of over 26 000 analyses. These fieldsare defined using contoured data density plots based on thespinel prism, and plots of T iO₂ vs ferric iron, for mantlexenoliths, ophiolitic rocks, continental layered intrusions,alkalic and lamprophyric rocks, tholeiitic basalts, Alaskanultramafic complexes and komatiites. Several trends appear regularlyin the various environments: a trend of widely variable Cr/(Cr+ Al) at low Fe²⁺/(Mg + Fe²⁺) (the Cr–Al trend); increasingFe³⁺, Fe²⁺/(Mg + Fe²⁺) and T iO₂ at constant Cr/(Cr + Al) (Fe–Ti trend); a trend found primarily in kimberlites, similar toFe–T i but at constant Fe²⁺/(Mg + Fe²⁺); and an unusualtrend of increasing Al found only in layered intrusions. TheCr–Al and Fe–T i trends are both found to varyingdegrees in tholeiitic basalts. The Cr–Al trend is prevalentin rocks that have equilibrated over a range of pressures, whereasthe Fe–T i trend is dominantly due to low-pressure fractionation.The most Cr-rich chromites found in nature occur in boninites,diamond-bearing kimberlites, some komatiites and ophioliticchromitites. Exceptionally reduced chromites are found in somekomatiites and in ophiolitic chromitites. Detrital chromitesfrom the Witwatersrand conglomerates are of komatiitic provenance. KEY WORDS: basalt; chromite; kimberlite; ophiolite; spinel  相似文献   

Flood Risk Management for Caravan Parks in New South Wales     

STEPHEN YEO 《The Australian geographer》2003,34(2):195-209

A survey of 71 caravan parks in coastal NSW indicates a high exposure to flooding. Most parks in NSW are flood-prone. A growing number of long-term residents in the 1980s, and essentially immovable manufactured homes in the 1990s, significantly increased flood risk. However, many parks are ill-equipped to deal with flooding: a high turnover of park managers means that most have no direct experience of floods; attitudes of denial prevail; most parks have no means of raising community flood awareness; and the process of flood response planning is patchy and of poor quality. Key strategies for the reduction of flood risk are suggested, including a more rigorous implementation of tighter regulations that better guard the health and safety of park residents, and the equipping of park managers to self-manage risk.  相似文献   

Metamorphic evolution of diamond-bearing and associated rocks from the Kokchetav Massif, northern Kazakhstan   总被引：10，自引：2，他引：10  

R. Y. ZHANG  J. G. LIOU  W. G. ERNST  R. G. COLEMAN  N. V. SOBOLEV  & V. S. SHATSKY 《Journal of Metamorphic Geology》1997,15(4):479-496

Representative diamond-bearing gneisses and dolomitic marble, eclogite and Ti-clinohumite-bearing garnet peridotite from Unit I at Kumdy Kol and whiteschist from Unit II at Kulet, eastern Kokchetav Massif, northern Kazakhstan, were studied. Diamond-bearing gneisses contain variable assemblages, including Grt+Bt+Qtz±Pl±Kfs±Zo±Chl±Tur±Cal and minor Ap, Rt and Zrn; abundant inclusions of diamond, graphite+chlorite (or calcite), phengite, clinopyroxene, K-feldspar, biotite, rutile, titanite, calcite and zircon occur in garnet. Diamond-bearing dolomitic marbles consist of Dol+Di±Grt+Phl; inclusions of diamond, dolomite±graphite, biotite, and clinopyroxene were identified in garnet. Whiteschists carry the assemblage Ky+Tlc+Grt+Rt; garnet shows compositional zoning, and contains abundant inclusions of talc, kyanite and rutile with minor phlogopite, chlorite, margarite and zoisite. Inclusions and zoning patterns of garnet delineate the prograde P–T path. Inclusions of quartz pseudomorphs after coesite were identified in garnet from both eclogite and gneiss. Other ultrahigh-pressure (UHP) indicators include Na-bearing garnet (up to 0.14 wt% Na₂O) with omphacitic Cpx in eclogite, occurrence of high-K diopside (up to 1.56 wt% K₂O) and phlogopite in diamond-bearing dolomitic marble, and Cr-bearing kyanite in whiteschist. These UHP rocks exhibit at least three stages of metamorphic recrystallization. The Fe-Mg partitioning between clinopyroxene and garnet yields a peak temperature of 800–1000 °C at P >40 kbar for diamond-bearing rocks, and about 740–780 °C at >28–35 kbar for eclogite, whiteschist and Ti-bearing garnet peridotite. The formation of symplectitic plagioclase+amphibole after clinopyroxene, and replacement of garnet by biotite, amphibole, or plagioclase mark retrograde amphibolite facies recrystallization at 650–680 °C and pressure less than about 10 kbar. The exsolution of calcite from dolomite, and development of matrix chlorite and actinolite imply an even lower grade greenschist facies overprint at c. 420 °C and 2–3 kbar. A clockwise P–T path suggests that supracrustal sediments together with basaltic and ultramafic lenses apparently were subjected to UHP subduction-zone metamorphism within the diamond stability field. Tectonic mixing may have occurred prior to UHP metamorphism at mantle depths. During subsequent exhumation and juxtaposition of many other tectonic units, intense deformation chaotically mixed and mylonitized these lithotectonic assemblages.  相似文献   

The Late Devensian Lateglacial palaeoenvironmental record from Whitrig Bog, SE Scotland. 2. Chironomidae (Insecta: Diptera)   总被引：1，自引：0，他引：1  

STEPHEN J. BROOKS  J. JOHN LOWE  FRANCIS E. MAYLE 《Boreas: An International Journal of Quaternary Research》1997,26(4):297-308

Changes in chironomid midge larval assemblages in Lateglacial (c. 13.5–10 ka yr BP) lake sediments from Whitrig Bog are used to infer climatic (temperature) change. The earliest sediments contain few, predominantly cold stenothermic taxa. This fauna is replaced by an assemblage dominated by thermophilic taxa, indicating rising temperatures. The relatively warm Interstadial is punctuated by at least two brief cold oscillations which are characterized by the return of certain cold-water taxa and the demise of some elements of the thermophilic fauna. The earlier of the two oscillations was apparently shorter and colder than the second. The highest Lateglacial Interstadial temperatures were attained either shortly before or after the first cold oscillation. This timing of the Lateglacial thermal maximum is apparently later than has been previously inferred from fossil beetle data. The Lateglacial Interstadial is terminated by the Loch Lomond (Young Dryas) Stadial, which is indicated in this monolith by an abrupt return of cold stenothermic Chironomidae and the virtual elimination of thermophilic taxa. Temperatures during the Younger Dryas appear to have been colder than during either of the previous minor cold oscillations. Climatic inferences from chironomid analysis broadly support and augment conclusions drawn from sediment chemistry and palynological evidence derived from the same monolith, although there is evidence that the vegetation and chironomid responses to early postglacial warming were out of phase.  相似文献