Finite-difference simulation of P–SV-wave propagation: a displacement-potential approach     

Shunhua Cao  Stewart Greenhalgh 《Geophysical Journal International》1992,109(3):525-535

  相似文献   

Northern Chile earthquake of 1980 May 26: evidence of unilateral fracture     

A. Douglas  A. F. Sheehan  R. C. Stewart 《Geophysical Journal International》1992,110(1):201-210

  相似文献   

Application of remote sensing to forest hydrology     

J. B. Stewart  J. W. Finch 《Journal of Hydrology》1993,150(2-4):701-716

The paper reviews the application of remote sensing to forest hydrology. After discussing the general advantages and disadvantages of satellite remote sensing, the estimation of precipitation, changes in soil moisture, runoff, radiation components, sensible heat flux, latent heat flux, soil heat flux, changes in energy storage in biomass, primary production and monitoring the extent, type and density of forests are reviewed. Finally, the paper looks forward to future developments and concludes that these are likely to come from the use of multitemporal data, combined analysis of different types of remotely sensed data and of remotely sensed and ground data, improved image analysis techniques and combining satellite data with models.  相似文献   

Environmental information for total catchment management: incorporating local knowledge     

Peter Martin  Stewart Lockie 《The Australian geographer》1993,24(1):75-85

Total Catchment Management (TCM) has been implemented in New South Wales to provide a more integrated, participatory' approach to natural resource management. This change in direction poses significant challenges for obtaining and integrating environmental information. This paper examines the adequacy of environmental information in terms of both the participatory turn in government policy and the management imperatives of the integrated, catchment‐wide approach of TCM. Drawing on empirical studies in the Hunter Valley, it is suggested that current information available for TCM is inadequate and reflects a fragmented approach that is primarily concerned with biophysical phenomena and is generated at inappropriate scales. Furthermore, most information is generated by government agencies, ignoring the substantial contribution that catchment occupiers could make. It is argued that the utilisation of the knowledge and experience of occupiers could provide more integrated catchment perspectives while meeting the participatory goals espoused in TCM.  相似文献   

Factors predisposing rata-kamahi(Metrosideros umbellata-Weinmannia racemosa) forests to canopy dieback,Westland, New Zealand     

G. H. Stewart Dr.  A. B. Rose 《GeoJournal》1988,17(2):217-223

In many areas of WestlandMetrosideros umbellata (southern rata) andWeinmannia racemosa (kamahi) have undergone apparently excessive canopy dieback over the las 30–40 years. Browsing by the introduced brushtail possum is the predominant trigger involved. However, the roles of predisposing factors have received little attention. Dieback patterns indicate that the susceptibility of Westland rata-kamahi forest depends on their composition and structure. Stands containing abundant seral shrub hardwoods and a high proportion of old canopy trees are highly predisposed to dieback. Less dieback occurs in mature stands lacking seral species or in young apparently vigorous stands. Forest composition and structure are largely determined by site stability, i.e., the frequency and magnitude of physical disturbances such as mass movements. The underlying stability of different parent materials and landforms therefore largely determines rata-kamahi dieback patterns.  相似文献   

Sedimentary macrofossil records reveal ecological change in English lakes: implications for conservation     

Helen Bennion  Carl D. Sayer  Stewart J. Clarke  Thomas A. Davidson  Neil L. Rose  Ben Goldsmith  Ruth Rawcliffe  Amy Burgess  Gina Clarke  Simon Turner  Emma Wiik 《Journal of Paleolimnology》2018,60(2):329-348

Aquatic macrophytes play a key role in providing habitat, refuge and food for a range of biota in shallow lakes. However, many shallow lakes have experienced declines in macrophyte vegetation in recent decades, principally due to eutrophication. As changes in macrophyte composition and abundance can affect overall ecological structure and function of a lake, an assessment of the timing and nature of such changes is crucial to our understanding of the wider lake ecosystem. In the typical absence of historical plant records, the macro-remains of macrophytes preserved in lake sediments can be used to assess long-term changes in aquatic vegetation. We generated recent (150–200 years) plant macrofossil records for six English lakes subject to conservation protection to define past macrophyte communities, assess trajectories of ecological change and consider the implications of our findings for conservation targets and strategies. The data for all six lakes reveal a diverse submerged macrophyte community, with charophytes as a key component, in the early part of the sedimentary records. The stratigraphies indicate considerable change to the aquatic vegetation over the last two centuries with a general shift towards species more typically associated with eutrophic conditions. A common feature is the decline in abundance of low-growing charophytes and an increase in tall canopy-forming angiosperms such as fine-leaved Potamogeton species, Zannichellia palustris and Callitriche species. We hypothesise, based on findings from long-term datasets and palaeoecological records from enriched shallow lakes where plants are now absent, that the observed shifts provide a warning to managers that the lakes are on a pathway to complete macrophyte loss such that nutrient load reduction is urgently needed. It is the sound understanding of present-day plant ecology that affords such reliable interpretation of the fossil data which, in turn, provide valuable context for current conservation decisions.  相似文献   

Using geolifespans to model dynamic geographic domains     

V. Nixon  K. Stewart Hornsby 《International journal of geographical information science》2013,27(9):1289-1308

Geographic objects are characterized by having different durations of existence, or geolifespans. A typology based on the concept of a geolifespan is developed to model variations in the longevity of entities that are stored in geographic information systems. The typology consists of two upper-level classes: Persistent and Ephemeral. The Ephemeral class is composed of three subclasses: Temporary, Transient and Brief. The set of possible transitions between classes in the typology is described, capturing how objects can change from one class to another, e.g., from Temporary to Brief or from Transient to Persistent. A transition sequence models the geolifespan class(es) to which an object belongs over a period of time and captures the evolution of dynamic geographic objects with respect to their longevity. Geolifespan classes are applied to scenarios of spatial change as well as a geosensor network to illustrate their role in modelling geographic dynamics.  相似文献   

Proceedings of the Workshop on the Role of Volatiles and Atmospheres on Martian Impact Craters     

Nadine G. Barlow  Sarah T. Stewart  Olivier S. Barnouin‐Jha 《Meteoritics & planetary science》2006,41(10):1423-1424

  相似文献   

Using geochemistry as a tool for correlating proximal andesitic tephra: case studies from Mt Rainier (USA) and Mt Ruapehu (New Zealand)     

Susan L. Donoghue  James Vallance  Ian E. M. Smith  Robert B. Stewart 《第四纪科学杂志》2007,22(4):395-410

Volcanic hazards assessments at andesite stratovolcanoes rely on the assessment of frequency and magnitude of past events. The identification and correlation of proximal and distal andesitic tephra, which record the explosive eruptive history, are integral to such assessments. These tephra are potentially valuable stratigraphic marker beds useful to the temporal correlation and age dating of Quaternary volcanic, volcaniclastic and epiclastic sedimentary deposits with which they are interbedded. At Mt Ruapehu (New Zealand) and Mt Rainier (USA), much of the detail of the recent volcanic record remains unresolved because of the difficulty in identifying proximal tephra. This study investigates the value of geochemical methods in discriminating andesitic tephra. Our dataset comprises petrological and geochemical analyses of tephra that span the late Quaternary eruptive record of each volcano. Our data illustrate that andesitic tephra are remarkably heterogeneous in composition. Tephra compositions fluctuate widely over short time intervals, and there are no simple or systematic temporal trends in geochemistry within either eruptive record. This complexity in tephra geochemistry limits the application of geochemical approaches to tephrostratigraphic studies, beyond a general characterisation useful to provenance assignation. Petrological and geochemical data suggest that the products of andesite systems are inherently variable and therefore intractable to discrimination by simple geochemical methods alone. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Extent of the last ice sheet in northern Scotland tested with cosmogenic 10Be exposure ages     

William M. Phillips  Adrian M. Hall  Colin K. Ballantyne  Steven Binnie  Peter W. Kubik  Stewart Freeman 《第四纪科学杂志》2008,23(2):101-107

The extent of the last British–Irish Ice Sheet (BIIS) in northern Scotland is disputed. A restricted ice sheet model holds that at the global Last Glacial Maximum (LGM; ca. 23–19 ka) the BIIS terminated on land in northern Scotland, leaving Buchan, Caithness and the Orkney Islands ice‐free. An alternative model implies that these three areas were ice‐covered at the LGM, with the BIIS extending offshore onto the adjacent shelves. We test the two models using cosmogenic ¹⁰Be surface exposure dating of erratic boulders and glacially eroded bedrock from the three areas. Our results indicate that the last BIIS covered all of northern Scotland during the LGM, but that widespread deglaciation of Caithness and Orkney occurred prior to rapid warming at ca. 14.5 ka. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献