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Spatial Coverage (spatial + coverage)
Selected AbstractsFading of the last giants: an assessment of habitat availability of the Sunda gharial Tomistoma schlegelii and coverage with protected areasAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 6 2010Dennis Rödder Abstract 1.The Sunda gharial Tomistoma schlegelii is, with 2500,3000 remaining specimens, one of the least studied and at the same time most endangered crocodile species. Inhabiting peat swamps in Southeast Asia, threats affecting the species are mainly associated with habitat loss and illegal hunting. 2.The effectiveness of the existing reserve network in Southeast Asia for the protection of the Sunda garial was assessed by combining spatially explicit habitat analyses derived from land cover information with species distribution modelling. Subsequently, possible improvements of the existing reserve network are derived from the habitat availability analyses. 3.The results of the spatially explicit analyses indicate that suitable habitats for the Sunda gharial in Southeast Asia, i.e. peat swamps and riverine forests, are highly fragmented. Spatial coverage of remaining habitats with protected areas fulfilling IUCN standards generally varies among regions and is best in Indonesia. However, large, currently unprotected suitable areas remain in Sumatra. Establishment of 10 additional, already proposed reserves may improve the protection of major parts of the remaining suitable habitats of the Sunda gharial. 4.According to the results of this study, the reserve network protecting this species could be significantly improved by expanding it to include seven national reserves not currently listed by the IUCN and an additional 10 reserves that have recently been proposed. Improvements and extensions of the existing reserve networks in Southeast Asia are pivotal to guarantee the long-term survival of the Sunda gharial. Copyright © 2010 John Wiley & Sons, Ltd. [source] Mapping the geochemistry of the northern Rub' Al Khali using multispectral remote sensing techniquesEARTH SURFACE PROCESSES AND LANDFORMS, Issue 7 2001Kevin White Abstract Spatial variations in sand sea geochemistry relate to mixing of different sediment sources and to variations in weathering. Due to problems of accessibility, adequate spatial coverage cannot be achieved using field surveys alone. However, maps of geochemical composition produced from remotely sensed data can be calibrated against limited field data and the results extrapolated over large, inaccessible areas. This technique is applied to part of the Rub' Al Khali in the northern United Arab Emirates. Trend surface analysis of the results suggests that the sand sea at this location can be modelled as an east,west mixing zone of two spectral components: terrestrial reddened quartz sands and marine carbonate sands. Optical dating of these sediments suggests that dune emplacement occurred rapidly around 10 ka BP, when sea level was rising rapidly. The spatial distribution of mineralogical components suggests that this phase of dune emplacement resulted from coastal dune sands being driven inland during marine transgression, thereby becoming mixed with rubified terrestrial sands. Copyright © 2001 John Wiley & Sons, Ltd. [source] The Assessment of Land Resources: Achievements and New ChallengesGEOGRAPHICAL RESEARCH, Issue 2 2002Donald A. Davidson It is surprising that despite all the pleas and policies regarding the development of sustainable land use systems, there is still considerable ignorance regarding the nature and significance of land resources. This paper traces the development and achievements of land evaluation during the 20th century, with particular reference to soils. The most active period was between 1950 and around 1980 with the development of soil and land capability surveys, methodological advances initiated with the FAO Framework for Land Evaluation, and regional land resource assessments. Thus there were considerable achievements in land evaluation by the early 1980s, and subsequently there have been important advances in the subject through the application of GIS, spatial analysis, modelling and fuzzy set algebra. Since the late 1990s there has been a phenomenal rise in interest in soil quality assessment. Considerable debate has focussed on definition, and methods of assessment and monitoring. The latter part of this paper discusses the major challenges to the development and application of land evaluation. The inadequacy of much soil survey data in terms of variables, quality, spatial coverage and scale is emphasised. Also, there is a continuing need to highlight the centrality of land resource issues in any attempt to develop sustainable land use systems. [source] The Geysers geothermal field: results from shear-wave splitting analysis in a fractured reservoirGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2005Maya Elkibbi SUMMARY Clear shear-wave splitting (SWS) is observed in 1757 high signal-to-noise ratio microearthquake seismograms recorded by two high density seismic arrays in the NW and the SE Geysers geothermal fields in California. The Geysers reservoir rocks within the study area are largely composed of lithic, low-grade metamorphism, well-fractured metagraywackes which commonly lack schistosity, warranting the general assumption that shear-wave splitting here is induced solely by stress-aligned fracturing in an otherwise isotropic medium. The high quality of observed shear-wave splitting parameters (fast shear-wave polarization directions and time delays) and the generally good data spatial coverage provide an unprecedented opportunity to demonstrate the applicability and limitations of the shear-wave splitting approach to successfully detect fracture systems in the shallow crust based on SWS field observations from a geothermal reservoir. Results from borehole stations in the NW Geysers indicate that polarization orientations range between N and N60E; while in the SE Geysers, ground surface stations show polarization directions that are generally N5E, N35E-to-N60E, N75E-to-N85E, and N20W-to-N55W. Crack orientations obtained from observed polarization orientations are in good agreement with independent field evidence, such as cracks in geological core data, tracer tests, locally mapped fractures, and the regional tectonic setting. Time delays range typically between 8 and 40 ms km,1, indicating crack densities well within the norm of fractured reservoirs. The sizeable collection of high resolution shear-wave splitting parameters shows evidence of prevalent vertical to nearly vertical fracture patterns in The Geysers field. At some locations, however, strong variations of SWS parameters with ray azimuth and incident angle within the shear-wave window of seismic stations indicate the presence of more complex fracture patterns in the subsurface. [source] Trends in extreme daily rainfall across the South Pacific and relationship to the South Pacific Convergence ZoneINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 8 2003G. M. Griffiths Abstract Daily rainfall records from 22 high-quality stations located in the South Pacific were analysed, over the common period 1961,2000, in order to assess whether extreme rainfall events have altered in their frequency or magnitude. A comprehensive spatial coverage across the South Pacific was provided, analysing a range of indices of extreme precipitation, which reflect both high rainfall events and drought. Clear spatial patterns emerged in the trends of extreme rainfall indices, with a major discontinuity across the diagonal section of the South Pacific Convergence Zone (SPCZ). Stations located between 180 and 155°W exhibit a greater number of significant abrupt changes in extreme climate than elsewhere in the South Pacific, and the majority of climatic jumps occur in the 1970s or 1980s (coincident with a displacement northeastward of the diagonal part of the SPCZ and a large local increase in mean annual temperature). Notably, all significant abrupt changes in an extreme rainfall intensity index occurred in the late 1970s or early 1980s, and in every case the index showed an increase in extremity following the change point, regardless of station location. For the stations located south of the SPCZ, this may also be linked to the observed warming since the 1970s. Significant abrupt changes in mean precipitation were also identified around the mid 1940s, for two longer, century-scale records, which again correspond to a major displacement of the diagonal section of the SPCZ. An indicator of the diagonal SPCZ position is significantly temporally correlated with an extreme rainfall intensity index, at two locations either side of the diagonal section of the SPCZ, at decadal time scales or longer. This suggests that the displacement of the diagonal portion of the SPCZ on decadal time scales influences not only mean precipitation, but also daily rainfall extremes. Copyright © 2003 Royal Meteorological Society [source] Systolic 3D first-pass myocardial perfusion MRI: Comparison with diastolic imaging in healthy subjectsMAGNETIC RESONANCE IN MEDICINE, Issue 4 2010Taehoon Shin Abstract Three-dimensional (3D) first-pass myocardial perfusion imaging (MPI) is a promising alternative to conventional two-dimensional multislice MPI due to its contiguous spatial coverage that is beneficial for estimating the size of perfusion defects. Data acquisition at mid-diastole is a typical choice for 3D MPI yet is sensitive to arrhythmia and variations in R-R interval that are common in cardiac patients. End systole is the second longest quiescent cardiac phase and is known to be less sensitive to the R-R variability. Therefore, 3D MPI with systolic acquisition may be advantageous in patients with severe arrhythmia once it is proven to be comparable to diastolic MPI in subjects with negligible R-R variation. In this work, we demonstrate the feasibility of 3D MPI with systolic data acquisition in five healthy subjects. We performed 3D MPI experiments in which 3D perfusion data were acquired at both end-systole and mid-diastole of every R-R interval and analyzed the similarity between resulting time intensity curves (TIC) from the two data sets. The correlation between systolic and diastolic TICs was extremely high (mean = 0.9841; standard deviation = 0.0166), and there was a significant linear correlation between the two time intensity curve upslopes and peak enhancements (P < 0.001). Magn Reson Med 63:858,864, 2010. © 2010 Wiley-Liss, Inc. [source] Myocardial perfusion MRI with sliding-window conjugate-gradient HYPRMAGNETIC RESONANCE IN MEDICINE, Issue 4 2009Lan Ge Abstract First-pass perfusion MRI is a promising technique for detecting ischemic heart disease. However, the diagnostic value of the method is limited by the low spatial coverage, resolution, signal-to-noise ratio (SNR), and cardiac motion-related image artifacts. In this study we investigated the feasibility of using a method that combines sliding window and CG-HYPR methods (SW-CG-HYPR) to reduce the acquisition window for each slice while maintaining the temporal resolution of one frame per heartbeat in myocardial perfusion MRI. This method allows an increased number of slices, reduced motion artifacts, and preserves the relatively high SNR and spatial resolution of the "composite images." Results from eight volunteers demonstrate the feasibility of SW-CG-HYPR for accelerated myocardial perfusion imaging with accurate signal intensity changes of left ventricle blood pool and myocardium. Using this method the acquisition time per cardiac cycle was reduced by a factor of 4 and the number of slices was increased from 3 to 8 as compared to the conventional technique. The SNR of the myocardium at peak enhancement with SW-CG-HYPR (13.83 ± 2.60) was significantly higher (P < 0.05) than the conventional turbo-FLASH protocol (8.40 ± 1.62). Also, the spatial resolution of the myocardial perfection images was significantly improved. SW-CG-HYPR is a promising technique for myocardial perfusion MRI. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc. [source] Fast measurement of intracardiac pressure differences with 2D breath-hold phase-contrast MRI,MAGNETIC RESONANCE IN MEDICINE, Issue 6 2003Richard B. Thompson Abstract Intracardiovascular blood pressure differences can be derived from velocity images acquired with phase-contrast (PC) MRI by evaluating the Navier-Stokes equations. Pressure differences within a slice of interest can be calculated using only the in-plane velocity components from that slice. This rapid exam is proposed as an alternative to the lengthy 3D velocity imaging exams. Despite their good spatial coverage, the 3D exams are prone to artifacts and errors from respiratory motion and insufficient temporal resolution, and are unattractive in the clinical setting due to their excessive scan times (>10 min of free breathing). The proposed single-slice approach requires only one or two breath-holds of acquisition time, and the velocity data can be processed for the calculation of pressure differences online with immediate feedback. The impact of reducing the pressure difference calculation to two dimensions is quantified by comparison with 3D data sets for the case of blood flow within the cardiac chambers. The calculated pressure differences are validated using high-fidelity pressure transducers both in a pulsatile flow phantom and in vivo in a dog model. There was excellent agreement between the transducer and PC-MRI results in all of the studies. Magn Reson Med 49:1056,1066, 2003. Published 2003 Wiley-Liss, Inc. [source] The SAURON project , VI.MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2006Line strength maps of 48 elliptical, lenticular galaxies ABSTRACT We present absorption line strength maps of 48 representative elliptical and lenticular galaxies obtained as part of a survey of nearby galaxies using our custom-built integral-field spectrograph, SAURON, operating on the William Herschel Telescope. Using high-quality spectra, spatially binned to a constant signal-to-noise ratio, we measure four key age, metallicity and abundance ratio sensitive indices from the Lick/IDS system over a two-dimensional field extending up to approximately one effective radius. A discussion of calibrations and offsets is given, along with a description of error estimation and nebular emission correction. We modify the classical Fe5270 index to define a new index, Fe5270S, which maximizes the useable spatial coverage of SAURON. Maps of H,, Fe5015, Mg b and Fe5270S are presented for each galaxy. We use the maps to compute average line strengths integrated over circular apertures of one-eighth effective radius, and compare the resulting relations of index versus velocity dispersion with previous long-slit work. The metal line strength maps show generally negative gradients with increasing radius roughly consistent with the morphology of the light profiles. Remarkable deviations from this general trend exist, particularly the Mg b isoindex contours appear to be flatter than the isophotes of the surface brightness for about 40 per cent of our galaxies without significant dust features. Generally, these galaxies exhibit significant rotation. We infer from this that the fast-rotating component features a higher metallicity and/or an increased Mg/Fe ratio as compared to the galaxy as a whole. The H, maps are typically flat or show a mild positive outwards radial gradient, while a few galaxies show strong central peaks and/or elevated overall H, strength likely connected to recent star formation activity. For the most prominent post-starburst galaxies, even the metal line strength maps show a reversed gradient. [source] | ||||||||||