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GPs
Terms modified by GPs Selected AbstractsSimulation of Accuracy Performance for Wireless Sensor-Based Construction Asset TrackingCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 5 2009Miros, aw J. Skibniewski In particular, identifying the location of distributed mobile entities throughout wireless communications becomes the primary task to realize the remote tracking and monitoring of the construction assets. Even though several alternative solutions have been introduced by utilizing recent technologies, such as radio frequency identification (RFID) and the global positioning system (GPS), they could not provide a solid direction to accurate and scalable tracking frameworks in large-scale construction domains due to limited capability and inflexible networking architectures. This article introduces a new tracking architecture using wireless sensor modules and shows an accuracy performance using a numerical simulation approach based on the time-of-flight method. By combining radio frequency (RF) and ultrasound (US) signals, the simulation results showed an enhanced accuracy performance over the utilization of an RF signal only. The proposed approach can provide potential guidelines for further exploration of hardware/software design and for experimental analysis to implement the framework of tracking construction assets. [source] Road Infrastructure Data Acquisition Using a Vehicle-Based Mobile Mapping SystemCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 5 2006Gi-Hong Kim The mobile mapping system that integrates the global positioning system (GPS), the inertial navigation system (INS), and digital cameras has been developed to collect data on position and attributes of road infrastructure. The vehicle-based mobile mapping system works by having the GPS and INS record the position and attitude data, and digital cameras take road images. The stereovision system can determine the position of objects that are visible on the image pair in the global coordinate system with GPS and INS data. As field data acquisition is a very expensive task, a mobile mapping system offers a greatly improved solution. In this study, we successfully created a road infrastructure map with mobile mapping technology and proposed automatic algorithms for detecting and identifying road signs from road images. The proposed detection algorithm includes line and color region extraction processes and uses the Hopfield neural networks. The identification algorithm uses seven invariant moments and parameters that present geometric characteristics. With this combined method, we could successfully detect and identify road signs. [source] Evaluation of Uncertainties Associated with Geocoding TechniquesCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 3 2004Hassan A. Karimi Geocoded data play a major role in numerous engineering applications such as transportation and environmental studies where geospatial information systems (GIS) are used for spatial modeling and analysis as they contain spatial information (e.g., latitude and longitude) about objects. The information that a GIS produces is impacted by the quality of the geocoded data (e.g., coordinates) stored in its database. To make appropriate and reasonable decisions using geocoded data, it is important to understand the sources of uncertainty in geocoding. There are two major sources of uncertainty in geocoding, one related to the database that is used as a reference data set to geocode objects and one related to the interpolation technique used. Factors such as completeness, correctness, consistency, currency, and accuracy of the data in the reference database contribute to the uncertainty of the former whereas the specific logic and assumptions used in an interpolation technique contribute to the latter. The primary purpose of this article is to understand uncertainties associated with interpolation techniques used for geocoding. In doing so, three geocoding algorithms were used and tested and the results were compared with the data collected by the Global Positioning System (GPS). The result of the overall comparison indicated no significant differences between the three algorithms. [source] A 3-D Graphical Database System for Landfill Operations Using GPSCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 5 2002H. Ping Tserng Landfill space is an important commodity for landfill companies. It is desirable to develop an efficient tool to assist space management and monitor space consumption. When recyclable wastes or particular waste materials need to be retrieved from the landfill site, the excavation operations become more difficult without an efficient tool to provide waste information (i.e., location and type). In this paper, a methodology and several algorithms are proposed to develop a 3-D graphical database system (GDS) for landfill operations. A 3-D GDS not only monitors the space consumption of a landfill site, but can also provide exact locations and types of compacted waste that would later benefit the landfill excavation operations or recycling programs after the waste is covered. [source] Soil erosion assessment using geomorphological remote sensing techniques: an example from southern ItalyEARTH SURFACE PROCESSES AND LANDFORMS, Issue 3 2010Sergio Lo Curzio Abstract The aim of this study is to assess of the distribution and map the geomorphological effects of soil erosion at the basin scale identifying newly-formed erosional landsurfaces (NeFELs), by means of an integration of Landsat ETM 7+ remotely sensed data and field-surveyed geomorphological data. The study was performed on a 228·6,km2 -wide area, located in southern Italy. The study area was first characterized from a lithological, pedological, land-use and morpho-topographic point of view and thematic maps were created. Then, the georeferenced Landsat ETM 7+ satellite imagery was processed using the RSI ENVI 4.0 software. The processing consisted of contrast stretching, principal component analysis (PCA), decorrelation stretching and RGB false colour compositing. A field survey was conducted to characterize the features detected on the imagery. Particular attention was given to the NeFELs, which were located using a global positioning system (GPS). We then delimited the Regions of Interest (ROI) on the Landsat ETM 7+ imagery, i.e. polygons representing the ,ground-truth', discriminating the NeFELs from the other features occurring in the imagery. A simple statistical analysis was conducted on the digital number (DN) values of the pixels enclosed in the ROI of the NeFELs, with the aim to determine the spectral response pattern of such landsurfaces. The NeFELs were then classified in the entire image using a maximum likelihood classification algorithm. The results of the classification process were checked in the field. Finally, a spatial analysis was performed by converting the detected landsurfaces into vectorial format and importing them into the ESRI ArcViewGIS 9.0 software. Application of these procedures, together with the results of the field survey, highlighted that some ,objects' in the classified imagery, even if displaying the same spectral response of NeFELs, were not landsurfaces subject to intense soil erosion, thus confirming the strategic importance of the field-checking for the automatically produced data. During the production of the map of the NeFELs, which is the final result of the study, these ,objects' were eliminated by means of simple, geomorphologically-coherent intersection procedures in a geographic information system (GIS) environment. The overall surface of the NeFELs had an area of 22·9,km2, which was 10% of the total. The spatial analysis showed that the highest frequency of the NeFELs occurred on both south-facing and southwest-facing slopes, cut on clayey-marly deposits, on which fine-textured and carbonate-rich Inceptisols were present and displaying slope angle values ranging from 12° to 20°. The comparison of two satellite imageries of different periods highlighted that the NeFELs were most clearly evident immediately after summer tillage operations and not so evident before them, suggesting that these practices could have played an important role in inducing the erosional processes. Copyright © 2009 John Wiley & Sons, Ltd. [source] A geomatics data integration technique for coastal change monitoringEARTH SURFACE PROCESSES AND LANDFORMS, Issue 6 2005J. P. Mills Abstract This paper reports research carried out to develop a novel method of monitoring coastal change, using an approach based on digital elevation models (DEMs). In recent years change monitoring has become an increasingly important issue, particularly for landforms and areas that are potentially hazardous to human life and assets. The coastal zone is currently a sensitive policy area for those involved with its management, as phenomena such as erosion and landslides affect the stability of both the natural and the built environment. With legal and financial implications of failing to predict and react to such geomorphological change, the provision of accurate and effective monitoring is essential. Long coastlines and dynamic processes make the application of traditional surveying difficult, but recent advances made in the geomatics discipline allow for more effective methodologies to be investigated. A solution is presented, based on two component technologies , the Global Positioning System (GPS) and digital small format aerial photogrammetry , using data fusion to elim-inate the disadvantages associated with each technique individually. A sparse but highly accurate DEM, created using kinematic GPS, was used as control to orientate surfaces derived from the relative orientation stage of photogrammetric processing. A least squares surface matching algorithm was developed to perform the orientation, reducing the need for costly and inefficient ground control point survey. Change detection was then carried out between temporal data epochs for a rapidly eroding coastline (Filey Bay, North Yorkshire). The surface matching algorithm was employed to register the datasets and determine dif-ferences between the DEM series. Large areas of change were identified during the lifetime of the study. Results of this methodology were encouraging, the flexibility, redundancy and automation potential allowing an efficient approach to landform monitoring. Copyright © 2005 John Wiley & Sons, Ltd. [source] Seasonal distribution and species composition of daytime biting mosquitoesENTOMOLOGICAL RESEARCH, Issue 2 2009Waseem AKRAM Abstract Adults and immatures of Aedes mosquito populations were collected at temperatures between 40 and 44°C (summer), while larvae were collected at 0°C (winter). Major mosquito activities were observed from February to mid-December at various collection sites that yielded high populations of Aedes spp. from May to September, and high populations of Culex spp. and Anopheles spp. from March to September. In June to July, mosquito activity was suspended because the relative humidity was high (70%); a result of the monsoon rains. In August, with temperature ranging from 38 to 42°C, the populations of Culex, Anopheles and Aedes began to increase (36.8, 32.1 and 26.3%, respectively). Population estimates (through standard prototype Centers for Disease Control (CDC) and Biogents (BG)-sentinel) and species composition of Aedes in forest habitats indicated a rapid increase in the populations of Ae. albopictus (52.3%), Ae. aegypti (19.1%) and Ae. vittatus (28.5%) following the rainy season in July. Areas positive for Ae. albopictus had identical population levels and distribution ranges of Ae. vittatus, however, there were no Ae. aegypti in Ae. albopictus areas from August to September. The population level, seasonal distribution, habitat and areas of adult activity marked by global positioning system (GPS) coordinates are being used for reference and for species composition data of Anopheles spp. (2), Culex spp. (10) and Aedes spp. (5) in addition to associated temperature, relative humidity and physico-chemical factors of larval habitat. Global meteorological changes have caused an expansion of the active period, leading to the mosquito's possibility of being a vector of disease increasing, resulting in the spread of dengue fever. [source] Official survey, in 2002, for detection of Erwinia amylovora in a proposed protected zone in Jihomoravsky region (Czech Republic)1EPPO BULLETIN, Issue 3 2004O. Vahala Inspectors of the Czech NPPO surveyed the occurrence of fireblight Erwinia amylovora in an area of Jihomoravsky region (South Moravia) proposed as an EU protected zone, including 16 designated buffer zones around nurseries. The disease was not detected in communes where fireblight hosts are grown (nurseries, variety testing stations, orchards) or in buffer zones around nurseries. In 902 communes where fireblight hosts are grown only in orchards or not at all, wild host plants were inspected at 2.629 observation points (2137 located by GARMIN GPS). In Vy,kov district, suspected fireblight was confirmed at one observation point on Crataegus, growing by a railway in Rousínov commune and, in the course of a delimiting survey outside observation points, in four other communes (Drnovice, Habrovany, Komo,any and Vy,kov). [source] Dynamic zone topology routing protocol for MANETsEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 4 2007Mehran Abolhasan The limited scalability of the proactive and reactive routing protocols have resulted in the introduction of new generation of routing in mobile ad hoc networks, called hybrid routing. These protocols aim to extend the scalability of such networks beyond several hundred to thousand of nodes by defining a virtual infrastructure in the network. However, many of the hybrid routing protocols proposed to date are designed to function using a common pre-programmed static zone map. Other hybrid protocols reduce flooding by grouping nodes into clusters, governed by a cluster-head, which may create performance bottlenecks or a single point of failures at each cluster-head node. We propose a new routing strategy in which zones are created dynamically, using a dynamic zone creation algorithm. Therefore, nodes are not restricted to a specific region. Additionally, nodes perform routing and data forwarding in a cooperative manner, which means that in the case failure, route recalculation is minimised. Routing overheads are also further reduced by introducing a number of GPS-based location tracking mechanisms, which reduces the route discovery area and the number of nodes queried to find the required destination. Copyright © 2006 AEIT [source] Use of GIS to predict effects of water level on the spawning area for smelt, Retropinna retropinna, in Lake Taupo, New ZealandFISHERIES MANAGEMENT & ECOLOGY, Issue 4 2002D. K. ROWE A GIS model of the littoral bathymetry and substrate composition of Lake Taupo was created using ArcInfo. Littoral substrates were mapped by aerial photography and confirmed by ground-truthing. Water depths were determined by echosounding linked to a differential GPS. These data were imported into ArcInfo where a 3D GIS model was used to calculate the total area of smelt, Retropinna retropinna Richardson, spawning habitat (i.e. clean sand between depths of 0.5,2.5 m) at each of five lake levels. There was little change in area over the first 50 cm below the natural maximum lake level, but spawning habitat decreased rapidly over the next 1.4 m such that a 30% reduction occurred at the natural minimum level. Anecdotal information on inter-annual variations in lake level and smelt abundance supported the notion that high lake levels in spring result in high recruitment of smelt. The GIS model also predicted effects of lake level change on areas of macrophyte cover and on other littoral substrates, and could be used to assess effects of lake level changes on the habitats of other biota. [source] A propensity score approach to correction for bias due to population stratification using genetic and non-genetic factorsGENETIC EPIDEMIOLOGY, Issue 8 2009Huaqing Zhao Abstract Confounding due to population stratification (PS) arises when differences in both allele and disease frequencies exist in a population of mixed racial/ethnic subpopulations. Genomic control, structured association, principal components analysis (PCA), and multidimensional scaling (MDS) approaches have been proposed to address this bias using genetic markers. However, confounding due to PS can also be due to non-genetic factors. Propensity scores are widely used to address confounding in observational studies but have not been adapted to deal with PS in genetic association studies. We propose a genomic propensity score (GPS) approach to correct for bias due to PS that considers both genetic and non-genetic factors. We compare the GPS method with PCA and MDS using simulation studies. Our results show that GPS can adequately adjust and consistently correct for bias due to PS. Under no/mild, moderate, and severe PS, GPS yielded estimated with bias close to 0 (mean=,0.0044, standard error=0.0087). Under moderate or severe PS, the GPS method consistently outperforms the PCA method in terms of bias, coverage probability (CP), and type I error. Under moderate PS, the GPS method consistently outperforms the MDS method in terms of CP. PCA maintains relatively high power compared to both MDS and GPS methods under the simulated situations. GPS and MDS are comparable in terms of statistical properties such as bias, type I error, and power. The GPS method provides a novel and robust tool for obtaining less-biased estimates of genetic associations that can consider both genetic and non-genetic factors. Genet. Epidemiol. 33:679,690, 2009. © 2009 Wiley-Liss, Inc. [source] Utilization of laser range finder and differential GPS for high-resolution topographic measurement at Hacitu,rul Tepe, TurkeyGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 2 2009Yuichi S. Hayakawa Topographic maps are fundamental for geoarchaeological field studies and archaeological excavations. However, traditional methods of topographic mapping, as well as modern high-tech methods such as airborne laser scanning and photogrammetry of high-resolution satellite images, are often cost-ineffective for field studies in terms of time, money, and labor. We here propose a method to measure topography for archaeological sites and surrounding areas quickly and accurately, using a laser range finder (LRF) and differential global positioning system DGPS. Three-dimensional coordinates of points on land surfaces are measured through the LRF, targeted from multiple measuring locations whose positions are acquired with the DGPS. The point data are then interpolated to produce a digital elevation model (DEM) using a geographic information system (GIS). High-resolution DEMs can be obtained with this method, with horizontal and vertical accuracies on the order of 10 cm. We here demonstrate the method for measuring detailed topography of the Hacitu,rul Tepe in central Turkey. Digital topography data incorporated in GIS can also be part of an archaeological database, providing opportunities for quantitative analyses of topography and archaeological materials. © 2009 Wiley Periodicals, Inc. [source] Surface deformation induced by present-day ice melting in SvalbardGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2009H. P. Kierulf SUMMARY The vertical movement of the Earth's surface is the result of a number of internal processes in the solid Earth, tidal forces and mass redistribution in the atmosphere, oceans, terrestrial hydrosphere and cryosphere. Close to ice sheets and glaciers, the changes in the ice loads can induce large vertical motions at intraseasonal to secular timescales. The Global Positioning System (GPS) and Very Long Baseline Interferometry (VLBI) antennas in Ny-Ĺlesund, Svalbard that started observations in 1991 and 1995, respectively, observe vertical uplift rates on the order of 8 ± 2 mm yr,1, which are considerably larger than those predicted by postglacial rebound (PGR) models (order 2 mm yr,1). The observations also indicate increased uplift rates starting some time in 2000. A local GPS campaign network that has been reoccupied annually since 1998, reveals a tilting away from the neighbouring glaciers. The Svalbard glaciers have been undergoing melting and retreat during the last century, with increased melting since about 2000. We compared the observed vertical motion to the motion predicted by loading models using a detailed ice model with annual time resolution as forcing. The model predictions correlate well with the observations both with respect to the interannual variations and the spatial pattern of long-term trends. The regression coefficients for predicted and observed interannual variations in height is 1.08 ± 0.38, whereas the regression coefficient for the predicted and observed spatial pattern turns out to be 1.26 ± 0.42. Estimates of the predicted secular trend in height due to PGR and present-day melting are on the order of 4.8 ± 0.3 mm yr,1 and thus smaller than the observed secular trend in height. This discrepancy between predictions and observations is likely caused by the sum of errors in the secular rates determined from observations (due to technique-dependent large-scale offsets) and incomplete or erroneous models (unaccounted tectonic vertical motion, errors in the ice load history, scale errors in the viscoelastic PGR models and the elastic models for present-day melting). [source] Interseismic Plate coupling and strain partitioning in the Northeastern CaribbeanGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2008D. M. Manaker SUMMARY The northeastern Caribbean provides a natural laboratory to investigate strain partitioning, its causes and its consequences on the stress regime and tectonic evolution of a subduction plate boundary. Here, we use GPS and earthquake slip vector data to produce a present-day kinematic model that accounts for secular block rotation and elastic strain accumulation, with variable interplate coupling, on active faults. We confirm that the oblique convergence between Caribbean and North America in Hispaniola is partitioned between plate boundary parallel motion on the Septentrional and Enriquillo faults in the overriding plate and plate-boundary normal motion at the plate interface on the Northern Hispaniola Fault. To the east, the Caribbean/North America plate motion is accommodated by oblique slip on the faults bounding the Puerto Rico block to the north (Puerto Rico subduction) and to the south (Muertos thrust), with no evidence for partitioning. The spatial correlation between interplate coupling, strain partitioning and the subduction of buoyant oceanic asperities suggests that the latter enhance the transfer of interplate shear stresses to the overriding plate, facilitating strike-slip faulting in the overriding plate. The model slip rate deficit, together with the dates of large historical earthquakes, indicates the potential for a large (Mw7.5 or greater) earthquake on the Septentrional fault in the Dominican Republic. Similarly, the Enriquillo fault in Haiti is currently capable of a Mw7.2 earthquake if the entire elastic strain accumulated since the last major earthquake was released in a single event today. The model results show that the Puerto Rico/Lesser Antilles subduction thrust is only partially coupled, meaning that the plate interface is accumulating elastic strain at rates slower than the total plate motion. This does not preclude the existence of isolated locked patches accumulating elastic strain to be released in future earthquakes, but whose location and geometry are not resolvable with the present data distribution. Slip deficit on faults from this study are used in a companion paper to calculate interseismic stress loading and, together with stress changes due to historical earthquakes, derive the recent stress evolution in the NE Caribbean. [source] 2001 August earthquake swarm at Shadwan Island, Gulf of Suez, EgyptGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2006Ahmed Badawy SUMMARY The earthquake swarm that struck Shadwan Island at the entrance of the Gulf of Suez in 2001 August included 408 events. Almost all of these events (94 per cent) were microearthquakes and only 6 per cent had small measurable magnitudes (5.0 > ML, 3.0). Most of the earthquakes were weak and followed each other so closely in time that they could not be identified at more distant stations. The fault plane solutions of the strongest events of the swarm show almost identical focal mechanisms, predominately normal faulting with a significant sinistral strike-slip component for nodal planes trending NW,SE. A comparison with the mechanisms of the 1969 and 1972 events which took place 20 km north of the swarm epicentral region shows similarities in faulting type and orientation of nodal planes. The azimuths of T -axes determined from focal mechanisms in this study are oriented in the NNE,SSW direction. This direction is consistent with the present-day stress field derived from borehole breakouts in the southern Gulf of Suez and the last phase of stress field changes in the Late Pleistocene, as well as with recent GPS results. The source parameters of the largest (ML, 3.0) events of the 2001 August Shadwan swarm have been estimated from the P -wave spectra of the Egyptian National Seismograph Network (ENSN). Averaging of the values obtained at different stations shows relatively similar source parameters, including a fault length of 0.65 ,L, 2 km, a seismic moment of 7.1 × 1012,Mo, 3.0 × 1014 N m and a stress drop of 0.4 ,,,, 10 bar. [source] Mechanical deformation model of the western United States instantaneous strain-rate fieldGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2006Fred F. Pollitz SUMMARY We present a relationship between the long-term fault slip rates and instantaneous velocities as measured by Global Positioning System (GPS) or other geodetic measurements over a short time span. The main elements are the secularly increasing forces imposed by the bounding Pacific and Juan de Fuca (JdF) plates on the North American plate, viscoelastic relaxation following selected large earthquakes occurring on faults that are locked during their respective interseismic periods, and steady slip along creeping portions of faults in the context of a thin-plate system. In detail, the physical model allows separate treatments of faults with known geometry and slip history, faults with incomplete characterization (i.e. fault geometry but not necessarily slip history is available), creeping faults, and dislocation sources distributed between the faults. We model the western United States strain-rate field, derived from 746 GPS velocity vectors, in order to test the importance of the relaxation from historic events and characterize the tectonic forces imposed by the bounding Pacific and JdF plates. Relaxation following major earthquakes (M, 8.0) strongly shapes the present strain-rate field over most of the plate boundary zone. Equally important are lateral shear transmitted across the Pacific,North America plate boundary along ,1000 km of the continental shelf, downdip forces distributed along the Cascadia subduction interface, and distributed slip in the lower lithosphere. Post-earthquake relaxation and tectonic forcing, combined with distributed deep slip, constructively interfere near the western margin of the plate boundary zone, producing locally large strain accumulation along the San Andreas fault (SAF) system. However, they destructively interfere further into the plate interior, resulting in smaller and more variable strain accumulation patterns in the eastern part of the plate boundary zone. Much of the right-lateral strain accumulation along the SAF system is systematically underpredicted by models which account only for relaxation from known large earthquakes. This strongly suggests that in addition to viscoelastic-cycle effects, steady deep slip in the lower lithosphere is needed to explain the observed strain-rate field. [source] Geodetic observations of ice flow velocities over the southern part of subglacial Lake Vostok, Antarctica, and their glaciological implicationsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2006Jens Wendt SUMMARY In the austral summer seasons 2001/02 and 2002/03, Global Positioning System (GPS) data were collected in the vicinity of Vostok Station to determine ice flow velocities over Lake Vostok. Ten GPS sites are located within a radius of 30 km around Vostok Station on floating ice as well as on grounded ice to the east and to the west of the lake. Additionally, a local deformation network around the ice core drilling site 5G-1 was installed. The derived ice flow velocity for Vostok Station is 2.00 m a,1± 0.01 m a,1. Along the flowline of Vostok Station an extension rate of about 10,5 a,1 (equivalent to 1 cm km,1 a,1) was determined. This significant velocity gradient results in a new estimate of 28 700 years for the transit time of an ice particle along the Vostok flowline from the bedrock ridge in the southwest of the lake to the eastern shoreline. With these lower velocities compared to earlier studies and, hence, larger transit times the basal accretion rate is estimated to be 4 mm a,1 along a portion of the Vostok flowline. An assessment of the local accretion rate at Vostok Station using the observed geodetic quantities yields an accretion rate in the same order of magnitude. Furthermore, the comparison of our geodetic observations with results inferred from ice-penetrating radar data indicates that the ice flow may not have changed significantly for several thousand years. [source] Analytical and 3-D numerical modelling of Mt. Etna (Italy) volcano inflationGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2005A. Bonaccorso SUMMARY Since 1993, geodetic data obtained by different techniques (GPS, EDM, SAR, levelling) have detected a consistent inflation of the Mt. Etna volcano. The inflation, culminating with the 1998,2001 strong explosive activity from summit craters and recent 2001 and 2002 flank eruptions, is interpreted in terms of magma ascent and refilling of the volcanic plumbing system and reservoirs. We have modelled the 1993,1997 EDM and GPS data by 3-D pressurized sources to infer the position and dimension of the magma reservoir. We have performed analytical inversions of the observed deformation using both spheroidal and ellipsoidal sources embedded in a homogeneous elastic half-space and by applying different inversion methods. Solutions for these types of sources show evidence of a vertically elongated magma reservoir located 6 km beneath the summit craters. The maximum elevation of topography is comparable to such depth and strong heterogeneities are inferred from seismic tomography; in order to assess their importance, further 3-D numerical models, employing source parameters extracted from analytical models, have been developed using the finite-element technique. The deformation predicted by all the models considered shows a general agreement with the 1993,1997 data, suggesting the primary role of a pressure source, while the complexities of the medium play a minor role under elastic conditions. However, major discrepancies between data and models are located in the SE sector, suggesting that sliding along potential detachment surfaces may contribute to amplify deformation during the inflation. For the first time realistic features of Mt. Etna are studied by a 3-D numerical model characterized by the topography and lateral variations of elastic structure, providing a framework for a deeper insight into the relationships between internal sources and tectonic structures. [source] BARGEN continuous GPS data across the eastern Basin and Range province, and implications for fault system dynamicsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2004Nathan A. Niemi SUMMARY We collected data from a transect of continuous Global Positioning System (GPS) sites across the eastern Basin and Range province at latitude 39°N from 1997,2000. Intersite velocities define a region ,350 km wide of broadly distributed strain accumulation at ,10 nstr yr,1. On the western margin of the region, site EGAN, ,10 km north of Ely, Nevada, moved at a rate of 3.9 ± 0.2 mm yr,1 to the west relative to site CAST, which is on the Colorado Plateau. Velocities of most sites to the west of Ely moved at an average rate of ,3 mm yr,1 relative to CAST, defining an area across central Nevada that does not appear to be extending significantly. The late Quaternary geological velocity field, derived using seismic reflection and neotectonic data, indicates a maximum velocity of EGAN with respect to the Colorado Plateau of ,4 mm yr,1, also distributed relatively evenly across the region. The geodetic and late Quaternary geological velocity fields, therefore, are consistent, but strain release on the Sevier Desert detachment and the Wasatch fault appears to have been anomalously high in the Holocene. Previous models suggesting horizontal displacement rates in the eastern Basin and Range near 3 mm yr,1, which focused mainly along the Wasatch zone and Intermountain seismic belt, may overestimate the Holocene Wasatch rate by at least 50 per cent and the Quaternary rate by nearly an order of magnitude, while ignoring potentially major seismogenic faults further to the west. [source] Contemporary kinematics of the southern Aegean and the Mediterranean RidgeGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2004Corné Kreemer SUMMARY This study focuses on the kinematics of the southern Aegean and the Mediterranean Ridge (MR). A quantification of the deformation of the MR is essential for both evaluating physical models of accretionary wedges in general and for obtaining a self-consistent model of the surface deformation over the entire Nubia,Eurasia (NU,EU) plate boundary zone in the eastern Mediterranean. Previous kinematic studies have not properly considered the deformation field south of the Hellenic arc. Although this study focuses on the deformation field of the MR, we also discuss the kinematics of the southern Aegean, because the geometry and movement of the Hellenic arc determine to a large extent the kinematic boundary conditions for kinematic studies of the MR. We calculate a continuous velocity and strain rate field by interpolating model velocities that are fitted in a least-squares sense to published Global Positioning System (GPS) velocities. In the interpolation, we use information from a detailed data set of onshore and offshore active faulting to place constraints on the expected style and direction of the model strain rate field. In addition, we use the orientations of tracks left by seamounts travelling into the wedge to further constrain the offshore deformation pattern. Our model results highlight the presence of active shear partitioning within the Mediterranean ridge. High compressional strain rates between the ridge crest and the deformation front accommodate approximately 60,70 per cent of the total motion over the wedge, and the outward growth rate of the frontal thrust is , 4 mm yr,1. Strain partitioning within the wedge leads to 19,23 mm yr,1 of dextral motion at the wedge,backstop contact of the western MR, whereas the Pliny and Strabo trenches in the eastern MR accommodate 21,23 mm yr,1 of sinistral motion. The backstop of the western MR is kinematically part of the southern Aegean, which moves as a single block [the Aegean block (AE)] at 33,34 mm yr,1 in the direction of S24°W ± 1° towards stable Nubia (NU). Our model confirms that there is a clear divergence between the western and eastern Hellenic arc and we argue for a causal relation between the outward motion of the arc and the gradient in the regional geoid anomaly. Our results suggest that a significant driving source of the surface velocity field lies south of the Hellenic arc and only for the southeastern Aegean could there be some effect as a result of gravitational collapse associated with density differences within the overriding plate. [source] Co-seismic slip from the 1995 July 30 Mw= 8.1 Antofagasta, Chile, earthquake as constrained by InSAR and GPS observationsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2002M. E. Pritchard Summary We analyse radar interferometric and GPS observations of the displacement field from the 1995 July 30 Mw= 8.1 Antofagasta, Chile, earthquake and invert for the distribution of slip along the co-seismic fault plane. Using a fixed fault geometry, we compare the use of singular-value decomposition and constrained linear inversion to invert for the slip distribution and find that the latter approach is better resolved and more physically reasonable. Separate inversions using only GPS data, only InSAR data from descending orbits, and InSAR data from both ascending and descending orbits without the GPS data illustrate the complimentary nature of GPS and the presently available InSAR data. The GPS data resolve slip near GPS benchmarks well, while the InSAR provides greater spatial sampling. The combination of ascending and descending InSAR data contributes greatly to the ability of InSAR to resolve the slip model, thereby emphasizing the need to acquire this data for future earthquakes. The rake, distribution of slip and seismic moment of our preferred model are generally consistent with previous seismic and geodetic inversions, although significant differences do exist. GPS data projected in the radar line-of-sight (LOS) and corresponding InSAR pixels have a root mean square (rms) difference of about 3 cm. Comparison of our predictions of vertical displacement and observed uplift from corraline algae have an rms of 10 cm. Our inversion and previous results reveal that the location of slip might be influenced by the 1987 Mw= 7.5 event. Our analysis further reveals that the 1995 slip distribution was affected by a 1988 Mw= 7.2 event, and might have influenced a 1998 Mw= 7.0 earthquake that occurred downdip of the 1995 rupture. Our slip inversion reveals a potential change in mechanism in the southern portion of the rupture, consistent with seismic results. Predictions of the satellite LOS displacement from a seismic inversion and a joint seismic/GPS inversion do not compare favourably with the InSAR observations. [source] Deformation and stress change associated with plate interaction at subduction zones: a kinematic modellingGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2000Shaorong Zhao The interseismic deformation associated with plate coupling at a subduction zone is commonly simulated by the steady-slip model in which a reverse dip-slip is imposed on the down-dip extension of the locked plate interface, or by the backslip model in which a normal slip is imposed on the locked plate interface. It is found that these two models, although totally different in principle, produce similar patterns for the vertical deformation at a subduction zone. This suggests that it is almost impossible to distinguish between these two models by analysing only the interseismic vertical deformation observed at a subduction zone. The steady-slip model cannot correctly predict the horizontal deformation associated with plate coupling at a subduction zone, a fact that is proved by both the numerical modelling in this study and the GPS (Global Positioning System) observations near the Nankai trough, southwest Japan. It is therefore inadequate to simulate the effect of the plate coupling at a subduction zone by the steady-slip model. It is also revealed that the unphysical assumption inherent in the backslip model of imposing a normal slip on the locked plate interface makes it impossible to predict correctly the horizontal motion of the subducted plate and the stress change within the overthrust zone associated with the plate coupling during interseismic stages. If the analysis made in this work is proved to be correct, some of the previous studies on interpreting the interseismic deformation observed at several subduction zones based on these two models might need substantial revision. On the basis of the investigations on plate interaction at subduction zones made using the finite element method and the kinematic/mechanical conditions of the plate coupling implied by the present plate tectonics, a synthesized model is proposed to simulate the kinematic effect of the plate interaction during interseismic stages. A numerical analysis shows that the proposed model, designed to simulate the motion of a subducted slab, can correctly produce the deformation and the main pattern of stress concentration associated with plate coupling at a subduction zone. The validity of the synthesized model is examined and partially verified by analysing the horizontal deformation observed by GPS near the Nankai trough, southwest Japan. [source] Seismicity of the Sea of Marmara (Turkey) since 1500GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2000N. N. Ambraseys Summary We use the earthquake history of the last 500 years to help evaluate the tectonic and hazard contexts of the 1999 earthquakes at Izmit and Düzce in western Turkey. The 20th century has been unusually active, but over the 500 year period the seismic moment release can account for the known right-lateral shear velocity across the Marmara region observed by GPS. Two areas of known late Quaternary faulting stand out as unusually quiet over this period: the northwest shore of the Sea of Marmara and the southern branch of the North Anatolian fault system between Bursa and Mudurnu. [source] Is food availability limiting African Penguins Spheniscus demersus at Boulders?IBIS, Issue 1 2006A comparison of foraging effort at mainland, island colonies The African Penguin Spheniscus demersus (Vulnerable) formed three new colonies during the 1980s, two on the South African mainland (Stony Point and Boulders) and one on Robben Island. One of the mainland colonies, at Boulders, Simon's Town, is in a suburban area, resulting in conflict with humans. Growth of the Boulders colony was initially rapid, largely through immigration, but has since slowed, possibly as a result of density-dependent effects either on land (where there has been active management to limit the spread of the colony) or at sea. We test the latter hypothesis by comparing the foraging effort of Penguins feeding small chicks at island and mainland sites, and relate this to the foraging area available to birds. Three-dimensional foraging paths of African Penguins were reconstructed using GPS and time,depth loggers. There were no intercolony differences in the rate at which birds dived during the day (33 dives/h), in diving depths (mean 17 m, max. 69 m) or in travelling speeds. The maximum speed recorded was 2.85 m/s, with birds travelling faster when commuting (average 1.18 m/s) than when foraging (0.93 m/s) or resting at sea (0.66 m/s during the day, 0.41 m/s at night). There were strong correlations between foraging trip duration, foraging range and total distance travelled. Foraging effort was correlated with chick age at Robben Island, but not at Boulders. Contrary to Ashmole's hypothesis, birds from Boulders (c. 1000 pairs) travelled further (46,53 km) and foraged for longer (13.2 h) than did birds from Robben Island (c. 7000 pairs) and Dassen Island (c. 21 000 pairs) (33 km, 10.3 h). The mean foraging range also differed significantly between mainland (18,20 km) and island colonies (9 km). The area available to central-place-foraging seabirds breeding on the mainland is typically less than that for seabirds breeding on islands, but the greater foraging range of Boulders birds results in an absolute foraging area roughly twice that of island colonies, and the area per pair is an order of magnitude greater for the relatively small Boulders colony. Ashmole's hypothesis assumes relatively uniform prey availability among colonies, but our results suggest this does not apply in this case. The greater foraging effort of Boulders birds probably reflects reduced prey availability in False Bay, and thus the recent slowing in growth at the colony may be the result of differential immigration rather than management actions to limit the spatial growth of the colony. [source] New centralized automatic vehicle location communications software system under GIS environmentINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 9 2005Omar Al-Bayari Abstract Recent advances in wireless communications and networks have integrated relatively new technologies such as Global Positioning System (GPS), to the popular Global System for Mobile Communication (GSM), second generation cellular systems and the Geographic Information Systems (GIS) technologies. Automatic Vehicle Location (AVL) is based on a combination of GPS, GIS and telecommunication technologies. Automatic Vehicle Tracking systems are more and more used for different purposes, especially those related to tracking one vehicle or a fleet of vehicles. In this work, we introduce a new AVL system, which is based and developed under GIS software environment. The centralized software at the control station offers a new technology of transferring the intelligence of tracking system from the car unit, into the control office PC software. Centralized software will reduce the programming efforts in the car unit and will offer better fleet management. Moreover, the core of our system is based on the objects or the controllers of the GIS software, which reduces dramatically the overall system cost. Our system provides an easy access to change the functions of the system, with great possibility to satisfy the local needs. The design of our software will be presented with an explanation of the new supporting technologies that were to create the system. Finally, our software system has been validated using data from local road networks. Copyright © 2005 John Wiley & Sons, Ltd. [source] Pinpointing users with location estimation techniques and Wi-Fi hotspot technologyINTERNATIONAL JOURNAL OF NETWORK MANAGEMENT, Issue 5 2008Kevin Curran Location awareness is becoming an important capability for mobile computing; however, it has not been possible until now to provide cheap pervasive positioning systems. Wide area coverage is most famously achieved by using global positioning systems (GPS). A constellation of low-orbit satellites cover the earth's surface. Unfortunately GPS does not work indoors and has limited success in big cities because of the ,urban canyon' effect. PlaceLab is a research project that attempts to solve the ubiquity issues surrounding 802.11-based location estimation. PlaceLab, like RADAR, uses a device's 802.11 interface; however, it does not require the area to be pre-calibrated. It predicts location via the known positions of the access points detected by the device. Commonly used systems have a number of drawbacks, including cost, accuracy and the ability to work indoors. PlaceLab is a piece of open source software developed by Intel Research that can pinpoint a user within a Wi-Fi network. We set out here to investigate whether PlaceLab can be used as a means of establishing a user's position. This type of investigation could, if successful, pave the way for the development of other location-based applications. This report documents the efforts to answer the above question. PlaceLab was found to work, but only in ideal locations where factors such as the number of floors and the lack of available APs did not affect its use. It was concluded that these factors prevent the system from being effective as a means of establishing a user's position in most locations on campus. Copyright © 2008 John Wiley & Sons, Ltd. [source] Low-complexity unambiguous acquisition methods for BOC-modulated CDMA signalsINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 6 2008Elena Simona Lohan Abstract The new M-code signals of GPS and the signals proposed for the future Galileo systems are of split-spectrum type, where the pseudorandom (PRN) code is multiplied with rectangular sub-carriers in one or several stages. Sine and cosine binary-offset-carrier (BOC) modulations are examples of modulations, which split the signal spectrum and create ambiguities in the envelope of the autocorrelation function (ACF) of the modulated signals. Thus, the acquisition of split-spectrum signals, based on the ambiguous ACF, poses some challenges, which might be overcome at the expense of higher complexity (e.g. by decreasing the step in searching the timing hypotheses). Recently, two techniques that deal with the ambiguities of the ACF have been proposed, and they were referred to as ,sideband (SB) techniques' (by Betz, Fishman et al.) or ,BPSK-like' techniques (by Martin, Heiries et al.), since they use SB correlation channels and the obtained ACF looks similar to the ACF of a BPSK-modulated PRN code. These techniques allow the use of a higher search step compared with the ambiguous ACF situation. However, both these techniques use SB-selection filters and modified reference PRN codes at the receivers, which affect the implementational complexity. Moreover, the ,BPSK-like' techniques have been so far studied for even BOC-modulation orders (i.e. integer ratio between the sub-carrier frequency and the chip rate) and they fail to work for odd BOC-modulation orders (or equivalently for split-spectrum signals with significant zero-frequency content). We propose here three reduced-complexity methods that remove the ambiguities of the ACF of the split-spectrum signals and work for both even and odd BOC-modulation orders. Two of the proposed methods are extensions of the previously mentioned techniques, and the third one is introduced by the authors and called the unsuppressed adjacent lobes (UAL) technique. We argue via theoretical analysis the choice of the parameters of the proposed methods and we compare the alternative methods in terms of complexity and performance. Copyright © 2008 John Wiley & Sons, Ltd. [source] Mobile GPS carrier phase tracking using a novel intelligent dual-loop receiverINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 2 2008Wei-Lung Mao Abstract Carrier phase information is necessary for accurate measurements in global positioning system (GPS) applications. This paper presents a novel intelligent GPS carrier tracking loop with variable-bandwidth characteristics for fast acquisition and better tracking capability in the presence of dynamic environments. Our dual-loop receiver is composed of a frequency-locked loop-assisted phase-locked loop structure, the fuzzy controllers (FCs), and the ATAN discriminator functions. The soft-computing FCs provide the time-varying loop gains to perform accurate and reliable control of the dual-loop paradigm. Once the phase dynamic errors become large under kinematic conditions, the fuzzy loop gains increase adaptively and achieve rapid acquisition. On the other hand, when the tracking errors approach zero in the steady state, the loop gains decrease and the corresponding dual-loop receiver returns to a narrowband system. Four types of carrier phase signals, i.e. phase offset, decaying sinusoidal phase jitter, frequency offset, and frequency ramp offset, are considered to emulate realistic mobile circumstances. Simulation results show that our proposed receiver does achieve a superior performance over conventional tracking loops in terms of faster settling time and wider acquisition range while preventing the occurrence of cycle slips. Copyright © 2008 John Wiley & Sons, Ltd. [source] Analyzing GPS signals to investigate path diversity effects of non-geostationary orbit satellite communication systemsINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 6 2002Hsin-Piao Lin Abstract The concept behind path diversity is that a user who can access several satellites simultaneously will be able to communicate more effectively than a user who could only access one. The success of this method depends on the environment, the satellite constellation, and diversity combining technology. This paper explores the path diversity effects of non-geostationary orbit (NGO) satellite personal communication services, for different degrees of user mobility, under various scenarios, using the constellation of the global positioning system (GPS). Measurements are taken near downtown Taipei. Three types of mobilities (fixed-point, pedestrian, and vehicular) are examined, and the switch diversity and maximum ratio combining method are applied to determine the path diversity gain and calculate bit error probability. The error probability performance of applying diversity schemes in coherent binary phase shift keying (BPSK) and non-coherent differential phase shift keying (DPSK) modulations over Rician fading channels are also analysed and evaluated by using the characteristic function method. The results show that fading can be significantly reduced and diversity greatly increased. A significant diversity gain and improvement in bit error rate (BER) can be expected in all cases by simply applying switch diversity scheme. Besides, for the maximum ratio combining method, the results imply that summing two satellite signals suffices to increase diversity and improve the bit error rate performance. Copyright © 2002 John Wiley & Sons, Ltd. [source] The future for in-vehicle information systems: The technology and its impactsJOURNAL OF ADVANCED TRANSPORTATION, Issue 3 2002Michael G H Bell In-vehicle information has an important social role to play in improving the efficiency and safety of travel by all modes. In this review, three generations of system are identified. The first generation consists of simple in-vehicle units relying heavily on external data. The second generation has more sophisticated in-vehicle units with colour TFT screens and DVD players for maps and entertainment. The third generation again makes use of external data, using the mobile phone network to download map sections and other data as and when required, thereby obviating the need for beacons and map CDs. For locationing, GPS (and/or Galileo, the European version of GPS) remains the favoured technology. Portable devices offering multi-modal information could improve inter-modal transport efficiency. [source] | ||||||||||||||||||||||||||||||||||||||||||||||