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Search Results: 1 - 10 of 2644 matches for " GPS "
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Assessment of Pseudorange Multipath at Continuous GPS Stations in Mexico  [PDF]
G. Esteban Vázquez, Rick Bennett, Joshua Spinler
Positioning (POS) , 2013, DOI: 10.4236/pos.2013.43025
Abstract: We conducted a study to quantify the amount of pseudorange multipath at continuous Global Positioning System (CGPS) stations in the Mexican territory. These CGPS stations serve as reference stations enabling rapid high-precision three-dimensional positioning capabilities, supporting a number of commercial and public safety applications. We studied CGPS data from a large number of publicly available networks spanning Mexico. These include the RGNA (National Active Geodetic Network) administered by INEGI (National Institute of Statistics and Geography), the PBO network (Plate Boundary Observatory) funded by the National Science Foundation (NSF) and operated by UNAVCO (University NAVstar Consortium), the Southern California Integrated GPS Network (SCIGN), which is a collaboration effort of the United States Geological Survey (USGS), Scripps Institution of Oceanography and the Jet Propulsion Laboratory (JPL), the UNAM network, operated by the National Seismological System (SSN) and the Institute of Geophysics of the National Autonomous University of Mexico (UNAM), the Suominet Geodetic Network (SNG) and the CORS (Continuously Operating Reference Station) network, operated by the Federal Aviation Administration (FAA). We evaluated a total of 53 CGPS stations, where dual-frequency geodetic-grade receivers collected GPS data continuously during the period from 1994 to 2012. Despite carefully selected locations, all GPS stations are, to some extent, affected by the presence of signal multipath. For GPS network users that rely on pseudorange observables, the existence of pseudorange multipath could be a critical source of error depending on the time scale of the application. Thus, to identify the most and the least affected GPS stations, we analyzed the averaged daily root mean square pseudorange multipath variations (MP1-RMS and MP2-RMS) for all feasible satellites tracked by the CGPS networks. We investigated the sources of multipath, including changes associated with hardware replacement (i.e., receiver and antenna type) and receiver firmware upgrades.
Variation of Altitude Observed on the Occasion of the Tohoku Earthquake (M = 9.0) Occurred on March 11, 2011  [PDF]
Pietro Milillo, Tommaso Maggipinto, Pier Francesco Biagi
Open Journal of Earthquake Research (OJER) , 2014, DOI: 10.4236/ojer.2014.31004

Since October 1, 2010, a GPS receiver is put into operation at Tokai (Japan) in an experiment on Neutrino Physics (T2K). A significant variation of the altitude was detected from the beginning of March 2011, so that it has made worthwhile to investigate the possibility that such variations could be correlated to the Tohoku earthquake. In order to investigate in details this possibility, we analyzed the GPS data collected during 2011 by GEONet the GPS Earth Observation Network (GEONET). GEONET is the GPS network of Japan and consists of 1240 permanent stations. Preliminary results of the analysis seemed to show ten days before the earthquake, some possible anomalous behaviors of the stations. These anomalous behaviors were particularly relevant for stations of the network near the epicentral area. While co-seismic and post-seismic variations are widely expected, the anomalies recorded about ten days before the earthquake could be seriously considered among short-term precursors of the earthquake. In order to confirm this possibility, more detailed studies have been performed. In particular, GEONET currently makes available only daily solutions of the stations coordinates. On the contrary, it is very important to improve the time resolution just to understand the features of the anomalies till the last hours before the Earthquake. For this reason, we have performed an analysis to evaluate the coordinates and movement on hourly basis so improving the time resolution.

An Improved Model for Single-Frequency GPS/GALILEO Precise Point Positioning  [PDF]
Akram Afifi, Ahmed El-Rabbany
Positioning (POS) , 2015, DOI: 10.4236/pos.2015.62002
Abstract: This paper introduces a new precise point positioning (PPP) model, which combines single-fre- quency GPS/Galileo observations in between-satellite single-difference (BSSD) mode. In the absence of multipath, all receiver-related errors and biases are cancelled out when forming BSSD for a specific constellation. This leaves the satellite originating errors and atmospheric delays un- modelled. Combining GPS and Galileo observables introduces additional biases that have to be modelled, including the GPS to Galileo time offset (GGTO) and the inter-system bias. This paper models all PPP errors rigorously to improve the single-frequency GPS/Galileo PPP solution. GPSPace PPP software of Natural Resources Canada (NRCan) is modified to enable a GPS/Galileo PPP solution and to handle the newly introduced biases. A total of 12 data sets representing the GPS/Galileo measurements of six IGS-MEGX stations are processed to verify the newly developed PPP model. Precise satellite orbit and clock corrections from IGS-MEGX networks are used for both GPS and Galileo measurements. It is shown that sub-decimeter level accuracy is possible with single-frequency GPS/Galileo PPP. In addition, the PPP solution convergence time is improved from approximately 100 minutes for the un-differenced single-frequency GPS/Galileo solution to approximately 65 minutes for the BSSD counterpart when a single reference satellite is used. Moreover, an improvement in the PPP solution convergence time of 35% and 15% is obtained when one and two reference satellites are used, respectively.
GNSS Multipath Reduction Using GPS and DGPS in the Real Case  [PDF]
Salem Titouni, Khaled Rouabah, Salim Atia, Mustapha Flissi, Oussama Khababa
Positioning (POS) , 2017, DOI: 10.4236/pos.2017.84004
Abstract: In Global Navigation Satellite System (GNSS) like Global Positioning System (GPS) and future Galileo, space signal reception in urban environment seems to be one of most significant. The urban environment is characterized by the presence of an excessive number of obstacles that produce Multiple Path (MP) in positioning the receiver. Consequently, it is of primary importance to characterize and ameliorate the performances of GNSS receiver for this type of application. In this paper, a method to mitigate MP in GNSS applications was proposed. Its principle is based on the addition, to the geographic map of a city or a neighborhood, of a supplementary information that consists of the correction of error caused by the MPs. The latter one was carried out by the comparison of the measurements, realized by Differential GPS (DGPS) and GPS, between two different sites with the same form. The first one was characterized by the presence of the MPs and the second one was completely clear of any type of obstacle. As a consequence, the measurements comparison has allowed us to deduce the GNSS MPs errors. This information can subsequently be used to make the corrections of the errors caused by MPs and it can be generalized by a measurement company to any entire city in order to identify errors in any neighborhood.
Discussion on Teaching of “GPS Measurement and Data Processing”

李敏, 郭向欣
Geomatics Science and Technology (GST) , 2014, DOI: 10.12677/GST.2014.21002
According to the development and application of GPS, “GPS measurement and data processing” has become a compulsory of Surveying Engineering undergraduate students. The main content and features taught in the process of theory and practice of “GPS measurement and data processing” are analyzed. Specifically, some problems of the course are discussed, while some teaching reform proposals are brought up.
When Technology Encounters Culture: A Closer Watch on Dajia Mazu Patrol and Pilgrimage in Taiwan  [PDF]
Ching-Yun Mu, Will Y. Lin, Zheng-Yu Chen, Tien-Yin Chou, Lung-Shih Yang, Cheng-Shu Kao
Journal of Geographic Information System (JGIS) , 2012, DOI: 10.4236/jgis.2012.42013
Abstract: Mazu, a protective sea God, has been worshipped by residents of Taiwan and southeast coast of mainland China as well as overseas Chinese around the globe for hundreds of years. The number of people around the world under her influence of religious belief and moral culture can reach up hundreds of million. Every year in lunar March, the over- one-week long Mazu patrol and pilgrimage held by Jenn Lann Temple in Dajia County of Taiwan attracts millions of pilgrims and tourists around the world to participate in one of the biggest religious events in the world. To keep track of the entire patrol and pilgrimage, Jenn Lann Temple has been cooperating with GIS Research Center, Feng-Chia University since 2008, setting up a GPS receiver, a digital camera, and 4 video recorders on Mazu’s palanquin. Both real-time position of the palanquin and live videos on the scene along the way of pilgrimage were published on the Internet, providing pilgrims, tourists and viewers around the world with an open access to observe the entire event. This paper details this initiative of introducing spatial technology to large cultural events. The study collects the historic tracks of Mazu’s palanquin during the pilgrimage from 2008 to 2010, analyzes their spatial-temporal attributes, and elicits several interesting facts behind the figures and maps. It also explores how spatial technologies can help organize large-scale events and even accelerate the dissemination of culture.
Spatiotemporal Cattle Data—A Plea for Protocol Standardization  [PDF]
Dean M. Anderson, Rick E. Estell, Andres F. Cibils
Positioning (POS) , 2013, DOI: 10.4236/pos.2013.41012

It was not until the end of the 1990’s that animal born satellite receivers catapulted range cattle ecology into the 21st century world of microchip technology with all of its opportunities and challenges. With the global navigation satellite system (GNSS), insight about how cattle use a landscape is being revealed from previously unknown temporal and spatial behaviors. The most common system to date for studying ungulate movement is the global positioning system (GPS). With its use has come a clarity and completeness in documenting spatial and temporal data in new and exciting ways that offer almost unlimited possibilities to better understand and manage economic and societal returns from animal dominated landscapes. However, its use on free-ranging cattle is not without challenges, some of which are yet to be optimally solved. To maximize the usefulness of GNSS data, consideration must be given to: 1) developing a standardized protocol for reporting and analyzing research that facilitates interpretation of results across different ecosystems; 2) develop optimum ranges over which to collect satellite fixes depending upon the particular behaviors of interest; and 3) concurrently develop electronic hardware and equipment platforms that are easily deployed on animals and that are light, robust, and can be worn by cattle for extended periods of time without human intervention (e.g., changing batteries). Once data are collected, appropriate geographic information system (GIS) based models should be used to produce a series of products that can be used to implement flexible management strategies, some of which may support methodologies that are yet to be commercialized and adopted into future plant-animal interface management routines.

GPS Signal Short-Term Propagation Characteristics Modeling in Urban Areas for Precise Navigation Applications  [PDF]
G. Sateesh Kumar, G. Sasi Bhushana Rao, M. N. V. S. S. Kumar
Positioning (POS) , 2013, DOI: 10.4236/pos.2013.42019

GPS navigation signal includes vital information such as orbital parameters, clock error coefficients etc. This received signal which is extremely weak is affected by several errors during its propagation and is of the order of 10-16 W. The noise floor of this signal is 400 times higher than the transmitted signal. The situation becomes much worse particularly when the GPS receiver is located at urban areas where the multipath effect is predominant in the code and carrier phase measurements. GPS usage is not limited to the aircraft en-route navigation and missile guidance where the user receives the satellite signals from the open sky. At the present time, it has become an essential utility in the car navigation, mobile phones, surveying and aircraft landing application. The signal propagation characteristics particularly the short-term variations severely affect the quality, availability and continuity of the system. In this paper, short-term propagation characteristics of GPS signal are modeled and analyzed. Short-term variations are mainly due to multipath reflections and Doppler shift which degrades the quality of received signal particularly in urban environments. The variation of signal quality with respect to user velocity is observed using Rayleigh and Rician fading models.

Improvement of Position Accuracy with GAGAN and the Impact of Scintillation on GNSS  [PDF]
Surendra Sunda, B. M. Vyas, S. V. Satish, K. S. Parikh
Positioning (POS) , 2013, DOI: 10.4236/pos.2013.44028

GAGAN is an Indian implementation of Satellite Based Augmentation System (SBAS), developed jointly by Airports Authority of India (AAI) and Indian Space Research Organisation (ISRO). It is in final operational phase with all the required ground and space segments ready. With the availability of GAGAN signal-in-space (SIS), the improvement in position solution is investigated using the two collocated dual frequency GPS receivers. One of the receivers was configured as SBAS receiver and the other was kept as GPS stand-alone receiver. It is found that accuracy in position improved significantly in SBAS receiver due to GAGAN correction. The impact of scintillation on GNSS was also investigated in terms of position degradation and loss of lock of the satellite signals. The manyfold effects of scintillation on GPS and SBAS are discussed in detail. The results indicate ~15% reduction in number of measurements due to loss of lock during severe scintillation.

Integrity Monitoring in Navigation Systems: Fault Detection and Exclusion RAIM Algorithm Implementation  [PDF]
Alban Rakipi, Bexhet Kamo, Shkelzen Cakaj, Vladi Kolici, Algenti Lala, Ilir Shinko
Journal of Computer and Communications (JCC) , 2015, DOI: 10.4236/jcc.2015.36004
Abstract: The use of GPS is becoming increasingly popular for real-time navigation systems. To ensure that satellite failures are detected and excluded at the receiver is of high importance for the integrity of the satellite navigation system. The focus of this paper is to implement a fault detection and exclusion algorithm in a software GPS receiver in order to provide timely warnings to the user when it is not advisable to use the GPS system for navigation. The GPS system currently provides some basic integrity information to users via the navigation message, but it is not timely enough for safety-critical applications. RAIM is a means of providing integrity with the capability of detecting when a satellite failure or a measurement error has occurred. It is the simplest and most cost effective technique for integrity monitoring. After applying the iterative fault detection and the exclusion algorithm, a significant improvement in positioning accuracy is achieved.
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