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1
Banerjee, P., D. Becker, K. H. Thiel e P. Hartl. "Timing experiment with geodetic GPS receiver". IEEE Transactions on Instrumentation and Measurement 43, n. 5 (1994): 700–705. http://dx.doi.org/10.1109/19.328899.
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Hassanien, Jasmien. "Multi-GNSS Software Receiver Design Optimization for Accuracy Improvement". International Journal for Research in Applied Science and Engineering Technology 9, n. 9 (30 settembre 2021): 1467–76. http://dx.doi.org/10.22214/ijraset.2021.38190.
Testo completoAbstract (sommario):
Abstract: Recently, tremendous research has been conducted on Global navigation satellite systems (GNSS) software receivers to better serve the current challenging environments that suffers from multipath fading. Therefore, the development of GNSS receivers has seen a new rush toward a multi-GNSS as a solution for fading problems. In this paper, a multi-GNSS software receiver is designed, optimized, and its performance is presented. The implemented software receiver covers three different signals from two GNSS constellations, namely GPS L1, GPS L2, and Galileo E1. In this paper. the fundamentals of stages of GNSS signal reception (acquisition, tracking, and navigation) are discussed where each stage is customized and optimized for each considered signal and the stage of mutli-GNSS data combination is optimized afterword. The performance of the optimized multi-GNSS software receiver is examined under different combination scenarios where the Least-Square Estimation (LSE) method using precise positioning (PP) algorithms is adopted. Results showed that using multi-GNSS receiver enhances the accuracy of Position, Velocity, and Timing (PVT) solution. Keywords: GNSS, PVT, GPS, Galileo, and accuracy
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MOSAVI, M. R. "GPS RECEIVERS TIMING DATA PROCESSING USING NEURAL NETWORKS: OPTIMAL ESTIMATION AND ERRORS MODELING". International Journal of Neural Systems 17, n. 05 (ottobre 2007): 383–93. http://dx.doi.org/10.1142/s0129065707001226.
Testo completoAbstract (sommario):
The Global Positioning System (GPS) is a network of satellites, whose original purpose was to provide accurate navigation, guidance, and time transfer to military users. The past decade has also seen rapid concurrent growth in civilian GPS applications, including farming, mining, surveying, marine, and outdoor recreation. One of the most significant of these civilian applications is commercial aviation. A stand-alone civilian user enjoys an accuracy of 100 meters and 300 nanoseconds, 25 meters and 200 nanoseconds, before and after Selective Availability (SA) was turned off. In some applications, high accuracy is required. In this paper, five Neural Networks (NNs) are proposed for acceptable noise reduction of GPS receivers timing data. The paper uses from an actual data collection for evaluating the performance of the methods. An experimental test setup is designed and implemented for this purpose. The obtained experimental results from a Coarse Acquisition (C/A)-code single-frequency GPS receiver strongly support the potential of methods to give high accurate timing. Quality of the obtained results is very good, so that GPS timing RMS error reduce to less than 120 and 40 nanoseconds, with and without SA.
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Straubmeier, Christian, e Gottfried Kanbach. "OPTIMA An Optical Pulsar Timing Analyser". International Astronomical Union Colloquium 177 (2000): 311–12. http://dx.doi.org/10.1017/s0252921100059844.
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AbstractOPTIMA is a small and mobile highspeed photometer which is primarily intended for the observation of young high energy pulsars at optical wavelengths. The detector system consists of a fiber fed photon counter based on avalanche photodiodes, a GPS timing receiver and an integrating CCD camera to ensure the correct positioning of the targeted object. In January 1999, OPTIMA proved its functionality by measuring the lightcurve of the Crab pulsar.
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Munghemezulu, C., L. Combrinck e O. J. Botai. "A case study of the application of GPS to lunar laser ranging timing systems". Journal of Applied Geodesy 12, n. 4 (25 ottobre 2018): 279–87. http://dx.doi.org/10.1515/jag-2018-0006.
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Abstract The Hartebeesthoek Radio Astronomy Observatory is currently building a Lunar Laser Ranging station. This geodetic technique requires a good timing system to measure a round trip of laser photons from the telescope to the Moon and back to the telescope. We test the newly acquired timing system using examples of the Global Positioning System applications. Data in Receiver Independent Exchange Format was processed using GAMIT/GLOBK software. The results were compared against those derived from the Global Positioning System receivers that were integrated with a frequency standard from a hydrogen maser and a standard internal quartz. The results indicate that (i) the rubidium clock operates optimally and the clock drifted to within error margins of sub-centimetre level during the period of 2.5 seconds, (ii) the selected site for the permanent installation of the timing antenna has minimal multipath effect and (iii) we observed no improvement in Global Positioning System products derived from receivers that were integrated with different frequency standards.
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Pitchumani, S. Naveen, S. Arun Sundar, T. Srinivasan e S. Savithri. "Mathematical Modelling of Indian Regional Navigation Satellite System Receiver". Defence Science Journal 67, n. 4 (30 giugno 2017): 443. http://dx.doi.org/10.14429/dsj.67.11547.
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<p class="p1">At present the armoured fighting vehicles are equipped with either global positioning system (GPS) receivers or integrated inertial navigation system (INS)/GPS navigation systems. During hostile situations, the denial/degradation of the GPS satellite signals may happen. This results in the requirement of an indigenous satellite based navigation system. Indian Space Research Organisation has developed an indigenous Indian regional navigation satellite system (IRNSS), with a seven satellite constellation to provide independent position, navigation and timing services over India and its neighbouring regions. In this paper, the development of IRNSS receiver using MATLAB as per IRNSS signal in space interface control document for standard positioning service is discussed. A method for faster IRNSS signal acquisition in frequency domain and delay locked loop code tracking for the acquired satellite signals are used. Models for navigation message decoding and pseudo range/user position calculations are developed using the algorithms provided in IRNSS ICD.</p>
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Spaans, Jac A. "GPS: The Holy Grail?" Journal of Navigation 53, n. 2 (maggio 2000): 293–97. http://dx.doi.org/10.1017/s0373463300008742.
Testo completoAbstract (sommario):
This paper was first presented at a workshop arranged by the Netherlands Institute of Navigation on 5 November 1999 at the Delft University of Technology, The Netherlands.The development and introduction of GPS in the early Eighties has led to an exponential growth in military and civilian applications. Worldwide, GPS is becoming a cornerstone in applications of transport, (offshore) survey, (precision) agriculture, network timing, military operations and many other applications. And yet, for a number of applications, GPS as sole-means or augmented – has some deficiencies, and its performance does not satisfy the user's requirements. Some of these deficiencies will be discussed in this paper. A number of maritime operations will be mentioned where (D)GPS as sole-means is considered by the author as unsafe navigational practice. Development and implementation of integrated navigation receivers using multiple navigation-signal sensors ((D)Galileo, (D)GPS, Eurofix, DR) using receiver autonomous integrity monitoring (RAIM) could solve the majority of the deficiencies of these systems in their stand-alone state.
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Doroshenko, O. V., Yu P. Ilyasov e V. V. Oreshko. "Pulsar timing at Kalyazin (Russia)". International Astronomical Union Colloquium 177 (2000): 57–60. http://dx.doi.org/10.1017/s0252921100059017.
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AbstractRegular timing observations of millisecond and binary pulsars are made with the 64-m radio telescope at Kalyazin (Russia). Filterbank 160-channel receiver is used for observations at 0.6 GHz in two circular orthogonal polarization. Precise local time service (based upon a rubidium standards and hydrogen maser) is used for measurements of Times-of-Arrival (TOA) from radio pulsars. A local time scale is compared by GPS and TV-systems with the basic AT-scales (UTC(USNO) and UTC(SU)) within an accuracy about 50nsper day. Recently the second 1.4 GHz receiver (250 kHz × 64 channels) was constructed and installed at Kalyazin radio telescope. There is a possibility to combine a part of the 1.4 GHz back-end with the 2.2 GHz front-end to produce timing observations at three frequencies simultaneously. We present a results of precise timing observations conducted by the Kalyazin pulsar system. Most of data were obtained at 0.6 GHz in 1997–1999. The data will be used for valuable applications in fundamental metrology, interstellar medium, general relativity and pulsar physics itself.
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Valk, M., H. H. G. Savenije, C. C. J. M. Tiberius e W. M. J. Luxemburg. "Determining slack tide with a GPS receiver on an anchored buoy". Hydrology and Earth System Sciences 18, n. 7 (11 luglio 2014): 2599–613. http://dx.doi.org/10.5194/hess-18-2599-2014.
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Abstract. In this paper we present a novel method to determine the time of occurrence of tidal slack with a GPS receiver mounted on an anchored buoy commonly used to delineate shipping lanes in estuaries and tidal channels. Slack tide occurs when the tide changes direction from ebb to flood flow or from flood to ebb. The determination of this point in time is not only useful for shipping and salvaging, it is also important information for calibrating tidal models, for determining the maximum salt intrusion and for the further refinement of the theory on tidal propagation. The accuracy of the timing is well within 10 min and the method – able to operate in real time – is relatively cheap and easy to implement on a permanent basis or in short field campaigns.
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Valk, M., H. H. G. Savenije, C. C. J. M. Tiberius e W. M. J. Luxemburg. "Determining slack tide with a GPS receiver on an anchored buoy". Hydrology and Earth System Sciences Discussions 10, n. 11 (14 novembre 2013): 13743–82. http://dx.doi.org/10.5194/hessd-10-13743-2013.
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Abstract. In this paper we present a novel method to determine the time of occurrence of tidal slack with a GPS receiver mounted on an anchored buoy commonly used to delineate shipping lanes in estuaries and tidal channels. Slack tide occurs when the tide changes direction from ebb to flood flow, or from flood to ebb. The determination of this point in time is not only useful for shipping and salvaging, it is also important information for calibrating tidal models, for determining the maximum salt intrusion and for the further refinement of the theory on tidal propagation. The accuracy of the timing is well within 10 min and the method – able to operate in real-time – is relatively cheap and easy to implement on a permanent basis or in short field campaigns.
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Tsai, Yung-Fu, Wen-Hao Yeh, Jyh-Ching Juang, Dian-Syuan Yang e Chen-Tsung Lin. "From GPS Receiver to GNSS Reflectometry Payload Development for the Triton Satellite Mission". Remote Sensing 13, n. 5 (5 marzo 2021): 999. http://dx.doi.org/10.3390/rs13050999.
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The global positioning system (GPS) receiver has been one of the most important navigation systems for more than two decades. Although the GPS system was originally designed for near-Earth navigation, currently it is widely used in highly dynamic environments (such as low Earth orbit (LEO)). A space-capable GPS receiver (GPSR) is capable of providing timing and navigation information for spacecraft to determine the orbit and synchronize the onboard timing; therefore, it is one of the essential components of modern spacecraft. However, a space-grade GPSR is technology-sensitive and under export control. In order to overcome export control, the National Space Organization (NSPO) in Taiwan completed the development of a self-reliant space-grade GPSR in 2014. The NSPO GPSR, built in-house, has passed its qualification tests and is ready to fly onboard the Triton satellite. In addition to providing navigation, the GPS/global navigation satellite system (GNSS) is facilitated to many remote sensing missions, such as GNSS radio occultation (GNSS-RO) and GNSS reflectometry (GNSS-R). Based on the design of the NSPO GPSR, the NSPO is actively engaged in the development of the Triton program (a GNSS reflectometry mission). In a GNSS-R mission, the reflected signals are processed to form delay Doppler maps (DDMs) so that various properties (including ocean surface roughness, vegetation, soil moisture, and so on) can be retrieved. This paper describes not only the development of the NSPO GPSR but also the design, development, and special features of the Triton’s GNSS-R mission. Moreover, in order to verify the NSPO GNSS-R receiver, ground/flight tests are deemed essential. Then, data analyses of the airborne GNSS-R tests are presented in this paper.
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Banerjee, P., Suman, A. K. Suri, Arundhati Chatterjee e Anindya Bose. "A study on the potentiality of the GPS timing receiver for real time applications". Measurement Science and Technology 18, n. 12 (1 novembre 2007): 3811–15. http://dx.doi.org/10.1088/0957-0233/18/12/016.
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Yang, Qiong, Yi Zhang, Chengkai Tang e Jie Lian. "A Combined Antijamming and Antispoofing Algorithm for GPS Arrays". International Journal of Antennas and Propagation 2019 (15 aprile 2019): 1–9. http://dx.doi.org/10.1155/2019/8012569.
Testo completoAbstract (sommario):
The Global Positioning System (GPS), with its accurate positioning and timing information, has become a commonly used navigation instrument for many applications. However, it is susceptible to intentional interference such as jamming and spoofing. The conventional antijamming GPS receiver fails to work in a combined jamming and spoofing attack scenario. To solve the problem, a combined antijamming and antispoofing algorithm for a GPS receiver based on an antenna array is proposed. In this method, the jamming is eliminated by subspace projection, and then a compressed sensing framework is adopted to obtain the direction of arrival (DOA) of the despreading satellite navigation signal and detect the spoofing signal. According to the DOA of the authentic and spoofing signals, the receiver uses adaptive multibeamforming to concurrently achieve the undistorted reception of the authentic satellite signal and the suppression of the spoofing. We analyse three aspects of algorithmic performance: the antenna array direction diagram, the spoofing detection and the acquisition results. The simulation results and their analysis preliminarily show that the proposed method can detect and suppress GPS jamming and spoofing effectively.
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Boehmer, Tyler, e Sven Bilén. "Low-Power GPS-Disciplined Oscillator Module for Distributed Wireless Sensor Nodes". Electronics 10, n. 6 (18 marzo 2021): 716. http://dx.doi.org/10.3390/electronics10060716.
Testo completoAbstract (sommario):
Many sensor systems, such as distributed wireless sensor arrays, require high-accuracy timing while maintaining low power consumption. Although the capabilities of chip-scale atomic clocks have advanced significantly, their cost continues to be prohibitive for many applications. GPS signals are commonly used to discipline local oscillators in order to inherit the long-term stability of GPS timing; however, commercially available GPS-disciplined oscillators typically use temperature-controlled oscillators and take an extended period of time to reach their stated accuracy, resulting in a large power consumption, usually over a watt. This has subsequently limited their adoption in low-power applications. Modern temperature-compensated crystal oscillators now have stabilities that enable the possibility of duty cycling a GPS receiver and intermittently correcting the oscillator for drift. Based on this principle, a design for a GPS-disciplined oscillator is presented that achieves an accuracy of 5 μs rms in its operational environment, while consuming only 45 mW of average power. The circuit is implemented in a system called geoPebble, which uses a large grid of wireless sensors to perform glacial reflectometry.
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Sun, Chun-I., Jung-Tang Huang, Shih-Chi Weng e Meng-Fan Chien. "City Marathon Active Timing System Using Bluetooth Low Energy Technology". Electronics 8, n. 2 (22 febbraio 2019): 252. http://dx.doi.org/10.3390/electronics8020252.
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This study proposes and implements city marathon timing technology using Bluetooth Low-Energy (BLE) communication technology. This study also performs a prevalidation of the athletes’ physiological sensory data that is sent out by the same timing system—the BLE active communication technology. In order to verify the timing and positioning technology, 621 K records of static measurement of the Received Signal Strength Indicator (RSSI) were first collected. The trend of the RSSI between the location and the BLE Receiver when the runners carried a BLE Tag was analyzed. Then, the difference between the runners’ passing timestamp and the runners’ actual passing time when the runners carried a BLE Tag and ran past the BLE Receivers was dynamically recorded and analyzed. Additionally, the timing sensing rate when multiple runners ran past the BLE Receivers was verified. In order to confirm the accuracy of the time synchronization in the remote timing device, the timing error, synced by the Network Time Protocol (NTP), was analyzed. A global positioning system (GPS) signal was used to enhance the time synchronization’s accuracy. Additionally, the timing devices were separated by 15 km, and it was verified that they remained within the timing error range of 1 ms. The BLE communication technology has at least one more battery requirement than traditional passive radio frequency identification (RFID) timing devices. Therefore, the experiment also verified that the BLE Tag of this system can continue to operate for at least 48 h under normal conditions. Based on the above experimental results, it is estimated that the system can provide a timing error of under ±156 ms for each athlete. The system can also meet the scale of the biggest international city marathon event.
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Mosavi, M. R., H. Nabavi e A. Nakhaei. "Neural Technologies for Precise Timing in Electric Power Systems with a Single-Frequency GPS Receiver". Wireless Personal Communications 75, n. 2 (11 settembre 2013): 925–41. http://dx.doi.org/10.1007/s11277-013-1398-z.
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PANAIT, Alexandru Marius. "Improved Timing for better performance of distributed data acquisition systems". INCAS BULLETIN 13, n. 1 (5 marzo 2021): 113–22. http://dx.doi.org/10.13111/2066-8201.2021.13.1.12.
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Distributed data acquisition systems are the norm in the great majority of industry branches where the process to be controlled covers a physically large and often fragmented area. Many local smaller data acquisition modules are interfaced and pass raw or pre-processed data along with the timing signals. These timing signals are a vital part of data acquisition as oftentimes raw data is processed as time series and correlations are made based on timestamps. This paper presents a study for implementation of a cost-effective high precision time base (reference clock) using a GPS receiver as a primary time source and a local high precision real time clock as a secondary oscillator.
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Grant, Alan, Paul Williams, Nick Ward e Sally Basker. "GPS Jamming and the Impact on Maritime Navigation". Journal of Navigation 62, n. 2 (12 marzo 2009): 173–87. http://dx.doi.org/10.1017/s0373463308005213.
Testo completoAbstract (sommario):
Versions of this paper were first presented at the Royal Institute of Navigation GNSS Vulnerabilities and Solutions Conference held at Baska, Croatia in September 2008 and the Royal Institute of Navigation NAV 08 Conference held at Church House, Westminster, London in October 2008.The US Global Positioning System (GPS) is currently the primary source of Position, Navigation and Timing (PNT) information in maritime applications, whether stand-alone or augmented with additional systems. This situation will continue in the future with GPS, possibly together with other Global Navigation Satellite Systems (GNSS) e.g. Galileo, being the core PNT technology for e-Navigation – the future digital maritime architecture. GPS signals, measured at the surface on the Earth, are very weak. As such, the system is vulnerable to unintentional interference and jamming, resulting in possible denial of service over large geographical areas. The result of such interference could be the complete failure of the mariner's GPS receiver or, possibly worse, the presentation to the mariner of hazardously misleading information (HMI) for navigation and situational awareness, depending on how the GPS receiver reacts to the jamming incident. Recognising this, the General Lighthouse Authorities of the United Kingdom and Ireland (GLA), in collaboration with the UK Ministry of Defence (MOD) Defence Science and Technology Laboratory (DSTL), have conducted a series of sea-trials with the aim of identifying the full effects of GPS jamming on safe navigation at sea.This paper presents the key findings of these trials and provides important information on the effect of GPS denial. The GLA are playing a pivotal role in the establishment of eLoran as an independent source of PNT, taking advantage of eLoran's complementary nature, having dissimilar failure modes to GPS and the future GNSS. This paper provides information on the performance of an eLoran receiver in an area of GPS service denial. The paper presents the rationale for the work, details the system architecture employed, the data gathering efforts and finally the data analysis procedures, results and conclusions.
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Kožović, Dejan, e Dragan Đurđević. "Spoofing in aviation: Security threats on GPS and ADS-B systems". Vojnotehnicki glasnik 69, n. 2 (2021): 461–85. http://dx.doi.org/10.5937/vojtehg69-30119.
Testo completoAbstract (sommario):
Introduction/purpose: The paper provides a review of recent research in the field of GPS and ADS-B spoofing. Systems that rely on satellite positioning technology can be targeted by spoofing in order to generate incorrect positioning/timing, which is accomplished by inserting false signals into the "victim's" receiver. Attackers try to insert false positioning information into systems that, for example, provide navigation of airplanes or drones for the purpose of hijacking or distracting security/safety in airspace surveillance. New concepts of navigation and ATC will thus be necessary. Methods: Using a scientific approach, the paper gives an evaluation of GPS and ADS-B spoofing/antispoofing and how spoofing affects the cyber security of aviation systems. Results: Based on the methodological analysis used, the importance of studying spoofing/anti-spoofing in aviation is shown. Conclusion: Although spoofing in aviation is only a potential threat, its technical feasibility is realistic and its potential is considerable; it becomes more flexible and cheaper due to very rapid advancement of SDR technologies. The real risk, in the time to come, are potential spoofing attacks that could occur from the air, using drones. However, aircraft systems are not exposed to spoofing without any defense; receivers can detect it by applying various anti-spufing techniques. Also, pilots are able to detect and solve problems at every stage of the flight. However, due to a possibility of more sophisticated spoofing attacks, international organizations such as ICAO are proactively working to increase GPS and ADS-B systems robustness on spoofing.
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Thongtan, Thayathip, Pawit Tirawanichakul e Chalermchon Satirapod. "Precise Receiver Clock Offset Estimations According to Each Global Navigation Satellite Systems (GNSS) Timescales". Artificial Satellites 52, n. 4 (1 dicembre 2017): 99–108. http://dx.doi.org/10.1515/arsa-2017-0009.
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Abstract Each GNSS constellation operates its own system times; namely, GPS system time (GPST), GLONASS system time (GLONASST), BeiDou system time (BDT) and Galileo system time (GST). They could be traced back to Coordinated Universal Time (UTC) scale and are aligned to GPST. This paper estimates the receiver clock offsets to three timescales: GPST, GLONASST and BDT. The two measurement scenarios use two identical multi-GNSS geodetic receivers connected to the same geodetic antenna through a splitter. One receiver is driven by its internal oscillators and another receiver is connected to the external frequency oscillators, caesium frequency standard, kept as the Thailand standard time scale at the National Institute of Metrology (Thailand) called UTC(NIMT). The three weeks data are observed at 30 seconds sample rate. The receiver clock offsets with respected to the three system time are estimated and analysed through the geodetic technique of static Precise Point Positioning (PPP) using a data processing software developed by Wuhan University - Positioning And Navigation Data Analyst (PANDA) software. The estimated receiver clock offsets are around 32, 33 and 18 nanoseconds from GPST, GLONASST and BDT respectively. This experiment is initially stated that each timescale is inter-operated with GPST and further measurements on receiver internal delay has to be determined for clock comparisons especially the high accuracy clock at timing laboratories.
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Elghamrawy, Haidy, Malek Karaim, Mohamed Tamazin e Aboelmaged Noureldin. "Experimental Evaluation of the Impact of Different Types of Jamming Signals on Commercial GNSS Receivers". Applied Sciences 10, n. 12 (20 giugno 2020): 4240. http://dx.doi.org/10.3390/app10124240.
Testo completoAbstract (sommario):
The received global navigation satellite system (GNSS) signal has a very low power due to traveling a very long distance and to the nature of the signal’s propagation medium. Thus, GNSS signals are easily susceptible to signal interference. Signal interference can cause severe degradation or interruption in GNSS position, navigation, and timing (PNT) services which could be very critical, especially in safety-critical applications. The objective of this paper is to evaluate the impact of the presence of jamming signals on a high-end GNSS receiver and investigate the benefits of using a multi-constellation system under such circumstances. Several jamming signals are considered in this research, including narrowband and wideband signals that are located on GPS L1 or GLONASS L1 frequency bands. Quasi-real dynamic trajectories are generated using the Spirent™ GSS6700 GNSS signal simulator combined with an interference signal generator through a Spirent™ GSS8366 unit. The performance evaluation was carried out using several evaluation metrics, including signal power degradation, navigation solution availability, dilution of precision (DOP), and positioning accuracy. The multi-constellation system presented better performance over the global positioning system (GPS)-only constellation in most cases. Moreover, jamming the GPS band caused more critical effects than jamming the GLONASS band.
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Rasson, Jean L., Olivier Hendrickx e Jean-Luc Marin. "Semiautomatic sun shots with the WIDIF DIflux". Geoscientific Instrumentation, Methods and Data Systems 6, n. 2 (13 luglio 2017): 257–61. http://dx.doi.org/10.5194/gi-6-257-2017.
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Abstract. The determination of magnetic declination angle entails finding two directions: geographic north and magnetic north. This paper deals with the former. The known way to do it by using the sun's calculable orientation in the sky is improved by using a device based on a WIDIF DIflux theodolite and split photocells positioned on its telescope ocular. Given the WIDIF accurate timing and location provided by the onboard GPS receiver, an astronomical computation can be effected to accurately and quickly determine the sun's azimuth and an auxiliary mark's azimuth. The precise sun's crossing of the split photocell, amplified by the telescope's magnification, allows azimuth accuracies of a few seconds of arc.
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Zhao, Shuang, Jun Liu e Yansong Li. "Online Calibration Method for Current Sensors Based on GPS". Energies 12, n. 10 (20 maggio 2019): 1923. http://dx.doi.org/10.3390/en12101923.
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At present, most sensor calibration methods are off-line calibration, which not only makes them time-consuming and laborious, but also causes considerable economic losses. Therefore, in this study, an online calibration method of current sensors is proposed to address the abovementioned issues. The principle and framework of online calibration are introduced. One of the calibration indexes is angular difference. In order to accurately verify it, data acquisition must be precisely synchronized. Therefore, a precise synchronous acquisition system based on GPS timing is proposed. The influence of ionosphere on the accuracy of GPS signal is analyzed and a new method for measuring the inherent delay of GPS receiver is proposed. The synchronous acquisition performance of the system is verified by inter-channel synchronization experiment, and the results show that the synchronization of the system is accurate. Lastly, we apply our online calibration method to the current sensor; the experimental results show that the angular difference and ratio difference meet the requirements of the national standard and the accuracy of the online calibration system can be achieved to 0.2 class, demonstrating the effectiveness of the proposed online calibration method.
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Ge, Yulong, Peipei Dai, Weijin Qin, Xuhai Yang, Feng Zhou, Shengli Wang e Xingwang Zhao. "Performance of Multi-GNSS Precise Point Positioning Time and Frequency Transfer with Clock Modeling". Remote Sensing 11, n. 3 (10 febbraio 2019): 347. http://dx.doi.org/10.3390/rs11030347.
Testo completoAbstract (sommario):
Thanks to the international GNSS service (IGS), which has provided multi-GNSS precise products, multi-GNSS precise point positioning (PPP) time and frequency transfer has of great interest in the timing community. Currently, multi-GNSS PPP time transfer is not investigated with different precise products. In addition, the correlation of the receiver clock offsets between adjacent epochs has not been studied in multi-GNSS PPP. In this work, multi-GNSS PPP time and frequency with different precise products is first compared in detail. A receiver clock offset model, considering the correlation of the receiver clock offsets between adjacent epochs using an a priori value, is then employed to improve multi-GNSS PPP time and frequency (scheme2). Our numerical analysis clarify how the approach performs for multi-GNSS PPP time and frequency transfer. Based on two commonly used multi-GNSS products and six GNSS stations, three conclusions are obtained straightforwardly. First, the GPS-only, Galileo-only, and multi-GNSS PPP solutions show similar performances using GBM and COD products, while BDS-only PPP using GBM products is better than that using COD products. Second, multi-GNSS time transfer outperforms single GNSS by increasing the number of available satellites and improving the time dilution of precision. For single-system and multi-GNSS PPP with GBM products, the maximum improvement in root mean square (RMS) values for multi-GNSS solutions are up to 7.4%, 94.0%, and 57.3% compared to GPS-only, BDS-only, and Galileo-only solutions, respectively. For stability, the maximum improvement of multi-GNSS is 20.3%, 84%, and 45.4% compared to GPS-only, BDS-only and Galileo-only solutions. Third, our approach contains less noise compared to the solutions with the white noise model, both for the single-system model and the multi-GNSS model. The RMS values of our approach are improved by 37.8–91.9%, 10.5–65.8%, 2.7–43.1%, and 26.6–86.0% for GPS-only, BDS-only, Galileo-only, and multi-GNSS solutions. For frequency stability, the improvement of scheme2 ranges from 0.2 to 51.6%, from 3 to 80.0%, from 0.2 to 70.8%, and from 0.1 to 51.5% for GPS-only, BDS-only, Galileo-only, and multi-GNSS PPP solutions compared to the solutions with the white noise model in the Eurasia links.
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Zhang, Baocheng, Yunbin Yuan e Yanju Chai. "QIF-based GPS Long-baseline Ambiguity Resolution with the Aid of Atmospheric Delays Determined by PPP". Journal of Navigation 69, n. 6 (27 maggio 2016): 1278–92. http://dx.doi.org/10.1017/s037346331600028x.
Testo completoAbstract (sommario):
The Global Positioning System (GPS) long-baseline set up has been widely employed to generate high-accuracy positioning, timing and atmospheric information. Bernese GPS software adopts two appropriate strategies for long-baseline Integer Ambiguity Resolution (IAR): Quasi Ionosphere-Free (QIF) and Wide-lane/Narrow-lane (WN). With the goal of reasonably shortening the time required for long-baseline IAR, we propose the Precise Point Positioning (PPP) method for estimating, on a per receiver basis, the Zenith Tropospheric Delays (ZTDs) and the Slant Ionospheric Delays (SIDs) from zero-differenced, uncombined GPS observables. We then reformulate these PPP-derived ZTDs and SIDs into two types of atmospheric constraints with proper uncertainties that could be readily assimilated into the process of IAR with the QIF. Our numerical tests based on five independent long-baselines (>1,000 kilometres) suggest that the empirical precision of PPP-derived ZTDs (SIDs) is always better than 2 (10) centimetres. The modified QIF would be able to correctly resolve at least 98% and 88% of the wide- and narrow-lane ambiguities for all the long-baselines relying on the very simple integer rounding method. However, under the same condition, the WN can only get the correct integers of 76·6% wide-lane ambiguities and 55·2% narrow-lane ones.
26
Isik, Oguz Kagan, Juhyeon Hong, Ivan Petrunin e Antonios Tsourdos. "Integrity Analysis for GPS-Based Navigation of UAVs in Urban Environment". Robotics 9, n. 3 (25 agosto 2020): 66. http://dx.doi.org/10.3390/robotics9030066.
Testo completoAbstract (sommario):
The increasing use of Unmanned Aerial Vehicles (UAVs) in safety-critical missions in both civilian and military areas demands accurate and reliable navigation, where one of the key sources of navigation information is presented by Global Navigation Satellite Systems (GNSS). In challenging conditions, for example, in urban areas, the accuracy of GNSS-based navigation may degrade significantly due to user-satellite geometry and obscuration issues without being noticed by the user. Therefore, considering the essentially dynamic rate of change in this type of environment, integrity monitoring is of critical importance for understanding the level of trust we have in positioning and timing data. In this paper, the dilution of precision (DOP) coefficients under nominal and challenging conditions were investigated for the purpose of integrity monitoring in urban environments. By analyzing positioning information in a simulated urban environment using a software-based GNSS receiver, the integrity monitoring approach based on joint consideration of GNSS observables and environmental parameters has been proposed. It was shown that DOP coefficients, when considered together with a number of visible satellites and cut-off elevations specific to the urban environment carry valuable integrity information that is difficult to get using existing integrity monitoring approaches. This has allowed generating indirect integrity measures based on cut-off elevation and satellite visibility that can be used for UAV path planning and guidance in urban environments.
27
Liu, Lichao, Denys Grombacher, Esben Auken e Jakob Juul Larsen. "Apsu: a wireless multichannel receiver system for surface nuclear magnetic resonance groundwater investigations". Geoscientific Instrumentation, Methods and Data Systems 8, n. 1 (22 gennaio 2019): 1–11. http://dx.doi.org/10.5194/gi-8-1-2019.
Testo completoAbstract (sommario):
Abstract. Surface nuclear magnetic resonance (surface NMR) has the potential to be an important geophysical method for groundwater investigations, but the technique suffers from a poor signal-to-noise ratio (SNR) and long measurement times. We present a new wireless, multichannel surface-NMR receiver system (called Apsu) designed to improve field deployability and minimize instrument dead time. It is a distributed wireless system consisting of a central unit and independently operated data acquisition boxes each with three channels that measure either the NMR signal or noise for reference noise cancellation. Communication between the central unit and the data acquisition boxes is done through long-distance Wi-Fi and recordings are retrieved in real time. The receiver system employs differential coils with low-noise preamplifiers and high-resolution wide dynamic-range acquisition boards. Each channel contains multistage amplifiers, short settling-time filters, and two 24 bit analog-to-digital converters in dual-gain mode sampling at 31.25 kHz. The system timing is controlled by GPS clock, and sample jitter between channels is less than 12 ns. Separated transmitter/receiver coils and continuous acquisition allow NMR signals to be measured with zero instrument dead time. In processed data, analog and digital filters cause an effective dead time of 5.8 ms including excitation current decay. Synchronization with an independently operated transmitter system is done with a current probe monitoring the NMR excitation pulses. The noise density measured in a shorted-input test is 1.8 nV Hz-1/2. We verify the accuracy of the receiver system with measurements of a magnetic dipole source and by comparing our NMR data with data obtained using an existing commercial instrument. The applicability of the system for reference noise cancellation is validated with field data.
28
Liu, Li, Xingqun Zhan, Wei Liu e Mancang Niu. "Assessment of Radio Frequency Compatibility between Compass Phase II and Other GNSSs". Journal of Navigation 64, S1 (14 ottobre 2011): S55—S72. http://dx.doi.org/10.1017/s0373463311000439.
Testo completoAbstract (sommario):
As the technology of global navigation satellite system (GNSS) and augmentation systems are evolving rapidly, compatibility becomes a critical issue for system providers. By April 2011, China had successfully launched eight satellites of the Compass phase II (CP II) navigation system, which will provide positioning, navigation, timing and communication services to the Asia-Pacific region by the year 2012. Due to the limitations of available radio frequency bandwidths, it is important to assess the compatibility and to design signals based on the compatibility within these limited radio frequency bandwidths. This paper presents a modified compatibility assessment methodology, derived from the traditional methodologies that are based on the spectral separation coefficient (SSC) and the effective carrier-power-to-noise density ratio. The modified methodology takes into account additional factors including the Doppler offset, code tracking loop, and band-limiting, sampling and quantisation (BSQ) of the GNSS receiver. In the simulation section, the comprehensive compatibility assessment between CP II and other GNSSs, such as GPS, Galileo, Wide Area Augmentation System (WAAS) and European Geostationary Navigation Overlay Service (EGNOS) on L1 Band are carried out and presented with some new results. Simulation results reveal that CP II does not cause serious interference on GPS, Galileo, WAAS and EGNOS as the interference level is below the 0·25 dB threshold recommended by ITU.
29
Shang, Xinlei, Chuandong Jiang, Zhongjun Ma e Shengwu Qin. "Combined System of Magnetic Resonance Sounding and Time-Domain Electromagnetic Method for Water-Induced Disaster Detection in Tunnels". Sensors 18, n. 10 (17 ottobre 2018): 3508. http://dx.doi.org/10.3390/s18103508.
Testo completoAbstract (sommario):
Underground construction projects such as tunnel construction are at high risk of water-induced disasters. Because this type of disaster poses a serious threat to worker safety and productivity, instruments and methods that can accurately detect the water source are critical. In this study, a water detection instrument that combines Magnetic Resonance Sounding (MRS) and Time-domain Electromagnetic Method (TEM) techniques to yield a joint MRS-TEM interpretation method was developed for narrow underground spaces such as tunnels. Joint modules including a transmitter and receiver were developed based on a dual-purpose and modular design concept to minimize the size and weight of the instrument and consequently facilitate transportation and measurement. Additionally, wireless control and communication technology was implemented to enable inter-module cooperation and simplify instrument wiring, and wireless synchronization was accomplished by implementing a Global Positioning System (GPS)-based timing scheme. The effectiveness and reliability of the instrument were verified via indoor laboratory tests and field measurement signal tests. Furthermore, the practicability of the combined instrument and its interpretation method was verified via a field case performed in a tunnel in Hubei, China.
30
Yassi, Nabeel. "Trends in onshore seismic data acquisition: a case study on cable-free nodal systems". APPEA Journal 56, n. 2 (2016): 601. http://dx.doi.org/10.1071/aj15107.
Testo completoAbstract (sommario):
The desire to conduct onshore seismic surveys without cables has been an elusive dream since the dawn of seismic exploration. Since the late 1970s, seismic surveys were conducted with cabled multi-channels acquisition systems. As the number of channels steadily grew, a fundamental restriction appeared with hundreds of kilometres of line cables dragged on the ground. Seismic surveys within rugged terrain—across rivers, steep cliffs, urban areas, and culturally and environmentally sensitive zones—were both challenging and expansive exercises. Modern technology has made different cable-free solutions practical. High-resolution analogue to digital converters are now affordable, as are GPS radios for timing and location. Microprocessors and memory are readily available for autonomous recording systems, along with a battery the size and weight of a field nodal now promising to power an acquisition unit for as long as required for normal seismic crew operations. Many successful 2D and 3D seismic data acquisition using cable-free autonomous nodal systems were attempted in the past few years; however, there remain a number of concerns with these systems. The first concern queries whether the units are working according to manufacturer specifications during the data acquisition window. The second is the limited or no real-time data quality control that inspires sceptics to use the term blind acquisition to nodal operations. The third is the traditional question of geophone array versus point receiver acquisition. Although a string of the geophone can be connected to autonomous nodes, the preference is to deploy a single or internal geophone with the nodes to maintain the proposed flexibility of cable-free recording systems. This case study elaborates on the benefits of the cable-free seismic surveys, with specific examples of 2D and 3D exploration programs conducted in Australia in the past few years. Optimisation of field crew size, field crew resources, cost implications, and footprint to the environment, wildlife and domestic livestock will be discussed. In addition, the study focuses on the data quality/data assurance and the processes implanted during data acquisition to maintain equivalent industry standards to cable recording. Emphases will also include data analysis and test results of the geophone array versus the cable-free point receiver recording.
31
Defraigne, P., W. Huang, B. Bertrand e D. Rovera. "Study of the GPS inter-frequency calibration of timing receivers". Metrologia 55, n. 1 (12 dicembre 2017): 11–19. http://dx.doi.org/10.1088/1681-7575/aa9b5b.
Testo completo
32
Pan, Xiao Shan, Zi Guan Zhou, Min Zhou e Bing Qi. "Design and Implementation of Dual-Channel and Dual-Mode Timing Module Based on Beidou & GPS". Applied Mechanics and Materials 241-244 (dicembre 2012): 2402–6. http://dx.doi.org/10.4028/www.scientific.net/amm.241-244.2402.
Testo completoAbstract (sommario):
Against the Status quo that satellite timing service in many fields of China mainly relies on the GPS system, for full use of the Beidou navigation satellite system with our own intellectual property, this paper presented a chip-level solution of dual-channel and dual-mode timing modules based on the Beidou-2 and GPS navigation system. The timing principle of Beidou navigation satellite system was first introduced, and then the hardware design of the timing module was presented with selection of highly-integrated RF chip and baseband processor chip. Furthermore, many kinds of output interfaces were designed to meet diverse service demand. By analyzing the format of the received signal, the flow chart for extracting timing information was also given. Finally, the designed timing module was tested by using the developed timing display system and test results show that the module has a better timing performance.
33
Daishido, T., N. Tanaka, S. Sudo, M. Suzuki, Y. Saito, R. Agehama, M. Adachi e N. Watanabe. "Design of (2+1+2)D FFT for Interferometric Pulsar Survey". International Astronomical Union Colloquium 160 (1996): 19–20. http://dx.doi.org/10.1017/s0252921100040914.
Testo completoAbstract (sommario):
AbstractThe Following design of a Pulsar Survey System with a Huge Interferometric Array is discussed. (1) A Huge Array of 320m × 320m with 256(= 16 × 16) spherical dishes of 20m in diameter, (2) RF is 1.4 GHz, (3) Receivers are frequency modified GPS(1.57542, 1.2276GHz) ones, (4) Phase and Delay Tracking, (5) Phase Calibration using Differential GPS(GPS signal × 2 → CW), (6) (2+1+2)D FFT /256 pixel Imaging + 256 ch Filtering + Dispersion Removal and Period finding(17M point floating 2DFFT by DSP), (8) Observing time required for the same sensitivity to Arecibo τ/τA: 0.88(Timing), 0.003(Survey).
34
Yahya, Fadi B., e Matthew A. Hathcock. "A Retrospective Review of Neonatal Sepsis among GBS-Colonized Women Undergoing Planned Cesarean Section after Labor Onset or Rupture of Membranes". Infectious Diseases in Obstetrics and Gynecology 2020 (16 gennaio 2020): 1–8. http://dx.doi.org/10.1155/2020/4365259.
Testo completoAbstract (sommario):
Background. Sepsis is a leading cause of mortality and morbidity in neonates, with group B streptococcus (GBS) remaining the most frequent pathogen isolated from term infants. Surveillance data showed that the majority of cases of early-onset GBS disease were neonates born to women who either received no or suboptimal intrapartum antibiotic prophylaxis with a notable portion of those women having a missed opportunity to receive ≥4 hours of chemoprophylaxis. Women planning delivery by cesarean section who present in labor or rupture of membranes prior to their scheduled surgery are unlikely to receive optimal GBS chemoprophylaxis and thus their neonates are at risk of having sepsis. Materials and Methods. A retrospective cohort study of women-infant dyads was extracted from the Consortium on Safe Labor dataset. Women who had an unlabored cesarean section at ≥37+0 week gestation were selected and divided into four groups based on GBS status and timing of cesarean section with respect to onset of labor or rupture of membranes. The rate of neonatal sepsis and the patterns of intrapartum antibiotic chemoprophylaxis were determined. Results. The sepsis rate (4.5%) among neonates of GBS-colonized women having their unlabored cesarean section after onset of labor or rupture of membranes was significantly higher than that in any other group in this study. In this group, 9.4% of women received chemoprophylaxis for ≥4 hours, while 31% had a missed opportunity to receive ≥4 hours of chemoprophylaxis. Conclusion. This study suggests that neonates of GBS-colonized women having a planned cesarean section after onset of labor or rupture of membranes are at increased risk of having a sepsis diagnosis. This finding suggest the need for additional studies to assess the risk of sepsis among neonates of women in this group.
35
den Ouden, M. A. G., C. H. Reijmer, V. Pohjola, R. S. W. van de Wal, J. Oerlemans e W. Boot. "Stand-alone single-frequency GPS ice velocity observations on Nordenskiöldbreen, Svalbard". Cryosphere Discussions 4, n. 3 (14 luglio 2010): 981–1010. http://dx.doi.org/10.5194/tcd-4-981-2010.
Testo completoAbstract (sommario):
Abstract. Precise measurements of ice-flow velocities are necessary for a proper understanding of the dynamical response of glaciers to climate change. We use stand-alone single-frequency GPS receivers for this purpose. They are designed to operate unattended for multiple years, allowing uninterrupted measurements for long periods with a reasonable temporal resolution. We present the system and illustrate its functioning using data from 9 GPS receivers deployed on Nordenskiöldbreen, Svalbard, for the period 2006–2009. The accuracy of the receivers is 1.62 m based on the standard deviation in the average location of a stationary reference station (NBRef). Both the location of NBRef and the observed flow velocities agree within one standard deviation with DGPS measurements. Periodicity in the NBRef data is explained by the atmospheric influence on the GPS signal and by the GPS satellite configuration. A (weighed) running-average on the observed locations significantly reduces the standard deviation and removes high frequency periodicities, but also reduces the temporal resolution. Results show annual average velocities varying between 40 and 55 m/yr at stations on the central flow-line. On weekly to monthly time-scales we observe a peak in the flow velocities (60 to 90 m/yr) at the beginning of July related to increased melt-rates. No significant lag is observed between the timing of the maximum speed between different stations. This is likely due to the limited temporal resolution in combination with the relatively small distance (max. ±13 km) between the stations.
36
Kerba, Marc, Ayn Sinnarajah, M. Sarah Rose, Lynn Nicholson, Barbara Wheler e Bert Enns. "End-of-life cancer care: Health service delivery in the last 12 months of life in Calgary, Alberta, Canada." Journal of Clinical Oncology 33, n. 29_suppl (10 ottobre 2015): 171. http://dx.doi.org/10.1200/jco.2015.33.29_suppl.171.
Testo completoAbstract (sommario):
171 Background: In Calgary, Alberta, the Calgary Zone Palliative Care Collaborative (CZPCC) undertook a study to examine the current state of cancer and palliative services and to recommend steps to address gaps in service delivery. We hypothesized that early access to palliative care services would reduce utilization of active cancer treatments and services for individuals nearing the end of life. Our study objectives were to determine the utilization and timing of acute, palliative and oncology-related services in Calgary. Methods: This retrospective study examined cancer registry and administrative data for patients > 18 years, who died in 2012. Measures of aggressive end of life care (EOL) were also collected. A combination of descriptive statistics, tests of association and multivariate regression analysis were conducted. Results: N = 1909 died of cancer in 2012: median age 73 years (IQR: 62-82 years) and median disease duration 364 days (IQR: 92-1114 days). 40.6% of patients received systemic treatment in last 12 months of life. 29.9% received radiotherapy and 13.0% received psychosocial/spiritual care. Palliative care contact was 80.7%, inclusive of 20.6% who had an intensive palliative care unit admission. 5.2% had EOL chemotherapy and 3.8% received EOL radiotherapy. Up to 10.4% of patients had one or more hospital admission. There was no significant effect of age on those who received aggressive EOL care. Men had an increased probability to receive aggressive EOL care (p = 0.015). Tumor group was also associated with receiving aggressive EOL (p < 0.001), with the highest utilization in Head and Neck and hematological malignancies. In patients with a disease duration of > 4 months those who received palliative care at least 2-3 months prior to death were less likely to receive aggressive EOL care (P < 0.001). Patients whose disease duration was < 1 month were less likely to receive aggressive EOL care if they received palliative care services (p = 0.02). Conclusions: The provision of palliative care services at the end of life is most needed among men and certain tumor groups who are the highest users of aggressive EOL care.
37
Roland, William F. "Loran-C Chain and UTC Synchronisation". Journal of Navigation 53, n. 2 (maggio 2000): 215–23. http://dx.doi.org/10.1017/s037346330000881x.
Testo completoAbstract (sommario):
There has been much discussion recently implying that Loran-C chain synchronisation using ‘System Area Monitor’ (SAM) control and using ‘Time of Transmission (or Emission)’ (TOT or TOE) are incompatible mechanisations of Loran-C chain time management because of their differing impact on users. Further, the mechanisation of UTC synchronisation is described as either satellite (GPS/GLONASS) based or Loran Chain measurement based, thereby excluding integrated use of both techniques for reliability. These differences are not mutually exclusive. Well-defined chain synchronisation can logically apply all measurement and control techniques as well as providing improved accuracy. This paper defines synchronisation and describes the history of Loran-C synchronisation control and the current methods employed. The existence of Cesium Standards at Loran stations, and the recent introduction of digital signal processing receivers, have greatly changed the potential for extremely precise timing control, detection of extraordinary timing changes, and the maintenance of very tight UTC synchronisation. This paper describes a number of techniques for defining, observing and applying the various sources of timing information, optimising performance for users and simplifying implementation for service providers.
38
Fritsche, Carsten, e Anja Klein. "Nonlinear Filtering for Hybrid GPS/GSM Mobile Terminal Tracking". International Journal of Navigation and Observation 2010 (17 agosto 2010): 1–17. http://dx.doi.org/10.1155/2010/149065.
Testo completoAbstract (sommario):
The Global Positioning System (GPS) has become one of the state-of-the-art location systems that offers reliable mobile terminal (MT) location estimates. However, there exist situations where GPS is not available, for example, when the MT is used indoors or when the MT is located close to high buildings. In these scenarios, a promising approach is to combine the GPS-measured values with measured values from the Global System for Mobile Communication (GSM), which is known as hybrid localization method. In this paper, three nonlinear filters, namely, an extended Kalman filter, a Rao-Blackwellized unscented Kalman filter, and a modified version of the recently proposed cubature Kalman filter, are proposed that combine pseudoranges from GPS with timing advance and received signal strengths from GSM. The three filters are compared with each other in terms of performance and computational complexity. Posterior Cramér-Rao lower bounds are evaluated in order to assess the theoretical performance. Furthermore, it is investigated how additional GPS reference time information available from GSM influences the performance of the hybrid localization method. Simulation and experimental results show that the proposed hybrid method outperforms the GSM method.
39
Wu, Peng Fei, Jian Xun Li, Yu Jian Wang e Jian Xun Li. "Design and Implementation of the Computer Monitoring and Management System for the Multi-Mode Combination Timer Device". Advanced Materials Research 760-762 (settembre 2013): 916–22. http://dx.doi.org/10.4028/www.scientific.net/amr.760-762.916.
Testo completoAbstract (sommario):
The multi-mode combination timer device can receive the GPS\GLONASS, No.1 BeiDou and loran-C at the same time. Since the multiple external frequency sources are introduced for the system, it is necessary to manage and monitor it. The wavelet decomposition atomic time algorithm is used to weight average the external reference signals in the wavelet domain, and the integrated time scales are obtained. The disciplined clock technology is employed to the time scale for calibrating the clock; the results indicate that the system can achieve fast timing and the complementary advantages of all kinds of resources.
40
Roy, Amal K., Claudia Wagner-Riddle, Bill Deen, John Lauzon e Tom Bruulsema. "Nitrogen application rate, timing and history effects on nitrous oxide emissions from corn (Zea maysL.)". Canadian Journal of Soil Science 94, n. 4 (agosto 2014): 563–73. http://dx.doi.org/10.4141/cjss2013-118.
Testo completoAbstract (sommario):
Roy, A. K., Wagner-Riddle, C., Deen, B., Lauzon, J. and Bruulsema, T. 2014. Nitrogen application rate, timing and history effects on nitrous oxide emissions from corn (Zea mays L.). Can. J. Soil Sci. 94: 563–573. Nitrous oxide (N2O) emissions resulting from application of nitrogen (N) fertilizer contribute to the greenhouse gas footprint of corn production. In eastern Canada, corn is a major crop with most N fertilizer applied pre- or at planting. This timing of application results in a lack of synchrony of soil N supply and crop N demand. Matching the amount and timing of application to crop uptake has been suggested as a mitigation measure to reduce N losses, and is an integral part of the 4R Nutrient Stewardship program. This study examined the effect of timing, rate and history of urea-ammonium nitrate application on N2O emissions in corn in 2011 and 2012 at Elora, ON, Canada. Treatments were three N rates (30, 145 and 218 kg N ha−1); two timings (N injected in mid-row at planting and at the 8th leaf stage, V8); two histories (short-term: applying N rate treatments on plots that had received 145 kg N ha−1in the previous year, and long-term: applying the same N rate to a given plot over the duration of the trial). N2O emissions were measured using static chambers. History of N application did not have an effect on N2O emissions or grain yield. In both years, cumulative N2O emissions during the growing season and corn yields increased significantly with increasing N application rates. In 2011, cumulative N2O emissions were significantly lower when N was applied as side-dress at V8 (0.88 kg N ha−1) compared with planting (2.12 kg N ha−1), with no significant impact on corn grain yield (average 9.1 Mg ha−1). In contrast, in 2012, limited rainfall reduced both N2O emissions and corn grain yield, and neither N2O emission (average 0.17 kg N ha−1) nor grain yield (average 6.7 Mg ha−1) was affected by timing of N application. Applying N as side-dress at V8 instead of at planting and using the recommended N rate were shown to be effective N2O emission mitigation practices without affecting corn yield during a typical wet spring in Ontario.
41
Rogova, Nina. "Geodetic work during implementation of environmental protection measures for the remediation of oil-contaminated lands". E3S Web of Conferences 157 (2020): 02024. http://dx.doi.org/10.1051/e3sconf/202015702024.
Testo completoAbstract (sommario):
At the present level, the production, transportation and primary processing of oil products is associated with the problem of environmental pollution. The ingress of oil products into the natural environment leads to negative consequences and requires the enterprise to incur additional costs to eliminate the emergency situation and to take environmental protection measures to restore oil-contaminated territories. To restore contaminated territories on the basis of field surveys, which are based on geodetic work, remediation projects are developed. Remediation is carried out on the basis of a project, the reliability of which is taken into account during field geodetic work on determining the site area. In the course of the calculations, it was found that the use of tacheometric survey can significantly increase the cost of field work. In most cases, to ensure the development of a remediation project, it is enough to use domestic GPS receivers. The use of this class of devices will reduce both the timing of field work and their cost. It should be borne in mind that the accuracy of domestic GPS receivers allows using them in determining sites with an area of more than 0.5 ha.
42
den Ouden, M. A. G., C. H. Reijmer, V. Pohjola, R. S. W. van de Wal, J. Oerlemans e W. Boot. "Stand-alone single-frequency GPS ice velocity observations on Nordenskiöldbreen, Svalbard". Cryosphere 4, n. 4 (15 dicembre 2010): 593–604. http://dx.doi.org/10.5194/tc-4-593-2010.
Testo completoAbstract (sommario):
Abstract. Precise measurements of ice-flow velocities are necessary for a proper understanding of the dynamics of glaciers and their response to climate change. We use stand-alone single-frequency GPS receivers for this purpose. They are designed to operate unattended for 1–3 years, allowing uninterrupted measurements for long periods with hourly temporal resolution. We present the system and illustrate its functioning using data from 9 GPS receivers deployed on Nordenskiöldbreen, Svalbard, for the period 2006–2009. The accuracy of the receivers is 1.62 m based on the standard deviation in the average location of a stationary reference station (NBRef). Both the location of NBRef and the observed flow velocities agree within one standard deviation with DGPS measurements. Periodicity (6, 8, 12, 24 h) in the NBRef data is largely explained by the atmospheric, mainly ionospheric, influence on the GPS signal. A (weighed) running-average on the observed locations significantly reduces the standard deviation and removes high frequency periodicities, but also reduces the temporal resolution. Results show annual average velocities varying between 40 and 55 m yr−1 at stations on the central flow-line. On weekly to monthly time-scales we observe a peak in the flow velocities (from 60 to 90 m yr−1) at the beginning of July related to increased melt-rates. No significant lag is observed between the timing of the maximum speed between different stations. This is likely due to the limited temporal resolution after averaging in combination with the relatively small distance (max. ±13 km) between the stations.
43
Nakamura, Hiromitsu, Shin Aoi, Takashi Kunugi, Wataru Suzuki e Hiroyuki Fujiwara. "Prototype of a Real-Time System for Earthquake Damage Estimation in Japan". Journal of Disaster Research 8, n. 5 (1 ottobre 2013): 981–89. http://dx.doi.org/10.20965/jdr.2013.p0981.
Testo completoAbstract (sommario):
J-RISQ, a real-time system for earthquake damage estimation, was developed provide information by combining amplification characteristic data for subsurface ground accumulated in the course of the development of the Japan Seismic Hazard Information Station (JSHIS), basic information on population and buildings, methods for predicting ground motion, methods for assessing building damage, and strong motion data observed by K-NET and KiK-net in real-time. J-RISQ estimates spatial ground motion distribution from seismic intensity information sent at different timing for observation stations, estimates population exposure to seismic intensity and building damage using estimated ground motion as input, and provides information to users via Web browser or email using Web GIS. J-RISQ estimation is based on intensity data obtained at different timing to ensure recency by updating results when it receives new data and updates results when it receives estimation results. J-RISQ provides and collects information using questionnaires from users on actual motion and damage situations. We have operated the system on trial from 2010 and estimated over 500 earthquakes in real-time. As a result, the system provides the first report 30 seconds after it receives intensity information at a certain level or larger, thus showing sufficient performance from the perspective of providing immediate information.
44
Bridgelall, Raj, e Denver Tolliver. "Accuracy Enhancement of Anomaly Localization with Participatory Sensing Vehicles". Sensors 20, n. 2 (11 gennaio 2020): 409. http://dx.doi.org/10.3390/s20020409.
Testo completoAbstract (sommario):
Transportation agencies cannot afford to scale existing methods of roadway and railway condition monitoring to more frequently detect, localize, and fix anomalies throughout networks. Consequently, anomalies such as potholes and cracks develop between maintenance cycles and cause severe vehicle damage and safety issues. The need for a lower-cost and more-scalable solution spurred the idea of using sensors on board vehicles for a continuous and network-wide monitoring approach. However, the timing of the full adoption of connected vehicles is uncertain. Therefore, researchers used smartphones to evaluate a variety of methods to implement the application using regular vehicles. However, the poor accuracy of standard positioning services with low-cost geospatial positioning system (GPS) receivers presents a significant challenge. The experiments conducted in this research found that the error spread can exceed 32 m, and the mean localization error can exceed 27 m at highway speeds. Such large errors can make the application impractical for widespread use. This work used statistical techniques to inform a model that can provide more accurate localization. The proposed method can achieve sub-meter accuracy from participatory vehicle sensors by knowing only the mean GPS update rate, the mean traversal speed, and the mean latency of tagging accelerometer samples with GPS coordinates.
45
Sandha, S., M. Bullard, B. Halloran, C. Joseph, D. Grigat, E. S. Lang e S. Veldhuyzen van Zanten. "P132: Real life management of patients presenting with upper gastrointestinal bleeding in a tertiary care emergency department - Are we delivering the standard of care?" CJEM 20, S1 (maggio 2018): S103—S104. http://dx.doi.org/10.1017/cem.2018.330.
Testo completoAbstract (sommario):
Introduction: Upper gastrointestinal bleeding (UGIB) is a common Emergency Department (ED) presentation. Early endoscopic intervention, supported by Glasgow Blatchford Score (GBS) severity, has been shown to reduce re-bleeding rates and lower morbidity and mortality. However, emergent endoscopy is not necessary for all patients. Low-risk patients can be managed with outpatient follow-up. Other important management decisions such as blood transfusion (Hb <70) and use of proton pump inhibitors (PPI) also warrant evaluation. The aim of this study was to compare the timing and appropriateness of endoscopy and blood transfusion and proton pump inhibitor (PPI) use in a tertiary care setting to the standard of care. Methods: A retrospective cohort study was conducted to examine the management of patients presenting with UGIB to the ED in 2016 using a standard chart review methodology. TANDEM and EDIS (Emergency Department Information System) databases were queried to identify patients using specified ICD 10 codes and the CEDIS (Canadian Emergency Department Information System) presenting complaints of vomiting blood or blood in stool/melena. Outcome measures included: patient characteristics, the GBS to determine appropriateness of endoscopic intervention, diagnoses, blood transfusion indications and utilization of oral or intravenous PPIs. Data were entered into a REDCap database and analyzed using standard non-parametric statistical tests. Results: A total of 200 patients, 59% male (118/200), mean age 59 years (range 18 - 92 years) were included. The median GBS was 9. 79% of patients (157/200) underwent endoscopy during the hospital visit: 30% of patients with GBS 0-3 (13/43) and 80% patients with GBS 4 (125/157) underwent endoscopy 24 hours. The two most common endoscopic diagnoses were peptic ulcers (39%, 61/157) and varices (18%, 28/157), while 14% (22/157) had a normal diagnosis or mild gastritis. 174/200 patients (87%) were given IV or oral PPI in the ED whereas the remaining 26 (13%) did not receive PPI in hospital. 46% of patients (89/194) received blood transfusion, but only 51% (45/89) were administered based on the 70 g/L threshold while in 40% (36/89) of patients the less restrictive threshold of 90 g/L was used. Conclusion: A majority of UGIB patients presenting to a tertiary hospital ED appropriately received endoscopy 24 hours based on a GBS score 4. PPI use was appropriate but a proportion of patients received inappropriate blood transfusions.
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Hanado, Y., M. Imae e M. Sekido. "Millisecond pulsar observation system using AOS". International Astronomical Union Colloquium 160 (1996): 27–28. http://dx.doi.org/10.1017/s0252921100040951.
Testo completoAbstract (sommario):
Communications Research Laboratory (CRL) developed a new millisecond pulsar observation system which used an Acousto-Optic Spectrometer (A0S). An AOS is simple and effective at dividing a wide band signal into many channels simultaneously. Using this system, we started preliminary observations of PSR1937+21 for the purpose of precise measurements of millisecond pulsar’s pulse timing.Fig. 1 shows a block diagram of our observation system using the 34m antenna of CRL. This antenna has several receivers (1.5, 2, 5, 8, 10, 15, 22, 43 GHz) with selective polarizer. We use 1.5GHz or 2GHz band for pulsar observations. An IF signal with 50MHz bandwidth is divided to 200kHz × 256ch by the AOS. The speed of data transporting rate from the camera is about 13μs which limits a time resolution. We get 100 bins per one period for PSR1937+21. The video averaging processor works as two 8bits A/D converters and an averager which allows 224pulses’ addition in each channel. The averaged data of each channel are combined after de-dispersion processing which is carried out in 1/1000 steps of the pulsar period. ¿From this final profile, the peak phase is defined as arrival pulse timing. Host#2 calculates thea prioripulse period by TEMPO program, and supplies it in real time to the synthesizer which controls the averaging trigger clock of the timing signal generator. The reference clock of this system is synchronized with UTC (CRL) via the GPS satellites. The difference between the reference clock and the internal clock of the timing signal generator is monitored using a time interval counter.
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Krishna, K. Siva, e D. Venkata Ratnam. "Analysis of differential code biases and inter-system biases for GPS and NavIC satellite constellations". AIMS Electronics and Electrical Engineering 5, n. 3 (2021): 194–205. http://dx.doi.org/10.3934/electreng.2021011.
Testo completoAbstract (sommario):
<abstract> <p>Multi Global Navigation Satellite System (GNSS) plays an essential role in navigation and geodesy fields for positioning, Navigation, and Timing (PNT) services. The predominant challenge of multi-GNSS is hardware bias errors such as Differential code Bias (DCB) and Inter System Biases (ISB). The estimation of DCB and ISB are essential for analyzing the GNSS system performance to improve the positional accuracy. Navigation with the Indian Constellation (NavIC) system consists of the entire constellation of seven Geo-Stationary satellites to cater to Position Navigation Time (PNT) services over India and adjacent areas. In this paper, the relation between DCB and ISB of Global Positioning System (GPS) and NavIC systems is investigated using two ground-based NovAtel GPS and three Accords NavIC Receivers data (January to April 2019) at Koneru Lakshamaiah Education Foundation (K.L. Deemed to University), Guntur, India (16.47°N, 80.61°E). The correlation results indicate that NavIC GSO satellites are more stable than GEO satellites from DCB and ISB analysis due to low elevation angles and multipath effects. A systematic bias error is observed between NavIC and GPS satellite systems from ISB and DCB results. The current research work outcome would be beneficial for modeling GNSS ionospheric Total Electron Content (TEC) for high precision multi-constellation and multi-frequency GNSS systems.</p> </abstract>
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Lopez-Martinez, Manuel, José-Manuel Álvarez, José-Maria Lorenzo e Carlos Garcia Daroca. "SBAS/EGNOS for Maritime". Journal of Marine Science and Engineering 8, n. 10 (30 settembre 2020): 764. http://dx.doi.org/10.3390/jmse8100764.
Testo completoAbstract (sommario):
The Global Navigation Satellite System (GNSS) has become the primary means of obtaining Position, Navigation, and Timing (PNT) information at sea. The current capabilities of the Global Positioning System (GPS) constellation, although adequate for ocean navigation, have some shortfalls for coastal navigation: some user communities have a need for enhanced performance and they can benefit from the available “augmentation” techniques, resulting in improved GPS performance. Nowadays, the users can take advantage of Satellite-Based Augmentation Systems (SBASs). The maritime domain has been used SBAS for several years and it is supported by GNSS receivers used in the recreational and professional sectors. The SBAS/European Geostationary Navigation Overlay Service (EGNOS) can be used to complement the differential GNSS (DGNSS) for the provision of enhanced accuracy and integrity information with additional benefits. There are different possible solutions for the transmission of SBAS/EGNOS information to maritime users, considering that the corrections can be available from different transmission means. The different options for the use of SBAS for maritime navigation, the benefits brought to mariners, as well as the associated regulations, standardization and service provision aspects, are presented in this article.
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Brčić, David, Renato Filjar, Serdjo Kos e Marko Valčić. "On Global Ionospheric Maps based winter-time GPS ionospheric delay with reference to the Klobuchar model". Pomorstvo 33, n. 2 (19 dicembre 2019): 210–21. http://dx.doi.org/10.31217/p.33.2.11.
Testo completoAbstract (sommario):
Modelling of the ionospheric Total Electron Content (TEC) represents a challenging and demanding task in Global Navigation Satellite Systems (GNSS) positioning performance. In terms of satellite Positioning, Navigation and Timing (PNT), TEC represents a significant cause of the satellite signal ionospheric delay. There are several approaches to TEC estimation. The Standard (Klobuchar) ionospheric delay correction model is the most common model for Global Positioning System (GPS) single-frequency (L1) receivers. The development of International GNSS Service (IGS) Global Ionospheric Maps (GIM) has enabled the insight into global TEC dynamics. GIM analyses in the Northern Adriatic area have shown that, under specific conditions, local ionospheric delay patterns differ from the one defined in the Klobuchar model. This has been the motivation for the presented research, with the aim to develop a rudimentary model of the TEC estimation, with emphasis on areas where ground truth data are not available. The local pattern of the ionospheric delay has been modelled with wave functions based on the similarity of waveforms, considering diurnal differences in TEC behavior from defined TEC patterns. The model represents a spatiotemporal winter-time ionospheric delay correction with the Klobuchar model as a basis. The evaluation results have shown accurate approximation of the local pattern of the ionospheric delay. The model was verified in the same seasonal period in 2007, revealing it successfulness under pre-defined conditions. The presented approach represents a basis for the further work on the local ionospheric delay modelling, considering local ionospheric and space weather conditions, thus improving the satellite positioning performance for single-frequency GNSS receivers.
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Giraldo, Elias A., Jay N. Mandrekar, Mark N. Rubin, Stefan A. Dupont, Yi Zhang, Giuseppe Lanzino, Eelco F. M. Wijdicks e Alejandro A. Rabinstein. "Timing of clinical grade assessment and poor outcome in patients with aneurysmal subarachnoid hemorrhage". Journal of Neurosurgery 117, n. 1 (luglio 2012): 15–19. http://dx.doi.org/10.3171/2012.3.jns11706.
Testo completoAbstract (sommario):
Object Timing of clinical grading has not been fully studied in patients with aneurysmal subarachnoid hemorrhage (SAH). The primary objective of this study was to identify at which time point clinical assessment using the World Federation of Neurosurgical Societies (WFNS) grading scale and the Glasgow Coma Scale (GCS) is most predictive of poor functional outcome. Methods This study is a retrospective cohort study on the association between poor outcome and clinical grading determined at presentation, nadir, and postresuscitation. Poor functional outcome was defined as a Glasgow Outcome Scale score of 1–3 at 6 months after SAH. Results The authors identified 186 consecutive patients admitted to a teaching hospital between January 2002 and June 2008. The patients' mean age (± SD) was 56.9 ± 13.7 years, and 63% were women. Twenty-four percent had poor functional outcome (the mortality rate was 17%). On univariable logistic regression analyses, GCS score determined at presentation (OR 0.80, p < 0.0001), nadir (OR 0.73, p < 0.0001), and postresuscitation (OR 0.53, p < 0.0001); modified Fisher scale (OR 2.21, p = 0.0013); WFNS grade assessed at presentation (OR 1.92, p < 0.0001), nadir (OR 3.51, < 0.0001), and postresuscitation (OR 3.91, p < 0.0001); intracerebral hematoma on initial CT (OR 4.55, p < 0.0002); acute hydrocephalus (OR 2.29, p = 0.0375); and cerebral infarction (OR 4.84, p < 0.0001) were associated with poor outcome. On multivariable logistic regression analysis, only cerebral infarction (OR 5.80, p = 0.0013) and WFNS grade postresuscitation (OR 3.43, p < 0.0001) were associated with poor outcome. Receiver operating characteristic/area under the curve (AUC) analysis demonstrated that WFNS grade determined postresuscitation had a stronger association with poor outcome (AUC 0.90) than WFNS grade assessed upon admission or at nadir. Conclusions Timing of WFNS grade assessment affects its prognostic value. Outcome after aneurysmal SAH is best predicted by assessing WFNS grade after neurological resuscitation.