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  Subjects -> GEOGRAPHY (Total: 493 journals)
Showing 1 - 200 of 277 Journals sorted by number of followers
Geophysical Research Letters     Full-text available via subscription   (Followers: 178)
Journal of Geophysical Research : Space Physics     Full-text available via subscription   (Followers: 157)
Journal of Geophysical Research : Atmospheres     Partially Free   (Followers: 144)
Journal of Geophysical Research : Planets     Full-text available via subscription   (Followers: 136)
Remote Sensing of Environment     Hybrid Journal   (Followers: 96)
Antipode     Hybrid Journal   (Followers: 65)
Journal of Geophysical Research : Earth Surface     Partially Free   (Followers: 60)
Journal of Geophysical Research : Oceans     Partially Free   (Followers: 60)
Progress in Human Geography     Hybrid Journal   (Followers: 59)
Journal of Geophysical Research : Solid Earth     Full-text available via subscription   (Followers: 58)
International Journal of Geographical Information Science     Hybrid Journal   (Followers: 55)
GIScience & Remote Sensing     Open Access   (Followers: 54)
Journal of Water and Climate Change     Open Access   (Followers: 53)
Climate Change Economics     Hybrid Journal   (Followers: 50)
Reviews of Geophysics     Full-text available via subscription   (Followers: 49)
Remote Sensing Letters     Hybrid Journal   (Followers: 46)
Annals of the American Association of Geographers     Hybrid Journal   (Followers: 43)
Economic Geography     Hybrid Journal   (Followers: 40)
Applied Geography     Hybrid Journal   (Followers: 38)
Geochemistry, Geophysics, Geosystems     Full-text available via subscription   (Followers: 35)
Urban Geography     Hybrid Journal   (Followers: 34)
Journal of Geophysical Research : Biogeosciences     Full-text available via subscription   (Followers: 34)
Climate and Development     Hybrid Journal   (Followers: 33)
Journal of Coastal Research     Hybrid Journal   (Followers: 31)
Annals of GIS     Open Access   (Followers: 31)
Cartography and Geographic Information Science     Hybrid Journal   (Followers: 31)
GPS Solutions     Hybrid Journal   (Followers: 28)
Transactions of the Institute of British Geographers     Hybrid Journal   (Followers: 27)
Journal of Urbanism: International Research on Placemaking and Urban Sustainability     Hybrid Journal   (Followers: 24)
Journal of the Middle East and Africa     Hybrid Journal   (Followers: 22)
China : An International Journal     Full-text available via subscription   (Followers: 20)
Urban Research & Practice     Hybrid Journal   (Followers: 20)
Dialogues in Human Geography     Hybrid Journal   (Followers: 20)
Imago Mundi: The International Journal for the History of Cartography     Hybrid Journal   (Followers: 20)
Atmospheric Measurement Techniques (AMT)     Open Access   (Followers: 19)
Advances in Geosciences (ADGEO)     Open Access   (Followers: 19)
Water International     Hybrid Journal   (Followers: 19)
Journal of the American Planning Association     Hybrid Journal   (Followers: 19)
Journal of Cultural Geography     Hybrid Journal   (Followers: 18)
Geography Compass     Hybrid Journal   (Followers: 18)
Professional Geographer     Hybrid Journal   (Followers: 17)
Cartographica : The International Journal for Geographic Information and Geovisualization     Full-text available via subscription   (Followers: 17)
Africa Insight     Full-text available via subscription   (Followers: 16)
The Geographical Journal     Hybrid Journal   (Followers: 16)
International Geology Review     Hybrid Journal   (Followers: 16)
Crossings : Journal of Migration & Culture     Hybrid Journal   (Followers: 16)
Computational Geosciences     Hybrid Journal   (Followers: 16)
Tectonics     Full-text available via subscription   (Followers: 15)
American Journal of Geographic Information System     Open Access   (Followers: 14)
Geographical Review     Hybrid Journal   (Followers: 13)
Buildings & Landscapes: Journal of the Vernacular Architecture Forum     Full-text available via subscription   (Followers: 13)
Geomatics, Natural Hazards and Risk     Open Access   (Followers: 13)
International Indigenous Policy Journal     Open Access   (Followers: 13)
Annual Review of Marine Science     Full-text available via subscription   (Followers: 13)
Progress in Physical Geography     Hybrid Journal   (Followers: 13)
Bulletin of Geosciences     Open Access   (Followers: 12)
American Journal of Human Ecology     Open Access   (Followers: 11)
Geographical Research     Hybrid Journal   (Followers: 11)
Geographical Analysis     Hybrid Journal   (Followers: 11)
Canadian Journal of Soil Science     Full-text available via subscription   (Followers: 11)
Geosciences Journal     Hybrid Journal   (Followers: 10)
GeoJournal     Hybrid Journal   (Followers: 10)
Journal of Geography     Hybrid Journal   (Followers: 10)
European Spatial Research and Policy     Open Access   (Followers: 9)
Cartographic Journal     Hybrid Journal   (Followers: 9)
Atmospheric Measurement Techniques Discussions (AMTD)     Open Access   (Followers: 9)
Journal of Borderlands Studies     Hybrid Journal   (Followers: 8)
Geography and Natural Resources     Hybrid Journal   (Followers: 8)
Physical Geography     Hybrid Journal   (Followers: 8)
Natural Science     Open Access   (Followers: 8)
Journal of Iberian and Latin American Research     Hybrid Journal   (Followers: 8)
Middle East Development Journal     Hybrid Journal   (Followers: 8)
Geo-spatial Information Science     Open Access   (Followers: 7)
Nordic Journal of Migration Research     Open Access   (Followers: 7)
Social Geography Discussions (SGD)     Open Access   (Followers: 7)
International Journal of Applied Geospatial Research     Hybrid Journal   (Followers: 7)
California Italian Studies Journal     Full-text available via subscription   (Followers: 7)
Journal of Latin American Geography     Full-text available via subscription   (Followers: 7)
Urban History Review / Revue d'histoire urbaine     Full-text available via subscription   (Followers: 7)
GeoInformatica     Hybrid Journal   (Followers: 7)
International Journal of Health Geographics     Open Access   (Followers: 7)
Northern Scotland     Hybrid Journal   (Followers: 6)
Journal of Geographical Systems     Hybrid Journal   (Followers: 6)
Asia Policy     Full-text available via subscription   (Followers: 6)
Singapore Journal of Tropical Geography     Hybrid Journal   (Followers: 6)
Australian Geographer     Hybrid Journal   (Followers: 6)
Ocean Science Journal     Hybrid Journal   (Followers: 6)
Journal of Maps     Open Access   (Followers: 6)
The Canadian Geographer/le Geographe Canadien     Hybrid Journal   (Followers: 6)
Journal of Map & Geography Libraries     Hybrid Journal   (Followers: 5)
ISPRS International Journal of Geo-Information     Open Access   (Followers: 5)
Journal of Developmental Entrepreneurship     Hybrid Journal   (Followers: 5)
Current Research in Geoscience     Open Access   (Followers: 5)
Creativity Studies     Open Access   (Followers: 5)
Australian Antarctic Magazine     Free   (Followers: 5)
Focus on Geography     Partially Free   (Followers: 5)
Asian Geographer     Hybrid Journal   (Followers: 5)
Journal of Australian Studies     Hybrid Journal   (Followers: 5)
Bulletin of the Ecological Society of America     Open Access   (Followers: 4)
Geografiska Annaler, Series A : Physical Geography     Hybrid Journal   (Followers: 4)
Journal of Sedimentary Research     Hybrid Journal   (Followers: 4)
Genre & histoire     Open Access   (Followers: 4)
Globe, The     Full-text available via subscription   (Followers: 4)
Latinoamérica. Revista de estudios Latinoamericanos     Open Access   (Followers: 4)
Applied Geomatics     Hybrid Journal   (Followers: 4)
Transmodernity : Journal of Peripheral Cultural Production of the Luso-Hispanic World     Open Access   (Followers: 4)
Interaction     Full-text available via subscription   (Followers: 3)
Journal of Western Archives     Open Access   (Followers: 3)
Limnological Review     Open Access   (Followers: 3)
Lithosphere     Open Access   (Followers: 3)
Bulletin of Geography. Socio-economic Series     Open Access   (Followers: 3)
Southeastern Europe     Hybrid Journal   (Followers: 3)
New Zealand Journal of Geography     Hybrid Journal   (Followers: 3)
International Journal of Image and Data Fusion     Hybrid Journal   (Followers: 3)
Économie rurale     Open Access   (Followers: 3)
Polar Research     Open Access   (Followers: 3)
South Asian Diaspora     Hybrid Journal   (Followers: 3)
Journal of Burma Studies     Full-text available via subscription   (Followers: 3)
Social Dynamics: A journal of African studies     Hybrid Journal   (Followers: 3)
All Earth     Open Access   (Followers: 3)
Pastoralism : Research, Policy and Practice     Open Access   (Followers: 2)
Maine Policy Review     Open Access   (Followers: 2)
The South Asianist     Open Access   (Followers: 2)
Provincial China     Hybrid Journal   (Followers: 2)
Geodesy and Cartography     Open Access   (Followers: 2)
Polar Journal     Hybrid Journal   (Followers: 2)
Regional Science Policy & Practice     Hybrid Journal   (Followers: 2)
History of Geo- and Space Sciences     Open Access   (Followers: 2)
Mineralogia     Open Access   (Followers: 2)
Eastern European Countryside     Open Access   (Followers: 2)
Regions and Cohesion     Open Access   (Followers: 2)
Geosphere     Open Access   (Followers: 2)
Journal of Earthquake and Tsunami     Hybrid Journal   (Followers: 2)
Cahiers franco-canadiens de l'Ouest     Full-text available via subscription   (Followers: 2)
Norois     Open Access   (Followers: 2)
Standort - Zeitschrift für angewandte Geographie     Hybrid Journal   (Followers: 2)
Études rurales     Open Access   (Followers: 2)
Polar Geography     Hybrid Journal   (Followers: 2)
Scottish Geographical Journal     Hybrid Journal   (Followers: 2)
Norsk Geografisk Tidsskrift - Norwegian Journal of Geography     Hybrid Journal   (Followers: 2)
Southeastern Geographer     Full-text available via subscription   (Followers: 2)
Yearbook of the Association of Pacific Coast Geographers     Full-text available via subscription   (Followers: 2)
BioRisk     Open Access   (Followers: 2)
Geographical Education     Full-text available via subscription   (Followers: 2)
Cahiers Balkaniques     Open Access   (Followers: 2)
Reflets : revue d'intervention sociale et communautaire     Full-text available via subscription   (Followers: 2)
Études internationales     Full-text available via subscription   (Followers: 1)
GEM - International Journal on Geomathematics     Hybrid Journal   (Followers: 1)
Recherches sociographiques     Full-text available via subscription   (Followers: 1)
Estudios Geográficos     Open Access   (Followers: 1)
Terrae Incognitae     Hybrid Journal   (Followers: 1)
Geoforum Perspektiv     Open Access   (Followers: 1)
Newfoundland and Labrador Studies     Full-text available via subscription   (Followers: 1)
South African Geographical Journal     Hybrid Journal   (Followers: 1)
Geochronometria     Open Access   (Followers: 1)
Amerika     Open Access   (Followers: 1)
Journal de la Société des Océanistes     Open Access   (Followers: 1)
Les Cahiers d'Outre-Mer     Open Access   (Followers: 1)
Revue archéologique du Centre de la France     Open Access   (Followers: 1)
Journal of Terrestrial Observation     Open Access   (Followers: 1)
PRISM : A Journal of Regional Engagement     Open Access   (Followers: 1)
Physio-Géo     Open Access   (Followers: 1)
Méditerranée     Open Access   (Followers: 1)
Indiana     Open Access   (Followers: 1)
Revista de Geografía Norte Grande     Open Access   (Followers: 1)
L'Année du Maghreb     Open Access   (Followers: 1)
European Countryside     Open Access   (Followers: 1)
Norteamérica     Open Access   (Followers: 1)
International Journal of Bahamian Studies     Open Access   (Followers: 1)
Journal of the Southwest     Full-text available via subscription   (Followers: 1)
PSC Discussion Papers Series     Open Access  
Anales de Geografía de la Universidad Complutense     Open Access  
International Journal of River Basin Management     Hybrid Journal  
Revista Geográfica de América Central     Open Access  
Multiciencias     Open Access  
Investigaciones Geográficas (Esp)     Open Access  
Sociedade & Natureza     Open Access  
Región y Sociedad     Open Access  
Migración y Desarrollo     Open Access  
Migraciones Internacionales     Open Access  
Investigaciones Geográficas     Open Access  
Frontera Norte     Open Access  
Cuadernos de Desarrollo Rural     Open Access  
Territoire en Mouvement     Open Access  
Quaestiones Geographicae     Open Access  
Limes. Cultural Regionalistics     Open Access  
GEOMATICA     Hybrid Journal  
Preview     Hybrid Journal  
Cuadernos de Geografía : Revista Colombiana de Geografía     Open Access  
Studia Universitatis Babes-Bolyai, Geologia     Open Access  
Recherches amérindiennes au Québec     Full-text available via subscription  
Rabaska : revue d'ethnologie de l'Amérique française     Full-text available via subscription  
Port Acadie : revue interdisciplinaire en études acadiennes / Port Acadie: An Interdisciplinary Review in Acadian Studies     Full-text available via subscription  
Études/Inuit/Studies     Full-text available via subscription  
Aurora Journal     Full-text available via subscription  
Revista de la Asociacion Geologica Argentina     Open Access  
San Francisco Estuary and Watershed Science     Open Access  
Journal of Alpine Research : Revue de géographie alpine     Open Access  
Géocarrefour     Open Access  
Confins     Open Access  

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Similar Journals
Journal Cover
GPS Solutions
Journal Prestige (SJR): 1.674
Citation Impact (citeScore): 5
Number of Followers: 28  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1521-1886 - ISSN (Online) 1080-5370
Published by Springer-Verlag Homepage  [2469 journals]
  • Impact of clock drift on WiFi round-trip-time ranging and positioning

    • Free pre-print version: Loading...

      Abstract: Abstract Indoor high-precision positioning is currently one of the most interesting topics in the location-tracking and positioning research area. Although the WiFi round-trip-time (RTT) provides a promising ranging and positioning method, it faces two issues that need to be addressed. One is the ranging error drift, and the other is the ranging information loss. Existing research has mainly focused on the ranging error, and several solutions have been proposed. However, these solutions are mostly applied to the data level, and the cause of phase distortion error has not been found. The loss of ranging information has been simply attributed to the poor external environment. In this work, the impact of clock drift on WiFi RTT positioning is investigated and considered the root cause of the abovementioned issues. On this basis, a theory of the clock drift model is established and experimentally verified. This model can effectively explain the mechanism of the ranging error drift and the ranging information loss. Furthermore, the impact of the clock drift on missing positioning observations is investigated in three actual applicational situations, including the sampling rate, multipath effect, and power-saving mode. Therefore, the proposed model is important for improving the accuracy and reliability of WiFi RTT-based positioning because it provides the basis for solving subsequent problems. This model provides a theory to capture the moment when the communication status changes accurately. Furthermore, the ranging error drift can be corrected to obtain high-precision positioning results.
      PubDate: 2022-08-11
       
  • Vector angle grouping-based solution separation for multipath/NLOS
           detection and exclusion with the enhancement of doppler test

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      Abstract: Abstract In urban areas, global navigation satellite system (GNSS) measurements are susceptible to multipath and non-line-of-sight (NLOS) effects, significantly degrading GNSS performance. Nowadays, multipath/NLOS effects have become the main cause of GNSS measurement fault in an urban environment. Our work mainly focuses on improving GNSS performance in urban areas without using any additional sensors. To achieve this, Doppler test-enhanced fault detection and exclusion (FDE) scheme is proposed to mitigate the influence of multipath/NLOS effects on GNSS positioning. The research is conducted in two folds. First, according to vector angle grouping (VAG) and multiple hypothesis solution separation (MHSS), the fault mode determination process is described. Since the spatial characteristic of multipath/NLOS effects are considered, the fault mode determined by VAG is able to monitor multiple measurement faults caused by multipath/NLOS effects. Second, by introducing Doppler test, Doppler test-enhanced FDE scheme is designed. The proposed FDE scheme combines VAG-based MHSS FDE and the continuity of users’ motion, which can obtain more accurate exclusion options. Experiments are carried out based on the open-source dataset, UrbanNav. The results suggest that the proposed algorithm can improve the navigation accuracy about 50% over the traditional receiver autonomous integrity monitoring-based Consistency Check method.
      PubDate: 2022-08-10
       
  • New time-differenced carrier phase approach to GNSS/INS integration

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      Abstract: Abstract The accuracy of navigation information is essential for modern transport systems. Such information includes position, velocity and attitude. Because of the physical characteristics of the operational environments, integration of GNSS with inertial measurement units (IMU) is commonly used. However, conventional integrated algorithms suffer from low-quality GNSS measurements due to either inaccurate pseudoranges or difficulty of ambiguity resolution when using carrier phase measurements in urban environments. We propose a Time-Difference-Carrier-Phase (TDCP) derivation controlled GNSS/IMU integration scheme. The proposed algorithm enables a TDCP-based control vector construction, including relative position, velocity, heading and pitch, which makes it possible to obtain accurate changes in position, namely delta position, altitude and velocity estimations. These estimated changes are then used to feed a loosely coupled GNSS/IMU integration system. Real-world test results show that the proposed integrated navigation scheme is superior to the conventional algorithm, with accuracy improvements of more than 38% in 3D positioning, 30% in 3D velocity, 35% in roll, 44% in pitch and 39% in heading.
      PubDate: 2022-08-10
       
  • Orbit determination of sentinel-6A using the galileo high accuracy service
           test signal

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      Abstract: Abstract The High Accuracy Service (HAS) is an upcoming addition to the Galileo service portfolio that offers free correction data for precise point positioning in real-time. Beyond terrestrial and aeronautical applications, precise orbit determination (POD) of satellites in low Earth orbit (LEO) has been proposed as a potential use case for HAS corrections in view of their global availability. Based on HAS data collected during a test campaign in September 2021, the benefit of HAS corrections is assessed for real-time, onboard navigation as well as near real-time POD on the ground using GNSS observations of the Sentinel-6A LEO satellite. Compared to real-time POD using only broadcast ephemerides, performance improvements of about 40%, 10%, and 5% in terms of 3D position error can already be achieved for GPS-only, GPS + Galileo, and Galileo-only navigation. While Galileo processing benefits only moderately from the HAS correction data during the early tests in view of an already excellent Open Service performance, their use is highly advantageous for GPS processing and enables dual-constellation navigation with balanced contributions of both GNSSs for improved robustness. For near real-time offline POD, HAS corrections offer reduced latency or accuracy compared to established ultra-rapid GNSS orbit and clock products as well as independence from external sources.
      PubDate: 2022-08-09
       
  • A comprehensive evaluation of utilizing BeiDou data to estimate snow
           depths from two ground-based stations

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      Abstract: Abstract The BeiDou Navigation Satellite System (BDS) of China started to provide global services in 2020, which provides a new data source for snow depth sensing through the Global Navigation Satellite System Interferometric Reflectometry (GNSS-IR) technique. This study, taking advantage of two stations in the snow season of 2020, first evaluates the performance of the five state-of-the-art snow depth models on BDS data and provides a comprehensive analysis of the characteristics of BDS data toward snow depth estimations. The results show that the snow depth estimations using the SNR, triple-frequency SNR combination (SNR_COM), and triple-frequency phase combination (F3) models are comparable, with high correlation coefficient R2 (root-mean-square error, RMSE) values of 0.93 (3.17 cm), 0.93 (3.12 cm), and 0.93 (3.27 cm), respectively. The models of geometry-free linear combinations of the phase measurements (L4) and combination of pseudorange and carrier phase of dual-frequency signals (F2C) are slightly poorer, with mean R2 (RMSE) values of 0.69 (7.18 cm) and 0.82 (4.68 cm), respectively. The snow depth retrieval results show similar accuracy using data from the BDS-3 and BDS-2 (RMSE = 3.63 cm vs. 3.72 cm). The results from the IGSO satellites are more reliable than those from the MEO satellites. The effects of satellite elevation angles and sampling rates are also analyzed to determine the optimal parameter selections (i.e., 5°–25° or 5°–30° and sampling rates < 120 s). The findings of this study can provide supporting information to determine the strategy for using BDS signals to retrieve snow depth.
      PubDate: 2022-08-09
       
  • Optimization of undifferenced and uncombined PPP stochastic model based on
           covariance component estimation

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      Abstract: Abstract A suitable stochastic model is important for parameter estimation in processing undifferenced and uncombined precise point positioning (UC-PPP). Since only when the correct stochastic model is applied can one obtain minimum variance estimations of the precise positioning in the linear adjustment model. However, current multi-frequency UC-PPP stochastic models were established mainly based on an empirical ionosphere-free combined PPP model, which makes it difficult for the established stochastic model to reflect the noise level of the raw observations objectively and truly. In order to solve this problem, an optimized stochastic model suitable for multi-frequency UC-PPP was constructed by considering the variance component factors (VCF) on the diagonal and the cross-correlation coefficients (CCC) between observations of the same type in the (co)variance matrix based on the empirical stochastic model, and a two-step evaluation and optimization procedure for the VCF and CCC was proposed based on the posterior estimation method of the variance–covariance components. To evaluate the stochastic models, 54 GPS dual-frequency observations from the multi-GNSS experiment (MGEX) stations with receivers of four mainstream brands were processed. The results show that all four types of receivers exhibited higher accuracy of observations at L2 frequency than at L1 frequency, and the VCF of the pseudorange was about 8–15 times higher than that of the carrier phase based on the empirical stochastic model. The accuracy of the pseudorange and carrier phase observations varied with the receiver brands. For example, the accuracy of the carrier phase of Leica receiver at L2 frequency was clearly higher than that at L1 frequency, while SEPT receivers showed more significant differences between the pseudorange values at these two frequencies. In terms of Javad and Trimble receivers, the accuracy of pseudorange observations at two frequencies was basically the same, while the carrier phase showed a larger difference. In addition, these four types of receivers presented smaller cross-correlations between observations at different frequencies with the coefficient below 0.04. To assess the UC-PPP performance, three different stochastic models were tested and analyzed. The test results indicate that the proposed stochastic models exhibited better performance with an increase in the positioning accuracy along east, north and vertical directions, i.e., 18.4%, 10.7% and 8.6% for static positioning, and 18.7%, 17.9% and 14.8% for dynamic positioning. However, UC-PPP accuracy and convergence time did not show significant variations when the covariance-related information was incorporated into the stochastic model.
      PubDate: 2022-08-09
       
  • Machine learning-based snow depth retrieval using GNSS signal-to-noise
           ratio data

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      Abstract: Abstract GNSS-IR enables the extraction of environmental parameters such as snow depth by analyzing signal-to-noise ratio, indicating the strength of the GNSS signal. We propose a machine learning (ML) classification approach for snow depth retrieval using the GNSS-IR technique. ML classifier algorithms were studied to classify the strong and weak ground reflections using input parameters (azimuth angle, satellite elevation angle, day of year, amplitude of reflected signal, epoch number, etc.) as independent variables. GPS data collected by UNAVCO AB39 and daily snow depth data from SNOTEL Fort Yukon for a 6-year period (2015–2020) were considered. The first 4-year data were trained by some well-known ML classifiers to weight the input data and then used to classify the strong and weak signals. Tree-based classifiers, Random Forest, AdaBoost, and Gradient Boosting overperformed the other classifiers since they have more than 70% accuracy, so we performed our analysis with these three methods. The last 2-year data were used to validate both trained models and snow depth retrievals. The results show that ML classifier algorithms perform better results than traditional GNSS-IR snow depth retrieval; they improve the correlations by up to 19%. Moreover, the root-mean-square errors decrease from 15.4 to 4.5 cm. This study has a novel approach to the use of ML techniques in GNSS-IR signal classification, and the proposed methods provide a critical improvement in accuracy compared to the traditional method.
      PubDate: 2022-08-08
       
  • Robust unambiguous ranging technique for BDS-3 B1 wideband composite
           signals

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      Abstract: Abstract During the evolution of global navigation satellite systems (GNSS), many new GNSS signals have been proposed to meet the demand of various applications for high-precision positioning. The single-sideband complex subcarrier (SCBOC) modulated signals, which are contained in China's third-generation BeiDou Navigation Satellite System (BDS-3) B1 wideband composite signals, have extremely high-precision ranging potential. Although high-precision ranging performance of SCBOC signals has been demonstrated by implementing a cross-assisted tracking (CAT) technique in previous studies, ambiguity threats are not effectively relieved, resulting in ambiguous ranging. Therefore, we propose a robust unambiguous ranging technique, which utilizes an ambiguity model established by observations derived from CAT to resolve ambiguous ranging results. Simulation experiments are implemented to quantitatively evaluate the proposed method’s performance and explore its effective ranges. Real data experiments are also implemented in static and dynamic cases to furtherly verify the effectiveness of the proposed method, exhibiting that the proposed method can take full advantage of the high-precision ranging potential contained in BDS-3 B1 wideband composite signals with less ambiguity threats.
      PubDate: 2022-08-05
       
  • Single-frequency cycle slip detection and repair based on Doppler
           residuals with inertial aiding for ground-based navigation systems

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      Abstract: Abstract As effective backups for global navigation satellite systems (GNSS), ground-based navigation systems can provide positioning, navigation, and timing services in situations in which the GNSS signal is degraded or denied, such as city canyons, underground, and tunnels. To handle the issue of the poor performance of small cycle slip detection in single-frequency receivers, we propose a single-frequency cycle slip detection and repair method based on Doppler residuals with inertial aiding (DRIA). A low-cost micro-electro-mechanical system inertial measurement unit (MEMS-IMU) is employed in a tightly coupled integration to predict Doppler measurements of the receiver accurately. The Doppler residuals are used as test statistics for cycle slip detection in the DRIA method, obtained by subtracting the predictions from the observed Doppler measurements. The performance of the DRIA method is tested using a ground-based high-precision local positioning system (GH-LPS) in an indoor environment. The test results demonstrate effective cycle slip detection even for one cycle in real time using only single-frequency measurements. The DRIA method achieved a 91.2% success rate, which is an improvement of 207% compared with the method based on carrier phase residuals. During the entire kinematic experiment, the root mean square of the horizontal positioning error was 1.3 cm, which is an improvement of 97.6% over the unrepaired condition (54.0 cm) and 83.4% over the method based on the carrier phase residuals (8.0 cm). The experimental results indicate the validity of the Doppler residual methods for small cycle slip detection and repair, providing a new basis to deal with cycle slips in ground-based navigation systems.
      PubDate: 2022-08-05
       
  • GNSS2TWS: an open-source MATLAB-based tool for inferring daily terrestrial
           water storage changes using GNSS vertical data

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      Abstract: Abstract Technological advances in global navigation satellite system (GNSS) offer a novel environmental sensor to measure terrestrial water cycles and provide independent constraints on total terrestrial water storage (TWS) changes over various spatiotemporal scales. This study aims to develop an open-source MATLAB-based tool for inferring daily TWS changes based on the relation between GNSS annual vertical displacement and hydrological cycles. The widely used spatial-domain Green's function approach is used to estimate regional equivalent water height changes. To recover daily water storage fluctuations, we integrate the principal component analysis into our time-varying inversion strategy. To demonstrate the implementation of the inversion tool, we invert the daily TWS changes in the Pacific Northwest River Basin, the United States of America, using GNSS-measured vertical surface motions. The primary goal is to share this inversion software for hydrogeodetic scientific communities to fully use the GNSS technique for hydrological applications.
      PubDate: 2022-08-04
       
  • Ionosphere-weighted post-processing kinematic for airborne positioning
           with refined modeling of receiver phase biases and tropospheric zenith wet
           delays

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      Abstract: Abstract The application of the global navigation satellite system (GNSS) in aviation effectively meets the requirements of aircraft location-based services. However, the GNSS application in airborne surveys mostly follows the land survey method, which ignores the particularity of the airborne flight operations, such as the rapid change of altitude difference. The present study contributes to this research trend by constructing a suitable positioning model for airborne kinematic precise positioning and analyzing the variation characteristics of receiver phase biases (RPBs) and tropospheric zenith wet delays (ZWDs) to explore their impact on airborne positioning. The ionosphere-weighted post-processing kinematic (PPK) model for long-distance high-altitude positioning is constructed by adding the between-station single-differenced ionospheric pseudo-observations. Aside from these, the correlation between the characteristics of RPBs, ZWDs, and environmental factors (temperature, vapor pressure) is analyzed and the kinematic constraint of the ionosphere-weighted PPK model on RPBs and ZWDs is adjusted based on their true variations. The results show that under the condition of large altitude differences, temperature-sensitive RPBs and ZWDs significantly impact positioning. Furthermore, pre-calibrating RPBs and ZWDs can significantly improve the ambiguity success rate and positioning performance. Based on the bias-calibrated ionosphere-weighted PPK model, the fixed solutions difference of the two common-antenna moving stations carried by the manned aircraft is stable for the positioning results of the two flight experiments. The 3-dimensional root-mean-square (3D-RMS) values are 1.4 cm and 0.5 cm, with 82% and 99% ambiguity success ratios.
      PubDate: 2022-08-03
       
  • GNSS atmosphere seismology for equatorial earthquakes: a case study from
           Central America

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      Abstract: Abstract We study the impact of the severe equatorial earthquakes on the ionospheric Equatorial Ionization Anomaly (EIA) to check the variations in the shape of electron concentrations along the earthquake longitudes as the possible precursors to the earthquakes by considering a case study of a strong Mw 7.3 seismic event from Honduras occurred in 2009. We have observed sharp increments in the atmospheric chemical potential and surface air temperature time series along with an abrupt decrease in the relative humidity simultaneously about 5–8 days before the impending earthquake indicating the procreation of the air ionization due to increased radon activity around the earthquake's epicenter. We further investigated the ionospheric conditions by estimating the total electron content (TEC) from 6 IGS stations. The results suggested that the 2 IGS stations operating within the earthquake preparation area (EPA) showed prominent TEC enhancements about 5 days before the impending earthquake, consistent with the seismic atmospheric circulations. The other 3 IGS stations, operating outside the EPA, did not show any perturbation. These TEC variations are quantified based on two different methods: (1) running interquartile method and (2) method of cognitive recognition (applied on station BOGT). Moreover, the TEC and electron density profiles, retrieved from station BOGT and the ISL probe of the DEMETER satellite, respectively, revealed that the local TEC enhancements further dispersed toward the magnetic equator at higher altitudes by developing an enormous two-hump-like EIA structure near the epicentral longitude that verifies the generation of the seismogenic electric field through air ionization. We believe that our multi-precursory analysis is another step forward in comprehending the seismic lithosphere–ionosphere interactions.
      PubDate: 2022-08-01
       
  • A Carrier phase tracking method for vector tracking loops

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      Abstract: Abstract Compared with the traditional scalar tracking structure, the vector tracking structure of the satellite navigation receiver has a better signal tracking sensitivity in high dynamic and other situations. However, due to the limited accuracy, it is really hard for a vector tracking loop to maintain the lock of carrier phase. In order to solve this problem, a carrier phase tracking method for vector tracking loops is proposed. First, three common vector tracking structures are analyzed. Second, in the structure of double vector loops, phase compensation is estimated and used to improve the tracking accuracy of the carrier phase. Finally, simulations have been carried out to analyze and verify the feasibility of the proposed scheme. This method estimates and reduces the phase tracking error and has a better tracking effect than the traditional scalar structure. It provides a reference for the implementation of the vector tracking structure and the ultra-tight integrated navigation system.
      PubDate: 2022-08-01
       
  • Minimum-observation method for rapid and accurate satellite coverage
           prediction

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      Abstract: Abstract Satellite coverage is one of the most important elements of satellite applications, which determines the range and duration of the service provided by the satellite. We propose a rapid one-dimensional method to predict when a ground target is visible from the satellite, which means the ground target is within the footprint of the satellite, for an arbitrary sensor field. The field is defined as the shape of the observable range of the sensor placed on the satellite. For instance, the cone field means the shape of the observable range of the sensor is a circle, while the rectangle field means the shape of the observable range of the sensor is a rectangle. First, the minimum-observation function is defined to describe the geometric properties of the sensor field of a satellite. Based on the geometric relationship between the satellite and a target, visible conditions at a ground point given the satellite field of view are obtained, considering the field and earth-occlusion constraints. In order to calculate the visible set during a given period, the Hermite cubic interpolation method is used to obtain the earth-occlusion-off intervals rapidly, and the field-constraint function is fitted by the linear fixed-step method. The visible intervals of the ground point from the sensor are obtained by finding the zero points of the fitting field-constraint function limited by the earth-occlusion-off intervals. To demonstrate the effectiveness of the proposed method, a series of numerical simulations are conducted. The simulation results indicate that the proposed method can balance computation time and precision, which is suitable for various types of satellite orbits and sensor fields. Thus, as a practical method, the proposed method can provide efficient communication, navigation, and remote sensing tool.
      PubDate: 2022-07-31
       
  • On the potential contribution of BeiDou-3 to the realization of the
           terrestrial reference frame scale

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      Abstract: Abstract Since the release of the phase center calibrations for both the receivers and the satellites, the BeiDou Navigation Satellite System (BDS) became a new potential contributor to the realization of the terrestrial reference frame (TRF) scale of future International Terrestrial Reference Frame releases. This study focuses on the evaluation of the potential usage of the BDS-3 Medium Earth Orbit (MEO) constellation to the definition of the TRF scale. To that aim, we used ground calibrated BDS-3 satellite PCOs provided by the China Satellite Navigation Office and multi-GNSS robot calibrations for the ground antennas conducted by Geo++. Two ionosphere-free linear combinations of signals, namely B1I/B3I and B1C/B2a, have been investigated to find out whether using different frequencies may lead to different TRF scale definitions. Differences between the z components of the satellite phase offsets as given by manufacturer calibrations and those estimated based on IGS14 scale amount to 6.55 ± 12.56 cm and − 0.32 ± 10.99 cm for B1I/B3I and B1C/B2a frequency pairs, respectively. On the one hand, the substantial deviation from the mean reflects the disparities in the quality of calibrations for the individual spacecraft, especially those manufactured by the Shanghai Engineering Center for Microsatellites (SECM). On the other hand, the difference between the two frequency pairs arises to a great extent from the doubtful quality of the SECM PCO calibrations, which certainly do not reflect the frequency dependence of the PCOs. Eventually, the mean scale bias with respect to IGS14 equals + 0.546 ± 0.085 ppb and + 0.026 ± 0.085 ppb for B1I/B3I and B1C/B2a solutions, respectively, when using all 24 BDS-3 MEO satellites.
      PubDate: 2022-07-29
       
  • DOA tracking using an improved direction lock loop based on a
           three-element L-shaped array

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      Abstract: Abstract Direction Lock Loop (DiLL) utilizes the direction of arrival (DOA) error obtained from the spatial correlation characteristics of the array antenna beamforming and dynamically adjusts the estimated DOA value through a closed-angle tracking loop. DiLL is a representative DOA tracking method for a direct sequence code division multiple access (DS-CDMA) system. Nevertheless, several issues prohibit employing DiLL in a global navigation satellite system (GNSS), such as limited tracking range, dead-zone effect, and separation of the capturing and tracking process. To solve these problems, we propose an improved DiLL tracking scheme based on a three-element L-shaped array named 3L-DiLL. The developed method exploits the 90-degree angular difference that naturally exists in the L-shaped array response of the normalized spatial correlation function and obtains the angular difference between the estimated and the true DOA to realize real-time DOA tracking of the target signal. Considering an incident signal of \(-180\mathrm{ to}+{180}^{\circ }\) azimuth range and \(0-9{0}^{\circ }\) elevation range, the proposed method tracks DOA arbitrarily and eliminates the dead zone effect. Additionally, if the estimated azimuth error is within \([-{90}^{^\circ },+{90}^{^\circ }]\) , capturing DOA requires only one 3L-DiLL tracking cycle. Compared with the traditional DiLL, the proposed method is simpler and easier to apply in engineering applications. Simulations verify that 3L-DiLL has a wider tracking range, faster capture speed, and higher tracking accuracy than traditional DiLL schemes.
      PubDate: 2022-07-28
       
  • Real-time precise point positioning based on BDS-3 global short message
           communication

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      Abstract: Abstract Real-time precise point positioning (RTPPP) has obtained much attention and has been widely used in recent years, yet it depends very much on real-time precise satellite orbit and clock products. However, precise products cannot be received in regions where the Internet and mobile communication are restricted or even unavailable. We proposed a method for RTPPP based on global short message communication of BeiDou navigation satellite system (BDS-3) since it can provide two-way communication and global services. Several optimization schemes are adopted to reduce the required broadcast bandwidth due to limited resources. First, the state space representation (SSR) satellite orbit and clock corrections are combined into an equivalent distance correction. Second, all satellites broadcast the difference of pseudo-random noise (PRN) and Issue of Data Ephemeris (IODE), except that the first satellite broadcasts absolute PRN and IODE values. Last, on the basis of analyzing the relationship between product accuracy loss and positioning accuracy, the coding scheme of the satellite product is determined. Compared to the data size required to encode satellite orbit and clock products in SSR format, the proposed method can reduce this by more than 89%. Both simulated and live RTPPP experiments are conducted to verify the method proposed. For the same satellite orbit and clock corrections, the simulated results demonstrate that RTPPP based on BDS-3 GSMC corrections can provide comparable performance with SSR format products. In addition, live RTPPP based on BDS-3 GSMC equipment shows that the dynamic RTPPP can achieve positioning accuracy within 20 cm after 7 min of convergence.
      PubDate: 2022-07-19
       
  • Estimation and analysis of BDS-3 satellite yaw attitude using
           inter-satellite link observations

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      Abstract: Abstract China has completed the full BDS-3 constellation with satellites manufactured, respectively, by China Academy of Space Technology (CAST) and Shanghai Engineering Center for Microsatellites (SECM). This study investigates BDS-3 satellite yaw attitudes using Ka-band inter-satellite link (ISL) observations with relatively large horizontal satellite antenna phase center offsets, which have the advantage in the satellite yaw attitude estimation and validation. Based on the ISL observation data, the BDS-3 satellite yaw angles are estimated with the reverse kinematic precise point positioning approach, and the RMS error of yaw estimates is smaller than 3°. Comparisons between nominal and estimated yaw angles demonstrate that the CAST satellites experience the midnight- or noon-turn maneuvers when the β angle lies in the range of (− 3°, 3°) and the orbital angle lies in the range of approximately (− 6°, 6°) or (174°, 186°), whereas the SECM satellites only need to meet that the β angle is in the range of (− 3°, 3°). Accordingly, the different attitude models are applicable for BDS-3 satellites from different manufacturers. However, discrepancies between the yaw directions in the vicinity of zero β angle are observed for SECM satellites. The main feature shows that the yaw attitude transition when the β angle changes sign may be delayed and occurs only when the yaw angle is within approximately ± 5°. A modified attitude model is developed to reproduce the yaw behaviors for SECM satellites more appropriately. After applying the yaw-attitude models suitable for BDS-3 CAST and SECM satellites to ISL data processing, the ISL observation residuals during yaw maneuvers are reduced down to the normal level, which confirms the effectiveness of models.
      PubDate: 2022-07-17
       
  • In-depth analysis of UTC information broadcast in GNSS navigation messages

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      Abstract: Abstract Global Navigation Satellite Systems allow the users to synchronize their clock on the international time reference, the Coordinated Universal Time (UTC). To that aim, they broadcast in their navigation messages a prediction of the offset between the system reference time scale GNSST and a prediction of UTC. Due to the regular update of the navigation messages at the satellite level, different satellites simultaneously broadcast different sets of parameters for the prediction of UTC. We show how the UTC broadcast parameters differ from each other within each constellation, either among the satellites or among the message types. We quantify the impact of such differences at the user level and determine the synchronization uncertainties associated with these differences in the navigation messages. Our results show that even if it depends on the constellation, the 1-sigma uncertainty on the synchronization associated with the dispersion of the navigation messages is always lower than 4 ns, while very large differences can exist on some specific signals.
      PubDate: 2022-07-16
       
  • Satellite laser ranging to GNSS-based Swarm orbits with handling of
           systematic errors

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      Abstract: Abstract Satellite laser ranging (SLR) retroreflectors along with GNSS receivers are installed onboard numerous active low earth orbiters (LEOs) for the independent validation of GNSS-based precise orbit determination (POD) products. SLR validation results still contain many systematic errors that require special handling of various biases. For this purpose, we derive methods of reducing systematic effects affecting the SLR residuals to LEO Swarm satellites. We test solutions incorporating the estimation of range biases, station coordinate corrections, tropospheric biases, and horizontal gradients of the troposphere delays. When estimating range biases once per day, the standard deviation (STD) of Swarm-B SLR residuals is reduced from 10 to 8 mm for the group of high-performing SLR stations. The tropospheric biases estimated once per day, instead of range biases, further reduce the STD of residuals to the level of 6 mm. The systematic errors that manifest as dependencies of SLR residuals under different measurement conditions, e.g., elevation angle, are remarkably diminished. Furthermore, introducing troposphere biases allows for the comparison of the orbit quality between kinematic and reduced-dynamic orbits as the GPS-based orbit errors become more pronounced when SLR observations are freed from elevation-dependent errors. Applying tropospheric biases in SLR allows obtaining the consistency between the POD solution and SLR observations that are two times better than when neglecting to model of systematic effects and by 29% better when compared with solutions considering present methods of range bias handling.
      PubDate: 2022-07-14
       
 
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