A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z  

        1 2 3 | Last   [Sort by number of followers]   [Restore default list]

  Subjects -> GEOGRAPHY (Total: 493 journals)
Showing 1 - 200 of 277 Journals sorted alphabetically
40 [degrees] South     Full-text available via subscription   (Followers: 1)
AAG Review of Books     Hybrid Journal   (Followers: 2)
AbeÁfrica : Revista da Associação Brasileira de Estudos Africanos     Open Access  
ACME : An International Journal for Critical Geographies     Open Access   (Followers: 1)
Acta Universitatis Lodziensis : Folia Geographica Socio-Oeconomica     Open Access   (Followers: 1)
Adam Academy : Journal of Social Sciences / Adam Akademi : Sosyal Bilimler Dergisi     Open Access   (Followers: 3)
Advances in Cartography and GIScience of the ICA     Open Access   (Followers: 3)
Advances in Geosciences (ADGEO)     Open Access   (Followers: 19)
Advances in Statistical Climatology, Meteorology and Oceanography     Open Access   (Followers: 11)
Africa Insight     Full-text available via subscription   (Followers: 16)
Africa Spectrum     Open Access   (Followers: 16)
African Geographical Review     Hybrid Journal   (Followers: 2)
Afrika Focus     Open Access   (Followers: 1)
AGORA Magazine     Open Access   (Followers: 1)
Agronomía & Ambiente     Open Access   (Followers: 1)
AGU Advances     Open Access   (Followers: 1)
All Earth     Open Access   (Followers: 3)
American Journal of Geographic Information System     Open Access   (Followers: 14)
American Journal of Human Ecology     Open Access   (Followers: 11)
American Journal of Rural Development     Open Access   (Followers: 5)
Amerika     Open Access   (Followers: 1)
Anales de Geografía de la Universidad Complutense     Open Access  
Anatoli     Open Access  
Annales Universitatis Paedagogicae Cracoviensis / Studia de Cultura     Open Access  
Annals of GIS     Open Access   (Followers: 32)
Annals of the American Association of Geographers     Hybrid Journal   (Followers: 43)
Annual Review of Marine Science     Full-text available via subscription   (Followers: 13)
Antipode     Hybrid Journal   (Followers: 65)
Anuario     Open Access  
Applied Geography     Hybrid Journal   (Followers: 39)
Applied Geomatics     Hybrid Journal   (Followers: 4)
Ar@cne     Open Access  
Arctic     Open Access   (Followers: 2)
Arctic Science     Open Access   (Followers: 7)
Area Development and Policy     Hybrid Journal   (Followers: 1)
Asia Policy     Full-text available via subscription   (Followers: 6)
Asian Geographer     Hybrid Journal   (Followers: 5)
Asian Journal of Geographical Research     Open Access   (Followers: 2)
Ateneo Korean Studies Conference Proceedings     Open Access  
Atmospheric Measurement Techniques (AMT)     Open Access   (Followers: 19)
Atmospheric Measurement Techniques Discussions (AMTD)     Open Access   (Followers: 9)
Aurora Journal     Full-text available via subscription  
Australian Antarctic Magazine     Free   (Followers: 5)
Australian Geographer     Hybrid Journal   (Followers: 6)
Bandung : Journal of the Global South     Open Access   (Followers: 1)
Barn : Forskning om barn og barndom i Norden     Open Access  
Baru : Revista Brasileira de Assuntos Regionais e Urbanos     Open Access  
Belgeo     Open Access   (Followers: 2)
Biblio3W : Revista Bibliográfica de Geografía y Ciencias Sociales     Open Access  
Biogeographia : The Journal of Integrative Biogeography     Open Access   (Followers: 2)
BioRisk     Open Access   (Followers: 2)
Boletim Campineiro de Geografia     Open Access  
Boletim de Ciências Geodésicas     Open Access  
Boletim Gaúcho de Geografia     Open Access  
Boletim Goiano de Geografia     Open Access  
Boletín de Estudios Geográficos     Open Access  
Boletín de la Asociación de Geógrafos Españoles     Open Access  
Brill Research Perspectives in Map History     Full-text available via subscription   (Followers: 1)
Buildings & Landscapes: Journal of the Vernacular Architecture Forum     Full-text available via subscription   (Followers: 13)
Bulletin de la Société Géographique de Liège     Open Access  
Bulletin de l’association de géographes français     Open Access   (Followers: 1)
Bulletin of Geography. Physical Geography Series     Open Access   (Followers: 4)
Bulletin of Geography. Socio-economic Series     Open Access   (Followers: 3)
Bulletin of Geosciences     Open Access   (Followers: 12)
Bulletin of the Ecological Society of America     Open Access   (Followers: 4)
Bulletin of the Serbian Geographical Society     Open Access  
Caderno de Geografia     Open Access  
Cahiers Balkaniques     Open Access   (Followers: 2)
Cahiers Charlevoix : Études franco-ontariennes     Full-text available via subscription  
Cahiers franco-canadiens de l'Ouest     Full-text available via subscription   (Followers: 2)
California Italian Studies Journal     Full-text available via subscription   (Followers: 7)
Canadian Journal of Latin American and Caribbean Studies     Hybrid Journal   (Followers: 10)
Canadian Journal of Soil Science     Full-text available via subscription   (Followers: 11)
Cardinalis     Open Access  
Carnets de géographes     Open Access  
Cartographic Journal     Hybrid Journal   (Followers: 9)
Cartographic Perspectives     Open Access   (Followers: 2)
Cartographica : The International Journal for Geographic Information and Geovisualization     Full-text available via subscription   (Followers: 17)
Cartography and Geographic Information Science     Hybrid Journal   (Followers: 31)
Check List : The Journal of Biodiversity Data     Open Access   (Followers: 2)
China : An International Journal     Full-text available via subscription   (Followers: 20)
Climate and Development     Hybrid Journal   (Followers: 34)
Climate Change Economics     Hybrid Journal   (Followers: 50)
Comparative Cultural Studies : European and Latin American Perspectives     Open Access   (Followers: 5)
Computational Geosciences     Hybrid Journal   (Followers: 15)
Computational Urban Science     Open Access   (Followers: 1)
Confins     Open Access  
Conjuntura Austral : Journal of the Global South     Open Access   (Followers: 2)
Coolabah     Open Access  
Creativity Studies     Open Access   (Followers: 5)
Critical Romani Studies     Open Access  
Crossings : Journal of Migration & Culture     Hybrid Journal   (Followers: 16)
Cuadernos de Desarrollo Rural     Open Access  
Cuadernos de Geografía : Revista Colombiana de Geografía     Open Access  
Cuadernos de Geografía de la Universitat de València     Open Access  
Cuadernos de Investigación Geográfica / Geographical Research Letters     Open Access  
Cuadernos Inter.c.a.mbio sobre Centroamérica y el Caribe     Open Access   (Followers: 1)
Current Research in Geoscience     Open Access   (Followers: 5)
Dela     Open Access  
Dialogues in Human Geography     Hybrid Journal   (Followers: 20)
Didáctica Geográfica     Open Access  
DIE ERDE : Journal of the Geographical Society of Berlin     Open Access   (Followers: 1)
Documenti Geografici     Open Access  
Documents d'Anàlisi Geogràfica     Open Access  
Doğu Coğrafya Dergisi : Eastern Geographical Review     Open Access  
DRd - Desenvolvimento Regional em debate     Open Access  
Earth System Governance     Open Access   (Followers: 1)
Earth Systems and Environment     Hybrid Journal   (Followers: 3)
East/West : Journal of Ukrainian Studies     Open Access  
Eastern European Countryside     Open Access   (Followers: 2)
Economic and Regional Studies / Studia Ekonomiczne i Regionalne     Open Access  
Economic Geography     Hybrid Journal   (Followers: 42)
Économie rurale     Open Access   (Followers: 3)
Ecosystems and People     Open Access   (Followers: 4)
Entorno Geográfico     Open Access  
Environment & Ecosystem Science     Open Access   (Followers: 3)
Environmental and Sustainability Indicators     Open Access   (Followers: 7)
Environmental Science : Atmospheres     Open Access   (Followers: 1)
Environmental Science and Sustainable Development : International Journal Of Environmental Science & Sustainable Development     Open Access   (Followers: 13)
Environmental Smoke     Open Access  
Ería : Revista Cuatrimestral de Geografía     Open Access  
Espacio y Desarrollo     Open Access  
Espacios : Revista de |Geografía     Open Access  
Espaço & Economia : Revista Brasileira de Geografia Econômica     Open Access  
Espaço Aberto     Open Access  
Espaço e Cultura     Open Access  
Espaço e Tempo Midiáticos     Open Access  
Estudios Geográficos     Open Access   (Followers: 1)
Estudios Socioterritoriales : Revista de Geografía     Open Access  
Ethnobiology Letters     Open Access  
Ethnoscientia : Brazilian Journal of Ethnobiology and Ethnoecology     Open Access  
eTropic : electronic journal of studies in the tropics     Open Access  
Études internationales     Full-text available via subscription   (Followers: 1)
Études rurales     Open Access   (Followers: 2)
Études/Inuit/Studies     Full-text available via subscription  
European Bulletin of Himalayan Research     Open Access   (Followers: 6)
European Countryside     Open Access   (Followers: 1)
European Spatial Research and Policy     Open Access   (Followers: 9)
Evolutionary Human Sciences     Open Access   (Followers: 5)
Fennia : International Journal of Geography     Open Access   (Followers: 1)
Finisterra : Revista Portuguesa de Geografia     Open Access  
Fire Ecology     Open Access   (Followers: 3)
Florida Geographer     Open Access   (Followers: 1)
Focus on Geography     Partially Free   (Followers: 5)
Forum Geografi     Open Access  
Frontera Norte     Open Access  
GEM - International Journal on Geomathematics     Hybrid Journal   (Followers: 1)
Genre & histoire     Open Access   (Followers: 4)
Geo : Geography and Environment     Open Access   (Followers: 8)
Geo UERJ     Open Access  
Geo-Image     Open Access   (Followers: 1)
Geo-spatial Information Science     Open Access   (Followers: 7)
GeoArabia     Hybrid Journal  
Géocarrefour     Open Access  
Geochemistry, Geophysics, Geosystems     Full-text available via subscription   (Followers: 34)
Geochronometria     Open Access   (Followers: 1)
Geoderma Regional : The International Journal for Regional Soil Research     Full-text available via subscription   (Followers: 4)
Geodesy and Cartography     Open Access   (Followers: 2)
Geoforum Perspektiv     Open Access   (Followers: 1)
Geofronter     Open Access  
Geografares     Open Access  
Geografisk Tidsskrift-Danish Journal of Geography     Hybrid Journal   (Followers: 3)
Geografiska Annaler, Series A : Physical Geography     Hybrid Journal   (Followers: 4)
Geographia     Open Access   (Followers: 1)
Geographica Helvetica     Open Access   (Followers: 13)
Geographical Analysis     Hybrid Journal   (Followers: 11)
Geographical Education     Full-text available via subscription   (Followers: 2)
Geographical Journal of Nepal     Open Access  
Geographical Research     Hybrid Journal   (Followers: 11)
Geographical Review     Hybrid Journal   (Followers: 13)
Geographicalia     Open Access  
Géographie et cultures     Open Access   (Followers: 3)
Geography and Natural Resources     Hybrid Journal   (Followers: 10)
Geography and Sustainability     Open Access   (Followers: 2)
Geography Compass     Hybrid Journal   (Followers: 18)
GeoHumanities     Hybrid Journal   (Followers: 2)
GeoInformatica     Hybrid Journal   (Followers: 7)
Geoinformatics & Geostatistics     Hybrid Journal   (Followers: 14)
Geoinformatics FCE CTU     Open Access   (Followers: 8)
Geoingá : Revista do Programa de Pós-Graduação em Geografia     Open Access  
GeoJournal     Hybrid Journal   (Followers: 11)
GEOMATICA     Hybrid Journal   (Followers: 1)
Geomatics, Natural Hazards and Risk     Open Access   (Followers: 14)
GEOmedia     Open Access   (Followers: 1)
Geopauta : Revista de Geografia da Universidade Estadual do Sudoeste da Bahia     Open Access  
Geophysical Research Letters     Full-text available via subscription   (Followers: 183)
Geoplanning : Journal of Geomatics and Planning     Open Access   (Followers: 5)
GeoScape     Open Access  
Geosciences Journal     Hybrid Journal   (Followers: 11)
Geosphere     Open Access   (Followers: 2)
GEOUSP : Espaço e Tempo     Open Access  
Ghana Journal of Geography     Open Access   (Followers: 11)
Ghana Studies     Full-text available via subscription   (Followers: 15)
GIScience & Remote Sensing     Open Access   (Followers: 54)
Global Challenges     Open Access   (Followers: 1)
Global Sustainability     Open Access   (Followers: 5)
Globe, The     Full-text available via subscription   (Followers: 4)
GPS Solutions     Hybrid Journal   (Followers: 28)
Grafo Working Papers     Open Access  
HiN : Alexander von Humboldt im Netz. Internationale Zeitschrift für Humboldt-Studien     Open Access  

        1 2 3 | Last   [Sort by number of followers]   [Restore default list]

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]
  • Improving the combined GNSS/INS positioning by using tightly integrated
           RTK

    • Free pre-print version: Loading...

      Abstract: GNSS/INS combined technology is nowadays one of the most widely used high-precision positioning methods for outdoor users. However, the performance of the GNSS/INS combined system will be degraded when the satellite signals are subject to long-term obstruction or interference. A common way to overcome this limitation is to integrate the additional sensors, which increases additional expenses. Motivated by our previous work that the Tightly integrated Real-Time Kinematic (TRTK), which makes use of the additional inter-system differential observations of overlapping frequencies and can significantly improve the performance of the Loosely integrated RTK (LRTK) which directly stacks the intra-system differential observations and is currently used in the GNSS/INS combined system, we further study the enhanced GNSS/INS combined technique to improve the positioning performance by using TRTK, particularly in harsh environments. First, the difference between TRTK and LRTK are analytically addressed, and the uniform expression for three TRTK models specified by differential inter-system biases, i.e., DISB-float, -constant and -fixed models, are presented. Then, the GNSS/INS combined equations are derived based on the DISB-fixed TRTK model. Both semi-simulated and real field tests are carried out in different environments to show the improvements of GNSS/INS with TRTK compared to that with LRTK. The result shows that the TRTK-specified GNSS/INS combined model can significantly improve positioning accuracy, especially when the satellite signals suffer severe occlusion. Thanks to the four-system dual-frequency observations we used, at most 6 additional redundant observations will be introduced at each epoch in TRTK. Compared to the traditional algorithm, our proposed algorithm on average reduces the averaged horizontal position error by 53.2% for the two tests, and even by 73.1% in a situation where the number of visible satellites is less than about 7.
      PubDate: 2022-09-20
       
  • Efficient chip-shape correlator implementation on a GPU-based real-time
           GNSS SDR receiver

    • Free pre-print version: Loading...

      Abstract: Global navigation satellite system (GNSS) software-defined radio (SDR) receivers play a very important role in many fields of GNSS due to their flexibility and configurability. In an SDR receiver, the correlation process is the main computational burden. Correlation acceleration based on a graphics processing unit (GPU) meets the real-time requirements of a modern SDR receiver. The chip-shape correlator based on signal compression can effectively measure the correlation function and chip shape, which is necessary for some multipath mitigation and signal quality monitoring algorithms. We present a GPU-based chip-shape correlator architecture implemented with CUDA, in which the chip transitions and multiple correlator values can be calculated by signal compression. Especially for the parallel algorithm of signal compression, a sample-to-thread mapping mechanism is further proposed to greatly reduce registers used per thread, which can avoid register spilling and improve performance. The test results show that while processing the 84 channels of 7 signals at the same time, our SDR receiver with the designed chip-shape correlator based on a GPU can complete chip shape transition measurement and calculation of 39 correlator values of 1 ms GNSS data within 0.6 ms, meeting the real-time processing requirement.
      PubDate: 2022-09-20
       
  • UTC and GNSS system time access using PPP with broadcast ephemerides

    • Free pre-print version: Loading...

      Abstract: The application of precise point positioning with broadcast ephemerides (PPP-BCE) is discussed as an alternative to the established all-in-view technique for multi-GNSS time transfer. It combines the use of broadcast ephemerides with low-noise carrier-phase observations for accessing GNSS system time scales and Coordinated Universal Time (UTC) with improved precision, and can be employed on stationary as well as mobile receivers in offline or real-time analyses. Using calibrated timing receivers, the method is shown to provide estimates of the GNSS-to-GNSS time offsets (XYTOs) with an accuracy at the 2 ns level. In the absence of prior calibrations, 0.5 ns consistency across different stations is achieved for GPS, Galileo, and BeiDou-3 after adjustment of systematic biases in comparison with calibrated reference stations or broadcast XYTO values. Furthermore, access to GNSS-specific UTC realizations can be obtained through predictions of the UTC offset from GNSS system time as provided in the broadcast ephemerides of individual constellations. The overall quality of the PPP-BCE-derived receiver clock offsets from UTC is assessed using calibrated receivers at various timing laboratories along with BIPM-provided UTC-UTC(k) measurements. Over the 1.5 years covered in the study, an accuracy of 1.8 ns for GPS and 2.5 ns for Galileo is demonstrated. For BeiDou, a slightly worse accuracy of 3 ns is obtained for a single timing laboratory over 9 months.
      PubDate: 2022-09-17
       
  • A weighted mean temperature (Tm) augmentation method based on global
           latitude zone

    • Free pre-print version: Loading...

      Abstract: The weighted mean temperature (Tm) is a function of atmospheric temperature and vertical humidity profiles. It plays a crucial role in the progress of retrieving water vapor information from the tropospheric delay of GNSS signals. The Tm estimated by the empirical models is always used to convert the zenith wet delay (ZWD) to precipitable water vapor (PWV) in GNSS meteorology. However, these empirical Tm models used trigonometric functions, making it difficult to describe Tm in detail and leading to an obvious accuracy difference with latitude changes. Thus, a global latitude zone augmentation mode was adopted for the empirical Tm models; the augmentation coefficients for each latitude zone were obtained by introducing the measured surface temperature and using the least-squares method. Using the Tm data of 2011–2015 derived from radiosonde, the GPT3 model, UNB3m model, and GWTMD model were augmented and analyzed. The results show that all augmentation models can improve the accuracy of the estimated Tm compared with their corresponding original models, and their levels of improvement are different. The three augmentation models achieved an average RMSE of 2.79 K, 3.47 K, and 3.22 K, which correspond to 22%, 49%, and 8% improvement against the GPT3 model, UNB3m model, and GWTMD model. In addition, the comparisons with the Tm linear formula were carried out and showed the superiority of the augmentation models.
      PubDate: 2022-09-16
       
  • Multi‑constellation GNSS interferometric reflectometry for the
           correction of long-term snow height retrieval on sloping topography

    • Free pre-print version: Loading...

      Abstract: Snow is a key parameter for global climate and hydrological systems. Global Navigation Satellite System interferometric reflectometry (GNSS-IR) has been applied to accurately monitor snow height (SH) with low cost and high temporal–spatial resolution. We proposed an improved GNSS-IR method using detrended signal-to-noise ratio ( \(\delta \;{\text{SNR}}\) ) arcs corresponding to multipath reflection tracks with different azimuths. After using wavelet decomposition and random sample consensus, noise with various frequencies for SNR arcs and outliers of reflector height (RH) estimations have been sequentially mitigated to enhance the availability of the proposed method. Thus, a height datum based on the ground RHs retrieved from multi-GNSS SNR data is established to compensate for the influence of topography variation with different azimuths in SH retrieval. The approximately 3-month \(\delta \,{\text{SNR}}\) datasets collected from three stations deployed on sloping topography were used to retrieve SH and compared with the existing method and in situ measurements. The results show that the root mean square errors of the retrievals derived from the proposed method for the three sites are between 4 and 8 cm, and the corresponding correlation surpasses 0.95 when compared to the reference SH datasets. Additionally, we compare the performance of a retrieval with the existing GNSS-IR Web App, and it shows an improvement in RMSE of about 7 cm. Furthermore, because topography variation has been considered, the average correction of SH retrievals is between 2 and 4 cm. The solution with the proposed method helps develop the applications of the GNSS-IR technique on complex topography.
      PubDate: 2022-09-15
       
  • A new efficient fusion positioning method for single-epoch multi-GNSS
           based on the theoretical analysis of the relationship between ADOP and
           PDOP

    • Free pre-print version: Loading...

      Abstract: The global navigation satellite system (GNSS) can provide single-epoch differential positioning services for geological disasters with a sudden and instantaneous nature. It needs fast and precise monitoring, which lies in the rapidly and correctly fixing ambiguities of GNSS. Compared to a single-frequency single system (SF-SS), multiple GNSSs (multi-GNSS) can achieve a high success rate (SR), but the positioning becomes time- and power-consuming due to its large number of visible satellites. Satellite selection and partial ambiguity resolution (PAR) can improve the positioning efficiency of multi-GNSS, but they cannot achieve precise and high-SR rapid positioning. How to effectively utilize multi-GNSS observations to achieve fast, precise, and high-SR single-epoch positioning becomes crucial. Hence, the following theory and method are developed. The roles of code and carrier observations in precise and high-SR positioning are theoretically analyzed. Then, the relationships between position dilution of precision and ambiguity dilution of precision (ADOP) are established by adopting the Schur-Horn Theorem, Majorization Theorem, and Weyl Theorem. Based on the above analyses, a PAR method of ADOP-based BeiDou navigation satellite system (BDS)/Galileo system (Galileo) augmenting global positioning system (GPS) (A-GPS/BDS/Galileo) is proposed. The single-epoch relative positioning results of SR, positioning accuracy, time consumption, and the R-ratio test-based fixed reliability demonstrate that A-GPS/BDS/Galileo outperforms the traditional SF-SS and single/dual-frequency multi-GNSS methods: it can achieve fast and precise positioning with an empirical SR of 100.0%; its R-ratio test-based accept, successfully fixed, failure, detection, and false alarm rates can be up to 98.5%, 100.0%, 0.0%, 0.01%, and 1.5%, respectively.
      PubDate: 2022-09-10
       
  • Estimation of ionospheric total electron content using GNSS observations
           derived from a smartphone

    • Free pre-print version: Loading...

      Abstract: The global navigation satellite system (GNSS) measurements to determine ionospheric total electron content (TEC) are mainly derived from expensive geodetic-grade receivers, which are not conducive to high-density placement. In this work, we present an analysis of the performance of ionospheric TEC determined by GNSS dual-frequency measurements derived from the smartphone, taking the Xiaomi 8 (XMI8) as an example. First, the ionospheric observable is retrieved from the code and carrier phase data using the carrier-to-code leveling technique and a new carrier-to-noise weighting strategy instead of an elevation weighting strategy, considering the characteristic of the GNSS measurements from smartphones. Then, the absolute ionospheric slant TEC (STEC) values are isolated from the ionospheric observables by modeling with the generalized trigonometric series function. The experimental data, covering over 120 h, were taken from two situations: one is the data collected by the original smartphone antenna; the other is the external geodetic-grade antenna. The TEC data obtained from the collocated geodetic-grade receiver are used as reference data to evaluate the performance of the TEC values from XMI8. Compared to the reference data, the evaluation results show that the ionospheric STEC extraction accuracy can reach total electron content unit (TECU) values of 0.17 and 0.11 under the two different situations in the continuous carrier phase satellite arc without cycle slips. In addition, the VTEC modeling accuracy is above 5 and 2 TECU in the two different situations, respectively. Thus, we concluded that consumer-level GNSS chipsets are highly potential in the future to increase the ionospheric monitoring station density due to their low costs and good data quality.
      PubDate: 2022-09-04
       
  • Precise orbit determination for the Haiyang-2D satellite using new onboard
           BDS-3 B1C/B2a signal measurements

    • Free pre-print version: Loading...

      Abstract: The GNSS receiver onboard the Haiyang-2D (HY-2D) China Ocean satellite tracks the new B1C and B2a signals of BDS-3 to orbit determination. This study analyzes one week of onboard dual-frequency BDS-3 data obtained during July 2021 from the HY-2D satellite. The quality of the onboard BDS-3 measurements is first evaluated in terms of the data quantity and code multipath error quantities. Thanks to the IGSO and GEO satellites of BDS-3, the HY-2D satellite can observe more BDS-3 satellites in China and surrounding areas. The multipath errors (MPs) of the B1C and B2a signals are approximately 0.6 m and 0.2 m, respectively; they have centimeter-level systematic biases which change linearly with elevation. For precise orbit determination (POD), the observable-specific signal biases (OSBs) are corrected by the OSB products obtained from the GNSS Research Center of Wuhan University (WHU), showing that the ionospheric-free code residuals of B1C and B2a signals are reduced from 5.6 to 1.3 m. The phase center variation (PCV) model is corrected by the residual approach, and the orbit determination residuals of carrier phases can be improved to 7.5 mm. The orbit accuracy, indicated by the satellite laser ranging (SLR) validation, is about 2.3 cm during the study period. Upon conducting the Doppler Orbitography and Radio-positioning Integrated by Satellite (DORIS) validation, orbit differences less than 5.2 cm in the 3D direction are obtained with the BDS-3-based orbits, and high consistency is achieved in the radial orbit component.
      PubDate: 2022-09-03
       
  • Improved method for the GPS high-precision real-time satellite clock error
           service

    • Free pre-print version: Loading...

      Abstract: The real-time service (RTS) of satellite clock offsets is one of the main routine tasks for real-time precise point positioning (PPP). The quadratic polynomial coefficients of the GPS satellite clock corrections in the International GNSS Service (IGS) RTS are updated every 5 s. This frequent updating of the satellite clock correction coefficients means that the quadratic polynomial adopted in IGS RTS is inadequate if a lack of connectivity necessitates extrapolation over minutes instead of seconds. An improved RTS, using a polynomial and harmonic-based function, is proposed to address this concern. Its functions are constructed based on the periodic variations in the GPS satellite clock corrections observed from the differences between the estimated satellite clock corrections and those of the broadcast ephemeris over one year. The eighth-order harmonic coefficients are updated in the improved RTS every 6 h. Extrapolation results show that the combined results of a quadratic polynomial plus an eighth-order harmonic-based function are better than those of a quadratic polynomial plus a fourth-order harmonic-based function. The 6 h extrapolation accuracy of the combined quadratic polynomial and eighth-order harmonic-based function reaches 0.81 ns and is significantly improved over that of the current IGS ultra-rapid products. Under good connectivity condition and eighth-order harmonic coefficients at 6 h intervals, which transmits linear polynomial coefficients at 1 min intervals, is better than the IGS RTS product, with a 5-day averaged root mean square of 0.10 ns. Although the update interval of the improved RTS is 12 times larger than that of the current IGS RTS, its 5-day static and kinematic PPP performances are better at all 55 IGS stations tested. Even if connectivity is interrupted for several minutes, the improved method can reach centimeter and even millimeter accuracy.
      PubDate: 2022-09-02
       
  • Estimating surface optical properties and thermal thrust for Galileo
           satellite body and solar panels

    • Free pre-print version: Loading...

      Abstract: Precise orbit determination of GNSS (Global Navigation Satellite System) satellites requires accurate models of perturbing forces acting on the spacecraft, i.e., solar radiation pressure (SRP) and thermal radiation forces. With the officially published satellite metadata, the analytical box-wing model is usually used to describe most of the SRP accelerations and the rest is assumed to be compensated by estimating ECOM/ECOM2 (Empirical CODE Orbit Model) parameters. However, we find that the precision of Galileo satellite orbits shows notable degradation inside eclipse seasons for 3-day-arc solutions and 24-h predictions. For instance, the RMS (root-mean-square) of orbit misclosures increases by about a factor of two in the eclipse season when using the box-wing model as the a priori and the 5-parameter ECOM model on top. The reason is proven to be mostly due to ignoring imbalanced thermal radiation forces (i.e., radiator emission and thermal radiation of solar panels) as satellite thermal properties are unknown. These imbalanced thermal effects cannot be fully absorbed by the ECOM/ECOM2 parameters inside eclipse seasons because the earth’s shadowing of a satellite in orbit causes periodic changes of the thermal environment. To cope with this problem, we first estimate satellite optical and thermal parameters as part of orbit determination based on Galileo tracking data covering 1 year. Then, we add physical thermal radiation models for radiators and solar panels as part of the a priori model and evaluate the performance of different ECOM models in Galileo satellite orbit determination. As shown by orbit misclosures, 24-h orbit predictions and SLR (Satellite Laser Ranging) residuals, the 7-parameter ECOM2 model performs better than the 5-parameter ECOM and the 9-parameter ECOM2 model for Galileo satellites. When using the 7-parameter ECOM2 model on top, the impact of the radiator emission and the thermal radiation of solar panels on Galileo satellite orbits is about 1 and 2 cm, respectively, inside eclipse seasons for 3-day-arc solutions.
      PubDate: 2022-08-30
       
  • Applying principal components to analyze the distribution of model biases
           in GNSS tropospheric tomography for a case study in Northwestern Iran

    • Free pre-print version: Loading...

      Abstract: Although GNSS tropospheric tomography is a powerful tool in meteorology, available validation data limit its accuracy and precision analysis. Moreover, it is customary to accept the validation results as a measure of the model performance. This study shows that this is only possible when the sensitivity of the model elements to the input perturbations is the same. We propose the principal component analysis for studying the sensitivity of a tomography model for this purpose. Our model includes 17 GNSS stations in Northwestern Iran. To analyze the contribution of the applied constraints in the sensitivity results, we use the 3D Gaussian, horizontal, numerical weather prediction model and virtual reference stations (VRS) in our analysis. The results show that some parts of our model are more sensitive to perturbations of input parameters, and therefore, they are more prone to regularization bias. This depends not only on time but also on the applied constraints for computing a unique solution. Results show that the response of our model to input perturbations is considerably different when we use the VRS concept for constraining the model. Using the proposed method and the traditional ways of validating a tomography model, one can develop a lower bound limit for the bias in the sensitive parts of the model and an upper bound limit for the bias in the other parts.
      PubDate: 2022-08-22
       
  • Two-step success rate criterion strategy: a model- and data-driven partial
           ambiguity resolution method for medium-long baselines RTK

    • Free pre-print version: Loading...

      Abstract: When GNSS measurement errors such as ionospheric delays remain large, full ambiguity resolution (FAR) takes an unacceptably long time to fix ambiguities to integers. Partial ambiguity resolution (PAR), under this circumstance, is a possible solution to obtain precise positioning before FAR is achieved. PAR fixes a subset of ambiguities instead of all to improve either the fix rate, success rate or positioning accuracy according to different criteria. This contribution proposes a two-step success rate criterion (TSRC) strategy that first chooses ambiguities to fix using a given success rate threshold and then adds more ambiguities to fix by maximizing the expectation of baseline precision improvement from fixing ambiguities. Then, the TSRC strategy is compared with two other commonly used PAR strategies and the FAR strategy in an experiment with real data forming a medium-long-baseline setup (baselines longer than 15 km and shorter than 50 km). The results show that in medium-long-baseline cases, the TSRC achieves the shortest time to first fix (TTFF), which is 100–200 s shorter than other PAR strategies and 400–800 s shorter than the FAR strategy, excluding cases in which FAR fixes no ambiguities at all. Consequently, the TSRC yields the highest positioning accuracy on average. In addition, the variance–covariance (VC)-matrix of the float ambiguities is found to have a heavy impact on the TSRC strategy in some cases, and amplifying the VC-matrix before the ambiguity fixing process can partly mitigate it.
      PubDate: 2022-08-22
       
  • Machine learning-based methods for sea surface rainfall detection from
           CYGNSS delay-doppler maps

    • Free pre-print version: Loading...

      Abstract: Because of its unique advantages of a short revisit period, cheap observation cost, and high spatial–temporal resolution, GNSS-Reflectometry (GNSS-R) technology has been used successfully in the field of ocean remote sensing. However, there is very limited research on rainfall detection (RD) using this technology. For this purpose, we aim to study the potential of spaceborne GNSS-R in RD Using Delay-Doppler Maps (DDMs) data collected by Cyclone GNSS (CYGNSS) satellites. First, a fast Non-Local Means (NLM) algorithm based on integral images is proposed for DDM denoising to enhance the quality of DDM data. Then, three GNSS-R observables [i.e., DDM average (DDMA), leading edge slope (LES), and trailing edge slope (TES)] derived from power DDM are calculated. In addition, because the RD method based on probability density function (PDF) observables threshold is greatly affected by factors such as geometry and sea state, we have proposed three new methods for spaceborne GNSS-R RD based on Support Vector Machines (SVM), Random Forests (RF) and Convolutional Neural Networks (CNN), respectively. These three methods have significant advantages in establishing multi-parameter models and can provide a strong alternative for spaceborne GNSS-R sea surface RD. To evaluate the RD performance of the proposed methods, the Integrated Multi-satellite Retrievals of Global Precipitation Measurements (GPM-IMERG) is used as reference data. The experimental results show that the proposed three methods are significantly better than the PDF method in precision, recall, and F1 score. Moreover, the RD accuracy of the proposed SVM and RF method is basically the same, while the proposed CNN method is significantly better than the other two methods. Especially compared with the PDF method, the RD accuracy is improved by more than 10%. Generally, when the wind speed is less than 10 m/s, our proposed CNN method can detect rainfall and achieve good detection performance with spaceborne GNSS-R data, which can be better than 78.5%, 83.8%, and 78.1% in precision, recall, and F1 score, respectively.
      PubDate: 2022-08-20
       
  • Motion model-assisted GNSS/MEMS-IMU integrated navigation system for land
           vehicle

    • Free pre-print version: Loading...

      Abstract: Micro-electromechanical systems and inertial measurement units (MEMS-IMUs) show great advantages in terms of price and size. Nevertheless, due to limitations of technology, their observations are easily affected by the surrounding environment (temperature, vibration, and electronic noise). Most methods resist the effect of gross errors by adjusting covariance matrices in the integrated navigation of a global navigation satellite system (GNSS) and inertial navigation system (INS). We propose a motion model-assisted integrated navigation method on the basis of a constant yaw rate and velocity (CTRV) model, which serves as a constraint condition and detects gross errors by a Chi-squared test. The results of the CTRV are used to correct the carrier state from INS mechanization. A field test was carried out to verify the performance of the CTRV-assisted method. Compared with a robust Kalman filter, the method improves the horizontal accuracy of position and velocity by more than 87% and 68%, respectively, in a medium-precision loosely and tightly coupled system, and of the velocity and attitude by more than 52% and 20%, respectively, in a low-precision loosely and tightly coupled system. Therefore, the CTRV-assisted method can significantly enhance the performance of GNSS/MEMS-IMU integrated navigation systems.
      PubDate: 2022-08-16
       
  • BDS-3 and GPS/Galileo integrated PPP using broadcast ephemerides

    • Free pre-print version: Loading...

      Abstract: Improved broadcast ephemerides of BDS-3 and Galileo systems provide new opportunities for precise point positioning with broadcast ephemerides (BE-PPP) instead of using precise ephemeris products. We propose an approach of BDS-3 and GPS/Galileo integrated BE-PPP, emphasizing modeling and mitigating specific errors of broadcast ephemerides. First, the standard precise point positioning (PPP) model is extended by considering systematic rotation errors implied in BDS-3 broadcast orbits. For each station, a comprehensive bias is then considered to account for the known signal-in-space error (SISE) bias and the satellite/receiver hardware delay unavailable for some observations before the positioning. Besides, an explicit parameter is included in the PPP model to compensate for the remaining errors of SISE for each satellite. Considering that the SISE discontinuity of BDS-3 is larger than that of Galileo, the SISE parameters for BDS-3 satellites are reset in all the BE-PPP solutions except the BDS-3 only kinematic positioning when broadcast ephemerides are updated. Tests performed with 64 global stations demonstrate that the three-dimensional (3D) position errors of BDS-3/GPS/Galileo integrated PPP can be 8.6 cm in static mode and 23.4 cm in simulated kinematic mode. Although suffering from fewer BDS-3 observations tracked by ground stations, triple-constellation solutions with BDS-3 still offer a 9% performance improvement for static mode and 20% for simulated kinematic mode compared to GPS/Galileo solutions. On the other hand, the orientation errors in BDS-3 broadcast orbits have been successfully mitigated by explicit estimations of rotation parameters in the integrated BE-PPP. The averaged rotation estimates derived from BDS-3/Galileo solutions agree well with those from orbit comparisons, and correlations of 0.79, 0.88 and 0.94 are obtained for x-, y- and z-rotations, respectively. With considering orientation and translation errors of BDS-3 orbits in integrated solutions, improvements of 3D position accuracy up to 1.7 cm (static) and 0.9 cm (kinematic) can be achieved, where the horizontals offer the dominating improvements.
      PubDate: 2022-08-15
       
  • Performance improvement of the GAGAN satellite-based augmentation system
           based on local ionospheric delay estimation in Thailand

    • Free pre-print version: Loading...

      Abstract: Satellite-Based Augmentation System (SBAS) is essential to support aircraft navigation. L1 SBAS operates on the L1 frequency (1575.42 MHz) and is currently still of interest since all GNSS satellites and receivers do not fully support additional frequencies such as L5 (1176.45 MHz). Although the Global Positioning System (GPS) aided Geo Augmented Navigation (GAGAN) SBAS is available, the performances are degraded due to the discrepancies of the ionospheric correction over Thailand and surrounding areas. Hence, in this work, we propose a new method based on the geometry-free ionospheric delay estimation with a single frequency (L1) and a single reference station requirement. The local ionospheric delays are estimated based on the proposed method with the observed GPS and GAGAN data in Thailand. Then the ionospheric corrections are obtained from the estimated local ionospheric delays. The analysis shows that using the estimated corrections, the positioning errors are reduced both on quiet days and locally disturbed days in 2019. More reductions in the positioning errors are found in September and December than other months. In addition, we perform a preliminary availability assessment of two critical phases of flights. The GAGAN performances with the proposed method for the APV-I and LPV-200 categories are improved up to 57% and 53%, respectively, in comparison with the baseline method of the IGP correction.
      PubDate: 2022-08-15
       
  • Improving GNSS baseband using an RTK-position-aided code tracking
           algorithm

    • Free pre-print version: Loading...

      Abstract: In an urbanized environment, a superior baseband algorithm fundamentally enhances global navigation satellite system (GNSS) receivers by resisting interferences such as reflection leading to multipath signals and abnormal dynamics caused by user’s motion or non-line-of-sight (NLOS) signals. A carrier aiding algorithm is frequently adopted to remove most dynamic errors on local code signals. Depending on this idea, all-channel spatial information based on the user’s velocity is also exploited by existing vector tracking techniques to aid code tracking. As known, a carrier phase is one order of magnitude less noisy and more capable of mitigating multipath than a code phase. The traditional carrier frequency aiding improves the precision of the code phase estimation by suppressing random noise, but it is powerless in eliminating the biased error. To solve this issue, a real-time kinematic (RTK) solution, which is the product of the carrier phase, is proposed to remove the absolute biased error in the vector delay/frequency lock loop (VDFLL). Thus, the GNSS baseband can be optimized with both the carrier frequency and the absolute carrier phase aiding. Two stationary real-world experiments are conducted in open-sky and light-urban situations to verify the proposed GNSS software-defined radio (SDR) using collected GPS L1 C/A intermediate frequency (IF) data. The testing results demonstrate that the proposed SDR improves the pseudorange quality and positioning accuracy by a maximum of 48.5% and 42.5%, respectively.
      PubDate: 2022-08-13
       
  • Toward BDS/Galileo/GPS/QZSS triple-frequency PPP instantaneous integer
           ambiguity resolutions without atmosphere corrections

    • Free pre-print version: Loading...

      Abstract: Multi-frequency precise point positioning (PPP) has drawn attention along with the modernization of the Global Navigation Satellite Systems. There are now nearly 90 satellites providing multi-frequency signals. This contribution aims to achieve fast convergence of a few seconds for BDS/Galileo/GPS/QZSS integrated triple-frequency PPP with integer ambiguity resolution (IAR) without atmosphere corrections. A unified model of an uncombined and undifferenced manner for PPP-IAR with dual- and triple-frequency observations is presented. The uncalibrated phase delays (UPD) of extra wide-lane (EWL), wide-lane (WL), and N1 ambiguities for triple-frequency PPP are estimated with standard deviations of 0.02, 0.05, and 0.10 cycles achieved, respectively. The PPP-IAR validation based on 20 stations evenly distributed in China is conducted using UPD products generated from a regional network covering a large part of China. The EWL, WL, and N1 ambiguities are sequentially fixed utilizing the least-squares ambiguity decorrelation adjustment (LAMBDA) technique. In terms of convergence time, PPP instantaneous IAR is achievable without using atmosphere corrections, thanks to the contribution of the multi-frequency and multi-constellation observations. This has been proved by performing PPP-IAR restart every 10-min over 2520 times in our case study. For PPP-IAR solutions produced with BDS/Galileo/GPS/QZSS triple-frequency observations with an interval of 1 s, the convergence is fulfilled within 1 s for the horizontal components with an accuracy of better than 5 cm, while 2 s for the vertical component with better than 10 cm accuracy, and both are at 95% confidence level.
      PubDate: 2022-08-13
       
  • Can sea ice thickness be retrieved using GNSS-interferometric
           reflectometry'

    • Free pre-print version: Loading...

      Abstract: A method for retrieving snow and sea ice thickness is developed and simulations are conducted to evaluate the feasibility of the proposed method. When using a defined envelope amplitude and phase, for the snow-free case, RMSEs of 0.24 and 0.34 m can be obtained; for the snow-covered case, the RMSEs of the retrieved sea ice thickness decrease to 0.45 and 0.48 m, and the RMSEs of the retrieved snow thickness are 0.12 and 0.13 m. A method combining the envelope amplitude and phase is proposed to further improve the retrieval accuracy. The simulated results show that combining these two observables can provide an RMSE of 0.19 m for the snow-free case, and for the snow-covered case, the RMSEs of the retrieved snow and sea ice thicknesses are reduced to 0.09 and 0.42 m, respectively. Furthermore, linear polarization observations are proposed and tested. The vertical polarization shows the best measurement performance. When the envelope amplitude and phase of the vertical polarization carrier to noise ratio (CNR) are combined to retrieve snow and sea ice thicknesses, the RMSEs of the retrieved sea ice thickness for the snow-free case decrease to 0.13, and for the snow-covered case, the RMSEs of the retrieved snow and sea ice thicknesses decrease to 0.07 and 0.17 m, respectively.
      PubDate: 2022-08-13
       
  • Impact of solar radiation pressure models on earth rotation parameters
           derived from BDS

    • Free pre-print version: Loading...

      Abstract: Earth rotation parameters (ERPs) are susceptible to absorbing the spurious effects from global navigation satellite system constellation characteristics and orbit modeling deficiencies, especially the deficiencies in the solar radiation pressure (SRP) models. This study investigates the impact of SRP modeling on the ERP estimation derived from BeiDou Navigation Satellite System (BDS). The adjusted optical properties are adopted in an a priori box-wing model and jointly used with the extended CODE orbit model (ECOM) for BDS ERP estimation. The BDS-derived ERPs are assessed by comparing them with International Earth Rotation and Reference Systems Service (IERS) 14C04 product. Our processing results of 3 years (2019–2021) show that the mean offsets of BDS-derived ERPs are nearly not affected by the a priori SRP model. However, the standard deviation (STD) is improved by approximately 20% for pole coordinates and their rates when considering an a priori box-wing model together with the ECOM1 (5 parameters). The a priori bow-wing model mitigates most spurious signals in the pole coordinate spectrum. It is noticeable that the BDS-derived ERPs are also affected by the system-specific spurious signals. The visible signals at the 3rd harmonics of draconitic year in the pole coordinates are related to the 3-plane constellations. The signal at the 2nd harmonics of the draconitic year for BDS-derived excess length of day (∆LOD) estimates is significantly larger than that of the GPS-derived. Additionally, the extension of the orbital arc in the BDS processing from 1 to 3 day is beneficial for the ERP quality. When switching to a 3-day arc length, the improvement of the ERP quality is about 28, 15 and 50 for X-pole, Y-pole coordinates and ∆ LOD, respectively. The STD is more than 3 times better than that of 1-day arc solutions for pole coordinate rates. The STD of the 3-day arc length BDS-derived ERPs with respect to the IERS 14C04 product reaches about 40 μas, 100 μas/day, 9 μs for pole coordinates, pole coordinate rates and ∆ LOD, respectively.
      PubDate: 2022-08-13
       
 
JournalTOCs
School of Mathematical and Computer Sciences
Heriot-Watt University
Edinburgh, EH14 4AS, UK
Email: journaltocs@hw.ac.uk
Tel: +00 44 (0)131 4513762
 


Your IP address: 3.235.173.74
 
Home (Search)
API
About JournalTOCs
News (blog, publications)
JournalTOCs on Twitter   JournalTOCs on Facebook

JournalTOCs © 2009-