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Wang, Xia Jun, Dong Lin Zhao, Dong Dong Zhang, Cheng Li, and Ran Ran Yao. "Remarkable Mechanical and Thermal Increments of Epoxy Composites by Graphene Nanosheets and Carbon Nanotubes Synergetic Reinforcement." Key Engineering Materials 727 (January 2017): 546–52. http://dx.doi.org/10.4028/www.scientific.net/kem.727.546.
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Graphene nanosheets (GNSs) were modified with aqueous ammonia and hydrogen peroxide, to obtain amine (–NH2) functionalized GNSs (AFGNSs) and enhance the bondings between the GNSs and epoxy matrix. We report an easy and efficient approach to improve the mechanical properties and thermal conductivity of epoxy matrix composites by combining one dimensional multi-walled carbon nanotubes and two dimensional AFGNSs. The long and tortuous MWCNTs can bridge adjacent AFGNSs and inhibit their aggregation, resulting in an increased contact surface area between GNS/MWCNT structures and the polymer. A remarkable synergetic effect between the GNSs and MWCNTs on the enhanced mechanical properties and thermal conductivity of the epoxy composites was demonstrated. The addition of 2 wt.% MWCNT-GNS hybrid fillers improved the tensile strength and flexural strength of the pristine epoxy by 20.71% and 55.51%, respectively. Thermal conductivity increased by 93.71% using MWCNT-GNS hybrid fillers compared to non-derivatised epoxy. This study has demonstrated that 2-D GNSs and 1-D MWCNTs have an obvious synergetic reinforcing effect on the mechanical properties and a remarkable thermal conductivity enhancement in epoxy composites which provides an easy and effective way to design and improve the properties of composite materials.
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Zhao, Qingzhi, Kefei Zhang, and Wanqiang Yao. "Influence of station density and multi-constellation GNSS observations on troposphere tomography." Annales Geophysicae 37, no. 1 (January 14, 2019): 15–24. http://dx.doi.org/10.5194/angeo-37-15-2019.
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Abstract. Troposphere tomography, using multi-constellation observations from global navigation satellite systems (GNSSs), has become a novel approach for the three-dimensional (3-D) reconstruction of water vapour fields. An analysis of the integration of four GNSSs (BeiDou, GPS, GLONASS, and Galileo) observations is presented to investigate the impact of station density and single- and multi-constellation GNSS observations on troposphere tomography. Additionally, the optimal horizontal resolution of the research area is determined in Hong Kong considering both the number of voxels divided, and the coverage rate of discretized voxels penetrated by satellite signals. The results show that densification of the GNSS network plays a more important role than using multi-constellation GNSS observations in improving the retrieval of 3-D atmospheric water vapour profiles. The root mean square of slant wet delay (SWD) residuals derived from the single-GNSS observations decreased by 16 % when the data from the other four stations are added. Furthermore, additional experiments have been carried out to analyse the contributions of different combined GNSS data to the reconstructed results, and the comparisons show some interesting results: (1) the number of iterations used in determining the weighting matrices of different equations in tomography modelling can be decreased when considering multi-constellation GNSS observations and (2) the reconstructed quality of 3-D atmospheric water vapour using multi-constellation GNSS data can be improved by about 11 % when compared to the SWD estimated with precise point positioning, but this was not as high as expected.
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Schweikert, Robert, Thomas W�rz, Riccardo De Gaudenzi, Alexander Steingass, and Armin Dammann. "On signal structures for GNSS-2." International Journal of Satellite Communications 18, no. 4-5 (2000): 271–91. http://dx.doi.org/10.1002/1099-1247(200007/10)18:4/5<271::aid-sat658>3.0.co;2-y.
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Guler, Omer, Yakup Say, and Burak Dikici. "The effect of graphene nano-sheet (GNS) weight percentage on mechanical and corrosion properties of AZ61 and AZ91 based magnesium matrix composites." Journal of Composite Materials 54, no. 28 (June 19, 2020): 4473–85. http://dx.doi.org/10.1177/0021998320933345.
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In this study, the effect of graphene nano-sheets (GNSs) on mechanical and corrosion properties of AZ61 and AZ91 based composites was investigated, detail. GNSs have been successfully produced by the liquid phase exfoliation (LPE) method and then, added AZ61 and AZ91 matrix with 01, 0.2, and 0.5 wt% GNSs for the production of the composites. The composite compacts were produced by powder metallurgy technique and sintered for 2 h at 500 °C under Ar atmosphere. The composite characterizations were carried out by scanning and transmission electron microscopes (SEM, TEM), electron dispersive spectroscope (EDS), Raman spectroscopy, and X-ray diffraction. The mechanical properties and corrosion behaviors of the composites have been compared with compression tests and potentiodynamic scanning (PDS) techniques, respectively. The results showed that the compressive strength of the composites increased with increasing GNS amount in both the AZ61 and AZ91 matrix alloys. The most susceptible composites to corrosion for both AZ61 and AZ91 matrix were observed in the 0.5 wt% GNS containing structures. However, there is a certain ratio of GNS in the Mg matrix to achieve good corrosion resistance.
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González, Emilio, Celso Prados, Virginia Antón, and Boris Kennes. "GRAIL-2: Enhanced Odometry based on GNSS." Procedia - Social and Behavioral Sciences 48 (2012): 880–87. http://dx.doi.org/10.1016/j.sbspro.2012.06.1065.
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Zhang, Jinglei, Xiaoming Wang, Zishen Li, Shuhui Li, Cong Qiu, Haobo Li, Shaotian Zhang, and Li Li. "The Impact of Different Ocean Tide Loading Models on GNSS Estimated Zenith Tropospheric Delay Using Precise Point Positioning Technique." Remote Sensing 12, no. 18 (September 20, 2020): 3080. http://dx.doi.org/10.3390/rs12183080.
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Global navigation satellite systems (GNSSs) have become an important tool to derive atmospheric products, such as the total zenith tropospheric delay (ZTD) and precipitable water vapor (PWV) for weather and climate studies. The ocean tide loading (OTL) effect is one of the primary errors that affects the accuracy of GNSS-derived ZTD/PWV, which means the study and choice of the OTL model is an important issue for high-accuracy ZTD estimation. In this study, GNSS data from 1 January 2019 to 31 January 2019 are processed using precise point positioning (PPP) at globally distributed stations. The performance of seven widely used global OTL models is assessed and their impact on the GNSS-derived ZTD is investigated by comparing them against the ZTD calculated from co-located radiosonde observations. The results indicate that the inclusion or exclusion of the OTL effect will lead to a difference in ZTD of up to 3–15 mm for island stations, and up to 1–2 mm for inland stations. The difference of the ZTD determined with different OTL models is quite small, with a root-mean-square (RMS) value below 1.5 mm at most stations. The comparison between the GNSS-derived ZTD and the radiosonde-derived ZTD indicates that the adoption of OTL models can improve the accuracy of GNSS-derived ZTD. The results also indicate that the adoption of a smaller cutoff elevation, e.g., 3° or 7°, can significantly reduce the difference between the ZTDs determined by GNSS and radiosonde, when compared against a 15° cutoff elevation. Compared to the radiosonde-derived ZTD, the RMS error of GNSS-derived ZTD is approximately 25–35 mm at a cutoff elevation of 15°, and 15–25 mm when the cutoff elevation is set to 3°.
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Calabia, Andres, Iñigo Molina, and Shuanggen Jin. "Soil Moisture Content from GNSS Reflectometry Using Dielectric Permittivity from Fresnel Reflection Coefficients." Remote Sensing 12, no. 1 (January 1, 2020): 122. http://dx.doi.org/10.3390/rs12010122.
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Global Navigation Satellite Systems-Reflectometry (GNSS-R) has shown unprecedented advantages to sense Soil Moisture Content (SMC) with high spatial and temporal coverage, low cost, and under all-weather conditions. However, implementing an appropriated physical basis to estimate SMC from GNSS-R is still a challenge, while previous solutions were only based on direct comparisons, statistical regressions, or time-series analyses between GNSS-R observables and external SMC products. In this paper, we attempt to retrieve SMC from GNSS-R by estimating the dielectric permittivity from Fresnel reflection coefficients. We employ Cyclone GNSS (CYGNSS) data and effectively account for the effects of bare soil roughness (BSR) and vegetation optical depth by employing ICESat-2 (Ice, Cloud, and land Elevation Satellites 2) and/or SMAP (Soil Moisture Active Passive) products. The tests carried out with ICESat-2 BSR data have shown the high sensitivity in SMC retrieval to high BSR values, due to the high sensitivity of ICESat-2 to land surface microrelief. Our GNSS-R SMC estimates are validated by SMAP SMC products and the results provide an R-square of 0.6, Root Mean Squared Error (RMSE) of 0.05, and a zero p-value, for the 4568 test points evaluated at the eastern region of China during April 2019. The achieved results demonstrate the optimal capability and potential of this new method for converting reflectivity measurements from GNSS-R into Land Surface SMC estimates.
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Smoliarova, T. E. "Synthesis, properties and functionalization of gold nanostars for medical diagnostics." Siberian Medical Review, no. 2 (2021): 97–99. http://dx.doi.org/10.20333/25000136-2021-2-97-99.
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Th e aim of the research. To evaluate two approaches to colloidal synthesis using two diff erent non-toxic surfactants (PVP and Triton X-100) and their properties for future use. Material and methods. (PVP) Th e solution of GNSs with short tips was prepared in 200 ml vial. 20 mg of PVP (Polyvinylpyrrolidone, 1-ethenylpyrrolidin-2-one) were dissolved in the 200 mL of DMF (N,N-Dimethylmethanamide) (with the sonication to dissolve well). (Triton X-100) In a typical preparation of GNSs with long tips, the seed solution was prepared in a 20mL vial: 5mL of HAuCl4 5∙10-4M in water are added to 5mL of an aqueous solution of TritonX-100 0.1M. To examinate the shape and properties of prepared gold nanostars Cary 100 Bio Spectrophotometer using quartz cuvettes was used to taken on UV-Vis spectra. Transmission Electron Microscopy (TEM) was used to obtain shape and size of prepared GNSs. Results. Microscopy analysis shows that the obtained GNSs have completely diff erent shapes. Th e GNSs fabricated using synthesis approach with PVP have shorter tips and the cores are larger than the GNSs synthesized with Triton X-100 synthesis approach. TEM-images of the second ones show smaller size nanoparticles with the longer and thinner tips. Optical properties of the synthesized GNSs were analyzed using UV-vis-NIR absorbtion spectra, which shows maximum plasmon existence at 800 nm for GNSs synthesized with PVP and at 850 nm for GNSs synthesized with Triton X-100. Conclusion. In summary, we developed GNSs using two colloidal synthesis approaches with the use of two diff erent non-toxic surfactants (PVP and Triton X-100). In the future, gold nanostars are planned to be used to develop highly sensitive methods of medical diagnostics.
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Kačmařík, Michal, Jan Douša, Galina Dick, Florian Zus, Hugues Brenot, Gregor Möller, Eric Pottiaux, et al. "Inter-technique validation of tropospheric slant total delays." Atmospheric Measurement Techniques 10, no. 6 (June 12, 2017): 2183–208. http://dx.doi.org/10.5194/amt-10-2183-2017.
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Abstract. An extensive validation of line-of-sight tropospheric slant total delays (STD) from Global Navigation Satellite Systems (GNSS), ray tracing in numerical weather prediction model (NWM) fields and microwave water vapour radiometer (WVR) is presented. Ten GNSS reference stations, including collocated sites, and almost 2 months of data from 2013, including severe weather events were used for comparison. Seven institutions delivered their STDs based on GNSS observations processed using 5 software programs and 11 strategies enabling to compare rather different solutions and to assess the impact of several aspects of the processing strategy. STDs from NWM ray tracing came from three institutions using three different NWMs and ray-tracing software. Inter-techniques evaluations demonstrated a good mutual agreement of various GNSS STD solutions compared to NWM and WVR STDs. The mean bias among GNSS solutions not considering post-fit residuals in STDs was −0.6 mm for STDs scaled in the zenith direction and the mean standard deviation was 3.7 mm. Standard deviations of comparisons between GNSS and NWM ray-tracing solutions were typically 10 mm ± 2 mm (scaled in the zenith direction), depending on the NWM model and the GNSS station. Comparing GNSS versus WVR STDs reached standard deviations of 12 mm ± 2 mm also scaled in the zenith direction. Impacts of raw GNSS post-fit residuals and cleaned residuals on optimal reconstructing of GNSS STDs were evaluated at inter-technique comparison and for GNSS at collocated sites. The use of raw post-fit residuals is not generally recommended as they might contain strong systematic effects, as demonstrated in the case of station LDB0. Simplified STDs reconstructed only from estimated GNSS tropospheric parameters, i.e. without applying post-fit residuals, performed the best in all the comparisons; however, it obviously missed part of tropospheric signals due to non-linear temporal and spatial variations in the troposphere. Although the post-fit residuals cleaned of visible systematic errors generally showed a slightly worse performance, they contained significant tropospheric signal on top of the simplified model. They are thus recommended for the reconstruction of STDs, particularly during high variability in the troposphere. Cleaned residuals also showed a stable performance during ordinary days while containing promising information about the troposphere at low-elevation angles.
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Wang, Jue-yao, and Bin Liang. "4-GNSS radio occultation satellite constellation design based on Dual-gate uniformity evaluation index." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 231, no. 1 (November 13, 2016): 3–16. http://dx.doi.org/10.1177/0954410016674746.
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A brand-new area of low earth orbit satellite constellation research has been expanded by global navigation satellite system (GNSS) radio occultation (RO) atmosphere sounding technology in the last decade. The possibility of reducing the sounding satellites while keeping the amount of atmosphere soundings increasing to produce low-cost meteorological data product is investigated, and a constellation capable of receiving the RO signals from all the 4-GNSS, such as GPS, GLONASS, Galileo, and Compass, is proposed in this paper. This paper focuses on the mathematical problems on the design of 4-GNSS RO satellite constellation. A forward GNSS RO sounding simulation algorithm based on ideal atmosphere model and two-dimensional radial tracing algorithm is presented for a rapidly and accurately sounding performance prediction of 4-GNSS RO satellite constellations. Then, an improved uniformity evaluation factor named Dual-gate is established for 4-GNSS RO satellite constellation optimization design, which is a combination of the uniformity evaluation factors for the latitudinal distribution of RO soundings and those for the gridding uniformity. On the basis of low earth orbit satellite orbit dynamics and spherical geometry, the impacts of partial constellation parameters on the amount and coverage performance accorded with Dual-gate uniformity evaluation index are derived, and a series of design criteria of 4-GNSS RO satellite constellation are summarized. A simplified 4-GNSS RO satellite constellation model is built on the basis of the design criteria, and an improved ant colony algorithm is used to optimize the parameters of a 4-GNSS RO constellation including as many satellites as COSMIC-2. The simulation result shows that this 4-GNSS RO constellation is capable of obtaining near 3000 atmosphere soundings per 3 h. It obtains 13% more soundings than COSMIC-2 with the same 4-GNSS RO sounding devices, and the uniformity of soundings is increased by 9%.
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Lee, Jisun, Jay Hyoun Kwon, and Yong Lee. "Analyzing Precision and Efficiency of Global Navigation Satellite System-Derived Height Determination for Coastal and Island Areas." Applied Sciences 11, no. 11 (June 7, 2021): 5310. http://dx.doi.org/10.3390/app11115310.
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The global navigation satellite system (GNSS)-derived height determination technique is applied in the field of surveying owing to the broad use of GNSS and the development of precise local geoid models. In Korea, this technique was officially adopted in 2020 for public surveying, such as urban facility mapping; it is also treated as an efficient way to unify the vertical datum of the inland and island areas of Korea. Here, GNSS surveying was conducted on 19 stations located in Korea’s coastal regions and islands, and GNSS-derived elevations were determined. When each GNSS-derived elevation was compared with elevations from spirit leveling, all stations showed differences of less than 3 cm when GNSS surveying was conducted for 4 h/day over two days; they were smaller than 5 cm with 2 h of surveying. These differences meet the standards of GNSS-derived elevations in Korea. In addition, GNSS-derived elevations were compared with those obtained via sea-crossing leveling in two regions, showing differences smaller than 1 cm. Sea-crossing leveling takes longer than GNSS-derived height determination, and its accuracy can be significantly affected by various environments, such as sea fog. Thus, GNSS-derived height determination represents a practical and useful technique.
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Lien, Nghiem Thi Ha, Vu Thi Thuy Duong, Vu Duong, Do Quang Hoa, and Tran Hong Nhung. "Theranostic Gold Nanoshells: from Synthesis to Imaging and Photothermal Therapy Applications." Communications in Physics 24, no. 3S2 (October 6, 2014): 63–70. http://dx.doi.org/10.15625/0868-3166/24/3s2/5061.
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Gold nanoshells (GNSs) were grown on monodispersed aminoprotpyltriethoxysilane (APTES) functionalized of silica nanoparticles (NPs) cores with varying sizes ranging from 40-180 nm synthesized by Stober route. Gold shells were deposited onto the surface of silica NPs by tetrakis(hydroxymethyl) phosphonium chloride (THPC) and electroless gold plating method. The coverage of the gold nanoshells on the surfaces of the silica NPs was evaluated using UV-VIS/NIR spectrospcopy and transmission electron microscopy (TEM). The plasmon resonance wavelengths of these gold nanoshells were tunable from visible to near infrared region. The GNSs were also bioconjugated with anti-HER2 monoclonal antibody for diagnostic breast cancer cells using dark field microscope technique. These GNS NPs play a role as nanoheaters transforming light to heat. With the present of these GNS NPs at volume density of $3.6\times 10^{10}$ NPs.cm$^3$ in chicken tissue samples, illuminated by 808 nm laser at the power density of 62~W.cm$^2$ the temperature of tissue sample reachs 110\rc{ }C after 20 minutes illumination.
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Aboutaleb, Ahmed, Amr S. El-Wakeel, Haidy Elghamrawy, and Aboelmagd Noureldin. "LiDAR/RISS/GNSS Dynamic Integration for Land Vehicle Robust Positioning in Challenging GNSS Environments." Remote Sensing 12, no. 14 (July 19, 2020): 2323. http://dx.doi.org/10.3390/rs12142323.
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The autonomous vehicles (AV) industry has a growing demand for reliable, continuous, and accurate positioning information to ensure safe traffic and for other various applications. Global navigation satellite system (GNSS) receivers have been widely used for this purpose. However, GNSS positioning accuracy deteriorates drastically in challenging environments such as urban environments and downtown cores. Therefore, inertial sensors are widely deployed inside the land vehicle for various purposes, including the integration with GNSS receivers to provide positioning information that can bridge potential GNSS failures. However, in dense urban areas and downtown cores where GNSS receivers may incur prolonged outages, the integrated positioning solution may become prone to severe drift resulting in substantial position errors. Therefore, it is becoming necessary to include other sensors and systems that can be available in future land vehicles to be integrated with both the GNSS receivers and inertial sensors to enhance the positioning performance in such challenging environments. This work aims to design and examine the performance of a multi-sensor system that fuses the GNSS receiver data with not only the three-dimensional reduced inertial sensor system (3D-RISS), but also with the three-dimensional point cloud of onboard light detection and ranging (LiDAR) system. In this paper, a comprehensive LiDAR processing and odometry method is developed to provide a continuous and reliable positioning solution. In addition, a multi-sensor Extended Kalman filtering (EKF)-based fusion is developed to integrate the LiDAR positioning information with both GNSS and 3D-RISS and utilize the LiDAR updates to limit the drift in the positioning solution, even in challenging or ultimately denied GNSS environment. The performance of the proposed positioning solution is examined using several road test trajectories in both Kingston and Toronto downtown areas involving different vehicle dynamics and driving scenarios. The proposed solution provided a performance improvement over the standalone inertial solution by 64%. Over a GNSS outage of 10 min and 2 km distance traveled, our solution achieved position errors less than 2% of the distance travelled.
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Tsugawa, Takuya, Michi Nishioka, Mamoru Ishii, Kornyanat Hozumi, Susumu Saito, Atsuki Shinbori, Yuichi Otsuka, et al. "Total Electron Content Observations by Dense Regional and Worldwide International Networks of GNSS." Journal of Disaster Research 13, no. 3 (June 1, 2018): 535–45. http://dx.doi.org/10.20965/jdr.2018.p0535.
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Two-dimensional ionospheric total electron content (TEC) maps have been derived from ground-based Global Navigation Satellite System (GNSS) receiver networks and applied to studies of various ionospheric disturbances since the mid-1990s. For the purpose of monitoring and researching ionospheric conditions and ionospheric space weather phenomena, we have developed TEC maps of areas over Japan using the dense GNSS network, GNSS Earth Observation NETwork (GEONET), which consists of about 1300 stations and is operated by the Geospatial Information Authority of Japan (GSI). Currently, we are providing high-resolution, two-dimensional maps of absolute TEC, detrended TEC, rate of TEC change index (ROTI), and loss-of-lock on GPS signal over Japan on a real-time basis. Such high-resolution TEC maps using dense GNSS receiver networks are one of the most effective ways to observe, on a scale of several 100 km to 1000 km, ionospheric variations caused by traveling ionospheric disturbances and/or equatorial plasma bubbles, which can degrade single-frequency and differential GNSS positioning/navigation. We have collected all the available GNSS receiver data in the world to expand the TEC observation area. Currently, however, dense GNSS receiver networks are available in only limited areas, such as Japan, North America, and Europe. To expand the two-dimensional TEC observation with high resolution, we have conducted the Dense Regional and Worldwide International GNSS TEC observation (DRAWING-TEC) project, which is engaged in three activities: (1) standardizing GNSS-TEC data, (2) developing a new high-resolution TEC mapping technique, and (3) sharing the standardized TEC data or the information of GNSS receiver network. We have developed a new standardized TEC format, GNSS-TEC EXchange (GTEX), which is included in the Formatted Tables of ITU-R SG 3 Databanks related to Recommendation ITU-R P.311. Sharing the GTEX TEC data would be easier than sharing the GPS/GNSS data among those in the international ionospheric researcher community. The DRAWING-TEC project would promote studies of medium-scale ionospheric variations and their effect on GNSS.
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Khoptar, Alina, and Stepan Savchuk. "Estimation of Ionospheric Delay Influence on the Efficiency of Precise Positioning of Multi-GNSS Observations." Baltic Surveying 12 (June 29, 2020): 14–18. http://dx.doi.org/10.22616/j.balticsurveying.2020.002.
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Currently, Global Navigation Satellite Systems (GNSS) are developing at a fairly rapid pace. Over the last years US GPS and Russian GLONASS were modernizing, whilst new systems like European Galileo and Chinese BDS are launched. The modernizations of the existing and the deployment of new GNSS made a whole range of new signals available to the users, and create a new concept multi-GNSS. Ionospheric delay is one of the major error sources in multi-GNSS observations. At present, GNSS users usually eliminate the influence of ionospheric delay of the first order items by dual-frequency ionosphere-free combinations. But there is still residual ionospheric delay error of higher orders. In this paper we present four different processing scenarios to exclude the higher orders ionospheric delay effects on multi-GNSS Precise Point Positioning (PPP) performance, including: “only GPS” and “GPS+GLONASS+Galileo+BDS” – without/with eliminating ionospheric delay error of higher orders. Dataset collected from one GNSS station BOR1 (Borowiec, Poland) over almost two years provided by multi-GNSS experiment (MGEX) were used for dual-frequency PPP tests with one- and quadconstellation signals. For the second pair of scenarios were used a IONosphere map EXchange format (IONEX) that supports the exchange of 2- and 3-dimensional TEC maps given in a geographic grid. Numeric experiments show that, the results of different pairs of scenarios differ at the submillimeter level. The results also show that the multi-GNSS processing are better than those based on “only GPS”.
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Kazancı, Selma Zengin, and Emine Tanır Kayıkçı. "Establishment of Karadeniz Technical University Permanent GNSS Station as Reactivated of TRAB IGS Station." Geodesy and Cartography 66, no. 2 (December 20, 2017): 253–58. http://dx.doi.org/10.1515/geocart-2017-0014.
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Abstract In recent years, Global Navigation Satellite Systems (GNSS) have gained great importance in terms of the benefi ts it provides such as precise geodetic point positioning, determining crustal deformations, navigation, vehicle monitoring systems and meteorological applications etc. As in Turkey, for this purpose, each country has set up its own GNSS station networks like Turkish National Permanent RTK Network analyzed precise station coordinates and velocities together with the International GNSS Service, Turkish National Fundamental GPS Network and Turkish National Permanent GNSS Network (TNPGN) stations not only are utilized as precise positioning but also GNSS meteorology studies so total number of stations are increased. This work is related to the reactivated of the TRAB IGS station which was established in Karadeniz Technical University, Department of Geomatics Engineering. Within the COST ES1206 Action (GNSS4SWEC) KTU analysis center was established and Trop-NET system developed by Geodetic Observatory Pecny (GOP, RIGTC) in order to troposphere monitoring. The project titled “Using Regional GNSS Networks to Strengthen Severe Weather Prediction” was accepted to the scientifi c and technological research council of Turkey (TUBITAK). With this project, we will design 2 new constructed GNSS reference station network. Using observation data of network, we will compare water vapor distribution derived by GNSS Meteorology and GNSS Tomography. At this time, KTU AC was accepted as E-GVAP Analysis Centre in December 2016. KTU reference station is aimed to be a member of the EUREF network with these studies.
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Sabatini, Roberto, Terry Moore, and Chris Hill. "A New Avionics-Based GNSS Integrity Augmentation System: Part 2 – Integrity Flags." Journal of Navigation 66, no. 4 (May 3, 2013): 501–22. http://dx.doi.org/10.1017/s0373463313000143.
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This paper presents the second part of the research activities carried out to develop a novel Global Navigation Satellite System (GNSS) Avionics-Based Integrity Augmentation (ABIA) system for manned and Unmanned Aerial Vehicle (UAV) applications. The ABIA system's architecture was developed to allow real-time avoidance of safety-critical flight conditions and fast recovery of the required navigation performance in case of GNSS data losses. In more detail, our novel ABIA system addresses all four cornerstones of GNSS integrity augmentation in mission- and safety-critical avionics applications: prediction (caution flags), avoidance (optimal flight path guidance), reaction (warning flags) and correction (recovery flight path guidance). Part 1 (Sabatini et al., 2012) presented the ABIA concept, architecture and key mathematical models used to describe GNSS integrity issues in aircraft applications. This second part addresses the ABIA caution and warning integrity flags criteria and presents the results of a simulation case study performed on the TORNADO Interdiction and Strike (IDS) aircraft.
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Allred, Barry, DeBonne Wishart, Luis Martinez, Harry Schomberg, Steven Mirsky, George Meyers, John Elliott, and Christine Charyton. "Delineation of Agricultural Drainage Pipe Patterns Using Ground Penetrating Radar Integrated with a Real-Time Kinematic Global Navigation Satellite System." Agriculture 8, no. 11 (October 24, 2018): 167. http://dx.doi.org/10.3390/agriculture8110167.
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Better methods are needed for mapping agricultural drainage pipe systems. Prior research on small test plots indicates that ground penetrating radar (GPR) is oftentimes capable of detecting buried drainage pipes; however, the feasibility of employing this geophysical technique in larger field areas has not been adequately evaluated. Ground penetrating radar integrated with a Real-Time Kinematic (RTK) Global Navigation Satellite System (GNSS) may be an effective and efficient means of mapping drain lines within agricultural fields. Therefore, GPR-RTK/GNSS was tested in three agricultural settings; with Site 1 and Site 2 located in Beltsville, MD, USA and Site 3 near Columbus, OH, USA. Soils at the three sites ranged from silty clay loam to loamy sand. A GPR unit with 250 MHz antennas was used to detect drainage pipes, and at Sites 1 and 2, a physical GNSS base station was utilized, while a virtual base station was employed at Site 3. The GPR-RTK/GNSS configurations used in this study delineated a complex rectangular drainage pipe system at Site 1, with one set of drainage pipes oriented southwest-northeast and a second oriented southeast-northwest. At Site 2, a herringbone drain line pattern was outlined, and at Site 3, random drain lines were found. When integrated with RTK/GNSS, spiral or serpentine GPR transects (or spiral/serpentine segments of a GPR transects) were utilized to provide insight on drain line directional trends. Consequently, given suitable field conditions, GPR integrated with RTK/GNSS can be a valuable tool for farmers and drainage contractors needing to map subsurface drainage systems.
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Guerova, G., T. Simeonov, and N. Yordanova. "The Sofia University Atmospheric Data Archive (SUADA)." Atmospheric Measurement Techniques 7, no. 8 (August 21, 2014): 2683–94. http://dx.doi.org/10.5194/amt-7-2683-2014.
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Abstract. Atmospheric sounding using the Global Navigation Satellite Systems (GNSS) is a well-established research field in Europe. At present, GNSS data from 1800 stations are available for model validation and assimilation in state-of-the-art models used for operational numerical weather prediction centres in Europe. Advances in GNSS data processing make it possible also to use the GNSS data for climatic trend analysis, an emerging new application. In Bulgaria and southeastern Europe, the use of GNSS for atmospheric sounding is currently under development. As a first step, the Sofia University Atmospheric Data Archive (SUADA) is developed. SUADA is a user-friendly database, and includes GNSS tropospheric products like zenith total delay (ZTD) and derivatives like vertically integrated water vapour (IWV), as well as observations from radiosonde (RS) and surface atmospheric data. Archived in SUADA are (1) GNSS tropospheric products (over 12 000 000 individual observations) and derivatives (over 55 000) from five GNSS processing strategies and 37 stations for the period 1997–2013, with temporal resolutions from 5 min to 6 h, and (2) radiosonde IWV data (over 6000 observations) for station Sofia (1999–2012). Presented are two applications of the SUADA data for the study of long- and short-term variations of IWV over Bulgaria during the 2007 heatwave and intense precipitation events in 2012.
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Guerova, G., Tzv Simeonov, and N. Yordanova. "The Sofia University Atmospheric Data Archive (SUADA)." Atmospheric Measurement Techniques Discussions 7, no. 3 (March 5, 2014): 2153–85. http://dx.doi.org/10.5194/amtd-7-2153-2014.
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Abstract. Atmospheric sounding using the Global Navigation Satellite Systems (GNSS) is a well established research field in Europe. At present, GNSS data from 1800 stations are available for model validation and assimilation in state-of-the-art models used for operational numerical weather prediction Centers in Europe. Advances in GNSS data processing is making possible to also use the GNSS data for climatic trend analysis, an emerging new application. In Bulgaria and Southeast Europe the use of GNSS for atmospheric sounding is currently under development. As a first step the Sofia University Atmospheric Data Archive (SUADA) is developed. SUADA is user friendly database and includes GNSS tropospheric products like Zenith Total Delay (ZTD) and derivatives like vertically Integrated Water Vapour (IWV) as well as observations from Radiosonde and surface atmospheric data. Archived in SUADA are: (1) GNSS tropospheric products (over 12 000 000 individual observations) and derivatives (over 55 000) from five GNSS processing strategies and 37 stations for the period 1997–2013 with temporal resolution from 5 min to 6 h and (2) Radiosonde IWV data (over 6000 observations) for station Sofia (1999–2012). Presented are two applications of the SUADA data for study of long and short term variation of IWV over Bulgaria during the 2007 heat wave and intense precipitation events in 2012.
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Wang, Huigai, Keke Zhang, Chenxiang Yin, and Meng Zhang. "Environmentally Friendly and Controllable Pyrolysis Method to Synthesize Ni-Modified Graphene Nanosheets as Reinforcement of Lead-Free Solder." Metals 9, no. 10 (October 19, 2019): 1123. http://dx.doi.org/10.3390/met9101123.
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A tactic for the synthesis of Ni-modified graphene nanosheets (Ni-GNSs) as a high-performance reinforcement of a lead-free solder is proposed and achieved via an environmentally friendly and controllable pyrolysis method. The segmented pyrolysis processes of an Ni(CH3COO)2∙4H2O@GNSs hybrid are discussed. The morphology, microstructure, phase transition, and adsorption strength of nanoparticles on the surface of GNSs with various theoretical Ni loadings are characterized. The adsorption mechanism of a single Ni atom on the surface of perfect graphene and defective graphene was studied based on density functional theory. The corresponding underlying formation mechanisms of Ni-GNSs are analyzed. The results show that the grain size, distribution and phase composition of the nanoparticles on GNSs could be controlled by changing the theoretical Ni loading level. The morphology and dispersity of Ni nanoparticles on GNSs did not significantly change after long-time or high-power ultrasonic treatment, suggesting that the adsorption strength between Ni nanoparticles and GNSs was relatively large and belonged to chemical adsorption based on first-principle calculation. Ni atoms tend to adsorb in the center of the carbon six-membered ring. The obtained Ni-GNSs nanohybrid exhibited a small size, fewer defects, and higher crystallinity and adsorption strength when the theoretical Ni loading was 17 mol %. The results have potential applications in the design of the reinforced phase of composites.
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Vu, Dinh Toan, Sean Bruinsma, Sylvain Bonvalot, Dominique Remy, and Georgios S. Vergos. "A Quasigeoid-Derived Transformation Model Accounting for Land Subsidence in the Mekong Delta towards Height System Unification in Vietnam." Remote Sensing 12, no. 5 (March 3, 2020): 817. http://dx.doi.org/10.3390/rs12050817.
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A vertical offset model for Vietnam and its surrounding areas was determined based on the differences between height anomalies derived from 779 Global Navigation Satellite System (GNSS)/levelling points and those derived from a dedicated high-resolution gravimetric-only quasigeoid model called GEOID_LSC. First, the deterministic transformation model to effectively fit the differences between the quasigeoid and GNSS/levelling heights was based on a third-order polynomial model. Second, the residual height anomalies have been interpolated to a grid employing Least-Squares Collocation. Finally, the distortions were restored to the residual grid. This model can be used for combination with a gravimetric quasigeoid model in GNSS levelling. The quality of GNSS/levelling data in Vietnam was analyzed and evaluated in this study. The annual subsidence rate from ALOS-1 was also used to analyze the effects of subsidence on the quality of GNSS/levelling data in the Mekong Delta. From this we made corrections to improve the accuracy of GNSS/levelling data in this region. The offset model was evaluated using cross-validation technique by comparing with GNSS/levelling data. Results indicate that the offset model has a standard deviation of 5.9 cm in the absolute sense. Based on this offset model, GNSS levelling can be carried out in most of Vietnam’s territory complying third-order levelling requirements, while the accuracy requirements for fourth-order levelling networks is met for the entire country. This model in combination with the developed gravimetric quasigeoid model should also contribute to the modernization of Vietnam’s height system. We also used high-quality GNSS/levelling data and the determined quasigeoid model to determine the geopotential value W0 for the Vietnam Local Vertical Datum. The gravity potential of the Vietnam Local Vertical Datum is estimated equal to W 0 LVD = 62,636,846.81 ± 0.70 m2s−2 with the global equipotential surface realized by the conventional value W0 = 62,636,853.4 m2s−2.
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Bosser, Pierre, Olivier Bock, Cyrille Flamant, Sandrine Bony, and Sabrina Speich. "Integrated water vapour content retrievals from ship-borne GNSS receivers during EUREC<sup>4</sup>A." Earth System Science Data 13, no. 4 (April 12, 2021): 1499–517. http://dx.doi.org/10.5194/essd-13-1499-2021.
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Abstract. In the framework of the EUREC4A (Elucidating the role of clouds–circulation coupling in climate) campaign that took place in January and February 2020, integrated water vapour (IWV) contents were retrieved over the open tropical Atlantic Ocean using Global Navigation Satellite System (GNSS) data acquired from three research vessels (R/Vs): R/V Atalante, R/V Maria S. Merian and R/V Meteor. This paper describes the GNSS processing method and compares the GNSS IWV retrievals with IWV estimates from the European Centre for Medium-range Weather Forecasts (ECMWF) fifth reanalysis (ERA5), from the Moderate Resolution Imaging Spectroradiometer (MODIS) infrared products and from terrestrial GNSS stations located along the tracks of the ships. The ship-borne GNSS IWV retrievals from R/V Atalante and R/V Meteor compare well with ERA5, with small biases (−1.62 kg m−2 for R/V Atalante and +0.65 kg m−2 for R/V Meteor) and a root mean square (rms) difference of about 2.3 kg m−2. The results for the R/V Maria S. Merian are found to be of poorer quality, with an rms difference of 6 kg m−2, which is very likely due to the location of the GNSS antenna on this R/V prone to multipath effects. The comparisons with ground-based GNSS data confirm these results. The comparisons of all three R/V IWV retrievals with MODIS infrared products show large rms differences of 5–7 kg m−2, reflecting the enhanced uncertainties in these satellite products in the tropics. These ship-borne IWV retrievals are intended to be used for the description and understanding of meteorological phenomena that occurred during the campaign, east of Barbados, Guyana and northern Brazil. Both the raw GNSS measurements and the IWV estimates are available through the AERIS data centre (https://en.aeris-data.fr/, last access: 20 September 2020). The digital object identifiers (DOIs) for R/V Atalante IWV and raw datasets are https://doi.org/10.25326/71 (Bosser et al., 2020a) and https://doi.org/10.25326/74 (Bosser et al., 2020d), respectively. The DOIs for the R/V Maria S. Merian IWV and raw datasets are https://doi.org/10.25326/72 (Bosser et al., 2020b) and https://doi.org/10.25326/75 (Bosser et al., 2020e), respectively. The DOIs for the R/V Meteor IWV and raw datasets are https://doi.org/10.25326/73 (Bosser et al., 2020c) and https://doi.org/10.25326/76 (Bosser et al., 2020f), respectively.
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YIN Xi-zhen, 尹喜珍, 于云丰 YU Yun-feng, 马成炎 MA Cheng-yan, and 叶甜春 YE Tian-chun. "Design of quadrature 2∶1 frequency divider for GNSS receivers." Optics and Precision Engineering 20, no. 5 (2012): 1015–21. http://dx.doi.org/10.3788/ope.20122005.1015.
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Jackson, Benjamin M., Ted Polglaze, Brian Dawson, Trish King, and Peter Peeling. "Comparing Global Positioning System and Global Navigation Satellite System Measures of Team-Sport Movements." International Journal of Sports Physiology and Performance 13, no. 8 (September 1, 2018): 1005–10. http://dx.doi.org/10.1123/ijspp.2017-0529.
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Purpose: To compare data from conventional global positioning system (GPS-) and new global navigation satellite system (GNSS-) enabled tracking devices and to examine the interunit reliability of GNSS devices. Methods: Interdevice differences between 10-Hz GPS and GNSS devices were examined during laps (n = 40) of a simulated game circuit and during elite hockey matches (n = 21); GNSS interunit reliability was also examined during laps of the simulated game circuit. Differences in distance values and measures in 3 velocity categories (low <3 m·s−1; moderate 3–5 m·s−1; and high >5 m·s−1) and acceleration/deceleration counts (>1.46 and <−1.46 m·s−2) were examined using 1-way analysis of variance. Interunit GNSS reliability was examined using the coefficient of variation (CV) and intraclass correlation coefficient. Results: Interdevice differences (P < .05) were found for measures of peak deceleration, low-speed distance, percentage of total distance at low speed, and deceleration count during the simulated game circuit and for all measures except total distance and low-speed distance during hockey matches. Interunit (GNSS) differences (P < .05) were not found. The coefficient of variation was below 5% for total distance, average and peak speeds and distance and percentage of total distance of low-speed running. The GNSS devices had a lower horizontal dilution of precision score than GPS devices in all conditions. Conclusions: These findings suggest that GNSS devices may be more sensitive than GPS devices in quantifying the physical demands of team-sport movements, but further study into the accuracy of GNSS devices is required.
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Webb, Samuel R., Nigel T. Penna, Peter J. Clarke, Stuart Webster, Ian Martin, and Gemma V. Bennitt. "Kinematic GNSS Estimation of Zenith Wet Delay over a Range of Altitudes." Journal of Atmospheric and Oceanic Technology 33, no. 1 (January 2016): 3–15. http://dx.doi.org/10.1175/jtech-d-14-00111.1.
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AbstractAtmospheric water vapor estimates from static ground-based Global Navigation Satellite System (GNSS) receivers are now operationally assimilated into numerical weather prediction models, either as total precipitable water vapor (PWV) or zenith total delay. To extend this concept, the estimation of water vapor using kinematic GNSS has been investigated for over a decade. Previous kinematic GNSS PWV studies suggest a 2–3-mm PWV measurement agreement with radiosondes, almost commensurate with static GNSS PWV measurement accuracy, but the only comprehensive experiments undertaken have been shipborne. As a first step toward extending sea level–based studies to airborne experiments that obtain atmospheric profiles, the authors considered the kinematic GNSS estimation of atmospheric water vapor along a repeatable trajectory spanning substantial topographic relief, namely, the Snowdon Mountain Railway, United Kingdom. The atmospheric water vapor was indirectly quantified through the GNSS estimation of zenith wet delay (ZWD). Static GNSS [GPS+ Globalnaya Navigatsionnaya Sputnikovaya Sistema (GLONASS)] reference receivers were installed at the 950-m-altitude profile’s extremities, providing ZWD reference values that were interpolated to the train’s altitude, together with profiles from 100-m-resolution runs of the Met Office Unified Model. Similar GNSS ZWD accuracies to those from shipborne studies are demonstrated, namely, 12.1 mm (RMS) using double-difference relative kinematic GPS and 16.2 mm using kinematic GPS precise point positioning (PPP), but which is improved to 11.6 mm when using kinematic GPS+GLONASS PPP, commensurate with the relative kinematic GPS. The PPP solution represents a more typical airborne estimation scenario, that is, without relying on nearby GNSS reference stations.
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Bock, Olivier, Pierre Bosser, Cyrille Flamant, Erik Doerflinger, Friedhelm Jansen, Romain Fages, Sandrine Bony, and Sabrina Schnitt. "Integrated water vapour observations in the Caribbean arc from a network of ground-based GNSS receivers during EUREC<sup>4</sup>A." Earth System Science Data 13, no. 5 (May 28, 2021): 2407–36. http://dx.doi.org/10.5194/essd-13-2407-2021.
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Abstract. Ground-based Global Navigation Satellite System (GNSS) measurements from nearly 50 stations distributed over the Caribbean arc have been analysed for the period 1 January–29 February 2020 in the framework of the EUREC4A (Elucidate the Couplings Between Clouds, Convection and Circulation) field campaign. The aim of this effort is to deliver high-quality integrated water vapour (IWV) estimates to investigate the moisture environment of mesoscale cloud patterns in the trade winds and their feedback on the large-scale circulation and energy budget. This paper describes the GNSS data processing procedures and assesses the quality of the GNSS IWV retrievals from four operational streams and one reprocessed research stream which is the main data set used for offline scientific applications. The uncertainties associated with each of the data sets, including the zenith tropospheric delay (ZTD)-to-IWV conversion methods and auxiliary data, are quantified and discussed. The IWV estimates from the reprocessed data set are compared to the Vaisala RS41 radiosonde measurements operated from the Barbados Cloud Observatory (BCO) and to the measurements from the operational radiosonde station at Grantley Adams International Airport (GAIA), Bridgetown, Barbados. A significant dry bias is found in the GAIA humidity observations with respect to the BCO sondes (−2.9 kg m−2) and the GNSS results (−1.2 kg m−2). A systematic bias between the BCO sondes and GNSS is also observed (1.7 kg m−2), where the Vaisala RS41 measurements are moister than the GNSS retrievals. The IWV estimates from a collocated microwave radiometer agree with the BCO soundings after an instrumental update on 27 January, while they exhibit a dry bias compared to the soundings and to GNSS before that date. IWV estimates from the ECMWF fifth-generation reanalysis (ERA5) are overall close to the GAIA observations, probably due to the assimilation of these observations in the reanalysis. However, during several events where strong peaks in IWV occurred, ERA5 is shown to significantly underestimate the GNSS-derived IWV peaks. Two successive peaks are observed on 22 January and 23–24 January which were associated with heavy rain and deep moist layers extending from the surface up to altitudes of 3.5 and 5 km, respectively. ERA5 significantly underestimates the moisture content in the upper part of these layers. The origins of the various moisture biases are currently being investigated. We classified the cloud organization for five representative GNSS stations across the Caribbean arc using visible satellite images. A statistically significant link was found between the cloud patterns and the local IWV observations from the GNSS sites as well as the larger-scale IWV patterns from the ECMWF ERA5 reanalysis. The reprocessed ZTD and IWV data sets from 49 GNSS stations used in this study are available from the French data and service centre for atmosphere (AERIS) (https://doi.org/10.25326/79; Bock, 2020b).
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Demyanov, Vladislav, and Yury Yasyukevich. "Space weather: risk factors for Global Navigation Satellite Systems." Solar-Terrestrial Physics 7, no. 2 (June 30, 2021): 28–47. http://dx.doi.org/10.12737/stp-72202104.
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Extreme space weather events affect the stability and quality of the global navigation satellite systems (GNSS) of the second generation (GPS, GLONASS, Galileo, BeiDou/Compass) and GNSS augmentation. We review the theory about mechanisms behind the impact of geomagnetic storms, ionospheric irregularities, and powerful solar radio bursts on the GNSS user segment. We also summarize experimental observations of the space weather effects on GNSS performance in 2000–2020 to confirm the theory. We analyze the probability of failures in measurements of radio navigation parameters, decrease in positioning accuracy of GNSS users in dual-frequency mode and differential navigation mode (RTK), and in precise point positioning (PPP). Additionally, the review includes data on the occurrence of dangerous and extreme space weather phenomena and the possibility for predicting their im- pact on the GNSS user segment. The main conclusions of the review are as follows: 1) the positioning error in GNSS users may increase up to 10 times in various modes during extreme space weather events, as compared to the background level; 2) GNSS space and ground segments have been significantly modernized over the past decade, thus allowing a substantial in- crease in noise resistance of GNSS under powerful solar radio burst impacts; 3) there is a great possibility for increasing the tracking stability and accuracy of radio navigation parameters by introducing algorithms for adaptive lock loop tuning, taking into account the influence of space weather events; 4) at present, the urgent scientific and technical problem of modernizing GNSS by improving the scientific methodology, hardware and software for monitoring the system integrity and monitoring the availability of required navigation parameters, taking into account the impact of extreme space weather events, is still unresolved.
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Demyanov, Vladislav, and Yury Yasyukevich. "Space weather: risk factors for Global Navigation Satellite Systems." Solnechno-Zemnaya Fizika 7, no. 2 (June 30, 2021): 30–52. http://dx.doi.org/10.12737/szf-72202104.
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Extreme space weather events affect the stability and quality of the global navigation satellite systems (GNSS) of the second generation (GPS, GLONASS, Galileo, BeiDou/Compass) and GNSS augmentation. We review the theory about mechanisms behind the impact of geomagnetic storms, ionospheric irregularities, and powerful solar radio bursts on the GNSS user segment. We also summarize experimental observations of the space weather effects on GNSS performance in 2000–2020 to confirm the theory. We analyze the probability of failures in measurements of radio navigation parameters, decrease in positioning accuracy of GNSS users in dual-frequency mode and differential navigation mode (RTK), and in precise point positioning (PPP). Additionally, the review includes data on the occurrence of dangerous and extreme space weather phenomena and the possibility for predicting their im- pact on the GNSS user segment. The main conclusions of the review are as follows: 1) the positioning error in GNSS users may increase up to 10 times in various modes during extreme space weather events, as compared to the background level; 2) GNSS space and ground segments have been significantly modernized over the past decade, thus allowing a substantial in- crease in noise resistance of GNSS under powerful solar radio burst impacts; 3) there is a great possibility for increasing the tracking stability and accuracy of radio navigation parameters by introducing algorithms for adaptive lock loop tuning, taking into account the influence of space weather events; 4) at present, the urgent scientific and technical problem of modernizing GNSS by improving the scientific methodology, hardware and software for monitoring the system integrity and monitoring the availability of required navigation parameters, taking into account the impact of extreme space weather events, is still unresolved.
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Li, Weiqiang, Dongkai Yang, Bo Zhang, Mingli Li, and Qishan Zhang. "Real-time Processing of Reflected GNSS Signals for Remote Sensing: System and Experiments." Journal of Navigation 64, S1 (October 14, 2011): S127—S140. http://dx.doi.org/10.1017/s0373463311000403.
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The GNSS-R technique brings out the need for signal receiver systems to process both direct and reflected GNSS signals. This paper describes the architecture of a new GNSS-R receiver system (GRrSv.2) that features enhanced capabilities for remote sensing based on reflected Global Positioning System (GPS) signals. Signal processing issues including DDM calculation, Carrier and Code Generation and DDM Synchronization are presented. Aircraft- and land-based verification experiments for ocean winds, ocean Significant Wave Heights (SWH) and soil moisture have been performed and some primary results are presented in this paper.
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Kersten, Tobias, and Jens-André Paffenholz. "Feasibility of Consumer Grade GNSS Receivers for the Integration in Multi-Sensor-Systems." Sensors 20, no. 9 (April 26, 2020): 2463. http://dx.doi.org/10.3390/s20092463.
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Various GNSS applications require low-cost, small-scale, lightweight and power-saving GNSS devices and require high precision in terms of low noise for carrier phase and code observations. Applications vary from navigation approaches to positioning in geo-monitoring units up to integration in multi-sensor-systems. For highest precision, only GNSS receivers are suitable that provide access to raw data such as carrier phase, code ranges, Doppler and signal strength. A system integration is only possible if the overall noise level is known and quantified at the level of the original observations. A benchmark analysis based on a zero baseline is proposed to quantify the stochastic properties. The performance of the consumer grade GNSS receiver is determined and evaluated against geodetic GNSS receivers to better understand the utilization of consumer grade receivers. Results indicate high similarity to the geodetic receiver, even though technical limitations are present. Various stochastic techniques report normally distributed carrier-phase noise of 2 mm and code-range noise of 0.5–0.8 m. This is confirmed by studying the modified Allan standard deviation and code-minus-carrier combinations. Derived parameters serve as important indicators for the integration of GNSS receivers into multi-sensor-systems.
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Männel, Benjamin, Florian Zus, Galina Dick, Susanne Glaser, Maximilian Semmling, Kyriakos Balidakis, Jens Wickert, Marion Maturilli, Sandro Dahlke, and Harald Schuh. "GNSS-based water vapor estimation and validation during the MOSAiC expedition." Atmospheric Measurement Techniques 14, no. 7 (July 28, 2021): 5127–38. http://dx.doi.org/10.5194/amt-14-5127-2021.
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Abstract. Within the transpolar drifting expedition MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate), the Global Navigation Satellite System (GNSS) was used among other techniques to monitor variations in atmospheric water vapor. Based on 15 months of continuously tracked GNSS data including GPS, GLONASS and Galileo, epoch-wise coordinates and hourly zenith total delays (ZTDs) were determined using a kinematic precise point positioning (PPP) approach. The derived ZTD values agree to 1.1 ± 0.2 mm (root mean square (rms) of the differences 10.2 mm) with the numerical weather data of ECMWF's latest reanalysis, ERA5, computed for the derived ship's locations. This level of agreement is also confirmed by comparing the on-board estimates with ZTDs derived for terrestrial GNSS stations in Bremerhaven and Ny-Ålesund and for the radio telescopes observing very long baseline interferometry in Ny-Ålesund. Preliminary estimates of integrated water vapor derived from frequently launched radiosondes are used to assess the GNSS-derived integrated water vapor estimates. The overall difference of 0.08 ± 0.04 kg m−2 (rms of the differences 1.47 kg m−2) demonstrates a good agreement between GNSS and radiosonde data. Finally, the water vapor variations associated with two warm-air intrusion events in April 2020 are assessed.
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Chen, Yong, Xi Shao, Changyong Cao, and Shu-peng Ho. "Simultaneous Radio Occultation Predictions for Inter-Satellite Comparison of Bending Angle Profiles from COSMIC-2 and GeoOptics." Remote Sensing 13, no. 18 (September 12, 2021): 3644. http://dx.doi.org/10.3390/rs13183644.
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The Global Navigation Satellite System (GNSS) radio occultation (RO) is a remote sensing technique that uses International System of Units (SI) traceable GNSS signals for atmospheric limb soundings. The RO bending angle/sounding profiles are needed for assimilation in Numerical Weather Prediction (NWP) models, weather, climate, and space weather applications. Evaluating these RO data to ensure the high data quality for these applications is becoming more and more critical. This study presents a method for predicting radio occultation events, from which simultaneous radio occultation (SRO) for a pair of low-Earth-orbit (LEO) satellites on the limb to the same GNSS satellite can be obtained. The SRO method complements the Simultaneous Nadir Overpass (SNO) method (for nadir viewing satellite instruments), which has been widely used to inter-calibrate LEO to LEO and LEO to geosynchronous-equatorial-orbit (GEO) satellites. Unlike the SNO method, the SRO method involves three satellites: a GNSS and two LEO satellites with RO receivers. The SRO method allows for the direct comparison of bending angles when the simultaneous RO measurements for two LEO satellites receiving the same GNSS signal pass through approximately the same atmosphere within minutes in time and within less than 200 km of distance from each other. The prediction method can also be applied to radiosonde overpass prediction, and coordinate radiosonde launches for inter-comparisons between RO and radiosonde profiles. The main advantage of the SRO comparisons of bending angles is the significantly reduced uncertainties due to the much shorter time and smaller atmospheric path differences than traditional RO comparisons. To demonstrate the usefulness of this method, we present a comparison of the Constellation Observing System for Meteorology, Ionosphere, and Climate-2 (COSMIC-2) and GeoOpitcs RO profiles using SRO data for two time periods: Commercial Weather Data (CWD) data delivery order-1 (DO-1): 15 December 2020–15 January 2021 and CWD DO-2: 17 March 2021–31 August 2021. The results show good agreement in the bending angles between the COSMIC-2 RO measurements and those from GeoOptics, although systematic biases are also found in the inter-comparisons. Instrument and processing algorithm performances for the signal-to-noise ratio (SNR), penetration height, and bending angle retrieval uncertainty are also characterized. Given the efficiency of this method and the many RO measurements that are publicly and commercially available as well as the expansion of receiver capabilities to all GNSS systems, it is expected that this method can be used to validate/inter-calibrate GNSS RO measurements from different missions.
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Zeng, Hong-Cheng, Jie Chen, Peng-Bo Wang, Wei Yang, and Wei Liu. "2-D Coherent Integration Processing and Detecting of Aircrafts Using GNSS-Based Passive Radar." Remote Sensing 10, no. 7 (July 23, 2018): 1164. http://dx.doi.org/10.3390/rs10071164.
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Long time coherent integration is a vital method for improving the detection ability of global navigation satellite system (GNSS)-based passive radar, because the GNSS signal is not radar-designed and its power level is very low. For aircraft detection, the large range cell migration (RCM) and Doppler frequency migration (DFM) will seriously affect the coherent processing of azimuth signals, and the traditional range match filter will also be mismatched due to the Doppler-intolerant characteristic of GNSS signals. Accordingly, the energy loss of 2-dimensional (2-D) coherent processing is inevitable in traditional methods. In this paper, a novel 2-D coherent integration processing and algorithm for aircraft target detection is proposed. For azimuth processing, a modified Radon Fourier Transform (RFT) with range-walk removal and Doppler rate estimation is performed. In respect to range compression, a modified matched filter with a shifting Doppler is applied. As a result, the signal will be accurately focused in the range-Doppler domain, and a sufficiently high SNR can be obtained for aircraft detection with a moving target detector. Numerical simulations demonstrate that the range-Doppler parameters of an aircraft target can be obtained, and the position and velocity of the aircraft can be estimated accurately by multiple observation geometries due to abundant GNSS resources. The experimental results also illustrate that the blind Doppler sidelobe is suppressed effectively and the proposed algorithm has a good performance even in the presence of Doppler ambiguity.
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Bernet, Leonie, Elmar Brockmann, Thomas von Clarmann, Niklaus Kämpfer, Emmanuel Mahieu, Christian Mätzler, Gunter Stober, and Klemens Hocke. "Trends of atmospheric water vapour in Switzerland from ground-based radiometry, FTIR and GNSS data." Atmospheric Chemistry and Physics 20, no. 19 (October 1, 2020): 11223–44. http://dx.doi.org/10.5194/acp-20-11223-2020.
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Abstract. Vertically integrated water vapour (IWV) is expected to increase globally in a warming climate. To determine whether IWV increases as expected on a regional scale, we present IWV trends in Switzerland from ground-based remote sensing techniques and reanalysis models, considering data for the time period 1995 to 2018. We estimate IWV trends from a ground-based microwave radiometer in Bern, from a Fourier transform infrared (FTIR) spectrometer at Jungfraujoch, from reanalysis data (ERA5 and MERRA-2) and from Swiss ground-based Global Navigation Satellite System (GNSS) stations. Using a straightforward trend method, we account for jumps in the GNSS data, which are highly sensitive to instrumental changes. We found that IWV generally increased by 2 % per decade to 5 % per decade, with deviating trends at some GNSS stations. Trends were significantly positive at 17 % of all GNSS stations, which often lie at higher altitudes (between 850 and 1650 m above sea level). Our results further show that IWV in Bern scales to air temperature as expected (except in winter), but the IWV–temperature relation based on reanalysis data in the whole of Switzerland is not clear everywhere. In addition to our positive IWV trends, we found that the radiometer in Bern agrees within 5 % with GNSS and reanalyses. At the Jungfraujoch high-altitude station, we found a mean difference of 0.26 mm (15 %) between the FTIR and coincident GNSS data, improving to 4 % after an antenna update in 2016. In general, we showed that ground-based GNSS data are highly valuable for climate monitoring, given that the data have been homogeneously reprocessed and that instrumental changes are accounted for. We found a response of IWV to rising temperature in Switzerland, which is relevant for projected changes in local cloud and precipitation processes.
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Dimitrov, Nikolay. "Deformation analysis in central west Bulgaria using triangulation and GPS data." Reports on Geodesy and Geoinformatics 108, no. 1 (December 8, 2019): 23–26. http://dx.doi.org/10.2478/rgg-2019-0009.
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AbstractThe article discusses a method applied for combining the results of Global Navigation Satellite Systems (GNSS) and 75-year old triangulation measurements to estimate the crustal movements in central western Bulgaria region. It was examined for joint analysis based on the results of GNSS with angular measurements of the first order triangulation network in Bulgaria during the period 1923–1930 year. As a result of the processing of GNSS and angular measurements, horizontal velocities of 15 points, strain rates, and rotation rates have been obtained. The results show dominating N–S extension at a rate of 1–2 mm/y and the deformation is not uniformly distributed over the studied area. The obtained results indicate the possibility of using old angular measurement of first-order triangulation points, together with GNSS data, to obtain estimates of the horizontal crustal movements.
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Liu, Yang, Yanxiong Liu, Ziwen Tian, Xiaolei Dai, Yun Qing, and Menghao Li. "Impact of ECOM Solar Radiation Pressure Models on Multi-GNSS Ultra-Rapid Orbit Determination." Remote Sensing 11, no. 24 (December 15, 2019): 3024. http://dx.doi.org/10.3390/rs11243024.
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The Global Navigation Satellite System (GNSS) ultra-rapid precise orbits are crucial for global and wide-area real-time high-precision applications. The solar radiation pressure (SRP) model is an important factor in precise orbit determination. The real-time orbit determination is generally less accurate than the post-processed one and may amplify the instability and mismodeling of SRP models. Also, the impact of different SRP models on multi-GNSS real-time predicted orbits demands investigations. We analyzed the impact of the ECOM 1 and ECOM 2 models on multi-GNSS ultra-rapid orbit determination in terms of ambiguity resolution performance, real-time predicted orbit overlap precision, and satellite laser ranging (SLR) validation. The multi-GNSS observed orbital arc and predicted orbital arcs of 1, 3, 6, and 24 h are compared. The simulated real-time experiment shows that for GLONASS and Galileo ultra-rapid orbits, compared to ECOM 1, ECOM 2 increased the ambiguity fixing rate to 89.3% and 83.1%, respectively, and improves the predicted orbit accuracy by 9.2% and 27.7%, respectively. For GPS ultra-rapid orbits, ECOM 2 obtains a similar ambiguity fixing rate as ECOM 1 but slightly better orbit overlap precision. For BDS GEO ultra-rapid orbits, ECOM 2 obtains better overlap precision and SLR residuals, while for BDS IGSO and MEO ultra-rapid orbits, ECOM 1 obtains better orbit overlap precision and SLR residuals.
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Jensen, Katherine, Kyle McDonald, Erika Podest, Nereida Rodriguez-Alvarez, Viviana Horna, and Nicholas Steiner. "Assessing L-Band GNSS-Reflectometry and Imaging Radar for Detecting Sub-Canopy Inundation Dynamics in a Tropical Wetlands Complex." Remote Sensing 10, no. 9 (September 7, 2018): 1431. http://dx.doi.org/10.3390/rs10091431.
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Despite the growing number of remote-sensing products from satellite sensors, mapping of the combined spatial distribution and temporal variability of inundation in tropical wetlands remains challenging. An emerging innovative approach is offered by Global Navigation Satellite System reflectometry (GNSS-R), a concept that takes advantage of GNSS-transmitting satellites and independent radar receivers to provide bistatic radar observations of Earth’s surface with large-scale coverage. The objective of this paper is to assess the capability of spaceborne GNSS reflections to characterize surface inundation dynamics in a complex wetlands environment in the Peruvian Amazon with respect to current state-of-the-art methods. This study examines contemporaneous ALOS2 PALSAR-2 L-band imaging radar, CYGNSS GNSS reflections, and ground measurements to assess associated advantages and challenges to mapping inundation dynamics, particularly in regions under dense tropical forest canopies. Three derivatives of CYGNSS Delay-Doppler maps (1) peak signal-to-noise ratio (SNR), (2) leading edge slope, and (3) trailing edge slope, demonstrated statistically significant logarithmic relationships with estimated flooded area percentages determined from SAR, with SNR exhibiting the strongest association. Aggregated Delay-Doppler maps SNR time series data examined for inundated regions undetected by imaging radar suggests GNSS-R exhibits a potentially greater sensitivity to inundation state beneath dense forest canopies relative to SAR. Results demonstrate the capability for mapping extent and dynamic wetlands ecosystems in complex tropical landscapes, alone or in combination with other remote-sensing techniques such as those based on imaging radar, contributing to enhanced mapping of these regions. However, several aspects of GNSS-R observations such as noise level, spatial resolution, and signal coherence need to be further examined.
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Taftazani, Muhammad Iqbal, and Yulaikhah Yulaikhah. "Studi Akurasi Pengukuran GNSS Jaring Makro Tahun 2016 dan 2017 pada Pemantauan Bendungan Sermo." Jurnal Nasional Teknologi Terapan (JNTT) 1, no. 1 (November 1, 2017): 50. http://dx.doi.org/10.22146/jntt.34086.
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Monitoring of deformation on Sermo Dam has been widely practiced. One of them is by installing the monitoring point, locate dinside the Sermo Dam area called the micro network, and outside the dam called macro network. The installation of the micro network monitoring point aims to monitor the deformation of the dam due to the volume of water. The macro network monitoring point aims to monitor the effect of the existence of an active fault under the dam. In the last few years, monitoring in Sermo Dam has been done using GNSS technology. This paper intends to present the results of the accuracy represented by the deviation standard value of the measurement point at the macro net on the GNSS observation in 2016 and 2017. The objective is to compare the accuracy resulting from various GNSS processing strategies in observation 2016 and 2017, evaluation of GNSS measurements that can be used as guidance in subsequent GNSS measurements. The result shows that GNSS measurement in 2017 using two IGS reference points (BAKO and COCO) has a better standard deviation value compared to the 2016 measurement by the difference 1-5 mm on the X axis, 1-9 mm on the Y axis, and 1-2 mm on the Z axis. In the GNSS data processing using seven IGS reference points (BAKO, COCO, KARR, DARW, GUUG, PIMO, SHAO) in 2016 mostly has a better standard deviation compared to 2017 measurement except in MAK5 with the difference 0-4 mm on the X axis, 1-10 mm on Y axis, and 0-2 mm on Z axis. As for the value of coordinate data processing in 2016 and 2017on the two processing strategies there are differences in coordinate values that indicate the movement of monitoring points of macro network. However, the vector of the point movement that occurs in the two strategies has a different direction. This requires verification in-depth research and focused on the deformation of the Sermo Dam monitoring point.
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Hamza, Veton, Bojan Stopar, Tomaž Ambrožič, Goran Turk, and Oskar Sterle. "Testing Multi-Frequency Low-Cost GNSS Receivers for Geodetic Monitoring Purposes." Sensors 20, no. 16 (August 5, 2020): 4375. http://dx.doi.org/10.3390/s20164375.
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Global Navigation Satellite System (GNSS) technology is widely used for geodetic monitoring purposes. However, in cases where a higher risk of receiver damage is expected, geodetic GNSS receivers may be considered too expensive to be used. As an alternative, low-cost GNSS receivers that are cheap, light, and prove to be of adequate quality over short baselines, are considered. The main goal of this research is to evaluate the positional precision of a multi-frequency low-cost instrument, namely, ZED-F9P with u-blox ANN-MB-00 antenna, and to investigate its potential for displacement detection. We determined the positional precision within static survey, and the displacement detection within dynamic survey. In both cases, two baselines were set, with the same rover point equipped with a low-cost GNSS instrument. The base point of the first baseline was observed with a geodetic GNSS instrument, whereas the second baseline was observed with a low-cost GNSS instrument. The results from static survey for both baselines showed comparable results for horizontal components; the precision was on a level of 2 mm or better. For the height component, the results show a better performance of low-cost instruments. This may be a consequence of unknown antenna calibration parameters for low-cost GNSS antenna, while statistically significant coordinates of rover points were obtained from both baselines. The difference was again more significant in the height component. For the displacement detection, a device was used that imposes controlled movements with sub-millimeter accuracy. Results, obtained on a basis of 30-min sessions, show that low-cost GNSS instruments can detect displacements from 10 mm upwards with a high level of reliability. On the other hand, low-cost instruments performed slightly worse as far as accuracy is concerned.
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Liu, Lou, Zhang, Huang, Zhou, and Zhang. "On the Study of Influences of Different Factors on the Rapid Tropospheric Tomography." Remote Sensing 11, no. 13 (June 28, 2019): 1545. http://dx.doi.org/10.3390/rs11131545.
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A rapid tropospheric tomography system was developed by using algebraicreconstruction technique. Influences of different factors on the tomographic results, including theground meteorological data, the multi-Global Navigation Satellite System (GNSS) observations, theground station distribution and the tomographic horizontal resolution, were systematicallyinvestigated. In order to exclude the impacts from discrepancies of water vapor informationbetween input observations and references on the tomographic results, the latest reanalysisproducts, ERA5, which were taken as references for result evaluations, were used to simulate slantwet delay (SWD) observations at GNSS stations. Besides, the slant delays derived from GNSSprocessing were also used to evaluate the reliability of simulated observations. Tomography resultsshow that the input both SWD and ground meteorological data could improve the tomographicresults where SWD mainly improve the results at middle layers (500 to 5000m, namely 2 to 16 layer)and ground meteorological data could improve the humidity fields at bottom layers further (0 to500m, namely 0 to 2 layer). Compared to the usage of Global Positioning System (GPS) only SWD,the inclusion of multi-GNSS SWD does not significantly improve the tomographic results at alllayers due to the almost unchanged dispersion of puncture points of GNSS signals. However,increases in the ground GNSS stations can benefit the tomography, with improvements of morethan 10% at bottom and middle layers. Higher tomographic horizontal resolution can furtherslightly improve the tomographic results (about 3-6% from 0.5 to 0.25 degrees), which, however,will also increase the computational burden at the same time.
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Su, Ke, and Shuanggen Jin. "Improvement of Multi-GNSS Precise Point Positioning Performances with Real Meteorological Data." Journal of Navigation 71, no. 6 (July 12, 2018): 1363–80. http://dx.doi.org/10.1017/s0373463318000462.
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Tropospheric delay is one of the main error sources in Global Navigation Satellite System (GNSS) Precise Point Positioning (PPP). Zenith Hydrostatic Delay (ZHD) accounts for 90% of the total delay. This research focuses on the improvements of ZHD from tropospheric models and real meteorological data on the PPP solution. Multi-GNSS PPP experiments are conducted using the datasets collected at Multi-GNSS Experiments (MGEX) network stations. The results show that the positioning accuracy of different GNSS PPP solutions using the meteorological data for ZHD correction can achieve an accuracy level of several millimetres. The average convergence time of a PPP solution for the BeiDou System (BDS), the Global Positioning System (GPS), Global Navigation Satellite System of Russia (GLONASS), BDS+GPS, and BDS+GPS+GLONASS+Galileo are 55·89 min, 25·88 min, 33·30 min, 20·50 min and 15·71 min, respectively. The results also show that atmospheric parameters provided by real meteorological data have little effect on the horizontal components of positioning compared to the meteorological model, while in the vertical component, the positioning accuracy is improved by 90·6%, 33·0%, 22·2% and 19·8% compared with the standard atmospheric model, University of New Brunswick (UNB3m) model, Global Pressure and Temperature (GPT) model, and Global Pressure and Temperature-2 (GPT2) model and the convergence times are decreased 51·2%, 32·8%, 32·5%, and 32·3%, respectively.
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Guo, Lijie, Liangke Huang, Junyu Li, Lilong Liu, Ling Huang, Bolin Fu, Shaofeng Xie, Hongchang He, and Chao Ren. "A Comprehensive Evaluation of Key Tropospheric Parameters from ERA5 and MERRA-2 Reanalysis Products Using Radiosonde Data and GNSS Measurements." Remote Sensing 13, no. 15 (July 30, 2021): 3008. http://dx.doi.org/10.3390/rs13153008.
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Tropospheric delay is a major error source in the Global Navigation Satellite System (GNSS), and the weighted mean temperature (Tm) is a key parameter in precipitable water vapor (PWV) retrieval. Although reanalysis products like the National Centers for Environmental Prediction (NCEP) and the European Center for Medium-Range Weather Forecasts (ECMWF) Re-Analysis-Interim (ERA-Interim) data have been used to calculate and model the tropospheric delay, Tm, and PWV, the limitations of the temporal and spatial resolutions of the reanalysis data have affected their performance. The release of the fifth-generation accurate global atmospheric reanalysis (ERA5) and the second Modern-Era Retrospective analysis for Research and Applications (MERRA-2) provide the opportunity to overcome these limitations. The performances of the zenith tropospheric delay (ZTD), zenith wet delay (ZWD), Tm, and zenith hydrostatic delay (ZHD) of ERA5 and MERRA-2 data from 2016 to 2017 were evaluated in this work using GNSS ZTD and radiosonde data over the globe. Taking GNSS ZTD as a reference, the ZTD calculated from MERRA-2 and ERA5 pressure-level data were evaluated in temporal and spatial scales, with an annual mean bias and root mean square (RMS) of 2.3 and 10.9 mm for ERA5 and 4.5 and 13.1 mm for MERRA-2, respectively. Compared to radiosonde data, the ZHD, ZWD, and Tm derived from ERA5 and MERRA-2 data were also evaluated on temporal and spatial scales, with annual mean bias values of 1.1, 1.7 mm, and 0.14 K for ERA5 and 0.5, 4.8 mm, and –0.08 K for MERRA-2, respectively. Meanwhile, the annual mean RMS was 4.5, 10.5 mm, and 1.03 K for ERA5 and 4.4, 13.6 mm, and 1.17 K for MERRA-2, respectively. Tropospheric parameters derived from MERRA-2 and ERA5, with improved temporal and spatial resolutions, can provide a reference for GNSS positioning and PWV retrieval.
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Rodriguez-Alvarez, Nereida, Erika Podest, Katherine Jensen, and Kyle C. McDonald. "Classifying Inundation in a Tropical Wetlands Complex with GNSS-R." Remote Sensing 11, no. 9 (May 4, 2019): 1053. http://dx.doi.org/10.3390/rs11091053.
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The use of global navigation satellite system reflectometry (GNSS-R) measurements for classification of inundated wetlands is presented. With the launch of NASA’s Cyclone Global Navigation Satellite System (CYGNSS) mission, space-borne GNSS-R measurements have become available over ocean and land. CYGNSS covers latitudes between ±38°, providing measurements over tropical ecosystems and benefiting new studies of wetland inundation dynamics. The GNSS-R signal over inundated wetlands is driven mainly by coherent scattering associated with the presence of surface water, producing strong forward scattering and a distinctive bistatic scattering signature. This paper presents a methodology used to classify inundation in tropical wetlands using observables derived from GNSS-R measurements and ancillary data. The methodology employs a multiple decision tree randomized (MDTR) algorithm for classification and wetland inundation maps derived from the phased-array L-band synthetic aperture radar (PALSAR-2) as reference for training and validation. The development of an innovative GNSS-R wetland classification methodology is aimed to advance mapping of global wetland distribution and dynamics, which is critical for improved estimates of natural methane production. The results obtained in this manuscript demonstrate the ability of GNSS-R signals to detect inundation under dense vegetation over the Pacaya-Samiria Natural Reserve, a tropical wetland complex located in the Peruvian Amazon. Classification results report an accuracy of 69% for regions of inundated vegetation, 87% for open water regions, and 99% for non-inundated areas. Misclassification of inundated vegetation, primarily as non-inundated area, is likely related to the combination of two factors: partial inundation within the GNSS-R scattering area, and signal attenuation from dense overstory vegetation, resulting in a low signal.
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Jiao, Guoqiang, Shuli Song, Yulong Ge, Ke Su, and Yangyang Liu. "Assessment of BeiDou-3 and Multi-GNSS Precise Point Positioning Performance." Sensors 19, no. 11 (May 31, 2019): 2496. http://dx.doi.org/10.3390/s19112496.
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With the launch of BDS-3 and Galileo new satellites, the BeiDou navigation satellite system (BDS) has developed from the regional to global system, and the Galileo constellation will consist of 26 satellites in space. Thus, BDS, GPS, GLONASS, and Galileo all have the capability of global positioning services. It is meaningful to evaluate the ability of global precise point positioning (PPP) of the GPS, BDS, GLONASS, and Galileo. This paper mainly contributes to the assessment of BDS-2, BDS-2/BDS-3, GPS, GLONASS, and Galileo PPP with the observations that were provided by the international Global Navigation Satellite System (GNSS) Monitoring and Assessment System (iGMAS). The Position Dilution of Precision (PDOP) value was utilized to research the global coverage of GPS, BDS-2, BDS-2/BDS-3, GLONASS, and Galileo. In particular, GPS-only, BDS-2-only, BDS-2/BDS-3, GLONASS-only, Galileo-only, and multi-GNSS combined PPP solutions were analyzed to verify the capacity of the PPP performances in terms of positioning accuracy, convergence time, and zenith troposphere delay (ZTD) accuracy. In view of PDOP, the current BDS and Galileo are capable of global coverage. The BDS-2/BDS-3 and Galileo PDOP values are fairly evenly distributed around the world similar to GPS and GLONASS. The root mean square (RMS) of positioning errors for static BDS-2/BDS-3 PPP and Galileo-only PPP are 10.7, 19.5, 20.4 mm, and 6.9, 18.6, 19.6 mm, respectively, in the geographic area of the selected station, which is the same level as GPS and GLONASS. It is worth mentioning that, by adding BDS-3 observations, the positioning accuracy of static BDS PPP is improved by 17.05%, 24.42%, and 35.65%, and the convergence time is reduced by 27.15%, 27.87%, and 35.76% in three coordinate components, respectively. Similar to the static positioning, GPS, BDS-2/BDS-3, GLONASS, and Galileo have the basically same kinematic positioning accuracy. Multi-GNSS PPP significantly improves the positioning performances in both static and kinematic positioning. In terms of ZTD accuracy, the difference between GPS, BDS-2/BDS-3, GLONASS, and Galileo is less than 1 mm, and the BDS-2/BDS-3 improves ZTD accuracy by 20.48% over the BDS-2. The assessment of GPS, BDS-2, BDS-2/BDS-3, GLONASS, Galileo, and multi-GNSS global PPP performance are shown to make comments for the development of multi-GNSS integration, global precise positioning, and the construction of iGMAS.
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He, Qimin, Kefei Zhang, Suqin Wu, Qingzhi Zhao, Xiaoming Wang, Zhen Shen, Longjiang Li, Moufeng Wan, and Xiaoyang Liu. "Real-Time GNSS-Derived PWV for Typhoon Characterizations: A Case Study for Super Typhoon Mangkhut in Hong Kong." Remote Sensing 12, no. 1 (December 27, 2019): 104. http://dx.doi.org/10.3390/rs12010104.
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Typhoons can be serious natural disasters for the sustainability and development of society. The development of a typhoon usually involves a pre-existing weather disturbance, warm tropical oceans, and a large amount of moisture. This implies that a large variation in the atmospheric water vapor over the path of a typhoon can be used to study the characteristics of the typhoon. This is the reason that the variation in precipitable water vapor (PWV) is often used to capture the signature of a typhoon in meteorology. This study investigates the usability of real-time PWV retrieved from global navigation satellite systems (GNSS) for typhoons’ characterizations, and especially, the following aspects were investigated: (1) The correlation between PWV and atmospheric parameters including pressure, temperature, precipitation, and wind speed; (2) water vapor transportation during a typhoon period; and (3) the correlation between the movement of a typhoon and the transportation of water vapor. The case study selected for this research was Super Typhoon Mangkhut that occurred in mid-September 2018 in Hong Kong. The PWV time series were obtained from a conversion of GNSS-derived zenith total delays (ZTDs) using observations at 10 stations selected from the Hong Kong GNSS continuously operating reference stations (CORS) network, which are also located along the path of the typhoon. The Bernese GNSS Software (ver. 5.2) was used to obtain the ZTDs; and the root mean square (RMS) of the differences between the GNSS-ZTDs and International GNSS Service post-processed ZTDs time series was less than 8 mm. The RMS of the differences between the GNSS-PWVs (i.e., the ZTDs converted PWVs) and radiosonde-derived PWVs (RS-PWVs) time series was less than 2 mm. The changes in PWV reflect the variation in wind speed during the typhoon period to a certain degree, and their correlation coefficient was 0.76, meaning a significant positive correlation. In addition, a new approach was proposed to estimate the direction and speed of a typhoon’s movement using the time difference of PWV arrival at different sites. The direction and speed estimated agreed well with the ones published by the China Meteorological Administration. These results suggest that GNSS-derived PWV has a great potential for the monitoring and even prediction of typhoon events, especially for near real-time warnings.
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FEDORCHUK, A. "Analysis of erypsoidal heights errors based on GNSS-leveling results." Modern achievements of geodesic science and industry 41, no. I (April 1, 2021): 37–45. http://dx.doi.org/10.33841/1819-1339-1-41-37-45.
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Research the influence of errors on the measurement results is always an urgent task. Analysis of such values makes it possible to assess the nature of the change and the magnitude of the impact of errors for their further consideration or compensation, or minimization. In this paper, the errors in determining ellipsoidal heights from GNSS observations are considered. In determining the ellipsoidal heights, this method can achieve an accuracy of 1–2 cm in static mode (Static) and 2–4 cm in real time mode (RTK). Thus, the accuracy of the chosen mode of observations will indicate the initial limits of the ellipsoidal heights errors influence, and the factors that arise directly during observations and data processing will determine the extent to which these errors will change relative to the initial limits. The purpose of this work is to analyze the errors of ellipsoidal heights based on the results of GNSS-leveling obtained in the static and RTK modes. Method. The study used GNSS-leveling data at 17 points (wall and soil benchmarks) of leveling lines of I–II classes, which are located within a radius of 15 km from the permanent station SULP of the Lviv Polytechnic National University. Observations were performed in static mode (4-hour) and RTK (8–10 measurements). Points are divided into three categories (5–6 points): 1) statics on wall benchmarks; 2) real-time mode on wall benchmarks; 3) static mode on soil benchmarks. By combining methods and categories, four GNSS networks were formed, including 11, 11, 12 and 17 points. Results. For each category, the percentages within which the errors of ellipsoidal heights change in static observation mode and real-time mode using the GNSS leveling method are presented. On the basis of the received information it is established that for the first case errors of ellipsoidal heights on the average change within ± 43 %, for the second ± 36 %, and for the third ± 14 %. The analysis of statistical characteristics for each category shows that the standard deviation of the static mode data is 2 % and 19 %, and the RTK mode – 12 %, respectively. Scientific novelty and practical significance. The nature of the change in the error limits of the ellipsoidal heights determination gives an idea of what accuracy should be expected when performing GNSS-leveling depending on the mode of observation. Such data play an important role in solving scientific and applied problems by GNSS leveling, such as the constructions of new leveling networks or monitoring the height points of existing networks.
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Tavani, Stefano, Antonio Pignalosa, Amerigo Corradetti, Marco Mercuri, Luca Smeraglia, Umberto Riccardi, Thomas Seers, Terry Pavlis, and Andrea Billi. "Photogrammetric 3D Model via Smartphone GNSS Sensor: Workflow, Error Estimate, and Best Practices." Remote Sensing 12, no. 21 (November 4, 2020): 3616. http://dx.doi.org/10.3390/rs12213616.
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Geotagged smartphone photos can be employed to build digital terrain models using structure from motion-multiview stereo (SfM-MVS) photogrammetry. Accelerometer, magnetometer, and gyroscope sensors integrated within consumer-grade smartphones can be used to record the orientation of images, which can be combined with location information provided by inbuilt global navigation satellite system (GNSS) sensors to geo-register the SfM-MVS model. The accuracy of these sensors is, however, highly variable. In this work, we use a 200 m-wide natural rocky cliff as a test case to evaluate the impact of consumer-grade smartphone GNSS sensor accuracy on the registration of SfM-MVS models. We built a high-resolution 3D model of the cliff, using an unmanned aerial vehicle (UAV) for image acquisition and ground control points (GCPs) located using a differential GNSS survey for georeferencing. This 3D model provides the benchmark against which terrestrial SfM-MVS photogrammetry models, built using smartphone images and registered using built-in accelerometer/gyroscope and GNSS sensors, are compared. Results show that satisfactory post-processing registrations of the smartphone models can be attained, requiring: (1) wide acquisition areas (scaling with GNSS error) and (2) the progressive removal of misaligned images, via an iterative process of model building and error estimation.
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Materna, Kathryn, Lujia Feng, Eric O. Lindsey, Emma M. Hill, Aktarul Ahsan, A. K. M. Khorshed Alam, Kyaw Moe Oo, et al. "GNSS characterization of hydrological loading in South and Southeast Asia." Geophysical Journal International 224, no. 3 (October 17, 2020): 1742–52. http://dx.doi.org/10.1093/gji/ggaa500.
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SUMMARY The elastic response of the lithosphere to surface mass redistributions produces geodetically measurable deformation of the Earth. This deformation is especially pronounced in South and Southeast Asia, where the annual monsoon produces large-amplitude hydrological loads. The Myanmar–India–Bangladesh–Bhutan (MIBB) network of about 20 continuously operating Global Navigation Satellite Systems (GNSS) stations, established in 2011, provides an opportunity to study the Earth's response to these loads. In this study, we use GRACE temporal gravity products as an estimate of long-wavelength surface water distribution and use this estimate in an elastic loading calculation. We compare the predicted vertical deformation from GRACE with that observed with GNSS. We find that elastic loading inferred from the GRACE gravity model is able to explain the phase and much of the peak-to-peak amplitude (typically 2–3 cm) of the vertical GNSS oscillations, especially in northeast India and central Myanmar. GRACE-based corrections reduce the RMS scatter of the GNSS data by 30–45% in these regions. However, this approach does not capture all of the seasonal deformation in central Bangladesh and southern Myanmar. We show by a synthetic test that local hydrological effects may explain discrepancies between the GNSS and GRACE signals in these places. Two independent hydrological loading models of water stored in soil, vegetation, snow, lakes and streams display phase lags compared to the GRACE and GNSS observations, perhaps indicating that groundwater contributes to the observed loading in addition to near-surface hydrology. The results of our calculations have implications for survey-mode GNSS measurements, which make up the majority of geodetic measurements in this region. By using the GNSS data together with estimates of hydrological loading from independent observations and models, we may be able to more accurately determine crustal motions caused by tectonic processes in South and Southeast Asia, while also improving our ability to monitor the annual monsoon and resulting water storage changes in the region.
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Chen, Biyan, Wujiao Dai, Zhizhao Liu, Lixin Wu, Cuilin Kuang, and Minsi Ao. "Constructing a precipitable water vapor map from regional GNSS network observations without collocated meteorological data for weather forecasting." Atmospheric Measurement Techniques 11, no. 9 (September 11, 2018): 5153–66. http://dx.doi.org/10.5194/amt-11-5153-2018.
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Abstract. Surface pressure (Ps) and weighted mean temperature (Tm) are two necessary variables for the accurate retrieval of precipitable water vapor (PWV) from Global Navigation Satellite System (GNSS) zenith total delay (ZTD) estimates. The lack of Ps or Tm information is a concern for those GNSS sites that are not collocated with meteorological sensors. This paper investigates an alternative method of inferring accurate Ps and Tm at the GNSS station using nearby synoptic observations. Ps and Tm obtained at the nearby synoptic sites are interpolated onto the location of the GNSS station by performing both vertical and horizontal adjustments, in which the parameters involved in Ps and Tm calculation are estimated from ERA-Interim reanalysis profiles. In addition, we present a method of constructing high-quality PWV maps through vertical reduction and horizontal interpolation of the retrieved GNSS PWVs. To evaluate the performances of the Ps and Tm retrieval, and the PWV map construction, GNSS data collected from 58 stations of the Hunan GNSS network and synoptic observations from 20 nearby sites in 2015 were processed to extract the PWV so as to subsequently generate the PWV maps. The retrieved Ps and Tm and constructed PWV maps were assessed by the results derived from radiosonde and the ERA-Interim reanalysis. The results show that (1) accuracies of Ps and Tm derived by synoptic interpolation are within the range of 1.7–3.0 hPa and 2.5–3.0 K, respectively, which are much better than the GPT2w model; (2) the constructed PWV maps have good agreements with radiosonde and ERA-Interim reanalysis data with the overall accuracy being better than 3 mm; and (3) PWV maps can well reveal the moisture advection, transportation and convergence during heavy rainfall.