| 1. |
- Abelev, Betty, et al.
(författare)
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Long-range angular correlations on the near and away side in p-Pb collisions at root S-NN=5.02 TeV
- 2013
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 719:1-3, s. 29-41
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Tidskriftsartikel (refereegranskat)abstract
- Angular correlations between charged trigger and associated particles are measured by the ALICE detector in p-Pb collisions at a nucleon-nucleon centre-of-mass energy of 5.02 TeV for transverse momentum ranges within 0.5 < P-T,P-assoc < P-T,P-trig < 4 GeV/c. The correlations are measured over two units of pseudorapidity and full azimuthal angle in different intervals of event multiplicity, and expressed as associated yield per trigger particle. Two long-range ridge-like structures, one on the near side and one on the away side, are observed when the per-trigger yield obtained in low-multiplicity events is subtracted from the one in high-multiplicity events. The excess on the near-side is qualitatively similar to that recently reported by the CMS Collaboration, while the excess on the away-side is reported for the first time. The two-ridge structure projected onto azimuthal angle is quantified with the second and third Fourier coefficients as well as by near-side and away-side yields and widths. The yields on the near side and on the away side are equal within the uncertainties for all studied event multiplicity and p(T) bins, and the widths show no significant evolution with event multiplicity or p(T). These findings suggest that the near-side ridge is accompanied by an essentially identical away-side ridge. (c) 2013 CERN. Published by Elsevier B.V. All rights reserved.
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| 2. |
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| 3. |
- Fabritz, Larissa, et al.
(författare)
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Dynamic risk assessment to improve quality of care in patients with atrial fibrillation : the 7th AFNET/EHRA Consensus Conference
- 2021
-
Ingår i: Europace. - : Oxford University Press. - 1099-5129 .- 1532-2092. ; 23:3, s. 329-344
-
Tidskriftsartikel (refereegranskat)abstract
- AimsThe risk of developing atrial fibrillation (AF) and its complications continues to increase, despite good progress in preventing AF-related strokes.Methods and resultsThis article summarizes the outcomes of the 7th Consensus Conference of the Atrial Fibrillation NETwork (AFNET) and the European Heart Rhythm Association (EHRA) held in Lisbon in March 2019. Sixty-five international AF specialists met to present new data and find consensus on pressing issues in AF prevention, management and future research to improve care for patients with AF and prevent AF-related complications. This article is the main outcome of an interactive, iterative discussion between breakout specialist groups and the meeting plenary. AF patients have dynamic risk profiles requiring repeated assessment and risk-based therapy stratification to optimize quality of care. Interrogation of deeply phenotyped datasets with outcomes will lead to a better understanding of the cardiac and systemic effects of AF, interacting with comorbidities and predisposing factors, enabling stratified therapy. New proposals include an algorithm for the acute management of patients with AF and heart failure, a call for a refined, data-driven assessment of stroke risk, suggestions for anticoagulation use in special populations, and a call for rhythm control therapy selection based on risk of AF recurrence.ConclusionThe remaining morbidity and mortality in patients with AF needs better characterization. Likely drivers of the remaining AF-related problems are AF burden, potentially treatable by rhythm control therapy, and concomitant conditions, potentially treatable by treating these conditions. Identifying the drivers of AF-related complications holds promise for stratified therapy.
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| 4. |
- Klopotek, Grzegorz, 1990, et al.
(författare)
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Results from the VLBI Analysis Software Comparison Campaign 2015
- 2016
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Ingår i: IVS 2016 General Meeting Proceedings "New Horizons with VGOS". Edited by Dirk Behrend, Karen D. Baver, and Kyla L. Armstrong, NASA/CP-2016-219016. ; , s. 203-207
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The aim of the VLBI Analysis Software Comparison Campaign 2015 (VASCC2015) was to compare differentVLBI analysis software packages on the basis of computed theoretical delays. Eleven research groups and institutes participated in this project which allowed us to compare software packages that are used in operational VLBI analyses or that are still under development. We present the first results and we show how well the individual software packages agree at this stage.
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| 5. |
- Schnabel, Renate B, et al.
(författare)
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Early diagnosis and better rhythm management to improve outcomes in patients with atrial fibrillation : the 8th AFNET/EHRA consensus conference
- 2023
-
Ingår i: Europace. - : Oxford University Press. - 1099-5129 .- 1532-2092. ; 25:1, s. 6-27
-
Tidskriftsartikel (refereegranskat)abstract
- Despite marked progress in the management of atrial fibrillation (AF), detecting AF remains difficult and AF-related complications cause unacceptable morbidity and mortality even on optimal current therapy. This document summarizes the key outcomes of the 8th AFNET/EHRA Consensus Conference of the Atrial Fibrillation NETwork (AFNET) and the European Heart Rhythm Association (EHRA). Eighty-three international experts met in Hamburg for 2 days in October 2021. Results of the interdisciplinary, hybrid discussions in breakout groups and the plenary based on recently published and unpublished observations are summarized in this consensus paper to support improved care for patients with AF by guiding prevention, individualized management, and research strategies. The main outcomes are (i) new evidence supports a simple, scalable, and pragmatic population-based AF screening pathway; (ii) rhythm management is evolving from therapy aimed at improving symptoms to an integrated domain in the prevention of AF-related outcomes, especially in patients with recently diagnosed AF; (iii) improved characterization of atrial cardiomyopathy may help to identify patients in need for therapy; (iv) standardized assessment of cognitive function in patients with AF could lead to improvement in patient outcomes; and (v) artificial intelligence (AI) can support all of the above aims, but requires advanced interdisciplinary knowledge and collaboration as well as a better medico-legal framework. Implementation of new evidence-based approaches to AF screening and rhythm management can improve outcomes in patients with AF. Additional benefits are possible with further efforts to identify and target atrial cardiomyopathy and cognitive impairment, which can be facilitated by AI.
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| 6. |
- Stevens, Kristen N, et al.
(författare)
-
19p13.1 is a triple negative-specific breast cancer susceptibility locus
- 2012
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Ingår i: Cancer Research. - 0008-5472 .- 1538-7445. ; 72, s. 1795-
-
Tidskriftsartikel (refereegranskat)abstract
- The 19p13.1 breast cancer susceptibility locus is a modifier of breast cancer risk in BRCA1 mutation carriers and is also associated with risk of ovarian cancer. Here we investigated 19p13.1 variation and risk of breast cancer subtypes, defined by estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor-2 (HER2) status, using 48,869 breast cancer cases and 49,787 controls from the Breast Cancer Association Consortium (BCAC). Variants from 19p13.1 were not associated with breast cancer overall or with ER-positive breast cancer but were significantly associated with ER-negative breast cancer risk [rs8170 Odds Ratio (OR)=1.10, 95% Confidence Interval (CI) 1.05 - 1.15, p=3.49 x 10-5] and triple negative (TN) (ER, PR and HER2 negative) breast cancer [rs8170 OR=1.22, 95% CI 1.13 - 1.31, p=2.22 x 10-7]. However, rs8170 was no longer associated with ER-negative breast cancer risk when TN cases were excluded [OR=0.98, 95% CI 0.89 - 1.07, p=0.62]. In addition, a combined analysis of TN cases from BCAC and the Triple Negative Breast Cancer Consortium (TNBCC) (n=3,566) identified a genome-wide significant association between rs8170 and TN breast cancer risk [OR=1.25, 95% CI 1.18 - 1.33, p=3.31 x 10-13]. Thus, 19p13.1 is the first triple negative-specific breast cancer risk locus and the first locus specific to a histological subtype defined by ER, PR, and HER2 to be identified. These findings provide convincing evidence that genetic susceptibility to breast cancer varies by tumor subtype and that triple negative tumors and other subtypes likely arise through distinct etiologic pathways.
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| 7. |
- Weil, Tatjana, et al.
(författare)
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Advanced Molecular Tweezers with Lipid Anchors against SARS-CoV-2 and Other Respiratory Viruses
- 2022
-
Ingår i: JACS Au. - : American Chemical Society (ACS). - 2691-3704. ; 2:9, s. 2187-2202
-
Tidskriftsartikel (refereegranskat)abstract
- The COVID-19 pandemic caused by SARS-CoV-2 presents a global health emergency. Therapeutic options against SARS-CoV-2 are still very limited but urgently required. Molecular tweezers are supramolecular agents that destabilize the envelope of viruses resulting in a loss of viral infectivity. Here, we show that first-generation tweezers, CLR01 and CLR05, disrupt the SARS-CoV-2 envelope and abrogate viral infectivity. To increase the antiviral activity, a series of 34 advanced molecular tweezers were synthesized by insertion of aliphatic or aromatic ester groups on the phosphate moieties of the parent molecule CLR01. A structure-activity relationship study enabled the identification of tweezers with a markedly enhanced ability to destroy lipid bilayers and to suppress SARS-CoV-2 infection. Selected tweezer derivatives retain activity in airway mucus and inactivate the SARS-CoV-2 wildtype and variants of concern as well as respiratory syncytial, influenza, and measles viruses. Moreover, inhibitory activity of advanced tweezers against respiratory syncytial virus and SARS-CoV-2 was confirmed in mice. Thus, potentiated tweezers are broad-spectrum antiviral agents with great prospects for clinical development to combat highly pathogenic viruses.
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| 8. |
- Albentosa, Ezequiel, et al.
(författare)
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Current Status of the EU-VGOS Project
- 2023
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Ingår i: International VLBI Service for Geodesy and Astrometry 2022 General Meeting Proceedings. ; NASA/ CP–20220018789, s. 85-89
-
Konferensbidrag (refereegranskat)abstract
- The EU-VGOS project began in 2018 with the aim of using the VGOS infrastructure in Europe to investigate methods for VGOS data processing. The project is now structured into Working Groups dealing with operations (stations), e-transfer, correlation and post-processing, and analysis. This is a report on the status of the project.
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| 9. |
- Balduini, Carlo, et al.
(författare)
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The EHA research roadmap : Platelet disorders
- 2021
-
Ingår i: HemaSphere. - 2572-9241. ; 5:7
-
Forskningsöversikt (refereegranskat)abstract
- In 2016, the European Hematology Association (EHA) published the EHA Roadmap for European Hematology Research1 aiming to highlight achievements in the diagnostics and treatment of blood disorders, and to better inform European policy makers and other stakeholders about the urgent clinical and scientific needs and priorities in the field of hematology. Each section was coordinated by 1 to 2 section editors who were leading international experts in the field. In the 5 years that have followed, advances in the field of hematology have been plentiful. As such, EHA is pleased to present an updated Research Roadmap, now including 11 sections, each of which will be published separately. The updated EHA Research Roadmap identifies the most urgent priorities in hematology research and clinical science, therefore supporting a more informed, focused, and ideally a more funded future for European hematology research. The 11 EHA Research Roadmap sections include Normal Hematopoiesis; Malignant Lymphoid Diseases; Malignant Myeloid Diseases; Anemias and Related Diseases; Platelet Disorders; Blood Coagulation and Hemostatic Disorders; Transfusion Medicine; Infections in Hematology; Hematopoietic Stem Cell Transplantation; CAR-T and Other Cellbased Immune Therapies; and Gene Therapy.
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| 10. |
- Budimir, Sanja, et al.
(författare)
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Reasons for Discontinuing Active Participation on the Internet Forum Tinnitus Talk : Mixed Methods Citizen Science Study
- 2021
-
Ingår i: JMIR Formative Research. - : JMIR Publications. - 2561-326X. ; 5:4
-
Tidskriftsartikel (refereegranskat)abstract
- Background: Tinnitus Talk is a nonprofit online self-help forum. Asking inactive users about their reasons for discontinued usage of health-related online platforms such as Tinnitus Talk is important for quality assurance. Objective: The aim of this study was to explore reasons for discontinued use of Tinnitus Talk, and their associations to the perceptions of Tinnitus Talk and the age of users who ceased logging on to the platform. Methods: Initially, 13,745 users that did not use Tinnitus Talk within the previous 2 months were contacted and the response rate was 20.47% (n=2814). After dataset filtering, a total of 2172 past members of Tinnitus Talk were included in the analyses. Nine predefined reasons for discontinued usage of Tinnitus Talk were included in the survey as well as one open question. Moreover, there were 14 predefined questions focusing on perception of Tinnitus Talk (usefulness, content, community, and quality of members' posts). Mixed methods analyses were performed. Frequencies and correlation coefficients were calculated for quantitative data, and grounded theory methodology was utilized for exploration of the qualitative data. Results: Quantitative analysis revealed reasons for discontinued use of Tinnitus Talk as well as associations of these reasons with perceptions of Tinnitus Talk and age. Among the eight predefined reasons for discontinued use of Tinnitus Talk, the most frequently reported was not finding the information they were looking for (451/2695, 16.7%). Overall, the highest rated perception of Tinnitus Talk was content-related ease of understanding (mean 3.9, SD 0.64). A high number (nearly 40%) of participants provided additional free text explaining why they discontinued use. Qualitative analyses identified a total of 1654 specific reasons, more than 93% of which (n=1544) could be inductively coded. The coding system consisted of 33 thematically labeled codes clustered into 10 categories. The most frequent additional reason for discontinuing use was thinking that there is no cure or help for tinnitus symptoms (375/1544, 24.3%). Significant correlations (P<.001) were observed between reasons for discontinued usage and perception of Tinnitus Talk. Several reasons for discontinued usage were associated with the examined dimensions of perception of Tinnitus Talk (usefulness, content, community, as well as quality of members' posts). Moreover, significant correlations (P<.001) between age and reasons for discontinued use were found. Older age was associated with no longer using Tinnitus Talk because of not finding what they were looking for. In addition, older participants had a generally less positive perception of Tinnitus Talk than younger participants (P<.001). Conclusions: This study contributes to understanding the reasons for discontinued usage of online self-help platforms, which are typically only reported according to the dropout rates. Furthermore, specific groups of users who did not benefit from Tinnitus Talk were identified, and several practical implications for improvement of the structure, content, and goals of Tinnitus Talk were suggested.
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| 11. |
- Egea, Joaquim, et al.
(författare)
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Regulation of EphA 4 kinase activity is required for a subset of axon guidance decisions suggesting a key role for receptor clustering in Eph function
- 2005
-
Ingår i: Neuron. - : Elsevier BV. - 0896-6273 .- 1097-4199. ; 47:4, s. 515-528
-
Tidskriftsartikel (refereegranskat)abstract
- Signaling by receptor tyrosine kinases (RTKs) is mediated by their intrinsic kinase activity. Typically, kinase-activating mutations result in ligand-independent signaling and gain-of-function phenotypes. Like other RTKs, Ephs require kinase activity to signal, but signaling by Ephs in vitro also requires clustering by their membrane bound ephrin ligands. The relative importance of Eph kinase activity and clustering for in vivo functions is unknown. We find that knockin mice expressing a mutant form of EphA4 (EphA4(EE)), whose kinase is constitutively activated in the absence of ephrinB ligands, are deficient in the development of thalamocortical projections and some aspects of central pattern generator rhythmicity. Surprisingly, other functions of EphA4 were regulated normally by EphA4(EE), including midline axon guidance, hindlimb locomotion, in vitro growth cone collapse, and phosphorylation of ephexin1. These results suggest that signaling of Eph RTKs follows a multistep process of induced kinase activity and higher-order clustering different from RTKs responding to soluble ligands.
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| 12. |
- Elgered, Gunnar, 1955, et al.
(författare)
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The Onsala Twin Telescopes Project
- 2017
-
Ingår i: The 23rd Working Meeting of the European VLBI Group for Geodesy and Astrometry (EVGA), Gothenburg, May 14–18, 2017.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The Onsala Space Observatory is the European site in the International VLBI Service for Geodesy and Astrometry (IVS) that has the longest history in VLBI. First geodetic VLBI measurements were performed already in 1968 with the 25 m radio telescope. Onsala is today one of the sites with thelongest time series in the IVS data base. The observatory is one of the unique fundamental space geodetic sites that have a direct access to the coast line and co-locate VLBI, GNSS, gravimetry, and sea-level monitoring. Onsala is thus an important co-location site for the GlobalGeodetic Observing System (GGOS). Being well aware of the VGOS standard it was clear around 2010 that Onsala was in need for a telescope with significantly faster slew rates than the existing radome-enclosed 20 m telescope.
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| 13. |
- Elgered, Gunnar, 1955, et al.
(författare)
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The Onsala Twin Telescopes: the Status at the Time for the Inauguration
- 2017
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Ingår i: Proceedings of the 23rd European VLBI Group for Geodesy and Astrometry Working Meeting. - 9789188041098 ; , s. 136-139
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We summarise the activities related to the Onsala Twin Telescopes (OTT), from the time when the decision was taken to fund the proposal, to the inauguration on 18 May 2017.
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| 14. |
- Escala-Garcia, M, et al.
(författare)
-
Germline variants and breast cancer survival in patients with distant metastases at primary breast cancer diagnosis
- 2021
-
Ingår i: Scientific reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 11:1, s. 19787-
-
Tidskriftsartikel (refereegranskat)abstract
- Breast cancer metastasis accounts for most of the deaths from breast cancer. Identification of germline variants associated with survival in aggressive types of breast cancer may inform understanding of breast cancer progression and assist treatment. In this analysis, we studied the associations between germline variants and breast cancer survival for patients with distant metastases at primary breast cancer diagnosis. We used data from the Breast Cancer Association Consortium (BCAC) including 1062 women of European ancestry with metastatic breast cancer, 606 of whom died of breast cancer. We identified two germline variants on chromosome 1, rs138569520 and rs146023652, significantly associated with breast cancer-specific survival (P = 3.19 × 10−8 and 4.42 × 10−8). In silico analysis suggested a potential regulatory effect of the variants on the nearby target genes SDE2 and H3F3A. However, the variants showed no evidence of association in a smaller replication dataset. The validation dataset was obtained from the SNPs to Risk of Metastasis (StoRM) study and included 293 patients with metastatic primary breast cancer at diagnosis. Ultimately, larger replication studies are needed to confirm the identified associations.
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| 15. |
- Geremia-Nievinski, F., et al.
(författare)
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SNR-based GNSS reflectometry for coastal sea-level altimetry: results from the first IAG inter-comparison campaign
- 2020
-
Ingår i: Journal of Geodesy. - : Springer Science and Business Media LLC. - 0949-7714 .- 1432-1394. ; 94:8
-
Tidskriftsartikel (refereegranskat)abstract
- Ground-based Global Navigation Satellite System Reflectometry (GNSS-R) is quickly maturing toward the objective of becoming a viable alternative for operational coastal sea-level (SL) altimetry in a geocentric reference frame. SL has immense societal implications related to climate change. Of particular interest is the exploitation of existing coastal GNSS sites for reflectometry by means of signal-to-noise ratio (SNR) observables. We report results from the first inter-comparison campaign on SNR-based GNSS-R. The goal was to cross-validate retrieval solutions from independent research groups under comparable conditions. This action was an initiative of the International Association of Geodesy working group 4.3.9 (2015–2019 term). Data collected at the Onsala Space Observatory for a 1-year period (2015–2016) were compared to a co-located tide gauge (TG). SNR data for the GPS L1-C/A signal were processed by four groups, in Sweden, Luxembourg/Brazil, Germany, and the UK. Semidiurnal tidal constituents showed good agreement between TG and all GNSS-R groups. SL variations at diurnal and longer periods were also well captured by all series. Most GNSS-R solutions exhibited spurious tones at integer fractions of one sidereal day, the satellite revisit time of the particular GNSS constellation employed (GPS). Band-pass filtering between 3 h and 30 h confirmed that the dominant tidal components were well captured by most GNSS-R solutions. Higher-frequency SL variations (periods < 3 h) are poorly represented by GNSS-R as a consequence of its low temporal resolution. The solution with the worst agreement neglects a correction associated with the rate of change in sea level and uses narrower satellite elevation ranges per retrieval. Overall, there was excellent agreement, with correlation coefficients exceeding 0.9 and RMSE smaller than 5 cm.
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| 16. |
- Groß, Rüdiger, et al.
(författare)
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Macromolecular Viral Entry Inhibitors as Broad-Spectrum First-Line Antivirals with Activity against SARS-CoV-2
- 2022
-
Ingår i: Advanced Science. - : Wiley. - 2198-3844. ; 9:20
-
Tidskriftsartikel (refereegranskat)abstract
- Inhibitors of viral cell entry based on poly(styrene sulfonate) and its core–shell nanoformulations based on gold nanoparticles are investigated against a panel of viruses, including clinical isolates of SARS-CoV-2. Macromolecular inhibitors are shown to exhibit the highly sought-after broad-spectrum antiviral activity, which covers most analyzed enveloped viruses and all of the variants of concern for SARS-CoV-2 tested. The inhibitory activity is quantified in vitro in appropriate cell culture models and for respiratory viral pathogens (respiratory syncytial virus and SARS-CoV-2) in mice. Results of this study comprise a significant step along the translational path of macromolecular inhibitors of virus cell entry, specifically against enveloped respiratory viruses.
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| 17. |
- Haas, Rüdiger, 1966, et al.
(författare)
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Contributions of Onsala Space Observatory to GGOS
- 2015
-
Ingår i: Proceedings of the 22nd European VLBI Group for Geodesy and Astrometry Working Meeting. - 9789892061917 ; , s. 125-129
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 18. |
- Haas, Rüdiger, 1966, et al.
(författare)
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GLONASS-VLBI: Onsala-Wettzell test observations
- 2015
-
Ingår i: Proceedings of the 22nd European VLBI Group for Geodesy and Astrometry Working Meeting. - 9789892061917 ; , s. 107-111
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 19. |
- Haas, Rüdiger, 1966, et al.
(författare)
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Near real-time monitoring of UT1 with geodetic VLBI
- 2011
-
Ingår i: Proceedings of the 20th Meeting of the European VLBI Group for Geodesy and Astrometry. - 1864-1113. ; , s. 64-66
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We give a short overview on the current status of near real-time monitoring of UT1 with geodetic VLBI. The use ofreal-time data transfer together with automated correlation and data analysis makes it possible to derive final dUT1-results with very low latency. The agreement with IERS C04 results is on the level of 30 msec. It is even possible to determine time series of dUT1 during ongoing 24 h IVS-sessions. The concept is highly relevant for future VLBI2010 operations.
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| 20. |
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| 21. |
- Haas, Rüdiger, 1966, et al.
(författare)
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Onsala Space Observatory – IVS Network Station Activities during 2014
- 2015
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We participated in 39 IVS sessions, includ-ing CONT14. Eleven out of the initially planned ses-sions could not be observed due to the installation ofa new radome for the 20-m radio telescope. As in theprevious six years, we used several of the sessions thatinvolved both Onsala and Tsukuba to perform ultra-rapid UT1-UTC sessions together with our colleaguesin Tsukuba. This included the complete CONT14 cam-paign where near real-time UT1-UTC on the baselineOnsala—Tsukuba could be determined. The procure-ment of the telescopes for the Onsala Twin Telescopeswas started in the summer of 2014. The contract to buytwo VGOS radio telescopes was signed at the end of the year.
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| 22. |
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| 23. |
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| 24. |
- Haas, Rüdiger, 1966, et al.
(författare)
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Status of the Onsala Twin Telescopes – One Year After the Inauguration
- 2019
-
Ingår i: IVS 2018 General Meeting Proceedings "Global Geodesy and the Role of VGOS – Fundamental to Sustainable Development". ; NASA/CP-2019-219039, s. 17-19
-
Konferensbidrag (refereegranskat)abstract
- We briefly describe the status of the Onsala twin telescopes and the experience gained since the official inauguration in May 2017.
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| 25. |
- Haas, Rüdiger, 1966, et al.
(författare)
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Ultra-Rapid DUT1-Observations with E-VLBI
- 2010
-
Ingår i: Artificial Satellites. - : Walter de Gruyter GmbH. - 0208-841X .- 2083-6104. ; 45:2 / 2010, s. 75-79
-
Konferensbidrag (refereegranskat)abstract
- We give a short overview about the achievements of the Fennoscandian- Japanese ultra-rapid dUT1-project that was initiated in early 2007. The combination of real-time data transfer, near real-time data conversion and correlation, together with near-real time data analysis allows to determine dUT1 with a very low latency of less than 5 minutes after the end of a VLBI-session. The accuracy of these ultra-rapid dUT1-results is on the same order than the results of the standard rapid-service of the International Earth Rotation and Reference Frame Service (IERS). The ultra-rapid approach is currently extended to 24 hour sessions and is expected to become an important contribution for the future next generation VLBI system called VLBI2010.
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| 26. |
- Haas, Rüdiger, 1966, et al.
(författare)
-
Ultra-rapid earth rotation determination with VLBI during CONT11 and CONT14
- 2017
-
Ingår i: Journal of Geodesy. - : Springer Science and Business Media LLC. - 0949-7714 .- 1432-1394. ; 91:7, s. 831-837
-
Tidskriftsartikel (refereegranskat)abstract
- We present earth rotation results from the ultra-rapid operations during the continuous VLBI campaigns CONT11 and CONT14. The baseline Onsala--Tsukuba, i.e., using two out of the 13 and 17 stations contributing to CONT11 and CONT14, respectively, was used to derive UT1-UTC in ultra-rapid mode during the ongoing campaigns. The latency between a new observation and a new UT1-UTC result was less than 10 min for more than 95{\%} of the observations. The accuracy of the derived ultra-rapid UT1-UTC results is approximately a factor of three worse than results from optimized one-baseline sessions and/or complete analysis of large VLBI networks. This is, however, due to that the one-baseline picked from the CONT campaigns is not optimized for earth rotation determination. Our results prove that the 24/7 operation mode planned for VGOS, the next-generation VLBI system, is possible already today. However, further improvements in data connectivity of stations and correlators as well in the automated analysis are necessary to realize the ambitious VGOS plans.
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| 27. |
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| 28. |
- Haas, Rüdiger, 1966, et al.
(författare)
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VLBI with GNSS signals on intercontinental baselines
- 2018
-
Ingår i: - 9789188041142
-
Konferensbidrag (refereegranskat)abstract
- The International Terrestrial Reference Frame (ITRF) is constructed based on analysis results of several space geodetic techniques, among them geodetic Very Long Baseline Interferometry (VLBI) and Global Navigation Satellite Systems (GNSS). The meaningful combination of the different techniques requires possibilities to link the various instruments and their reference points. So-called co-location stations that are equipped with instrumentation for several techniques play an important role for the ITRF combination since so-called local-tie vectors on the ground enable the connection between the various instruments. Since several years, ideas have been discussed to include additional possibilities to link the different techniques, with the main goal to improve the ITRF. One of these ideas is to use GNSS signals for VLBI observations and by this improve the link between VLBI and GNSS. In our presentations we describe so-called GNSS-VLBI experiments performed in 2017 with VLBI stations at intercontinental distances. The observations, data correlation and data analysis is described and initial results are presented.
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| 29. |
- Hobiger, Thomas, 1978, et al.
(författare)
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Combining GPS and VLBI for inter-continental frequency transfer
- 2015
-
Ingår i: Metrologia. - : IOP Publishing. - 0026-1394 .- 1681-7575. ; 52:2, s. 251-261
-
Tidskriftsartikel (refereegranskat)abstract
- For decades the global positioning system (GPS) has been the only space geodetic technique routinely used for inter-continental frequency transfer applications. In the past very long baseline interferometry (VLBI) has also been considered for this purpose and the method's capabilities were studied several times. However, compared to GPS current VLBI technology only provides few observations per hour, thus limiting its potential to improve frequency comparisons. We therefore investigate the effect of combining GPS and VLBI on the observation level in order to draw the maximum benefit from the strength of each individual technique. As a test-bed for our study we use the CONT11 campaign observed in 2011. First we review the frequency transfer performance that can be achieved with independent technique-specific analyses, both with individual software packages and with the multi-technique software c5++. With this analysis approach both techniques, GPS and VLBI, show similar frequency link instabilities at the level of 10−14 to 10−15 (MDEV) on inter-continental baselines for averaging times of one day. Then we use the c5++ software for a combined analysis of GPS and VLBI data on the observation level. We demonstrate that our combination approach leads to small but consistent improvements for frequency transfer of up to 10%, in particular for averaging periods longer than 3000 s.
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| 30. |
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| 31. |
- Hobiger, Thomas, 1978, et al.
(författare)
-
Combining VLBI and GPS for inter-continental frequency transfer
- 2015
-
Ingår i: 22nd European VLBI for Geodesy and Astrometry (EVGA) Working Meeting.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- For decades the Global Positioning System (GPS) has been the only space geodetic technique routinely used for inter-continental frequency transfer applications. In the past VLB) has also been considered for this purpose and the method's capabilities were studied several times. However, compared to GPS current VLBI technology only provides few observations per hour, thus limiting its potential to improve frequency comparisons. We therefore investigate the effect of combining VLBI and GPS on the observation level in order to draw the maximum benefit from the strength of each individual technique. As a test-bed for our study we use the CONT11 campaign observed in 2011. First we review the frequency transfer performance that can be achieved with independent technique-specific analyses. With this analysis approach both techniques, GPS and VLBI, show similar frequency link instabilities at the level of 1e-14 to 1e-15 (MDEV) on inter-continental baselines for averaging times of one day. We also perform a combined analysis of VLBI and GPS data on the observation level and demonstrate that our combination approach leads to small but consistent improvements for frequency transfer of up to 10%, in particular for averaging periods longer than 3000 s. We discuss the implications of these findings and present our ideas about how VLBI can contribute to international frequency transfer tasks.
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| 32. |
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| 33. |
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| 34. |
- Hobiger, Thomas, 1978, et al.
(författare)
-
GLONASS-R: GNSS reflectometry with an FDMA based satellite navigation system
- 2014
-
Ingår i: Radio Science. - 0048-6604 .- 1944-799X. ; 49:4, s. 271-282
-
Tidskriftsartikel (refereegranskat)abstract
- The information from reflected Global Navigation Satellite System (GNSS) signals can become a valuable data source, from which geophysical properties can be deduced. This approach, called GNSS Reflectometry (GNSS-R), can be used to develop instruments that act like an altimeter when arrival times of direct and reflected signals are compared. Current GNSS-R systems usually entirely rely on signals from the Global Positioning Service (GPS), and field experiments could demonstrate that information from such systems can measure sea level with an accuracy of a few centimeters. However, the usage of the Russian GLONASS system has the potential to simplify the processing scheme and to allow handling of direct and reflected signals like a bistatic radar. Thus, such a system has been developed and deployed for test purposes at the Onsala Space Observatory, Sweden, that has an operational GPS-based GNSS-R system. Over a period of 2 weeks in October 2013, GPS-based GNSS-R sea level monitoring and measurements with the newly developed GLONASS-R system were carried out in parallel. In addition, data from colocated tide gauge measurements were available for comparison. It can be shown that precision and accuracy of the GLONASS-based GNSS-R system is comparable to, or even better than, conventional GPS-based GNSS-R solutions. Moreover, the simplicity of the newly developed GLONASS-R system allows to make it a cheap and valuable tool for various remote sensing applications.
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| 35. |
- Hobiger, Thomas, 1978, et al.
(författare)
-
Ground-based GNSS-R solutions by means of software defined radio
- 2016
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Ingår i: Proceedings of the 2016 IEEE International Geoscience and Remote Sensing Symposium (IGARSS 2016). Beijing; China; 10-15 July 2016. - 9781509033324 ; 2016-November, s. Art no 7730472, Pages 5635-5637
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Konferensbidrag (refereegranskat)abstract
- Usually ground-based GNSS-R installations are either existing geodetic GNSS stations or they are built with dedicated components that enable the deduction and monitoring of physical and geometrical properties of the reflecting area around that particular site. In both cases, hardware components usually enable real-time operation of such instruments. However, as software-defined radio (SDR) technology has advanced in the recent years it is now possible to carry out signal processing in real-time, which makes it an ideal candidate for the realization of a flexible GNSS-R system. It is shown how SDR can help to realize GNSS-R solutions for sea-level monitoring at the Onsala Space Observatory, Sweden. Moreover, such SDR solutions can be mounted on an unmanned aerial vehicle (UAV) in order to collect data from higher altitudes and even provide Delay-Doppler information for extended GNSS-R studies.
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| 36. |
- Hobiger, Thomas, 1978, et al.
(författare)
-
Hard and Software Tools for the Education of Geodetic VLBI
- 2016
-
Ingår i: IVS 2016 General Meeting Proceedings "New Horizons with VGOS". ; :NASA/CP-2016-219016, s. 234-238
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The Onsala Space Observatory hosts two 2.3 m radio telescopes called SALSA (”Such a lovely small antenna”) which are utilised to bring front-line interactive astronomy to the classroom. Until now SALSA has been used for astronomical educational purposes solely, in particular demonstrating the concept of single dish measurements. However, it is possible to combine both SALSAs to an interferometer by making use of hardware which has been developedfor software-defined radio. In doing so, one can utilise the SALSA antenna pair as a student demonstrator for geodetic Very Long Baseline Interferometry. Itis discussed which COTS hardware components are necessary to turn the SALSA installation into an interferometer. A simple Octave-based correlator hasbeen written in order to process SALSA data. Results from a test run during which the Sun was tracked are presented and discussed here.
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| 37. |
- Hobiger, Thomas, 1978, et al.
(författare)
-
Hard- and software tools for the education of Geodetic VLBI
- 2016
-
Ingår i: 9th IVS General Meeting, March 2016, Johannesburg, South Africa.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Onsala Space Observatory hosts two 2.3 m radio telescopes called SALSA ("Such a lovely small antenna") which are utilised to bring front-line interactive astronomy to the classroom. Until now SALSA has been used for astronomical educational purposes solely, in particular demonstrating the concept of single dish measurements. However, it is possible to combine both SALSAs to an interferometer by making use of hardware which has been developed for software-defined radio. In doing so, one can utilise the SALSA antenna pair as a student demonstrator for geodetic Very Long Baseline Interferometry. We will discuss the COTS hardware components that are necessary to turn the SALSA installation into an interferometer. Moreover, we will show how a simple correlator has been used to detect fringes and provide single-band delays. Such delays were then processed with our analysis software c5++. We are going to discuss how it is possible to mimic the complete processing chain of geodetic VLBI and how this can be used for training of students and other interested parties.
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| 38. |
- Hobiger, Thomas, 1978, et al.
(författare)
-
Inverse modeling of ground-based GNSS-r - Results and new possibilities
- 2017
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Ingår i: International Geoscience and Remote Sensing Symposium (IGARSS). ; 2017-July, s. 2671-2681
-
Konferensbidrag (refereegranskat)abstract
- Inverse modeling of ground-based GNSS reflections has the potential to improve existing GNSS-R applications and lead to novel concepts for retrieving geophysical parameters around existing or deliberately built GNSS sites. As we will show in this paper, consistent, accurate and precise determination of sea-surface heights can be realized. Moreover, we demonstrate that it is possible to detect sea-ice freeze states at coastal GNSS sites. In addition, it will be shown how the inverse modeling approach can be used for self-calibration of troposphere delays, which would otherwise bias the target parameters and need to be corrected for by external measurements or data-sets.
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| 39. |
- Hobiger, Thomas, 1978, et al.
(författare)
-
Software-Defined Radio Direct Correlation GNSS Reflectometry by Means of GLONASS
- 2016
-
Ingår i: IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing. - 2151-1535 .- 1939-1404. ; 9:10, s. 4834-4842
-
Tidskriftsartikel (refereegranskat)abstract
- Ground-based GNSS reflectometry (GNSS-R)systems can be realized by different means. The concept ofcorrelation between direct and reflected GNSS signals is basicallypossible with all GNSS systems. However, using signals fromthe Russian GLONASS system simplifies the signal processingso that software-defined radio (SDR) components can be usedat replace expensive hardware solutions. This paper discusseshow such a solution, called GLONASS-R, can be realized usingentirely off-the-shelf components. Field tests with such a systemdemonstrate the capability to monitor sea surface heights with aprecision of 3 cm or better even with a sampling rate of 1.5 Hz.The flexibility of a SDR and the simple concept of GLONASS-Rallow build such a system with low costs and adapt it to the needsof any ground-based GNSS-R problem.
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| 40. |
- Hobiger, Thomas, 1978, et al.
(författare)
-
Software defined radio for ground and airborne GNSS reflectometry
- 2018
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Ingår i: Proceedings of the European Navigation Conference 2018 (ENC 2018) Abstracts and Technical Papers. - 9789188041142 ; , s. 49-50
-
Konferensbidrag (refereegranskat)abstract
- Software defined radio (SDR) appears as a suitable solution for dedicated GNSS reflectometry (GNSS-R) applications. Not only does the flexibility of SDR allow for easy and rapid prototyping, but also do recent technological developments of SDR front-ends support real-time operation of GNSS-R. Our presentation includes a discussion about the technical aspects of SDR for GNSS-R and we show results from a ground-based GNSS-R SDR receiver which was operated continuously over a more than a month at the Onsala Space Observatory. A summary of our current activities in relation to airborne GNSS-R solutions and initial results in the form of Delay-Doppler Maps (DDMs) will conclude the presentation.
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| 41. |
- Hunkeler, Priska A., et al.
(författare)
-
Improved 1D inversions for sea ice thickness and conductivity from electromagnetic induction data : Inclusion of nonlinearities caused by passive bucking
- 2016
-
Ingår i: Geophysics. - 0016-8033 .- 1942-2156. ; 81:1, s. WA45-WA58
-
Tidskriftsartikel (refereegranskat)abstract
- The porosity of sea ice is a fundamental physical parameter that governs the mechanical strength of sea ice and the mobility of gases and nutrients for biological processes and biogeochemical cycles in the sea ice layer. However, little is known about the spatial distribution of the sea ice porosity and its variability between different sea ice types; an efficient and nondestructive method to measure this property is currently missing. Sea ice porosity is linked to the bulk electrical conductivity of sea ice, a parameter routinely used to discriminate between sea ice and seawater by electromagnetic (EM) induction sensors. Here, we have evaluated the prospect of porosity retrieval of sea ice by means of bulk conductivity estimates using 1D multi-frequency EM inversion schemes. We have focused on two inversion algorithms, a smoothness-constrained inversion and a Marquardt-Levenberg inversion, which we modified for the nonlinear signal bias caused by a passive bucking coil operated in such a highly conductive environment. Using synthetic modeling studies, 1D inversion algorithms and multiple frequencies, we found that we can resolve the sea ice conductivity within +/- 0.01 S/m. Using standard assumptions for the conductivity-porosity relation of sea ice, we were able to estimate porosity with an uncertainty of +/- 1.2%, which enables efficient and nondestructive surveys of the internal state of the sea ice cover.
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| 42. |
- Kareinen, Niko Petteri, 1986, et al.
(författare)
-
Automated ambiguity estimation for VLBI Intensive sessions using L1-norm
- 2016
-
Ingår i: Journal of Geodynamics. - : Elsevier BV. - 0264-3707. ; 102, s. 39-46
-
Tidskriftsartikel (refereegranskat)abstract
- Very Long Baseline Interferometry (VLBI) is a space-geodetic technique that is uniquely capable of direct observation of the angle of the Earth's rotation about the Celestial Intermediate Pole (CIP) axis, namely UT1. The daily estimates of the difference between UT1 and Coordinated Universal Time (UTC) provided by the 1-h long VLBI Intensive sessions are essential in providing timely UT1 estimates for satellite navigation systems and orbit determination. In order to produce timely UT1 estimates, efforts have been made to completely automate the analysis of VLBI Intensive sessions. This involves the automatic processing of X- and S-band group delays. These data contain an unknown number of integer ambiguities in the observed group delays. They are introduced as a side-effect of the bandwidth synthesis technique, which is used to combine correlator results from the narrow channels that span the individual bands. In an automated analysis with the c5++ software the standard approach in resolving the ambiguities is to perform a simplified parameter estimation using a least-squares adjustment (L2-norm minimisation). We implement L1-norm as an alternative estimation method in c5++. The implemented method is used to automatically estimate the ambiguities in VLBI Intensive sessions on the Kokee–Wettzell baseline. The results are compared to an analysis set-up where the ambiguity estimation is computed using the L2-norm. For both methods three different weighting strategies for the ambiguity estimation are assessed. The results show that the L1-norm is better at automatically resolving the ambiguities than the L2-norm. The use of the L1-norm leads to a significantly higher number of good quality UT1-UTC estimates with each of the three weighting strategies. The increase in the number of sessions is approximately 5% for each weighting strategy. This is accompanied by smaller post-fit residuals in the final UT1-UTC estimation step.
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| 43. |
- Kareinen, Niko Petteri, 1986, et al.
(författare)
-
Automated analysis of Kokee–Wettzell intensive sessions
- 2015
-
Ingår i: Proceedings of the 22nd European VLBI Group for Geodesy and Astrometry Working Meeting. - 9789892061917 ; , s. 235-239
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 44. |
- Kareinen, Niko Petteri, 1986, et al.
(författare)
-
Automated analysis of Kokee–Wettzell Intensive VLBI sessions—algorithms, results, and recommendations
- 2015
-
Ingår i: Earth, Planets and Space. - : Springer Science and Business Media LLC. - 1880-5981 .- 1343-8832. ; 67:181
-
Tidskriftsartikel (refereegranskat)abstract
- The time-dependent variations in the rotation and orientation of the Earth are represented by a set of Earth Orientation Parameters (EOP). Currently, Very Long Baseline Interferometry (VLBI) is the only technique able to measure all EOP simultaneously and to provide direct observation of universal time, usually expressed as UT1-UTC. To produce estimates for UT1-UTC on a daily basis, 1-h VLBI experiments involving two or three stations are organised by the International VLBI Service for Geodesy and Astrometry (IVS), the IVS Intensive (INT) series. There is an ongoing effort to minimise the turn-around time for the INT sessions in order to achieve near real-time and high quality UT1-UTC estimates. As a step further towards true fully automated real-time analysis of UT1-UTC, we carry out an extensive investigation with INT sessions on the Kokee–Wettzell baseline. Our analysis starts with the first versions of the observational files in S- and X-band and includes an automatic group delay ambiguity resolution and ionospheric calibration. Several different analysis strategies are investigated. In particular, we focus on the impact of external information, such as meteorological and cable delay data provided in the station log-files, and a priori EOP information. The latter is studied by extensive Monte Carlo simulations.Our main findings are that it is easily possible to analyse the INT sessions in a fully automated mode to provide UT1-UTC with very low latency. The information found in the station log-files is important for the accuracy of the UT1-UTC results, provided that the data in the station log-files are reliable. Furthermore, to guarantee UT1-UTC with an accuracy of less than 20 μs, it is necessary to use predicted a priori polar motion data in the analysis that are not older than 12 h.
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| 45. |
- Kareinen, Niko Petteri, 1986, et al.
(författare)
-
Identifying optimal tag-along station locations for improving VLBI Intensive sessions
- 2017
-
Ingår i: Earth, Planets and Space. - : Springer Science and Business Media LLC. - 1880-5981 .- 1343-8832. ; 69:1, s. 16-
-
Tidskriftsartikel (refereegranskat)abstract
- Very Long Baseline Interferometry (VLBI) is a unique space-geodetic technique capable of direct observation of the Earth’s phase of rotation, namely Universal Time (UT1). The International VLBI Service for Geodesy and Astrometry (IVS) conducts daily 1-h Intensive VLBI sessions to determine rapid variations in the difference between UT1 and Coordinated Universal Time (UTC). The main objective of the Intensive sessions is to provide timely UT1–UTC estimates. These estimates are especially crucial for Global Navigation Satellite Systems (GNSS). The monitoring of rapid variations in Earth rotation also provides insight into various geophysical phenomena. There is an ongoing effort to improve the quality of the UT1–UTC estimates from single-baseline Intensive sessions to realise the expected accuracy and to bring them to a better agreement with the 24-h VLBI sessions. In this paper, we investigate the possibility to improve the Intensives by including a third station in tag-along mode to these regularly observed sessions. The impact of the additional station is studied via extensive simulations using the c5++ analysis software. The location of the station is varied within a predetermined grid. Based on actual Intensive session schedules, a set of simulated observations are generated for the two original stations and each grid point. These simulated data are used to estimate UT1–UTC for every Intensive session scheduled during the year 2014 on the Kokee–Wettzell and Tsukuba–Wettzell baselines, with the addition of a third station. We find that in tag-along mode when a third station is added to the schedule we can identify areas where the UT1–UTC estimates are improved up to 67% w.r.t. the original single-baseline network. There are multiple operational VLBI stations in these areas, which could with little effort be included in a tag-along mode to the currently scheduled Intensive sessions, thus providing the possibility to improve the UT1–UTC estimates by extending the observation network.
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| 46. |
- Kareinen, Niko Petteri, 1986, et al.
(författare)
-
Robust Ambiguity Estimation for an Automated Analysis of the Intensive Sessions
- 2016
-
Ingår i: IVS 2016 General Meeting Proceedings "New Horizons with VGOS". ; :(NASA/CP-2016-219016), s. 198-202
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Very Long Baseline Interferometry (VLBI) is a unique space-geodetictechnique that can directly access the Earth's phase of rotation, namely UT1.The daily estimates of the difference between UT1 and Coordinated UniversalTime (UTC) are computed from 1-hour long VLBI Intensive sessions. Thesesessions are essential in providing timely UT1 estimates for satellitenavigation systems. To produce timely UT1 estimates, efforts have been made tocompletely automate the analysis of VLBI Intensive sessions. This requiresautomated processing of X- and S-band group delays. These data often contain anunknown number of integer ambiguities in the observed group delays. In anautomated analysis with the c5++ software the standard approach in resolvingthe ambiguities is to perform a simplified parameter estimation using aleast-squares adjustment (L2-norm minimisation). We implement the robustL1-norm with an alternative estimation method in c5++. The implemented methodis used to automatically estimate the ambiguities in VLBI Intensive sessions onthe Kokee-Wettzell baseline. The results are compared to an analysis setupwhere the ambiguity estimation is computed using the L2-norm. Additionally, weinvestigate three alternative weighting strategies for the ambiguityestimation. The results show that in automated analysis the L1-norm resolvesambiguities better than the L2-norm. The use of the L1-norm leads to asignificantly higher number of good quality UT1-UTC estimates with each of thethree weighting strategies.
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| 47. |
- Kaufmann, Thomas, et al.
(författare)
-
Meshless eigenvalue analysis for resonant structures based on the radial point interpolation method
- 2009
-
Ingår i: Microwave conference. - : IEEE. - 9781424428021 - 9781424428014 ; , s. 818-821
-
Konferensbidrag (refereegranskat)abstract
- Meshless methods are a promising field of numerical methods recently introduced to computational electromagnetics. The potential of conformal and multi-scale modeling and the possibility of dynamic grid refinements are very attractive features that appear more naturally in meshless methods than in classical methods. The radial point interpolation method (RPIM) uses radial basis functions for the approximation of spatial derivatives. In this publication an eigenvalue solver is introduced for RPIM in electromagnetics. Eigenmodes are calculated on the example of a cylindrical resonant cavity. It is demonstrated that the computed resonance frequencies converge to the analytical values for increasingly fine spatial discretization. The computation of eigenmodes is an important tool to support research on a time-domain implementation of RPIM. It allows a characterization of the method's accuracy and to investigate stability issues caused by the possible occurrence of non-physical solutions
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| 48. |
- Klopotek, Grzegorz, 1990, et al.
(författare)
-
Geodetic VLBI for precise orbit determination of Earth satellites: a simulation study
- 2020
-
Ingår i: Journal of Geodesy. - : Springer Science and Business Media LLC. - 0949-7714 .- 1432-1394. ; 94:6
-
Tidskriftsartikel (refereegranskat)abstract
- Recent efforts of tracking low Earth orbit and medium Earth orbit (MEO) satellites using geodetic very long baseline interferometry (VLBI) raise questions on the potential of this novel observation concept for space geodesy. Therefore, we carry out extensive Monte Carlo simulations in order to investigate the feasibility of geodetic VLBI for precise orbit determination (POD) of MEO satellites and assess the impact of quality and quantity of satellite observations on the derived geodetic parameters. The MEO satellites are represented in our study by LAGEOS-1/-2 and a set of Galileo satellites. The concept is studied on the basis of 3-day solutions in which satellite observations are included into real schedules of the continuous geodetic VLBI campaign 2017 (CONT17) as well as simulated schedules concerning the next-generation VLBI system, known as the VLBI Global Observing System (VGOS). Our results indicate that geodetic VLBI can perform on a comparable level as other space-geodetic techniques concerning POD of MEO satellites. For an assumed satellite observation precision better than 14.1 mm (47 ps), an average 3D orbit precision of 2.0 cm and 6.3 cm is found for schedules including LAGEOS-1/-2 and Galileo satellites, respectively. Moreover, geocenter offsets, which were so far out of scope for the geodetic VLBI analysis, are close to the detection limit for the simulations concerning VGOS observations of Galileo satellites, with the potential to further enhance the results. Concerning the estimated satellite orbits, VGOS leads to an average precision improvement of 80% with respect to legacy VLBI. In absolute terms and for satellite observation precision of 14.1 mm (47 ps), this corresponds to an average value of 17 mm and 7 mm concerning the 3D orbit scatter and precision of geocenter components, respectively. As shown in this study, a poor satellite geometry can degrade the derived Earth rotation parameters and VLBI station positions, compared to the quasar-only reference schedules. Therefore, careful scheduling of both quasar and satellite observations should be performed in order to fully benefit from this novel observation concept.
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| 49. |
- Klopotek, Grzegorz, 1990, et al.
(författare)
-
Geodetic VLBI with an artificial radio source on the Moon: a simulation study
- 2018
-
Ingår i: Journal of Geodesy. - : Springer Science and Business Media LLC. - 0949-7714 .- 1432-1394. ; 92:5, s. 457-469
-
Tidskriftsartikel (refereegranskat)abstract
- We perform extensive simulations in order to assess the accuracy with which the position of a radio transmitter on the surface of the Moon can be determined by geodetic VLBI. We study how the quality and quantity of geodetic VLBI observations influence these position estimates and investigate how observations of such near-field objects affect classical geodetic parameters like VLBI station coordinates and Earth rotation parameters. Our studies are based on today's global geodetic VLBI schedules as well as on those designed for the next-generation geodetic VLBI system. We use Monte Carlo simulations including realistic stochastic models of troposphere, station clocks, and observational noise. Our results indicate that it is possible to position a radio transmitter on the Moon using today's geodetic VLBI with a two-dimensional horizontal accuracy of better than one meter. Moreover, we show that the next-generation geodetic VLBI has the potential to improve the two-dimensional accuracy to better than 5 cm. Thus, our results lay the base for novel observing concepts to improve both lunar research and geodetic VLBI.
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| 50. |
- Klopotek, Grzegorz, 1990, et al.
(författare)
-
Implementation of VLBI Near-Field Delay Models in the c5++ Analysis Software
- 2017
-
Ingår i: Proceedings of the First International Workshop on VLBI Observations of Near-field Targets, October 5 - 6, 2016, A. Nothnagel and F. Jaron (eds.). - 1864-1113. ; 54, s. 29-33
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We describe the implementation of two near-field delay models in the c5++ analysis software. The motivation for this work is to allow the calculation of a priori delay information for the correlation of VLBI raw observations of near-field targets and to prepare for the analysis of VLBI data of near-field objects. The software is tested by correlating VLBI observations of the Chinese Chang’E lunar lander on the Onsala– Wettzell baseline.
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