scholarly journals Quality Assessment of the Homogeneous Coordinate Time Series of Eastern European GNSS Stations in the IGS05 Reference Frame

2014 ◽  
Vol 49 (3) ◽  
pp. 137-150
Author(s):  
M. Ishchenko
Keyword(s):  
Reference Frame ◽  
Data Center ◽  
A Priori ◽  
Correlation Coefficients ◽  
Astronomical Observatory ◽  
International Gnss Service ◽  
Main Astronomical Observatory ◽  
Ocean Loading ◽  
Tropospheric Refraction ◽  
Gnss Data

Abstract For the first time, a homogeneous coordinate solution in the IGS05 reference frame and the values of the zenith tropospheric refraction for the GPS weeks 935-1399 (from December 12, 1997 to November 4, 2006) were obtained at the GNSS Data Center Analysis of the Main Astronomical Observatory NAS of Ukraine. The obtained solution is devoid of effects, brought by changes in the methods of processing models, a priori data and software (absolute phase center model combinations of antenna-dome instead of relative models, model of ocean loading FES2004 instead of GOT00.2_PP, the elevations cut-off angle 3° instead of 10°, etc. were used). To estimate the quality of the solution, a comparison with the international combined solutions using the Helmert transformation was carried out. The RMS of direct station coordinate differences and correlation coefficients between the solutions estimated by the Main Astronomical Observatory, European GNSS Permanent Network and International GNSS Service are presented. The obtained results allow making the conclusion that the solution obtained at the GNSS Data Center Analysis of the Main Astronomical Observatory shows a good quality and agrees well with other solutions.

GPS z-PCO and GNSS-based scale determined by integrated processing with LEOs and Galileo

2021 ◽  
Author(s):  
Wen Huang ◽  
Benjamin Männel ◽  
Andreas Brack ◽  
Harald Schuh
Keyword(s):  
Reference Frame ◽  
A Priori ◽  
Terrestrial Reference Frame ◽  
International Gnss Service ◽  
Satellite Transmitter ◽  
Ground Station ◽  
Station Coordinates ◽  
Integrated Processing ◽  
Current Constellation ◽  
The Impact

<p>The Global Positioning System (GPS) satellite transmitter antenna phase center offsets (PCOs) in z-direction and the scale of the terrestrial reference frame are highly correlated when neither of them is constrained to an a priori value in a least-squares adjustment. The commonly used PCO values offered by the International GNSS Service (IGS) are estimated in a global adjustment by constraining the ground station coordinates to the current International Terrestrial Reference Frame (ITRF). As the scale of the ITRF is determined by other techniques, the estimated GPS z-PCOs are not independent. Consequently, the z-PCOs transfer the scale to any subsequent GNSS solution. To get a GNSS-based scale that can contribute to a future ITRF realization, two methods are proposed to determine scale-independent GPS z-PCOs. One method is based on the gravitational constraint on Low Earth Orbiters (LEOs) in an integrated processing of the GPS satellites and LEOs. The correlation coefficient between the GPS PCO-z and the scale is reduced from 0.85 to 0.3 by supplementing a 54-ground-station network with seven LEOs. The impact of individual LEOs on the estimation is discussed by including different subsets of the LEOs. The accuracy of the z-PCOs of the LEOs is very important for the accuracy of the solution. In another method, the GPS z-PCOs and the scale are determined in a GPS+Galileo processing where the PCOs of Galileo are fixed to the values calibrated on ground from the released metadata. The correlation between the GPS PCO-z and the scale is reduced to 0.13 by including the current constellation of Galileo with 24 satellites. We use the whole constellation of Galileo and the three LEOs of the Swarm mission to perform a direct comparison and cross-check of the two methods. The two methods provide mean GPS z-PCO corrections of -186±25 mm and -221±37 mm with respect to the IGS values, and +1.55±0.22 ppb (part per billion) and +1.72±0.31 ppb in the terrestrial scale with respect to the IGS14 reference frame. The results of both methods agree with each other with only small differences. Due to the larger number of Galileo observations, the Galileo-PCO-fixed method leads to more precise and stable results. In the joint processing of GPS+Galileo+Swarm in which both methods are applied, the constraint on Galileo dominates the results. We also discuss how fixing either the Galileo transmitter antenna z-PCO or the Swarm receiver antenna z-PCOs in the GPS+Galileo+Swarm processing propagates to the respective freely estimated z-PCOs of Swarm or Galileo.</p>

Twenty-Five Years of the International GNSS Service

2020 ◽  
Author(s):  
Allison Craddock ◽  
Gary Johnston ◽  
Felix Perosanz ◽  
Rolf Dach ◽  
Charles Meertens ◽  
...  
Keyword(s):  
Reference Frame ◽  
Open Data ◽  
Cost Effective ◽  
Satellite System ◽  
Terrestrial Reference Frame ◽  
International Gnss Service ◽  
Quarter Century ◽  
Long Baseline ◽  
International Terrestrial Reference Frame ◽  
Gnss Data

<p>For over twenty-five years, the <strong>International Global Navigation Satellite System (GNSS) Service (IGS)</strong> has carried out its mission to advocate for and provide freely and openly available high-precision GNSS data and products.</p><p>The IGS is an essential component of the <strong>IAG’s Global Geodetic Observing System (GGOS)</strong>, where it facilitates cost-effective geometrical linkages with and among other precise geodetic observing techniques, including: Satellite Laser Ranging (SLR), Very Long Baseline Interferometry (VLBI), and Doppler Orbitography and Radio Positioning Integrated by Satellite (DORIS). These linkages are fundamental to generating and accessing the International Terrestrial Reference Frame (ITRF).  As it enters its second quarter-century, the IGS is evolving into a truly multi-GNSS service, and at its heart is a strong culture of sharing expertise, infrastructure, and other resources for the purpose of encouraging global best practices for developing and delivering GNSS data and products all over the world.</p><p>This poster will present an update on current IGS products and operations, as well as highlights on recent organizational developments and community activities. The impacts and benefits of global cooperation and openly available data will be emphasized, and information about the IGS stations and network, contributions to the International Terrestrial Reference Frame solutions, and product applications will be presented. A summary of IGS products, with emphasis on analysis, coordination, applications, and their availability will be described. Information about efforts to form new groups supporting product generation within IGS open data and product policies will be included. Information about the themes and topics of discussion for the upcoming 2020 IGS Workshop in Boulder, Colorado, USA will also be provided.</p>

scholarly journals Standardising the measurement of physical activity in people receiving haemodialysis: considerations for research and practice

2019 ◽  
Vol 20 (1) ◽  
Author(s):  
Hannah M. L. Young ◽  
Mark W. Orme ◽  
Yan Song ◽  
Maurice Dungey ◽  
James O. Burton ◽  
...  
Keyword(s):  
Physical Activity ◽  
Sample Size ◽  
Repeated Measures ◽  
A Priori ◽  
Intraclass Correlation ◽  
Correlation Coefficients ◽  
Future Research ◽  
Wear Time ◽  
Minimum Number ◽  
The Uk

Abstract Background Physical activity (PA) is exceptionally low amongst the haemodialysis (HD) population, and physical inactivity is a powerful predictor of mortality, making it a prime focus for intervention. Objective measurement of PA using accelerometers is increasing, but standard reporting guidelines essential to effectively evaluate, compare and synthesise the effects of PA interventions are lacking. This study aims to (i) determine the measurement and processing guidance required to ensure representative PA data amongst a diverse HD population, and; (ii) to assess adherence to PA monitor wear amongst HD patients. Methods Clinically stable HD patients from the UK and China wore a SenseWear Armband accelerometer for 7 days. Step count between days (HD, Weekday, Weekend) were compared using repeated measures ANCOVA. Intraclass correlation coefficients (ICCs) determined reliability (≥0.80 acceptable). Spearman-Brown prophecy formula, in conjunction with a priori ≥  80% sample size retention, identified the minimum number of days required for representative PA data. Results Seventy-seven patients (64% men, mean ± SD age 56 ± 14 years, median (interquartile range) time on HD 40 (19–72) months, 40% Chinese, 60% British) participated. Participants took fewer steps on HD days compared with non-HD weekdays and weekend days (3402 [95% CI 2665–4140], 4914 [95% CI 3940–5887], 4633 [95% CI 3558–5707] steps/day, respectively, p < 0.001). PA on HD days were less variable than non-HD days, (ICC 0.723–0.839 versus 0.559–0.611) with ≥ 1 HD day and ≥  3 non-HD days required to provide representative data. Using these criteria, the most stringent wear-time retaining ≥ 80% of the sample was ≥7 h. Conclusions At group level, a wear-time of ≥7 h on ≥1HD day and ≥ 3 non-HD days is required to provide reliable PA data whilst retaining an acceptable sample size. PA is low across both HD and non- HD days and future research should focus on interventions designed to increase physical activity in both the intra and interdialytic period.

scholarly journals Impact of network constraining on the terrestrial reference frame realization based on SLR observations to LAGEOS

2019 ◽  
Vol 93 (11) ◽  
pp. 2293-2313 ◽  
Author(s):  
R. Zajdel ◽  
K. Sośnica ◽  
M. Drożdżewski ◽  
G. Bury ◽  
D. Strugarek
Keyword(s):  
Reference Frame ◽  
A Priori ◽  
Terrestrial Reference Frame ◽  
Laser Ranging ◽  
Potential Core ◽  
North East ◽  
The North ◽  
Station Coordinates ◽  
Earth Rotation Parameters ◽  
Variable List

Abstract The Satellite Laser Ranging (SLR) network struggles with some major limitations including an inhomogeneous global station distribution and uneven performance of SLR sites. The International Laser Ranging Service (ILRS) prepares the time-variable list of the most well-performing stations denoted as ‘core sites’ and recommends using them for the terrestrial reference frame (TRF) datum realization in SLR processing. Here, we check how different approaches of the TRF datum realization using minimum constraint conditions (MCs) and the selection of datum-defining stations affect the estimated SLR station coordinates, the terrestrial scale, Earth rotation parameters (ERPs), and geocenter coordinates (GCC). The analyses are based on the processing of the SLR observations to LAGEOS-1/-2 collected between 2010 and 2018. We show that it is essential to reject outlying stations from the reference frame realization to maintain a high quality of SLR-based products. We test station selection criteria based on the Helmert transformation of the network w.r.t. the a priori SLRF2014 coordinates to reject misbehaving stations from the list of datum-defining stations. The 25 mm threshold is optimal to eliminate the epoch-wise temporal deviations and to provide a proper number of datum-defining stations. According to the station selection algorithm, we found that some of the stations that are not included in the list of ILRS core sites could be taken into account as potential core stations in the TRF datum realization. When using a robust station selection for the datum definition, we can improve the station coordinate repeatability by 8%, 4%, and 6%, for the North, East and Up components, respectively. The global distribution of datum-defining stations is also crucial for the estimation of ERPs and GCC. When excluding just two core stations from the SLR network, the amplitude of the annual signal in the GCC estimates is changed by up to 2.2 mm, and the noise of the estimated pole coordinates is substantially increased.

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