scholarly journals Ionosphere-weighted undifferenced and uncombined PPP-RTK: theoretical models and experimental results

GPS Solutions ◽  
2021 ◽  
Vol 25 (4) ◽  
Author(s):  
Jiuping Zha ◽  
Baocheng Zhang ◽  
Teng Liu ◽  
Pengyu Hou
Keyword(s):  
Ionospheric Disturbance ◽  
Vertical Component ◽  
Critical Factor ◽  
Theoretical Models ◽  
Integer Ambiguity ◽  
High Solar Activity ◽  
Satellite Orbits ◽  
Positioning Errors ◽  
Kinematic Ppp ◽  
Mean Time

AbstractPrecise ionospheric information, as like precise satellite orbits, clocks, and code/phase biases, is a critical factor for achieving fast integer ambiguity resolution in precise point positioning (PPP-AR). This study develops an ionosphere-weighted (IW) undifferenced and uncombined PPP real-time kinematic (PPP-RTK) network model using code and phase observations. We introduce between-station single-differenced ionospheric delay pseudo-observations to take advantage of the similar characteristics of ionospheric delays between two receivers tracking the same satellite. The estimable ionospheric parameters are commonly affected by the differential code bias referring to a particular receiver assigned as pivot, which facilitates the ionospheric interpolation at the user side. Then, the kinematic positioning performance of the IW PPP-RTK user model is analyzed and compared with those of PPP-AR without ionospheric corrections, RTK, and IW-RTK models during low and high solar activity days. The results show that for the PPP-RTK model, the positioning errors converge to thresholds of 2 cm for the horizontal components and 5 cm for the vertical component within 20 epochs, and the positioning errors become stable after an initialization of 20 epochs with root-mean-squared (RMS) values of approximately 0.47, 0.58 and 1.66 cm for the east, north and up components, respectively, which are superior to those of the other three models. Owing to the high ionospheric disturbance influence, the RMS values of the east and up components increase by approximately double and the mean time-to-first-fix increases by 61.5% for the PPP-RTK case.

scholarly journals New Satellite Selection Approach for GPS/BDS/GLONASS Kinematic Precise Point Positioning

2019 ◽  
Vol 9 (24) ◽  
pp. 5280
Author(s):  
Liu Yang ◽  
Jingxiang Gao ◽  
Zengke Li ◽  
Fangchao Li ◽  
Chao Chen ◽  
...  
Keyword(s):  
Computational Complexity ◽  
Precise Point Positioning ◽  
Integer Ambiguity ◽  
Selection Algorithm ◽  
Positioning Accuracy ◽  
Satellite Selection ◽  
Selection Approach ◽  
Point Positioning ◽  
Kinematic Ppp ◽  
Selection Algorithms

With the development of global satellite navigation systems, kinematic Precise Point Positioning (PPP) is facing the increasing computational load of instantaneous (single-epoch) processing due to more and more visible satellites. At this time, the satellite selection algorithm that can effectively reduce the computational complexity causes us to consider its application in GPS/BDS/GLONASS kinematic PPP. Considering the characteristics of different systems and satellite selection algorithms, we proposed a new satellite selection approach (NSS model) which includes three different satellite selection algorithms (maximum volume algorithm, fast-rotating partition satellite selection algorithm, and elevation partition satellite selection algorithm). Additionally, the inheritance of ambiguity was also proposed to solve the situation of constantly re-estimated integer ambiguity when the satellite selection algorithm is used in PPP. The results show that the NSS model had a centimeter-level positioning accuracy when the original PPP and optimal dilution of precision (DOP) algorithm solution were compared in kinematic PPP based on the data at five multi-GNSS Experiment (MGEX) stations. It can also reduce a huge amount of computation at the same time. Thus, the application of the NSS model is an effective method to reduce the computational complexity and guarantee the final positioning accuracy in GPS/BDS/GLONASS kinematic PPP.

Repeatability issues of 3-D VSP data

Geophysics ◽  
1999 ◽  
Vol 64 (6) ◽  
pp. 1673-1679 ◽  
Author(s):  
Martin Landrø
Keyword(s):  
Vertical Component ◽  
Time Lapse ◽  
Management Tool ◽  
Data Set ◽  
Hydrocarbon Reservoir ◽  
Vertical Seismic Profiling ◽  
Positioning Errors ◽  
Vsp Data ◽  
The Difference ◽  
Pressure Changes

Increased repeatability is recognized as one major issue for improving the time‐lapse seismic technology as a reservoir management tool. A 3-D vertical seismic profiling (VSP) data set, acquired over a period of two days, is used to analyze how repeatable a permanent installed geophone array can be and how repeatability changes with inaccuracies in source positioning. It is found that for a frequency range between 3.5 and 50 Hz, the difference root‐mean‐square (rms) level between two recorded traces belonging to two different shots is about 8%. This fact shows that there is a potential for acquiring very accurate time‐lapse seismic data by using a permanently installed downhole geophone array. Repeatability variation with increasing shot separation distances is analyzed, showing a rapid decrease in repeatability as the accuracy of the positioning of the repeat survey decreases. Horizontal geophone components show approximately the same degree of repeatability compared to the vertical component, but horizontal geophone data is slightly more sensitive to positioning errors. The results show that repeated 3-D VSP surveys (preferably using permanently installed geophone arrays) might be an efficient tool for detailed and precise monitoring of fluid and pressure changes within a hydrocarbon reservoir.

Le Fort III Distraction Osteogenesis: Early Experience With an Internal Bilevel Midface Distraction System

FACE ◽  
2020 ◽  
pp. 273250162097640
Author(s):  
Colin M. Brady ◽  
Jordan P. Steinberg ◽  
Marisa Parks ◽  
Stacy Mobley ◽  
Joseph K. Williams
Keyword(s):  
Operative Time ◽  
Soft Tissues ◽  
Vertical Component ◽  
Early Experience ◽  
Differential Resistance ◽  
Patient Demographics ◽  
Le Fort Iii ◽  
The Mean ◽  
Mean Time ◽  
Internal Distraction

Internal distraction devices for severe midface hypoplasia are often criticized for their distraction at a single pivot point, resulting in “mid-face tipping,” a phenomenon which is in part related to the differential resistance of the soft tissues at orbital and maxillary levels. To address this deficiency, we present our early experience with an internal bi-level midface distraction system. Four patients underwent midface advancement with an internal bi-level distraction system. The specifics of design, application, distraction, and removal are detailed. Hospital records were reviewed to capture patient demographics, length of stay, OR times, and complications. Relevant cephalometry was performed pre- and post-operatively, and compared. In 2015, 4 patients with severe mid-face hypoplasia were treated with an internal bi-level mid-face distraction system. The mean age was 13.5 ± 1.7 years. The mean operative time was 269.7 ± 67.4 min. The mean LOS was 10 ± 7.4 days. The on-table distraction was 5 mm. Distraction subsequently proceeded at a variable rate of 0.5 to 1.0 mm daily with a maximal distraction of 20 and 30 mm at orbital and maxillary levels, respectively. Mean time to distractor removal was 11.2 ± 1.1 weeks. Device design allowed facile removal through minimally invasive incisions. Cephalometry was seen to progress towards age-matched norms. There were no major complications. Minor complications included breakage of the vertical component of the maxillary arm at the time of device removal in 1 patient. By allowing real-time adjustment at the orbital and maxillary levels to combat differential resistance, early experience with our device maximizes occlusal advancement without overcompensating orbital translation.

Fluorescein dye-dilution technique and retinal circulation

1978 ◽  
Vol 234 (3) ◽  
pp. H315-H322 ◽  
Author(s):  
C. E. Riva ◽  
G. T. Feke ◽  
I. Ben-Sira
Keyword(s):  
Fluorescence Intensity ◽  
Time Course ◽  
Theoretical Models ◽  
Normal Function ◽  
Fluorescent Light ◽  
Circular Aperture ◽  
Excitation Light ◽  
On Line ◽  
Log Normal ◽  
Mean Time

Using theoretical models for the flow of fluourescein dye in retinal arteries and veins, we have determined the effects of optical absorption in blood of the incident excitation light and the emitted fluorescent light on the time course of measured fluorescence intensity, I(t). Our results indicate that I(t) curves recorded from arteries adequately represent the mean time course of the fluorescein concentration (C(t)), when either a circular or rectangular light-collecting aperture is used. I(t) curves recorded from veins adequately represent C(t), but only when a circular aperture of approximately the same diameter as that of the vessel is used. A two-point fluorophotometer, which provides simultaneous, on-line measurements of arterial and venous I(t) curves is described. Typical recordings obtained with the instrument are shown and the method employed to analyze the curves quantitatively is described in detail. This method, which consists of fitting the first passage of the fluorescence intensity curve with a log-normal function, provides results that are more accurate than those obtained using the standard exponential extrapolation method.

scholarly journals Relating the Progeny Production Curve to the Speed of an Epidemic

2013 ◽  
Vol 103 (3) ◽  
pp. 204-215 ◽  
Author(s):  
Francis J. Ferrandino
Keyword(s):  
Theoretical Models ◽  
Basic Reproductive Number ◽  
Reproductive Number ◽  
Progeny Production ◽  
A Value ◽  
Order Expansion ◽  
Mckendrick Equation ◽  
Temporal Moments ◽  
Production Curve ◽  
Mean Time

The dependence of the initial infection rate, r, on the basic reproductive number, R0, and the temporal moments of the progeny production curve are examined. A solution to the linearized Kermack-McKendrick equation is presented and used to analyze a variety of theoretical models of pathogen reproduction. The solution yields a relation between r and the basic reproductive number, R0; the mean time between pathogen generations, μ; and the standard deviation about this mean, σ. A transformation using the dimensionless variables rμ and rσ is introduced, which maps the solution onto a one-dimensional curve. An approximation for the value of r in terms of R0 and the first four temporal moments of the reproductive curve is derived. This allows direct comparison of epidemics resulting from theoretical models with those generated using experimentally obtained reproduction curves. For epidemics characterized by a value of rμ < 5, the value of r is well determined (<2%) by this fourth-order expansion regardless of the functional form of the reproduction curve.

scholarly journals Real-Time PPP-RTK Performance Analysis Using Ionospheric Corrections from Multi-Scale Network Configurations

Sensors ◽  
2020 ◽  
Vol 20 (11) ◽  
pp. 3012 ◽  
Author(s):  
Dimitrios Psychas ◽  
Sandra Verhagen
Keyword(s):  
Real Time ◽  
Ambiguity Resolution ◽  
Ionospheric Disturbance ◽  
The United States ◽  
Integer Ambiguity ◽  
Convergence Time ◽  
Dual Frequency ◽  
Multi Scale ◽  
Time Required ◽  
The Impact

The long convergence time required to achieve high-precision position solutions with integer ambiguity resolution-enabled precise point positioning (PPP-RTK) is driven by the presence of ionospheric delays. When precise real-time ionospheric information is available and properly applied, it can strengthen the underlying model and substantially reduce the time required to achieve centimeter-level accuracy. In this study, we present and analyze the real-time PPP-RTK user performance using ionospheric corrections from multi-scale regional networks during a day with medium ionospheric disturbance. It is the goal of this contribution to measure the impact the network dimension has on the ambiguity-resolved user position through the predicted ionospheric corrections. The user-specific undifferenced ionospheric corrections are computed at the network side, along with the satellite phase biases needed for single-receiver ambiguity resolution, using the best linear unbiased predictor. Such corrections necessitate the parameterization of an estimable user receiver code bias, on which emphasis is given in this study. To this end, we process GPS dual-frequency data from four four-station evenly distributed CORS networks in the United States with varying station spacings in order to evaluate if and to what extent the ionospheric corrections from multi-scale networks can improve the user convergence times. Based on a large number of samples, our experimental results showed that sub-10 cm horizontal accuracy can be achieved almost instantaneously in the ionosphere-weighted partially-ambiguity-fixed kinematic PPP-RTK solutions based on corrections from a network with 68 km spacing. Most of the solutions (90%) were shown to require less than 6.0 min, compared to the ionosphere-float PPP solutions that needed 68.5 min. In case of sparser networks with 115, 174 and 237 km spacing, 50% of the horizontal positioning errors are shown to become less than one decimeter after 1.5, 4.0 and 7.0 min, respectively, while 90% of them require 10.5, 16.5 and 20.0 min. We also numerically demonstrated that the user’s convergence times bear a linear relationship with the network density and get shorter as the density increases, for both full and partial ambiguity resolution.

scholarly journals Quasi-static electric fields phenomena in the ionosphere associated with pre- and post earthquake effects

2008 ◽  
Vol 8 (1) ◽  
pp. 101-107 ◽  
Author(s):  
M. Gousheva ◽  
D. Danov ◽  
P. Hristov ◽  
M. Matova
Keyword(s):  
Pacific Ocean ◽  
Electric Field ◽  
Electric Fields ◽  
Seismic Data ◽  
Seismic Activity ◽  
Vertical Component ◽  
Satellite Orbits ◽  
Static Electric Field ◽  
Earthquake Zone ◽  
Earthquake Effects

Abstract. To prove a direct relationship between the quasi-static electric field disturbances and seismic activity is a difficult, but actual task of the modern ionosphere physics. This paper presents new results on the processing and analysis of the quasi-static electric field in the upper ionosphere (h=800–900 km) observed from the satellite INTERCOSMOS-BULGARIA-1300 over earthquakes' source regions (seismic data of World Data Center, Denver, Colorado, USA). Present research focuses on three main areas (i) development of methodology of satellite and seismic data selecting, (ii) data processing and observations of the quasi-static electric field (iii) study and accumulation of statistics of possible connection between anomalous vertical electric fields penetrating from the earthquake zone into the ionosphere, and seismic activity. The most appropriate data (for satellite orbits above sources of forthcoming or just happened seismic events) have been selected from more than 250 investigated cases.The increase of about 5-10-15 mV/m in the vertical component of the quasi-static electric field observed by INTERCOSMOS-BULGARIA-1300 during seismic activity over Southern Ocean, Greenland Sea, South-Weat Pacific Ocean, Indian Ocean, Central America, South-East Pacific Ocean, Malay Archipelago regions are presented. These anomalies, as phenomena accompanying the seismogenic process, can be considered eventually as possible pre-, co- (coeval to) and post-earthquake effects in the ionosphere.

scholarly journals Relativistic positioning: including the influence of the gravitational action of the Sun and the Moon and the Earth’s oblateness on Galileo satellites

2021 ◽  
Vol 366 (7) ◽  
Author(s):  
Neus Puchades Colmenero ◽  
José Vicente Arnau Córdoba ◽  
Màrius Josep Fullana i Alfonso
Keyword(s):  
Space Time ◽  
Satellite Orbits ◽  
The Sun ◽  
The Moon ◽  
Schwarzschild Metric ◽  
Positioning Systems ◽  
Positioning Errors ◽  
The Earth ◽  
Realistic Description ◽  
The Difference

AbstractUncertainties in the satellite world lines lead to dominant positioning errors. In the present work, using the approach presented in Puchades and Sáez (Astrophys. Space Sci. 352, 307–320, 2014), a new analysis of these errors is developed inside a great region surrounding Earth. This analysis is performed in the framework of the so-called Relativistic Positioning Systems (RPS). Schwarzschild metric is used to describe the satellite orbits corresponding to the Galileo Satellites Constellation. Those orbits are circular with the Earth as their centre. They are defined as the nominal orbits. The satellite orbits are not circular due to the perturbations they have and to achieve a more realistic description such perturbations need to be taken into account. In Puchades and Sáez (Astrophys. Space Sci. 352, 307–320, 2014) perturbations of the nominal orbits were statistically simulated. Using the formula from Coll et al. (Class. Quantum Gravity. 27, 065013, 2010) a user location is determined with the four satellites proper times that the user receives and with the satellite world lines. This formula can be used with any satellite description, although photons need to travel in a Minkowskian space-time. For our purposes, the computation of the photon geodesics in Minkowski space-time is sufficient as demonstrated in Puchades and Sáez (Adv. Space Res. 57, 499–508, 2016). The difference of the user position determined with the nominal and the perturbed satellite orbits is computed. This difference is defined as the U-error. Now we compute the perturbed orbits of the satellites considering a metric that takes into account the gravitational effects of the Earth, the Moon and the Sun and also the Earth oblateness. A study of the satellite orbits in this new metric is first introduced. Then we compute the U-errors comparing the positions given with the Schwarzschild metric and the metric introduced here. A Runge-Kutta method is used to solve the satellite geodesic equations. Some improvements in the computation of the U-errors using both metrics are introduced with respect to our previous works. Conclusions and perspectives are also presented.

scholarly journals Initial Assessment of BDS PPP-B2b Service: Precision of Orbit and Clock Corrections, and PPP Performance

2021 ◽  
Vol 13 (11) ◽  
pp. 2050
Author(s):  
Zhixi Nie ◽  
Xiaofei Xu ◽  
Zhenjie Wang ◽  
Jun Du
Keyword(s):  
Global Navigation Satellite Systems ◽  
Convergence Time ◽  
Initial Assessment ◽  
Satellite Orbits ◽  
Navigation Satellite ◽  
Positioning Accuracy ◽  
Global Navigation ◽  
Kinematic Ppp ◽  
Global Navigation Satellite ◽  
Better Than

On 31 July 2020, the Beidou global navigation satellite system (BDS-3) was officially announced as being commissioned. In addition to offering global positioning, navigation, and timing (PNT) services, BDS-3 also provides precise point positioning (PPP) augmentation services. The satellite orbit correction, clock correction and code bias correction of BDS-3 and other global navigation satellite systems (GNSS) are broadcast by the BDS-3 geostationary earth orbit (GEO) satellites through the PPP-B2b signal. The PPP-B2b service is available for users in China and the surrounding area. In this study, an initial assessment of the PPP-B2b service is presented, with collected 3-day PPP-B2b messages. Based on broadcast ephemeris and PPP-B2b messages, the precise satellite orbits and clock offsets can be recovered. This precision is evaluated with the precise ephemeris from the GeoForschungsZentrum Potsdam (GFZ) analysis center as references. The results indicate that the accuracy of BDS-3 satellite orbits in the direction of radial, along-track, and cross-track is 0.138, 0.131, and 0.145 m, respectively, and for GPS a corresponding accuracy of 0.104, 0.160, and 0.134 m, respectively, could be obtained. The precision of clock offsets can reach a level of several centimeters for both GPS and BDS-3. Both the performance of static PPP and kinematic PPP are evaluated using the observations from four international GNSS monitoring assessment service (iGMAS) stations. Regarding static PPP, the average convergence time is 17.7 minutes to achieve a horizontal positioning accuracy of better than 0.3 m, and a vertical positioning accuracy of better than 0.6 m. The average positioning accuracy in the direction of east, north, and up-directions are 2.4, 1.6, and 2.3 cm. As to kinematic PPP, the average RMS values of positioning errors in the direction of east, north, and up are 8.1 cm, 3.6 cm, and 8.0 cm after full convergence.

scholarly journals Assessment of GPS/Galileo/BDS Precise Point Positioning with Ambiguity Resolution Using Products from Different Analysis Centers

2021 ◽  
Vol 13 (16) ◽  
pp. 3266
Author(s):  
Chao Chen ◽  
Guorui Xiao ◽  
Guobin Chang ◽  
Tianhe Xu ◽  
Liu Yang
Keyword(s):  
Ambiguity Resolution ◽  
Precise Point Positioning ◽  
Satellite System ◽  
Convergence Time ◽  
Major Drawback ◽  
System Combination ◽  
North East ◽  
Positioning Errors ◽  
Point Positioning ◽  
Kinematic Ppp

Suffering from hardware phase biases originating from satellites and the receiver, precise point positioning (PPP) requires a long convergence time to reach centimeter coordinate accuracy, which is a major drawback of this technique and limits its application in time-critical applications. Ambiguity resolution (AR) is the key to a fast convergence time and a high-precision solution for PPP technology and PPP AR products are critical to implement PPP AR. Nowadays, various institutions provide PPP AR products in different forms with different strategies, which allow to enable PPP AR for Global Positioning System (GPS) and Galileo or BeiDou Navigation System (BDS). To give a full evaluation of PPP AR performance with various products, this work comprehensively investigates the positioning performance of GPS-only and multi-GNSS (Global Navigation Satellite System) combination PPP AR with the precise products from CNES, SGG, CODE, and PRIDE Lab using our in-house software. The positioning performance in terms of positioning accuracy, convergence time and fixing rate (FR) as well as time to first fix (TTFF), was assessed by static and kinematic PPP AR models. For GPS-only, combined GPS and Galileo PPP AR with different products, the positioning performances were all comparable with each other. Concretely, the static positioning errors can be reduced by 21.0% (to 0.46 cm), 52.5% (to 0.45 cm), 10.0% (to 1.33 cm) and 21.7% (to 0.33 cm), 47.4% (to 0.34 cm), 9.5% (to 1.16 cm) for GPS-only and GE combination in north, east, up component, respectively, while the reductions are 20.8% (to 1.13 cm), 42.9% (to 1.15 cm), 19.9% (to 3.4 cm) and 20.4% (to 0.72 cm), 44.1% (to 0.66 cm), 10.1% (to 2.44 cm) for kinematic PPP AR. Overall, the positioning performance with CODE products was superior to the others. Furthermore, multi-GNSS observations had significant improvements in PPP performance with float solutions and the TTFF as well as the FR of GPS PPP AR could be improved by adding observations from other GNSS. Additionally, we have released the source code for multi-GNSS PPP AR, anyone can freely access the code and example data from GitHub.

Sign in / Sign up

Export Citation Format

Share Document