The effect of multi-GNSS and ionospheric delay on real-time velocity estimation with the variometric approach

2020 ◽  
Author(s):  
Tao Geng ◽  
Zhihui Ding
Keyword(s):  
Time Series ◽  
Solar Activity ◽  
Real Time ◽  
Sunspot Number ◽  
Seismic Velocity ◽  
Vertical Component ◽  
Velocity Estimation ◽  
Ionospheric Delay ◽  
High Solar Activity ◽  
Variometric Approach

<p>The variometric approach, based on time difference technique in which single-receiver code and carrier phase observations are processed along with available broadcast orbits and clocks, presents a high accuracy on estimating receiver velocity (at mm/s level) in real time. In order to analyze the effect of ionospheric delay on velocity estimation, we evaluate the velocity estimation accuracy of six selected stations with different latitude at approximately 120-degree longitudes during a solar cycle from 2009 to 2019. Compared with the low-solar activity year, velocity estimation RMS during the high-solar activity year will increase by 2-4 mm/s in the east, north and up direction. Velocity estimation RMS time series agree well with the sunspot number time series. The correlation coefficients of six stations between RMS values and sunspot number are 0.45-0.66, 0.39-0.52, 0.39-0.63 in the east, north and up direction respectively. The accuracy of velocity estimation is positively correlated with the sunspot number. We also reconstructed seismic velocity waveforms caused by the 2017 Mw 6.5 Jiuzhaigou earthquake using variometric approach. The results show that multi-GNSS fusion can improve the velocity accuracy by 1-2 mm/s in the horizontal component and 3-4 mm/s in vertical component, with an improvement of 47%, 54%, 41% in the east, north, up direction compared with GPS-only results.</p>

scholarly journals New possibilities of the PCA-Seq method in the analysis of time series (on the example of solar activity)

2021 ◽  
Vol 2099 (1) ◽  
pp. 012034
Author(s):  
V M Efimov ◽  
K V Efimov ◽  
D A Polunin ◽  
V Y Kovaleva
Keyword(s):  
Time Series ◽  
Solar Activity ◽  
Maunder Minimum ◽  
High Solar Activity ◽  
External Influence ◽  
Average Period ◽  
Time Axis ◽  
Constant Amplitude ◽  
The Impact ◽  
Analysis Of Time Series

Abstract When analyzing a 1D time series, it is traditional to represent it as the sum of the trend, cyclical components and noise. The trend is seen as an external influence. However, the impact can be not only additive, but also multiplicative. In this case, not only the level changes, but also the amplitude of the cyclic components. In the PCA-Seq method, a generalization of SSA, it is possible to pre-standardize fragments of a time series to solve this problem. The algorithm is applied to the Anderson series – a sign alternating version of the well-known Wolf series, reflecting the 22-year Hale cycle. The existence of this cycle is not disputed at high solar activity, but there are doubts about the constancy of its period at this time, as well as its existence during the epoch of low solar activity. The processing of the series by the PCA-Seq method revealed clear oscillations fluctuations of almost constant amplitude with an average period of 21.9 years, and it was found that the correlation of these oscillations with the time axis for 300 years does not differ significantly from zero. This confirms the hypothesis of the existence of 22-year oscillations in solar activity even at its minima, like the Maunder minimum.

scholarly journals Assessing the Performance of EUHFORIA Modeling the Background Solar Wind

Solar Physics ◽  
2019 ◽  
Vol 294 (12) ◽  
Author(s):  
Jürgen Hinterreiter ◽  
Jasmina Magdalenic ◽  
Manuela Temmer ◽  
Christine Verbeke ◽  
Immanuel Christopher Jebaraj ◽  
...  
Keyword(s):  
Time Series ◽  
Solar Wind ◽  
Solar Activity ◽  
Coronal Holes ◽  
High Solar Activity ◽  
Time Interval ◽  
Input Parameters ◽  
First Results ◽  
Combined Time Series

AbstractIn order to address the growing need for more accurate space-weather predictions, a new model named (EUropean Heliospheric FORecasting Information Asset) was recently developed. We present the first results of the performance assessment for the solar-wind modeling with and identify possible limitations of its present setup. Using the basic 1.0.4 model setup with the default input parameters, we modeled background solar wind (no coronal mass ejections) and compared the obtained results with Advanced Composition Explorer (ACE) in-situ measurements. For the purposes of statistical study we developed a technique of combining daily runs into continuous time series. The combined time series were derived for the years 2008 (low solar activity) and 2012 (high solar activity), from which in-situ speed and density profiles were extracted. We find for the low-activity phase a better match between model results and observations compared to the high-activity time interval considered. The quality of the modeled solar-wind parameters is found to be rather variable. Therefore, to better understand the results obtained we also qualitatively inspected characteristics of coronal holes, i.e. the sources of the studied fast streams. We discuss how different characteristics of the coronal holes and input parameters to influence the modeled fast solar wind, and suggest possibilities for the improvement of the model.

scholarly journals Long-term solar activity explored with wavelet methods

2006 ◽  
Vol 24 (2) ◽  
pp. 769-778 ◽  
Author(s):  
H. Lundstedt ◽  
L. Liszka ◽  
R. Lundin ◽  
R. Muscheler
Keyword(s):  
Solar Activity ◽  
Production Rate ◽  
Sunspot Number ◽  
Maunder Minimum ◽  
High Solar Activity ◽  
Solar Modulation ◽  
Group Sunspot ◽  
Group Sunspot Number ◽  
Wavelet Methods

Abstract. Long-term solar activity has been studied with a set of wavelet methods. The following indicators of long-term solar activity were used; the group sunspot number, the sunspot number, and the 14C production rate. Scalograms showed the very long-term scales of 2300 years (Hallstat cycle), 900-1000 years, 400-500 years, and 200 years (de Vries cycle). Scalograms of a newly-constructed 14C production rate showed interesting solar modulation during the Maunder minimum. Multi-Resolution Analysis (MRA) revealed the modulation in detail, as well as peaks of solar activity not seen in the sunspot number. In both the group sunspot number scalogram and the 14C production rate scalogram, a process appeared, starting or ending in late 1700. This process has not been discussed before. Its solar origin is unclear. The group sunspot number ampligram and the sunspot number ampligram showed the Maunder and the Dalton minima, and the period of high solar activity, which already started about 1900 and then decreased again after mid 1990. The decrease starts earlier for weaker components. Also, weak semiperiodic activity was found. Time Scale Spectra (TSS) showed both deterministic and stochastic processes behind the variability of the long-term solar activity. TSS of the 14C production rate, group sunspot number and Mt. Wilson sunspot index and plage index were compared in an attempt to interpret the features and processes behind the long-term variability.

Eliminating TRF-related System Errors Through Recursive TRF Realization Strategy for the CMONOC GPS Stations

2020 ◽  
Author(s):  
weiwei wu ◽  
Guojie Meng ◽  
Jicang Wu ◽  
Guoqiang Zhao
Keyword(s):  
Time Series ◽  
Vertical Component ◽  
Velocity Estimation ◽  
Reference Network ◽  
Gps Data ◽  
Time Series Modeling ◽  
Related System ◽  
Coordinate Time ◽  
Coordinate Time Series ◽  
System Errors

Abstract It is vital in the study of crustal deformation to reduce system errors and enhance the accuracy of GPS coordinate time series. To eliminate system errors associated in the coordinate time series, which are related to the terrestrial reference frame (TRF) realization, we develop a recursive TRF realization strategy in regional GPS data processing. We have processed the whole set of CMONOC (Crustal Movement Observation Network of China) GPS data by the Bernese software, and employ the controlled datum removal (CDR) filter to solve the rank defect problem in the daily coordinate normal equations. On the recursive TRF realization of stations’ coordinates, we iteratively perform time series modeling with integral trajectory models, TRF realization with all continuous stations treated as “pseudo” fiducial stations, and frame alignment to the ITRF2014 with the 6-parameters Helmert transformation. We obtain the final coordinate time series through 3 times of iterations for the CMONOC data. Compared to the results derived from the conventional TRF realization strategy with the average root mean squares (RMS) being 1.98mm, 2.62 mm and 5.39 mm for east, north and up components, respectively, the average RMS earn significant reduction up to 30%, 43% and 16% in the first loop, with their quantities being 1.41 mm, 1.51 mm and 4.57 mm for east, north and up components, respectively, and negligible changes in the following 2 loops. In contrast to previous studies, our strategy is feasible in the processing of regional geodetic networks, and is concentrated on the TRF-related system errors without any pre-assumption and spatial limitation. In essence, our recursive strategy is to tighten the constraints for the CMONOC GPS stations in the TRF realization through the leaning of the barycenter of the processed geodetic network, thus inevitably loosening the constraints for other globally distributed stations, and slightly magnifying their RMS. On the whole, the north component of coordinates time series has a maximum RMS reduction, resulting in identical precision for both horizontal components, thus indicating that our strategy remedies the frame defects stemming from the extremely uneven distribution of the reference network, and retrieves the “real” precision of GPS observations. The insignificant RMS reduction on the vertical component may be attributed to insufficient time series modeling. Our recursive TRF realization strategy can benefit the velocity estimation for campaign stations.

Relationship of cholera incidence to El Niño and solar activity elucidated by time-series analysis

2009 ◽  
Vol 138 (1) ◽  
pp. 99-107 ◽  
Author(s):  
K. OHTOMO ◽  
N. KOBAYASHI ◽  
A. SUMI ◽  
N. OHTOMO
Keyword(s):  
Time Series ◽  
Solar Activity ◽  
Time Series Analysis ◽  
Surface Temperature ◽  
Sunspot Number ◽  
El Niño ◽  
El Nino ◽  
Sea Surface ◽  
Series Analysis ◽  
Relationship Of

SUMMARYUsing time-series analysis, we investigated the monthly cholera incidence in Dhaka, Bangladesh during an 18-year period for its relationship to the sea surface temperature (SST) linked to El Niño, and to the sunspot number. Dominant periodic modes identified for cholera incidence were 11·0, 4·8, 3·5, 2·9, 1·6, 1·0 and 0·5 years. The majority of these modes, e.g. the 11·0-, 4·8-, 3·5-, 1·6- and 1·0-year modes, were essentially consistent with those obtained for the SST data (dominant modes: 5·1, 3·7, 2·5, 2·1, 1·5, 1·0 years) and the sunspot number data (dominant modes: 22·1, 11·1, 7·3, 4·8, 3·1 years). We confirmed that the variations of cholera incidence were synchronous with SSTs, and were inversely correlated to the sunspot numbers. These results suggest that the cholera incidence in Bangladesh may have been influenced by the occurrence of El Niño and also by the periodic change of solar activity.

scholarly journals Modification of the solar activity indices in the International Reference Ionosphere IRI and IRI-Plas models due to recent revision of sunspot number time series

2016 ◽  
Vol 2 (3) ◽  
pp. 59-68 ◽  
Author(s):  
Тамара Гуляева ◽  
Tamara Gulyaeva
Keyword(s):  
Time Series ◽  
Solar Activity ◽  
Sunspot Number ◽  
International Reference Ionosphere ◽  
Electron Content ◽  
Prediction Errors ◽  
Solar Cycles ◽  
Total Electron ◽  
International Reference ◽  
Ionospheric Models

The International Reference Ionosphere (IRI) imports global effective ionospheric IG12 index based on ionosonde measurements of the critical frequency foF2 as a proxy of solar activity. Similarly, the global electron content (GEC), smoothed by the sliding 12-months window (GEC12), is used as a solar proxy in the ionospheric and plasmaspheric model IRI-Plas. GEC has been calculated from global ionospheric maps of total electron content (TEC) since 1998 whereas its productions for the preceding years and predictions for the future are made with the empirical model of the linear dependence of GEC on solar activity. At present there is a need to re-evaluate solar and ionospheric indices in the ionospheric models due to the recent revision of sunspot number (SSN2) time series, which has been conducted since 1st July, 2015 [Clette et al., 2014]. Implementation of SSN2 instead of the former SSN1 series with the ionospheric model could increase model prediction errors. A formula is proposed to transform the smoothed SSN212 series to the proxy of the former basic SSN112=R12 index, which is used by IRI and IRI-Plas models for long-term ionospheric predictions. Regression relationships are established between GEC12, the sunspot number R12, and the proxy solar index of 10.7 cm microwave radio flux, F10.712. Comparison of calculations by the IRI-Plas and IRI models with observations and predictions for Moscow during solar cycles 23 and 24 has shown the advantage of implementation of GEC12 index with the IRI-Plas model.

scholarly journals Solar activity explored with new wavelet methods

2005 ◽  
Vol 23 (4) ◽  
pp. 1505-1511 ◽  
Author(s):  
H. Lundstedt ◽  
L. Liszka ◽  
R. Lundin
Keyword(s):  
Time Series ◽  
Solar Activity ◽  
Sunspot Number ◽  
Time Scale ◽  
Power Spectra ◽  
Nonlinear Phenomena ◽  
Dynamo Theory ◽  
Terrestrial Environment ◽  
The Impact ◽  
Wavelet Methods

Abstract. In order to improve the forecasts of the impact of solar activity on the terrestrial environment on time scales longer than days, improved understanding and forecasts of the solar activity are needed. The first results of a new approach of modelling and forecasting solar activity are presented. Time series of solar activity indicators, such as sunspot number, group sunspot number, F10.7, E10.7, solar magnetic mean field, Mount Wilson plage and sunspot index, have been studied with new wavelet methods; ampligrams and time-scale spectra. Wavelet power spectra of the sunspot number for the period 1610 up to the present show not only that a dramatic increase in the solar activity took place after 1940 but also that an interesting change occurred in 1990. The main 11-year solar cycle was further studied with ampligrams for the period after 1850. time-scale spectra were used to examine the processes behind the variability of the solar activity. Several interesting deterministic and more stochastic features were detected in the time series of the solar activity indicators. The solar nature of these features will be further studied. Keywords. Solar physics, astrophysics and astronomy (Magnetic fields; Stellar interiors and dynamo theory) – Space plasma physics (nonlinear phenomena)

The cosmic-ray intensity variations with periods of 19-24 days

1968 ◽  
Vol 46 (10) ◽  
pp. S831-S834
Author(s):  
G. A. Bazilevskaya
Keyword(s):  
Solar Activity ◽  
Sunspot Number ◽  
Neutron Monitor ◽  
Cosmic Ray ◽  
High Solar Activity ◽  
Radio Emissions ◽  
Cosmic Ray Intensity ◽  
Cyclic Variations

Sporadic cyclic variations of the cosmic-ray intensity with periods of 19 to 24 days have been found from the results of balloon and neutron monitor observations. These variations were observed mainly in the years of high solar activity, 1958–62. They appeared to be caused by the general solar activity which, as our treatment has shown, undergoes similar cyclic variations (according to sunspot number or 10.7-cm radio-emissions). The variations under investigation appear with a lag of about 1.5 months compared with the solar-activity variations.

scholarly journals Real-Time Geophysical Applications with Android GNSS Raw Measurements

2019 ◽  
Vol 11 (18) ◽  
pp. 2113 ◽  
Author(s):  
Marco Fortunato ◽  
Michela Ravanelli ◽  
Augusto Mazzoni
Keyword(s):  
Real Time ◽  
Noise Level ◽  
Vertical Component ◽  
Satellite System ◽  
Electron Content ◽  
Dual Frequency ◽  
Total Electron ◽  
Variometric Approach ◽  
Global Navigation Satellite ◽  
Slant Total Electron Content

The number of Android devices enabling access to raw GNSS (Global Navigation Satellite System) measurements is rapidly increasing, thanks to the dedicated Google APIs. In this study, the Xiaomi Mi8, the first GNSS dual-frequency smartphone embedded with the Broadcom BCM47755 GNSS chipset, was employed by leveraging the features of L5/E5a observations in addition to the traditional L1/E1 observations. The aim of this paper is to present two different smartphone applications in Geoscience, both based on the variometric approach and able to work in real time. In particular, tests using both VADASE (Variometric Approach for Displacement Analysis Stand-alone Engine) to retrieve the 3D velocity of a stand-alone receiver in real-time, and VARION (Variometric Approach for Real-Time Ionosphere Observations) algorithms, able to reconstruct real-time sTEC (slant total electron content) variations, were carried out. The results demonstrate the contribution that mass-market devices can offer to the geosciences. In detail, the noise level obtained with VADASE in a static scenario—few mm/s for the horizontal components and around 1 cm/s for the vertical component—underlines the possibility, confirmed from kinematic tests, of detecting fast movements such as periodic oscillations caused by earthquakes. VARION results indicate that the noise level can be brought back to that of geodetic receivers, making the Xiaomi Mi8 suitable for real-time ionosphere monitoring.

scholarly journals Comparison of chaotic aspects of magnetosphere under various physical conditions using AE index time series

2008 ◽  
Vol 26 (4) ◽  
pp. 941-953 ◽  
Author(s):  
K. Unnikrishnan
Keyword(s):  
Time Series ◽  
Solar Activity ◽  
Lyapunov Exponent ◽  
Degrees Of Freedom ◽  
High Solar Activity ◽  
Nonlinear Prediction ◽  
Physical Conditions ◽  
Ae Index ◽  
Significant Difference ◽  
Index Time Series

Abstract. The deterministic chaotic behaviour of magnetosphere was analyzed, using AE index time series. The significant chaotic quantifiers like, Lyapunov exponent, spatio-temporal entropy and nonlinear prediction error for AE index time series under various physical conditions were estimated and compared. During high solar activity (1991), the values of Lyapunov exponent for AE index time series representing quiet conditions (yearly mean = 0.5±0.1 min−1) have no significant difference from those values for corresponding storm conditions (yearly mean = 0.5±0.17 min−1). This implies that, for the cases considered here, geomagnetic storms may not be an additional source to increase or decrease the deterministic chaotic aspects of magnetosphere, especially during high solar activity. During solar minimum period (1994), the seasonal mean value of Lyapunov exponent for AE index time series belong to quiet periods in winter (0.7±0.11 min−1) is higher compared to corresponding value of storm periods in winter (0.36±0.09 min−1). This may be due to the fact that, stochastic part, which is Dst dependent could be more prominent during storms, thereby increasing fluctuations/stochasticity and reducing determinism in AE index time series during storms. It is observed that, during low solar active period (1994), the seasonal mean value of entropy for time series representing storm periods of equinox is greater than that for quiet periods. However, significant difference is not observed between storm and quiet time values of entropy during high solar activity (1991), which is also true for nonlinear prediction error for both low and high solar activities. In the case of both high and low solar activities, the higher standard deviations of yearly mean Lyapunov exponent values for AE index time series for storm periods compared to those for quiet periods might be due to the strong interplay between stochasticity and determinism during storms. It is inferred that, the external driving forces, mainly due to solar wind, make the solar-magnetosphere-ionosphere coupling more complex, which generates many active degrees of freedom with various levels of coupling among them, under various physical conditions. Hence, the superposition of a large number of active degrees of freedom can modify the stability/instability conditions of magnetosphere.

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