The study investigates a relative analysis of two regional navigation satellite systems namely the Indian regional navigation satellite system (IRNSS) and the Quasi-zenith satellite system (QZSS) ...working in the Asia–Pacific region. It was expected that the combined precise point positioning (PPP) will attain a highly stable and accurate positioning compared to the IRNSS-only and QZSS-only solutions, but the visual results are different. In the case of India combined (IRNSS + QZSS), PPP has a minute level of increment in the east and up direction, compared to IRNSS standalone while in the case of Japan combined (QZSS + IRNSS), PPP becomes worse compared to QZSS alone. The obtained results indicate that it is difficult to achieve high accuracy of PPP in the Asia–Pacific region for (IRNSS + QZSS) constellations, hence a basic idea of wavelet algorithm is presented for the GNSS positioning. The results showed that wavelet analysis is an effective tool to detect and eliminate outliers and can attain high accuracy of PPP.
The study investigates sea-level measurements observed from 12 tide gauge sites over the Indian coastal area during the last two decades. Initially, the rise of sea-level (slope) and acceleration is ...estimated by fitting the linear and parabolic equations in the recorded data from tide gauge measurements. The estimated results showed the abrupt change of relative sea-level measurements at the distinct site depends upon the tide gauge site locations. To accurately analyse the regional coastal sea level pattern, the tide gauge time series data are decomposed in sine and cosine functions at different frequencies followed by the spectral analysis. Analysis of the results confirmed that the tide gauges peaks do not occur at the fixed period at each tide gauge site, instead they repeat with varying time periods. The spectrum peaks width fluctuate at distinct sites and the general pattern of frequency spectrum does not follow a unique model. Such type of characteristic variation with the time is possibly because of the effective variables, which affects the steadiness of sea-level changes. The study concludes that the experimental results from the Indian coastal region must be included during the comparison of global data sets and other contemporary oceanic models.
The tide gauge measurements from global navigation satellite system reflectometry (GNSS-R) observables are considered to be a promising alternative to the traditional tide gauges in the present days. ...In the present paper, we deliver a comparative analysis of tide-gauge (TG) measurements retrieved by quasi-zenith satellite system-reflectometry (QZSS-R) and the legacy TG recordings with additional observables from other constellations viz. GPS-R and GLONASS-R. The signal-to-noise ratio data of QZSS (L1, L2, and L5 signals) retrieved at the P109 site of GNSS Earth Observation Network in Japan (37.815° N; 138.281° E; 44.70 m elevation in ellipsoidal height) during 01 October 2019 to 31 December 2019. The results from QZSS observations at L1, L2, and L5 signals show respective correlation coefficients of 0.8712, 0.6998, and 0.8763 with observed TG measurements whereas the corresponding root means square errors were 4.84 cm, 4.26 cm, and 4.24 cm. The QZSS-R signals revealed almost equivalent precise results to that of GPS-R (L1, L2, and L5 signals) and GLONASS-R (L1 and L2 signals). To reconstruct the tidal variability for QZSS-R measurements, a machine learning technique, i.e., kernel extreme learning machine (KELM) is implemented that is based on variational mode decomposition of the parameters. These KELM reconstructed outcomes from QZSS-R L1, L2, and L5 observables provide the respective correlation coefficients of 0.9252, 0.7895, and 0.9146 with TG measurements. The mean errors between the KELM reconstructed outcomes and observed TG measurements for QZSS-R, GPS-R, and GLONASS-R very often lies close to the zero line, confirming that the KELM-based estimates from GNSS-R observations can provide alternative unbiased estimations to the traditional TG measurement. The proposed method seems to be effective, foreseeing a dense tide gauge estimations with the available QZSS-R along with other GNSS-R observables.
This analysis is an extension of the studies based on the space–time–magnitude domain nearest-neighborhood distances (
ƞ
) obtained from two successive earthquakes. We included epicentral depth as a ...parameter, and established a new analytical solution for seismicity clustering in the space–time–depth–magnitude domain. The proposed technique was applied to SW Japan seismic observation data for 2011–2018, and revealed that the temporal, spatial, and epicentral (
T
,
R
,
E
) components of the joint distribution for
ƞ
were prominently bimodal, indicating the presence of two, statistically distinct, earthquake populations. We used the Lomb–Scargle periodogram (LSP) to generate a power spectrum preceding the Kumamoto earthquake, and detected the periodic component of unequally spaced points for log
10
ƞ
(logarithmic scale of
ƞ
). The LSP showed a dominant peak corresponding to the time period between foreshocks and aftershocks, due to the highest number of recorded
ƞ
observations. The technique presented in this paper can be applied globally for any time period and any seismotectonic zone preceding large earthquakes of interest.
South Korea forms the Korean Peninsula and is considered to be tectonically more stable than the other regions of Eastern Asia. Global Navigation Satellite System (GNSS) sites installed in the ...country contribute to geoscientific studies on contemporary deformation, strain pattern, and current kinematics of tectonic blocks. In the current study, we used long-term GNSS measurements (from 1 January 2000 to 31 December 2018) to study block-wise geodetic deformation and strain pattern of the country, including the co-seismic effect of the 2011 Tohoku-Oki (TO) Earthquake. Measured velocities of GNSS sites are modelled via exponential smoothing method to analyse the GNSS time-series and obtain the secular tectonic crustal deformation. The analysis of strain pattern and vertical displacements indicates that extensional deformation followed compressional deformation from the northern Korean blocks to the southern Korean blocks. Finally, we examined the angular velocity and pole of rotation of the South Korean blocks using pre-seismic and post-seismic displacements of the GNSS sites. The results indicate that the angular velocity of the northern blocks was lower, while the southern block velocity is higher after the TO earthquake. We believe that the integrated approaches applied in the study would provide better insights into the active deformation of South Korea.
This study investigates the real-time sea-level measurement from six tide gauge stations in the coastal area of Japan. Initially, the six co-located global navigation satellite station sites vertical ...velocity has been observed followed by estimation of the relative tide gauge velocities. The results showed that the estimated relative sea-level changes abruptly at different sites depending on the location of tide gauge stations. To accurately analyse the regional tide gauge patterns at each site, a continuous wavelet transforms based on Morse wavelet as a default transformation has been applied. Analysis showed that the peaks of tide gauges have not occurred at a static time at each site, rather they were repeating with the variation of time. The width of the spectrum peaks varied with different sites and the overall spectrum frequency was not unique. These characteristics variation with time may be due to the variables that affect the stability of the sea level measurements. Finally, the kernel extreme learning machine (KELM) approach based on variational mode decomposition is used to reconstruct the tide gauge measurements. The correlation coefficients between observed and reconstructed data sets are very high varying from 0.91 to 0.96. The estimated root mean square error between two data sets is varying from 0.04 to 0.06 m at the entire region. This means that the KELM reconstructed tide gauge showed good agreement with the observed tidal waveforms. Thus, it can be concluded that the proposed techniques can be implemented for effective real-time sea-level monitoring changes with the available data.
Real-time positioning (RTP) is a technique used to locate the static or moving objects with an error as small as possible. Although significant work has been conducted, and several kinds of ...methodologies are planned on high-precision positioning and surveying applications, there is, however, a substantial scope for new techniques that would afford additional communicational and navigational assistance. Therefore, in this letter, an adaptive Kalman Filter (KF) based on the singular spectrum analysis (SSA) forecasting method is proposed for RTP. First, an explanation of KF is introduced, and then the SSA method is incorporated into KF for 3-D state estimation. RTP positioning test has been carried out to demonstrate the accuracy of positioning for the proposed algorithm. The simulation result reveals that the implication of SSA with KF has high-precision estimates than the only common discrete KF model.
The dynamic geological features of the Pieniny Klippen Belt (PKB) in southern Poland are nowadays a focal point of researchers as it is recognised as an active zone of crustal discontinuity. In the ...present study, we employed long-term analysis of ground-based global navigation satellite system (GNSS) measurements (from 2004 to 2020) to probe the crustal deformation, strain rates, and rotational rates in the PKB unit and the surrounding region, i.e., Magura Nappe (MN) and Podhale Flysch (PF) units. Measured velocities from GNSS observables are modelled by the auto-regressive integrated moving average (ARIMA) method to comprehend the long-term tectonic deformation. Our results showed that the ARIMA-modelled velocity varied from ~ 0.15 to ~ 8.86 mm/yr, indicating about 8.71 mm/yr difference along all units. Such differences suggest that crustal slip along the active thrusts and folds is the major factor causing regional deformation. The strain rates in PKB are also varying from the western to the eastern part. The rotational rates in PKB show a counterclockwise (CCW) pattern similar to the strain rates. These patterns suggesting that the PKB was rotated in the CCW direction with a large angle during the Miocene period. Finally, we analysed the seismicity for a period from 2004 to 2020 by using Bayesian moment tensor inversion and multivariate Bayesian inversion. The Bayesian inversion was applied based on bootstrapping chain analysis to figure out the earthquake mechanism using moment tensor inversion for the mainshock that occurred in Poland on 20 July 2018. The inversion results for the 2018 earthquake resolved a thrusting mechanism with nodal plane-1 having a strike of 346°, dip of 32°, and rake of 92° and a nodal plane-2 with a strike of 163°, dip of 58°, and rake of 89°. Since the seismicity in the Poland region has experienced less significant earthquakes in the last century, it is reasonable to attribute this lower seismic activity to the correspondingly low slip rates discerned through geodetic monitoring efforts.
The study investigates sea-level measurements along the coastal area of Europe for the 60-year (1961–2020) time span. Linear and quadratic modeling of tide gauge measurements showed an almost ...positive rate of trend of sea-level rise (0.09 to 3.6 mm/yr) and low acceleration (−0.05 to 0.40 mm/yr 2 ). A least-squares harmonic estimation tidal modeling was carried out to estimate frequency (cycles per day) for a certain period. The smaller and higher tidal frequencies of these stations indicate their stability in terms of their surface variation. We used the 1993–2020 satellite altimetry data from the nearest grid points of the tide gauge station. The correlation coefficient between observed and satellite altimetry (lowest 0.53 and highest 0.93) varies at each station. This happens because of many factors that can affect the large difference in the sea-level trend between the satellite-derived and tide gauge results. Finally, to implement a global reference system for physical heights, the offshore topographic slope direction and slope range with contour spacing from the sea to the associated coastline were analyzed using bathymetry data. The abrupt change in slope from the coastline toward the sea can be seen toward the east, west, and southeast on the European coast. This is also an important factor that affects the variation of sea level.
