Wei E. | Yan W. | Jin S. | Wei J. | Kutoglu H. | Li X. | Adam J.

Makale | 2015 | Aerospace Science and Technology46 , pp.256 - 263

Space very long baseline interferometry (SVLBI) is an extension of ground based VLBI to space, which has advantages, such as improving the precision and geometry structure of time delay observables with interconnecting multiple spatial coordinate systems directly. In this paper, a mathematical model of relativistic simulated SVLBI observables for estimating Chang'E-1 (CE-1) transfer orbit and Earth orientation Parameters (EOPs) is derived and discussed. A comparison of parameter estimation precision between ground ?VLBI measurements and simulated SVLBI observables is carried out to verify the contribution of SVLBI. The optimal obser . . .vation condition of CE-1 for SVLBI simulated observables is determined based on the analysis of parameter estimation results under CE-1 current observation condition. By using simulated SVLBI time delay observables under the optimal observation condition, the estimation precision of CE-1 orbit can achieve a level of 2 m. On the other side, the precision of some EOPs components can be improved when compared with their predicted values by fixed remaining components as known values. The method discussed in this paper provides a new attempt of deep space probe orbit determination and EOPs estimation. © 2015 Elsevier Masson SAS Daha fazlası Daha az

Jin S. | Jin R. | Li D.

Makale | 2017 | Journal of Geophysical Research: Space Physics122 ( 1 ) , pp.1360 - 1372

The processes and sources of seismo-ionospheric disturbances are still not clear. In this paper, coseismic ionospheric disturbances (CIDs) are investigated by dual-frequency GPS observations following the Mw = 7.8 earthquake as results of the oblique-thrust fault in the Haida Gwaii region, Canada, on 28 October 2012. Results show that the CIDs with an amplitude of up to 0.15 total electron content units (TECU) are found with spreading out at 2.20 km/s, which agree well with the Rayleigh wave propagation speed at 2.22 km/s detected by the bottom pressure records at about 10 min after the onset. The CIDs are a result of the upward pro . . .pagation acoustic waves trigged by the Rayleigh wave in sequence from near field to far field. The strong correlation is found between the CIDs and the vertical ground motion recorded by seismometers nearby the epicenter. The total electron content (TEC) series from lower-elevation angle GPS observations have higher perturbation amplitudes. Furthermore, the simulated ionospheric disturbance following a vertical Gauss pulse on the ground based on the finite difference time domain method confirms the ionospheric Rayleigh wave signature in the near field and the vertical ground motion dependence theoretically. The vertical ground motion is the dominant source of the ionospheric Rayleigh wave and affects the CID waveform directly. ©2017. American Geophysical Union. All Rights Reserved Daha fazlası Daha az

Khan A. | Jin S.

Makale | 2016 | Journal of Atmospheric and Solar-Terrestrial Physics138-139 , pp.23 - 31

The tropopause plays an important role in climate change, particularly in Tibet with complex topography and climate change system. In this paper, the temperature and height of the Cold Point Tropopause (CPT) in Tibet are obtained and investigated from COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) GPS Radio Occultation (RO) during June 2006-Feb 2014, which are compared with Lapse Rate Tropopause (LRT) from Atmospheric Infrared Sounder (AIRS/NASA). Furthermore, the impact of Gravity waves (GW) potential energy (Ep) on the CPT-Temperature, CPT-Height, and the variation of stratospheric water vapor with . . . GW Ep variations are presented. Generally the coldest CPT temperature is in June-July-August (JJA) with -76.5°C, resulting less water vapor into the stratosphere above the cold points. The temperature of the cold point increases up to -69°C during the winter over the Tibetan Plateau (25-40°N, 70-100°E) that leads to increase in water vapor above the cold points (10hPa). Mean vertical fluctuations of temperature are calculated as well as the mean gravity wave potential energy Ep for each month from June 2006 to Feb 2014. Monthly Ep is calculated at 5°×5° grids between 17km and 24km in altitude for the Tibetan Plateau. The Ep raises from 1.83 J/Kg to 3.4 J/Kg from summer to winter with mean Ep of 2.5 J/Kg for the year. The results show that the gravity waves affect the CPT temperature and water vapor concentration in the stratosphere. Water vapor, CPT temperature and gravity wave (Ep) have good correlation with each other above the cold points, and water vapor increases with increasing Ep. © 2015 Elsevier Ltd Daha fazlası Daha az

Jin S. | Jin R. | Kutoglu H.

Makale | 2017 | Journal of Geodesy91 ( 6 ) , pp.613 - 626

The most intense geomagnetic storm in solar cycle 24 occurred on March 17, 2015, and the detailed ionospheric storm morphologies are difficultly obtained from traditional observations. In this paper, the Geostationary Earth Orbit (GEO) observations of BeiDou Navigation Satellite System (BDS) are for the first time used to investigate the ionospheric responses to the geomagnetic storm. Using BDS GEO and GIMs TEC series, negative and positive responses to the March 2015 storm are found at local and global scales. During the main phase, positive ionospheric storm is the main response to the geomagnetic storm, while in the recovery phas . . .e, negative phases are pronounced at all latitudes. Maximum amplitudes of negative and positive phases appear in the afternoon and post-dusk sectors during both main and recovery phases. Furthermore, dual-peak positive phases in main phase and repeated negative phase during the recovery are found from BDS GEO observations. The geomagnetic latitudes corresponding to the maximum disturbances during the main and recovery phases show large differences, but they are quasi-symmetrical between southern and northern hemispheres. No clear zonal propagation of traveling ionospheric disturbances is detected in the GNSS TEC disturbances at high and low latitudes. The thermospheric composition variations could be the dominant source of the observed ionospheric storm effect from GUVI [O]/[N 2 ] ratio data as well as storm-time electric fields. Our study demonstrates that the BDS (especially the GEO) observations are an important data source to observe ionospheric responses to the geomagnetic storm. © 2016, Springer-Verlag Berlin Heidelberg Daha fazlası Daha az

Najibi N. | Jin S. | Wu X.

Makale | 2015 | IEEE Transactions on Antennas and Propagation63 ( 6 ) , pp.2646 - 2654

The variability of snow accumulation and melting is one of the most important interactions of the Earth's surface with atmosphere through energy transmission and mass balance. In this paper, the effects of snow accumulation and melting together with bare soil and fixed snow depth on the reflected global positioning system (GPS) signals are investigated using GPS antenna gains and multipath signal. The reflected GPS signals are modeled and employed to analyze the interactions of snow accumulation, snow melting, bare soil, and fixed snow depth at BAKE and KUUJ GPS stations in Northern Canada. The results show the clear independency of . . . the snow accumulation and melting variations with bare soil and fixed snow depth, which are validated from GPS-reflected signals as well. The modeled reflected GPS signals indicate the higher frequency of snow accumulation and snow melting than that of bare soil and fixed snow depth, while the estimated power spectral density of the GPS-reflected signals shows the higher signal power of coherence function difference. Furthermore, the GPS observations at BAKE and KUUJ sites confirm such variations with a good agreement during the snow accumulation, melting, bare soil, and fixed snow depth on the ground. © 1963-2012 IEEE Daha fazlası Daha az

Zhang T. | Jin S.

Makale | 2016 | IEEE Transactions on Geoscience and Remote Sensing54 ( 8 ) , pp.4694 - 4701

Evapotranspiration (ET) is one of the key variables in water cycle and ecological systems, whereas it is difficult to quantify ET variations from traditional observations in large river basins, e.g., Mississippi River basin (MRB). In this paper, a new geodetic tool, i.e., Global Positioning System (GPS), is used for the first time to estimate monthly ET variations at a regional scale. Based on the water balance equation, the monthly ET variation is estimated using the GPS-derived terrestrial water storage (TWS) from January 2006 to July 2015 in MRB. The annual amplitude of GPS-inferred TWS in MRB agrees well with the results of Grav . . .ity Recovery and Climate Experiment. The ET variations from the water balance approach agree well with the land surface modeling and remote sensing data. The correlation of GPS-inferred ET with other ET products is higher than 0.8, which indicates that the GPS-estimated ET well characterizes the ET variations in MRB. The annual amplitude of GPS-inferred ET variations is 47.9 mm/month, which is close to that from land surface modeling of North American Land Data Assimilation System, and a little larger than MODerate Resolution Imaging Spectroradiometer. The mean monthly ET reaches its maximum in June-July and its minimum in December, which is consistent with the periodic pattern of radiative energy in a year. Furthermore, the ET variations are mainly dominated by the temperature change in MRB. © 2016 IEEE Daha fazlası Daha az

Li J. | Jin S.

Makale | 2017 | Annales Geophysicae35 ( 3 ) , pp.403 - 411

GPS radio occultation can estimate ionospheric electron density and total electron content (TEC) with high spatial resolution, e.g., China's recent Fengyun-3C GPS radio occultation. However, high-order ionospheric delays are normally ignored. In this paper, the high-order ionospheric effects on electron density estimation from the Fengyun-3C GPS radio occultation data are estimated and investigated using the NeQuick2 ionosphere model and the IGRF12 (International Geomagnetic Reference Field, 12th generation) geomagnetic model. Results show that the high-order ionospheric delays have large effects on electron density estimation with . . .up to 800 el cm-3, which should be corrected in high-precision ionospheric density estimation and applications. The second-order ionospheric effects are more significant, particularly at 250-300 km, while third-order ionospheric effects are much smaller. Furthermore, the high-order ionospheric effects are related to the location, the local time, the radio occultation azimuth and the solar activity. The large high-order ionospheric effects are found in the low-latitude area and in the daytime as well as during strong solar activities. The second-order ionospheric effects have a maximum positive value when the radio occultation azimuth is around 0-20°, and a maximum negative value when the radio occultation azimuth is around -180 to -160 °. Moreover, the geomagnetic storm also affects the high-order ionospheric delay, which should be carefully corrected. © Author(s) 2017. CC Attribution 3.0 License Daha fazlası Daha az

Zhang T. | Jin S.

Kitap Bölümü | 2015 | Planetary Exploration and Science: Recent Results and Advances , pp.101 - 118

Impact craters are the most outstanding and attractive geomorphological features on the surface of the planets, showing variety and complexity of the surface morphology. The accurate recognition of impact craters on Mars is very useful to analyze and understand the relative dating of Martian surface. In this chapter, four crater-detection methods have been presented and discussed with various extent of discrimination ability on Martian images or topography data. Themodified ad boosting approach demonstrates the best performance in classification of craters, while the algorithms based on topography data have low efficiency in automat . . .ic detection. Comparing to previous solutions, the modified ad boosting method has greatly improved the detecting performance of the algorithm and reduced detection time. © Springer-Verlag Berlin Heidelberg 2015 Daha fazlası Daha az

Pulvirenti F. | Aloisi M. | Jin S.

Makale | 2017 | Journal of Volcanology and Geothermal Research344 , pp.185 - 196

In this paper, the relationship between the dike-forming magmatic intrusions and the faulting process at Mount Etna is investigated in terms of Coulomb stress changes. As case study, a complete time-dependent 3-D finite element model for the 2002–2003 eruption at Mount Etna is presented. In the model, which takes into account the topography, medium heterogeneities and principal fault systems in a viscoelastic/plastic rheology, we sequentially activated three dike-forming processes and looked at the induced temporal evolution of the Coulomb stress changes, during the co-intrusive and post-intrusive periods, on Pernicana and Santa Ven . . .erina faults. We investigated where and when fault slips were encouraged or not, and consequently how earthquakes may have been triggered. Results show positive Coulomb stress changes for the Pernicana Fault in accordance to the time, location and depth of the 27th October 2002 Pernicana earthquake (Md = 3.5). The amount of Coulomb stress changes in the area of Santa Venerina Fault, as induced by dike-forming intrusions only, is instead almost negligible and, probably, not sufficient to trigger the 29th October Santa Venerina earthquake (Md = 4.4), occurred two days after the start of the eruption. The necessary Coulomb stress change value to trigger this earthquake is instead reached if we consider it as induced by the 27th October Pernicana biggest earthquake, combined with the dike-induced stresses. © 2016 Elsevier B.V Daha fazlası Daha az

Barkin Y.V. | Ferrandiz J. | Jin S. | Barkin M.Y.

Makale | 2018 | Geodesy and Geodynamics9 ( 6 ) , pp.474 - 484

On the basis of conditionally-periodic solutions of Hamiltonian systems at resonance of main frequencies Cassini's motions, their stability, Cassini's angle and periods of free librations of the Moon and Mercury have been recently studied and determined. The generalized formulations of Cassini's laws for the motion of the Moon and Mercury, that are considered as absolutely rigid non-spherical bodies, have been determined. The study of the second approximation equations of the desired quasi-periodic solutions in the case of the Moon allows us to determine the constant components of the first order for six Andoyer variables and the co . . .nstant component of the second order for the angular velocity of the Moon. These effects are caused by the influence of the third harmonic of selenopotential. In this paper, these effects are described by analytical formulas, the dynamic and geometric interpretations are given, and a new interpretation of Mercury's motion under the generalized Cassini's laws has been proposed. Predictions of the existence of free librations of significant amplitude in the Mercury longitude, that are confirmed by the radar measurements data of the Mercury angular velocity, and in its pole motion in the body and in space have been made. The mechanism describing free librations of celestial bodies and their pole oscillations has been proposed due to the forced relative oscillations and wobble of the core-mantle system of celestial bodies (Moon, Mercury, Earth and other bodies in the solar system) under gravitational action of the external celestial bodies. The paper shows that the ascending node of equator of Mercury (and the intermediate plane orthogonal to the angular momentum) of epoch 2000.0 on the ecliptic does not coincide with the ascending node of orbital plane of Mercury on the same plane, and is ahead of it at an angle 23º4’. Angular momentum vector of the rotational motion of Mercury forms a constant angle ?G=4’1±1’1 with normal to the moveable plane of its orbit. The observed inclination of the angular velocity??=2’1±0’1, can be considered as a possible evidence of a significant amplitude of the poles free motion of the Mercury rotation axis (c amplitude of about 2'- 4'). © 2018 The Author Daha fazlası Daha az

Dong Z. | Jin S.

Makale | 2018 | Remote Sensing10 ( 1 ) , pp.474 - 484

Three-dimensional water vapor can be reconstructed from Global Navigation Satellite System (GNSS) observations, which can study 3-D profile variations of atmospheric water vapor and climate. However, there is a large uncertainty of water vapor tomography from single GPS system observations due to limited satellites. The rapid development of multi-GNSS, including China's Beidou Navigation Satellite System (BDS) and Russia's GLONASS, has greatly improved the geometric distribution of satellite ray-path signals, which may improve the performance of water vapor tomography by combining multi-GNSS. In this paper, 3-D water vapor tomograph . . .y results are the first time obtained using multi-GNSS data from Continuously Operating Reference Stations (CORS) network in Wuhan, China, whose performances are validated by radiosonde and the latest ECMWF ERA5 reanalysis products. The results show that the integrated multi-GNSS can pronouncedly increase the number of effective signals, and 3-D water vapor results are better than those from the GPS-only system, improving by 5% with GPS + GLONASS or GPS + GLONASS + BDS, while BDS has results that are not improved too much. Therefore, multi-GNSS will enhance the reliability and accuracy of 3-D water vapor tomography, which has more potential applications in the future Daha fazlası Daha az

Calabia A. | Jin S.

Makale | 2016 | Aerospace Science and Technology49 , pp.80 - 87

The accuracy of the conservative force-models is not clear and the new space accelerometers provide a unique opportunity for their validation. In this paper, the conservative-force model deficiencies are investigated via Principal Component Analysis (PCA) using 4 years of GRACE measurements (2006-2009). The deficiencies are assessed by comparing the accelerometer readouts with the differences between the conservative force-model and the precise orbit accelerations. Within this scheme, the spatiotemporal data analysis is synthesized in a time-series of grids whose latitudinal and longitudinal variations are respectively influenced by . . . the half orbital period and the equatorial orbit shift. With maximum amplitude of 50 nm/s2, the mean map shows a positive overestimation in Canada and Brazil and negative in Greenland. Explaining the 74% of the variability, the two first pairs of PCA modes show un-modeled patterns with amplitudes maxima of 80 nm/s2 and 50 nm/s2. Their periodic behavior and wave-length of degree-6 and degree-11s spherical harmonics strongly suggest an additional modeling and improvement. As for the long-term variations, our results show a latitudinal variation of 15 nm/s2 maximum amplitude correlated with the day-night periods. Performing a combined analysis of ascending and descending orbits, a trend of 3 nm/s2yr in the Indian Ocean is also observed. Our new approach for orbital force-models validation can be considered crucial for the current state-of-the-art of precise orbit determination (POD) and Time-Varying Gravity (TVG) modeling. © 2015 Elsevier Masson SAS Daha fazlası Daha az