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Cassini's motions of the Moon and Mercury and possible excitations of free librations

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

Article | 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

Evaluation of regional ionospheric grid model over China from dense GPS observations

Zhao X. | Jin S. | Mekik C. | Feng J.

Article | 2016 | Geodesy and Geodynamics7 ( 5 ) , pp.361 - 368

The current global or regional ionospheric models have been established for monitoring the ionospheric variations. However, the spatial and temporal resolutions are not enough to describe total electron content (TEC) variations in small scales for China. In this paper, a regional ionospheric grid model (RIGM) with high spatial-temporal resolution (0.5° × 0.5° and 10-min interval) in China and surrounding areas is established based on spherical harmonics expansion from dense GPS measurements provided by Crustal Movement Observation Network of China (CMONOC) and the International GNSS Service (IGS). The correlation coefficient between . . . the estimated TEC from GPS and the ionosonde measurements is 0.97, and the root mean square (RMS) with respect to Center for Orbit Determination in Europe (CODE) Global Ionosphere Maps (GIMs) is 4.87 TECU. In addition, the impact of different spherical harmonics orders and degrees on TEC estimations are evaluated and the degree/order 6 is better. Moreover, effective ionospheric shell heights from 300 km to 700 km are further assessed and the result indicates that 550 km is the most suitable for regional ionospheric modeling in China at solar maximum. © 2016 Institute of Seismology, China Earthquake Administratio Daha fazlası Daha az

Sea level change along the Black Sea coast from satellite altimetry, tide gauge and GPS observations

Avsar N.B. | Jin S. | Kutoglu H. | Gurbuz G.

Article | 2016 | Geodesy and Geodynamics7 ( 1 ) , pp.50 - 55

Sea level change affects human living conditions, particularly ocean coasts. However, sea level change is still unclear along the Black Sea coast due to lack of in-situ measurements and low resolution satellite data. In this paper, sea level change along the Black Sea coast is investigated from joint satellite altimetry, tide gauge (TG) and Global Positioning System (GPS) observations. The linear trend and seasonal components of sea level change are estimated at 8 TG stations (Amasra, Igneada, Trabzon-II, Sinop, Sile, Poti, Tuapse, and Batumi) located along the Black Sea coast, which are compared with Satellite Altimetry and GPS. At . . . the tide gauge stations with long-term records such as Poti (about 21 years) and Tuapse (about 19 years), the results obtained from the satellite altimetry and tide gauge observations show a remarkably good agreement. While some big differences are existed between Satellite Altimetry and TG at other stations, after adding vertical motion from GPS, correlation coefficients of the trend have been greatly improved from 0.37 to 0.99 at 3 co-located GPS and TG stations (Trabzon-II, Sinop and Sile). © 2016 Institute of Seismology, China Earthquake Administration Daha fazlası Daha az

Evaluation of ocean tide loading effects on GPS-estimated precipitable water vapour in Turkey

Gokhan G. | Jin S.

Article | 2016 | Geodesy and Geodynamics7 ( 1 ) , pp.32 - 38

Global Positioning System (GPS) has been widely used to estimate the total zenith tropospheric delay (ZTD) and precipitable water vapour (PWV) for weather prediction and atmospheric research as a continuous and all-weather technique. However, estimations of ZTD and PWV are subject to effects of geophysical models with large uncertainties, particularly imprecise ocean tide models of inland seas in Turkey. In this paper, GPS data from Jan. 1, 2010 to Dec. 31, 2011 are processed using GAMIT/GLOBK at four co-located GPS stations (ISTN, ERZR, SAMN, and IZMI) with Radiosonde from the Turkish Met-Office together with several nearby IGS sta . . .tions. Four widely used ocean tide models are adopted to evaluate their effects on GPS-estimated PWV, such as IERS recommended FES2004, NAO99b, CSR4.0 and GOT00. Five different strategies are taken without ocean tide model and with four ocean tide models, respectively, which are used to evaluate ocean tide models effects on GPS-estimated PWV through comparing with co-located Radiosonde. Results showed that ocean tide models have greatly affected the estimation of the precipitable water vapour at stations near coasts. The ocean tide model FES2004 gave the best results when compared to Radiosonde with ±2.12 mm in PWV at stations near coastline. While other ocean tides models agree each other at millimeter level in PWV. However, at inland GPS stations, ocean tide models have less effect on GPS-estimated PWV. © 2016 Institute of Seismology, China Earthquake Administration Daha fazlası Daha az

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