Key Laboratory of Geospace Environment and Geodesy
Key Laboratory of Geospace Environment and Geodesy
Wang H.,Wuhan University |
Wang H.,Key Laboratory of Geospace Environment and Geodesy |
Luo B.,Wuhan University
Wuhan Daxue Xuebao (Xinxi Kexue Ban)/Geomatics and Information Science of Wuhan University | Year: 2017
Numerical calculation of crossovers is important groundwork for satellite altimeter data processing. The criteria for judging the existence of crossover are extended to be applicable to any two satellite ground tracks. A fast numerical algorithm named rectangle shrinking method is proposed in order to improve the computational efficiency. Based on a cycle of simulated orbit data of Topex/Poseidon(T/P) and a pass of observations from HY-2, two experiments are performed to assess the precision and efficiency of the algorithm. The results demonstrate that the rectangle shrinking method can rapidly work out all of crossovers with high precision. Another test on Envisat data validated the applicability to near polarorbit. The proposed algorithm has strong universality, not only solving the crossovers from tracks of a single satellite, but also two satellites with different inclinations. © 2017, Research and Development Office of Wuhan University. All right reserved.
Xu X.,Wuhan University |
Xu X.,Key Laboratory of Geospace Environment and Geodesy |
Zhao Y.,Wuhan University |
Reubelt T.,University of Stuttgart |
Tenzer R.,Wuhan University
Geodesy and Geodynamics | Year: 2017
We compile the GOCE-only satellite model GOSG01S complete to spherical harmonic degree of 220 using Satellite Gravity Gradiometry (SGG) data and the Satellite-to-Satellite Tracking (SST) observations along the GOCE orbit based on applying a least-squares analysis. The diagonal components (V xx, V yy, V zz) of the gravitational gradient tensor are used to form the system of observation equations with the band-pass ARMA filter. The point-wise acceleration observations (a x, a y, a z) along the orbit are used to form the system of observation equations up to the maximum spherical harmonic degree/order 130. The analysis of spectral accuracy characteristics of the newly derived gravitational model GOSG01S and the existing models GOTIM04S, GODIR04S, GOSPW04S and JYY_GOCE02S based on their comparison with the ultra-high degree model EIGEN-6C2 reveals a significant consistency at the spectral window approximately between 80 and 190 due to the same period SGG data used to compile these models. The GOCE related satellite gravity models GOSG01S, GOTIM05S, GODIR05S, GOTIM04S, GODIR04S, GOSPW04S, JYY_GOCE02S, EIGEN-6C2 and EGM2008 are also validated by using GPS-leveling data in China and USA. According to the truncation at degree 200, the statistic results show that all GGMs have very similar differences at GPS-leveling points in USA, and all GOCE related gravity models have better performance than EGM2008 in China. This suggests that all these models provide much more information on the gravity field than EGM2008 in areas with low terrestrial gravity coverage. And STDs of height anomaly differences in China for the selected truncation degrees show that GOCE has improved the accuracy of the global models beyond degree 90 and the accuracies of the models improve from 24 cm to 16 cm. STDs of geoid height differences in USA show that GOSG01S model has best consistency comparing with GPS-leveling data for the frequency band of the degree between 20 and 160. © 2017 The Authors.
Wang Z.,Wuhan University |
Li J.,Wuhan University |
Li J.,Key Laboratory of Geospace Environment and Geodesy
Cehui Xuebao/Acta Geodaetica et Cartographica Sinica | Year: 2017
Random drift error of fiber optic gyroscope is the crucial factor that influences the calculation accuracy of the attitude of airborne vector gravimetry. Modeling and compensating it can restrain this type of error significantly. Given the problem that traditional ARMA model can be only applied in the case of stable random drift, which cannot meet the need of real-time filtering, an ARIMA model (autoregressive integrated moving average) which is suitable for non-stable random drift is introduced along with the detailed procedure in this paper. The algorithm that can eliminate the constant component of original sampling sequence with real-time averaging method is also proposed as well as the real-time Kalman filtering estimation of the random drift. With the methods proposed above, the variance of random drift can be reduced by 46.5%. The analysis of Allan variance suggests that the coefficients of random drift for angle and angular speed have decreased about 50% and 40%, respectively. The results showed that non-stable random drift can be accurately characterized by ARIMA model and that online estimation of random drift can be realized by real-time average algorithm, indicating the potential to improve the calculation accuracy of the attitude of airborne vector gravimetry. © 2017, Surveying and Mapping Press. All right reserved.
Wu C.,Wuhan University |
Wu C.,Key Laboratory of Geospace Environment and Geodesy |
Wu C.,State Observatory for Atmospheric Remote Sensing |
Yi F.,Wuhan University |
And 2 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2017
Observations with lidars at Wuhan (30.5°N, 114.4°E), China, from 2010 to 2013 captured nine cases of slowly ascending humid aerosol/liquid water layers that occurred at altitudes of ~2–4 km in winter. Each of them was almost transparent initially with the backscatter ratio far less than 7.0 and depolarization ratio less than 0.03. With a slow ascent, the layer developed into a nearly opaque liquid cloud layer and then ice crystals abruptly formed at the upper edge of the cloud layer with very high liquid water content. The ice crystals likely came from water drop freezing. The freezing temperatures estimated from radiosonde measurements were −3 to −8°C. For two available long-lived (>16 h) cases, the layer was observed to always lie just below an inversion layer. The ice development on the layer was followed by rainfall. ©2017. American Geophysical Union. All Rights Reserved.
Liu X.,Hubei University |
Wei E.,Hubei University |
Wei E.,Key Laboratory of Geospace Environment and Geodesy |
Wang L.,Hubei University
Lecture Notes in Electrical Engineering | Year: 2017
The earth rotation parameters (ERP) have a strong correlation with the migration and movement of earth materials, extraterrestrial world gravity and the load deformation of solid earth. On the other hand, ERP is a very important parameter when converting the earth reference system to the celestial reference system. But the International Earth Rotation Service(IERS) and International GNSS Service(IGS) only release one ERP per day which cannot satisfy the user who need the high frequency of ERP. However, there are amounts of Global Positioning System(GPS) data which can be used to estimate ERP with high time resolution and long time span. Based on this, global uniformly distributed 40 IGS stations are selected to estimate ERP by using the data of the Day of Year(DOY) from 1 to 180 of 2015 with Bernese soft 5.0. In the first part, 24 h resolution of ERP is estimated. The precision of polar motion xp, yp can be achieved at the precision 0.289, 0.245 mas while the precision of UT1-UTC can be achieved at 0.0342 ms which are made a difference with the results of IGS. In the last part of the paper, the 2 h resolution of ERP are estimated and high frequency time series are got. The precision of high frequency polar motion xp, yp can be achieved at the precision 0.754, 0.688 mas and the precision of high frequency UT1-UTC can be achieved at 0.1050 ms which are made a difference with the results of IGS at UTC 12:00. The high frequency results have lower precision and stability compared with 24 h resolution results, but still in the acceptable range. Both the results of 24 h resolution and high frequency series have different degrees of systematic deviation. The research above can provide a reference for calculating ERP using BeiDou observations. © Springer Nature Singapore Pte Ltd. 2017.
Chen L.,Wuhan University |
Yi F.,Key Laboratory of Geospace Environment and Geodesy
Annales Geophysicae | Year: 2011
We report the average properties and small-scale variation features of the mesospheric Na and Fe layers at 30° N from extensive simultaneous and common-volume Na and Fe lidar measurements at Wuhan, China. The annual mean Na and Fe density profiles are derived in terms of an averaging method taken from an early literature. The mean Na and Fe profiles preserve the sharp gradients present in most individual density profiles near the layer bottom. Near the bottommost of the layers the mean Na and Fe scale heights are respectively -0.42 and -0.30 km. The mean layer parameters coincide well with the previous report. The Na and Fe densities in the lowest several kilometers of the layers consistently exhibit nearly the same time variations. A clear- cut distinction between the Na and Fe time variations always appears in an altitude range near 90 km. A relatively weak positive correlation between them persistently occurs also in an altitude range near 100 km. The mean increase and decrease rates for both Na and Fe are altitude dependent and have a single-peak structure. The time constant of the layer variation is ~0.07-2.0hforNaand ~0.02-1.7hforFe, suggesting that the variability is dominated by small-scale processes. However, there is also a slow net increase in each of the annual mean column abundances (Na and Fe) during night. Keywords. Atmospheric composition and structure (Middle atmosphere - composition and chemistry). © European Geosciences Union 2011.
Ma Z.,Wuhan University |
Ma Z.,Key Laboratory of Geospace Environment and Geodesy |
Ma Z.,State Observatory for Atmospheric Remote Sensing |
Yi F.,Wuhan University |
And 2 more authors.
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2010
The seasonal/annual characteristics of the high-altitude sporadic metal atom layers are presented on the basis of extensive Na and Fe lidar measurements at 30°N during the past several years. It is found that the extremely high sporadic Na (Nas) and Fe (Fes) layers above 105km occurred mostly during summer. They had long durations (a few hours) and broad layer widths (much larger than 2km). Their absolute peak densities could be comparable to or even larger than those of the corresponding main layers on a few nights. By using all the raw data profiles including sporadic layers, we have constructed the contour plots of Na and Fe densities versus month and altitude at 30°N. The Na and Fe layers both exhibit evidence for summer topside extension, which is consistent with the earlier observations for K and Ca at different latitudes. The summer topside extension of mean metal atom layers might represent a universal phenomenon that is alike for different atom species, different geographic locations and different measurement years. The extremely high sporadic metal atom layers above 105km occurring during summer give rise to the phenomenon. © 2010 Elsevier Ltd.
Chen W.,Wuhan University |
Chen W.,State Key Laboratory of Information Engineering in Surveying |
Shen W.,Wuhan University |
Shen W.,State Key Laboratory of Information Engineering in Surveying |
Shen W.,Key Laboratory of Geospace Environment and Geodesy
Journal of Geophysical Research: Solid Earth | Year: 2010
The Earth's rotation is perturbed by mass redistributions and relative motions within the Earth system, as well as by the torques from both the internal Earth and celestial bodies. The present study aims to establish a theory to incorporate all these factors perturbing the rotation state of the triaxial Earth, just like the traditional rotation theory of the axial-symmetric Earth. First of all, we reestimate the Earth's inertia tensor on the basis of two new gravity models, EIGEN-GL05C and EGM2008. Then we formulate the dynamic equations and obtain their normal modes for an Earth model with a triaxial anelastic mantle, a triaxial fluid core, and dissipative oceans. The periods of the Chandler wobble and the free core nutation are successfully recovered, being ∼433 and ∼430 mean solar days, respectively. Further, the Liouville equations and their general solutions for that triaxial nonrigid Earth are deduced. The Liouville equations are characterized by the complex frequency-dependent transfer functions, which incorporate the effects of triaxialities and deformations of both the mantle and the core, as well as the effects of the mantle anelasticity, the equilibrium, and dissipative ocean tides. Complex transfer functions just reflect the fact that decays and phase lags exist in the Earth's response to the periodic forcing. Our theory reduces to the traditional rotation theory of the axial-symmetric Earth when assuming rotational symmetry of the inertia tensor. Finally, the present theory is applied to the case of atmospheric-oceanic excitation. The effective atmospheric-oceanic angular momentum function (AMF) χeff = χeff1 + iχeff2 for the present theory is compared with the AMF χeff sym = χeff1 sym + iχeff2 sym for the traditional theory and the observed AMF χobs = χ1 obs + iχ2 obs; we find that the difference between χeff and χeff sym is of a few milliseconds of arc (mas) and can sometimes exceed 10 mas. In addition, spectrum analyses indicate that χeff is in good agreement with χeff sym and, further, show an increase of coherency with χobs especially in the low-frequency band. The obvious advantage of χeff in the low-frequency band with respect to χeff sym is the critical support of the present theory. However, still better performance of our theory can be expected if the models of the mantle anelasticity and oceanic dynamics were improved. Thus we conclude that the traditional Earth rotation theory should be revised and upgraded to include the effects of the Earth's triaxiality, the mantle anelasticity, and oceanic dynamics. The theory presented in this study might be more appropriate to describe the rotation of the triaxial Earth (or other triaxial celestial bodies such as Mars), though further studies are needed to incorporate the effects of the solid inner core and other possible influences. Copyright 2010 by the American Geophysical Union.
Wen Y.,Hubei University |
Wen Y.,Key Laboratory of Geospace Environment and Geodesy |
Wen Y.,University of Glasgow |
Li Z.,University of Glasgow |
And 4 more authors.
Journal of Geophysical Research: Solid Earth | Year: 2012
On November 14th 2001, a Mw 7.8 earthquake occurred in the Kokoxili region of northern Tibet. The earthquake ruptured more than 400 km along the western part of the Kunlun fault with a maximum of 8 m left-lateral slip. In this paper, we use a multitemporal Interferometric SAR (InSAR) time series technique to map the postseismic motion following the large Kokoxili event. SAR data from Envisat descending orbits along five adjacent tracks covering almost the entire ruptured fault length are used to calculate the displacement time series for a period between 2 and 6 years after the earthquake. A peak-to-trough signal of 8 cm in the radar line of sight is observed during the period between 2003 and 2008. Two different mechanisms are employed to explain the observed surface displacements, namely afterslip and viscoelastic relaxation. The observations inverted for afterslip on and below the coseismic rupture plane shows that the maximum slip in the afterslip model is 0.6 m. The position of the maximum postseismic slip is located in the middle of two relatively high coseismic slip patches, which suggests that afterslip is a plausible mechanism. Models of viscoelastic stress relaxation in a Maxwell half-space give a best fitting viscosity for the mid-to-lower crust of 2-5 × 1019 Pa s, and the principal postseismic relaxation process is due to viscous flow in the lower crust to upper mantle. However, the InSAR observations are incapable of distinguishing between localized (afterslip) and distributed (viscoelastic relaxation) deformation. And the lowest misfits are produced by mixed models of viscoelastic relaxation in the mantle below 70 km and afterslip in the crust. Modeling of viscoelastic relaxation in a Maxwell half-space, and also a mixed mechanism model, enables us to place an effective viscosity of 2 × 10 19 Pa s on the lower crust to mantle of northern Tibet. © 2012. American Geophysical Union. All Rights Reserved.
Ping P.,Wuhan University |
Zhang Y.,Wuhan University |
Zhang Y.,Key Laboratory of Geospace Environment and Geodesy |
Xu Y.,Wuhan University
Journal of Applied Geophysics | Year: 2014
In order to conquer the spurious reflections from the truncated edges and maintain the stability in the long-time simulation of elastic wave propagation, several perfectly matched layer (PML) methods have been proposed in the first-order (e.g., velocity-stress equations) and the second-order (e.g., energy equation with displacement unknown only) formulations. The multiaxial perfectly matched layer (M-PML) holds the excellent stability for the long-time simulation of wave propagation, even though it is not perfectly matched in the discretized M-PML equation system. This absorbing boundary approach can offer an alternative way to solve the problem of the late-time instability, especially for anisotropic media, which is also suffered by the convolutional perfectly matched layer (C-PML) that is supposed to be competent to handle most stable problems. The M-PML termination implementation in the first-order formulations is well proposed. The common drawback of the implementation of the first-order M-PML formulations is that it necessitates fundamental reconstruction of the existing codes of the second-order spectral element method (SEM) or finite element method (FEM). Therefore, we propose a nonconvolutional second-order M-PML absorbing boundary condition approach for the wave propagation simulation in elastic media that has not yet been developed before. Two-dimensional numerical simulation validations demonstrate that the proposed second-order M-PML has good performances: 1) superior efficiency and stability of absorbing the spurious elastic wavefields, both the surface waves and body waves, reflected on the boundaries; 2) superior stability in the long-time simulation even in the isotropic medium with a high Poisson's ratio; 3) superior efficiency and stability in the long-time simulation for anisotropic media. This method hence makes the SEM and FEM in the second-order wave equation formulation more efficient and stable for the long-time simulation. © 2013 Elsevier B.V.