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Is the Chandler Period Stable?

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Science China Chemistry 1994年第1期37卷 84-93页

作者：高布锡 institute of geodesy and geophysics Academia Sinica Wuhan 430077 PRC

The problem on the Chandler period is an unsolved one. Several authors suggested a hypothesis that the Chandler wobble is only one free period which slightly changes in time and is amplitude-dependent. In this paper, we shall examine the hypothesis more rigorous than that which has been carried yet. A new deconvolution method for Fourier transform is suggested. Using this method, the polar motion data since 1900 are analysed and the varying process of the Chandlerian period and amplitude are given. The analytical results show that the Chandler period is not stable and is indeed amplitude-dependent. The probable explanation for this phenomenon is that it might be caused by non-equilibrium response of the ocean.

关键词： Chandler period amplitude-dependent deconvolution method.

Detection of spheriodal free oscillation excited by Peru 8.2 M_(s) earthquake with five international superconducting gravimeter data

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Science China Earth Sciences 2005年第1期48卷 123-133页

作者： LEI Xiang'e XU Houze SUN Heping Key Laboratory of Dynamic geodesy Institute of Geodesy and Geophysics. Chinese Academy of Sciences Wuhan 430077 China Key Laboratory of Dynamic Geodesy Institute of Geodesy and Geophysics. Chinese Academy of Sciences Wuhan 430077 China Key Laboratory of Dynamic Geodesy Institute of Geodesy and Geophysics. Chinese Academy of Sciences Wuhan 430077 China

In this paper, authors obtain the spectral peaks of the earth free oscillation and check all normal modes from 0S0 to 0S48 accurately, with the Fourier analysis and the maximum entropy spectrum method dealing jointly with six groups of the observational residual data from five international superconducting gravimeter stations. By comparing the observational results in this paper with three former groups of observations or models, authors notice an extra discrepancy between two observational 0S2 modes excited separately by Peru earthquake and Alaska earthquake, which probably mirrors the anisotropy of the Earth's inner core. The analysis on the splitting 1S2 mode shows that the asymmetric factor of rotationwise spectral splitting is possible to be different from that of anti-rotationwise spectral splitting.

关键词： 8.2 Ms Peru earthquake, detection of Earth free oscillation, observation of superconducting gravimeter,anisotropy of earth's inner core.

Improved retracking algorithm for oceanic altimeter waveforms

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Progress in Natural Science:Materials International 2009年第2期19卷 195-203页

作者： Lifeng Bao,Yang Lu,Yong Wang institute of geodesy and geophysics,Chinese Academy of Sciences,wuhan 430077,China [a]institute of geodesy and geophysics Chinese Academy of Sciences Wuhan 430077 China

Over the deep oceans without land/ice interference,the waveforms created by the return altimeter pulse generally follow the ocean model of Brown,and the corresponding range can be properly determined using the result from an onboard tracker. In the case of com-plex altimeter waveforms corrupted due to a variety of reasons,the processor on the satellite cannot properly determine the center of the leading edge,and range observations can be in error. As an efficacious method to improve the precision of those altimeter observations with complex waveforms,waveform retracking is required to reprocess the original returning pulse. Based on basic altimeter theory and the geometric feature of altimeter waveforms,we developed a new altimeter waveform retracker,which is valid for all altimeter wave-forms once there exists a reasonable returning signal. The performances of the existing Beta-5 retracker,threshold retracker,improved threshold retracker,and the new retracker are assessed in the experimental regions (China Seas and its adjacent regions),and the improvements in the accuracy of sea surface height are investigated by the difference between retracked altimeter observations and ref-erenced geoid. The comparisons denote that the new algorithm gives the best performance in both the open ocean and coastal regions. Also,the new retracker presents a uniform performance in the whole test region. Besides,there is a significant improvement in the short-wavelength precision and the spatial resolution of sea surface height after retracking process.

关键词： Altimetry Waveform retracking Sea surface height

Changes of Urban Wetland Landscape Pattern and Impacts of Urbanization on Wetland in wuhan City

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Chinese Geographical Science 2008年第1期18卷 47-53页

作者： WANG Xuelei NING Longmei YU Jing XIAO Rui LI Tao institute of geodesy and geophysics Chinese Academy of Sciences Wuhan 430077 China

In this study,remote sensing data of wuhan City,Hubei Province,China in 1996-2001 were selected to ex-tract wetland landscape *** landscape indices were used to evaluate the changes of landscape pattern within the five years,including patch number,patch density,patch fractal dimension,landscape diversity,dominance,evenness,and fragmentation ***,transformation probabilities of wetland landscapes into non-wetland land-scapes were calculated based on Markov Model,and on these grounds the relationship between changes of wetland landscape pattern and urban construction was *** results showed that fragmentation degree of all wetland types increased,lake area declined,and dominance of natural wetland *** reasons for these results were mainly because of urban *** to the features of abundant wetland in wuhan City,we suggested that protection of wetland landscape should cooperate with urban construction,which means wetland should become im-portant part of urban landscape.

关键词： wetland landscape urban wetland wetland protection wuhan City

Digital Extraction of Altitudinal Belt Spectra in the West Kunlun Mountains Using SPOT-VGT NDVI and SRTM DEM

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Journal of Mountain Science 2010年第2期7卷 133-145页

作者： XIAO Fei LING Feng DU Yun XUE Huaiping WU Shengjun institute of geodesy & geophysics Chinese Academy of Sciences Wuhan 430077 China

In this paper, a digital identification method for the extraction of altitudinal belt spectra of montane natural belts is presented. Acquiring the sequential spectra of digital altitudinal belts in mountains at an acceptable temporal frequency and over a large area requires extensive time and work if traditional methods of field investigation are to be used. Such being the case, often the altitudinal belts of a whole mountain or the belts at a regional scale are represented by single points. However, single points obviously cannot accurately reflect the spatial variety of altitudinal belts. In this context, a digital method was developed to extract the spectra of altitudinal belts from remote sensing data and SRTM DEM in the *** Kunlun Mountains. By means of the 4km resolution SPOT-4 vegetation 10-day composite NDVI, the horizontal distribution of altitudinal belts were extracted through supervised classification, with a total classification accuracy of 72.23%. Then, a way of twice-scan was used to realize the automatic transition of horizontal maps to vertical belts. The classification results of remote-sensing data could thus be transformed automatically to sequential spectra of digital altitudinal belts. The upper and lower lines of the altitudinal belts were then extracted by vertical scanning of the belts. Relationships between the altitudinal belts based on the montane natural zones concerning vegetation types and the geomorphological altitudinal belts discussed. As a tentative method, were also the digital extraction method presented here is effective at digitally identifying altitudinal belts, and could be helpful in rapid information extraction over large-scale areas.

关键词： Altitudinal belt spectra Kunlun Mountains NDVI Digital extraction

Check of Earth's free oscillations excited by Sumatra-Andaman Large Earthquake and discussions on the anisotropy of inner core

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Science China Earth Sciences 2007年第6期50卷 909-917页

作者： HSU HouTse Key Laboratory of Dynamic geodesy Institute of Geodesy and GeophysicsChinese Academy of SciencesWuhan 430077China

Sumatra-Andaman Large Earthquake on Dec. 26,2004 generated not only the Indian Ocean Tsunami but also the Earth's free oscillations (EFO). The signals of Earth's free oscillations were perfectly re-corded by the superconducting gravimeter C0-32 at wuhan station in China. After the pre-treatment and spectral analysis on the observational data from wuhan station,we obtained more than ninety EFO modes including 42 fundamental modes,2 radial modes and 49 harmonic modes. On the basis of the discussions on some observed harmonic modes and abnormal splitting phenomena,we considered that the real rigidity might be lower than the theoretical prediction of PREM model in the inner core and however the anisotropy of compressive wave was brightly higher than the present estimations in the inner core. This suggested that the anisotropy of the inner core could be much more complicated than our present understanding,and there might be some new geophysical phenomena in the formation process of the inner core.

关键词： Sumatra-Andaman Large Earthquake Earth’s free oscillations superconducting gravimeter abnormal spectral splitting anisotropy of inner core

Atmospheric gravity Green's functions

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Chinese Science Bulletin 1997年第20期42卷 1712-1719页

作者： SUN HepingLaboratory of Dynamic geodesy, institute of geodesy and geophysics, Chinese Academy of Sciences, wuhan 430077, China Laboratory of Dynamic geodesy Institute of Geodesy and Geophysics Chinese Academy of Sciences Wuhan China

THE observational accuracy of the superconducting gravimeter has now reached 0.1 μGal levelor better, with characteristics of the low noise, high sensitivity and better continuity and sta-bility. It will play an important part in the study of the change in (non-) tidal gravity signals,especially in the application of the geophysics and geodynamics. However, the instrument

关键词： air pressure Green’s functions atmospheric gravity admittance.

LOADING CORRECTION OF OCEANIC TIDES IN THE MAINLAND OF CHINA

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Science China Chemistry 1989年第5期32卷 618-630页

作者：许厚泽毛伟健 institute of geodesy and geophysics Academia Sinica Wuhan

The response of radial inhomogeneous elastic earth under the action of oceanic tides is studied by use of the combination of convolution integral with spherical harmonic expansion. In the meantime, the effect of oceanic tides on gravity, tilt and strain in the mainland of China is estimated, and the accuracy of loading correction is also briefly analysed. Results show that the loading effect along the coast of China cannot be neglected, for gravity it is about 5％ of body tides, for tilt it reaches the same magnitude as body tides, for strain about 50％. The result obtained can be used to provide the tidal correction for various precision geodesy. The proposal method may also be applied to the effect of other surface loading except oceanic tides.

关键词： earth tides loading correction interaction between earth and ocean tides loading Love numbers Green function.

Determination of vertical gradient of gravity anomaly with topographic data

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Chinese Science Bulletin 1999年第11期44卷 1029-1034页

作者： ZHANG Chijuninstitute of geodesy and geophysics , Chinese Academy of Sciences , wuhan 430077 , China institute of geodesy and geophysics Chinese Academy of Sciences Wuhan China

The role of vertical gradient of gravity anomaly in the solution and interpretation of geological and geophysical problems on superficial layer is increasingly evident. However, it is difficult to directly observe the vertical gradient of gravity anomaly in mountainous area. Moreover,aerial and satellite gravity gradient measurments have not been put into practice up to date *** vertical gradient of gravity anomaly is calculated by use of topographic data and several problems concerned are investigated and discussed. It turns out in theory and practice that the relative error of the vertical gradient determined with the method is only 5%, and when the vertical gradient of gravity anomaly reaches the maximum 1 000 ns-2 the error is only 50 ns-2. In addition, how to divide ring zones in calculation and the errors caused by the inaccuracy of landform elevation and rock density has been quantitatively analysed.

关键词： vertical gradient gravity anomaly topographic mass geoid.