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11 June 2011, Volume 31 Issue 2
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. 2011, 31(2): 1-3.
Using 102 GRACE monthly solutions, the gravity precursor caused by
Ms9.0 strong earthquake occurred on 11 March,2011 near the east coast of Honshu, Japan, had calculated and co-seismic gravity changes by using fault models from USGS with upword technology, then analyzed and compared both the results with each other.
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. 2011, 31(2): 4-8.We have chosen fourteen gPhone spring gravimeters of China Gravity Network to form two observation sections, and analyzed the observation records(in March 1 to10) before the Ms9.0 earthquake near Japan east coast. The results indicate that a kind of belllike of abnormal gravity disturbance occurring at all littoral observation stations and the magnitude of abnormal gravity disturbance attenuate with the distance from epicenter.
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. 2011, 31(2): 9-11.After Ms9.0 earthquake in Japan, the data of 17 gPhones and GS15 continuous relative gravimeters 3 days before the huge earthquake were analyzed. It is shown that there were some unknown gravity anomalies of gPhone and GS15 in Wushi, Zhengzhou and Chengdu station. The preliminay analysis shows that the records at Chengdu and Wushi stations had the type of spindle gravity disturbance
16 hours before the Ms7.3 earthquake of Japan in 2011-03-09. And the gravimeter’s records in Zhengzhou station had the cylindrical gravity disturbance not only before the Ms7.3 earquake but also the Ms9.0 earquake in Japan. Although the tropical cyclones, the impact of human disturbance and other factor can be ruled out, the relationship between the gravity disturbance and the earthquake in Japan and the data of even more time scale are remained to be further analyzed. -
. 2011, 31(2): 12-16.The dynamic environment of the Ms9.0 earthquake off the east coast of Honshu,Japan preliminarily discussed by using Japanese lacal geological structure,plate tectonics,post and cosmemic displacement at GPS stations in Japan area,focal mechanisms and so on.It can be compresses judged that the earthquake might happen in this way that the Pacific plate dives and compresses to below Eurasian plate, the stress between Pacific plate and Eurasian plate accumulates along with time, when the stress/strain intensity exceeds friction intensity or stress intensity of rock,thus the fault which at the depth of 10-20 km in the Eurasian plate became a thrust fault whose dip angle less than WadatiBenioff belt’s, and the earthquake occared.This earthquake makes a fault zone with about 600 km length and nearly the same strike as WadatiBenioff’s.The fault zone located at the boundary between Pacific plate and Eurasian plate close to southnorth strike.
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. 2011, 31(2): 17-22.From the repeted gravimetry data of Dianxi Experimental Field from 2005 to 2009, local differential and cumulate gravity change pictures have been obtained. The study results from the data are as follows.1)The dynamic evolvement pictures of gravity field can generally reflect the movement state of the crustal substance before earthquake. Shortterm local effect is obviously reflected by the
differential dynamic change, while local tectonic movement and fault structure effect by the cumulate dynamic change. 2)A positive and negative transitional gravity gradient zone across the epicenter along almost northsouth direction appeared two years before the earthquake, and a symmetrical fourquadrant distribution of the gravity change appeared too around the epicenter half year before the earthquake. They were the prominent gravity precursor marks of the Yaoan earthquake. 3)Durative positive gravity change appeared in the west to the epicenter three years before the earthquake. It was helpfull for energy accumulation. 4)The relatively highlow fourquadrant distribution picture may reflect that there exist a shearing stress. So we put forward a ‘lock in shearing force mode’ for the precursor model. -
. 2011, 31(2): 23-27.We have detected the anomalies of groundbased GPS TEC data by using Kalman filtering. We made a concrete discussion of approaches for carrying out Kalman filtering, and practically applied it to an analysis of 2dimensional TEC data. Considering SolarTerrestrial environmental factors such as solar activity, magnetic storms and disturbances, we analyzed the TEC anomalies processed with Kalman filtering, discussed the creditability and the exciting mechanism of the anomalies and confirmed that these distinct TEC anomalies occurred on May 9 and 10 were linked to Wenchuan Ms8.0 earthquake impending and would be one of the seismoionospheric precursors. Meanwhile, we proved Kalman filtering practical and effectual in processing of ionospheric TEC anomalies.
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. 2011, 31(2): 28-31.On 12 May 2008 at 06:28UT a major earthquake of Mw 7.9 struck Wenchuan County(31.0°N,103.4°) in China. Occultation profiles derived from FORMOSAT3/COSMIC between 2007 and 2010, were used to investigate the ionoshperic precursor of the Wenchuan earthquake area and magnetic conjugate area. Relative to the NmF2(F2peak electron density) of 6-17 days(25 April-6 May) prior to earthquake, it has been determined that near the epicenter the NmF2, decreased during 04:00-08:00UT(12：00-16：00LT) within 5 days(7-11 May) prior to the earthquake,and the maximum deviation was about (2-4)×10 5 el/cm 3. Furthermore we choose the NmF2 data derived from 3 years(12：00-14：00LT ,7-11 May,2007-2010, except 2008) as background value. The NmF2 5 days prior to earthquake was lower than background value. The maximum deviation was about (2-4)×10 5 el/cm 3. And there was similar phenomenon detected in magnetic conjugate area.
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. 2011, 31(2): 32-37.In order to detect surface deformation caused by the Wenchuan Ms8.0 earthquake, the twopass differential interferometric synthetic aperture radar (DInSAR) method is employed for analyzing the ground displacement due to the main shock by using both the ALOS satellite PALSAR Lband SAR data and GPS data. We computed the coseismic interferogram and the deformation field with spatial resolution of 15 m in an area of about 83 194 km 2. Moreover, the accuracy of deformation values derived interferometrically is evaluated by taking the GPS measurements at 16 sites as the reference data. The results show that the two types of measurements are in good agreement, except that there exist remarkable discrepancy in the nearfault areas.
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. 2011, 31(2): 38-43.The destructive ChiChi earthquake occurred in 1999, which had a full impact on the stress state in Taiwan. The strain rates based on the GPS data before and after the 1999 ChiChi earthquake in the period of 1990-1995 and of 2003-2005 were estimated respectively. The computed results show that the pattern of strain rate distribution in Taiwan is not changed much before and after the ChiChi earthquake. The highest value of the maximum principle strain rates is located on the Coastal Range, which orientated obliquely to the trend of Taiwan. Deceasing rapidly from east to west, the values of principle compressive strain rates are less than those of extensive strain rates on the Central Range, behaving on tensile strain state there. And principle compressive strain rates are very small on the western Coastal Plain. At the same time, the orientations of principle strain rates are agreement with those of Pand Taxis in focal mechanisms in Taiwan. The high value of the maximum shear strain rates is located on the Coastal Range where the surface dilatation rates are negative, and the absolute value is highest in Taiwan. However surface dilatation rates are positive on both the northern and southern sides of the Central Range. The computed results demonstrate that the Coastal Range is the central collision zone between Taiwan and Luzon arc, and material escapes toward two directions of NE and SW, respectively. In the period of 2003-2005, after 4 years since the ChiChi earthquake, the maximum shear strain rates become much larger than those in the period of time before the mainshock which may be resulted from the changes of the physical properties of the medium in focal regions, also suggesting that the medium did not resume to the state before the ChiChi earthquake,yet.
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. 2011, 31(2): 44-47.The maximum principal stress and shear in depth 15 km of earth crust in Fenwei basin are computed by using GPS data observed from 2004—2007. The computed results show the following situatuins.1) The distribution of maximum principal stress variation are not uniform that the principal stress increased in mountain area and decreased in basin area. 2)The shear decreased in BaojiXianyang and increased in TangyuPucheng.
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. 2011, 31(2): 48-52.The main states of borehole strain measurement, a variety of earthquake cases were analyzed. The results show that the borehole strain anomalies before earthquakes in most cases were located in the region far from the source, while near the source region significant precursor were rarely observed. This fact, on the one hand, may reflect the lack of the borehole strain sites and uneven distribution of them; the other hand, may reflect the mechanical properties of the focal region, that in a focal region before the rupture there are high strain accumulation and small deformation.
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. 2011, 31(2): 53-55.From the results combined with geology, geophysics and fine positioning of small earthquakes,
the fault segment parameters were selected reasonably and the a certain scope of differences in Xiaojiang fault segments was set,
and the deformation of fault segments was analyzed using GPS data. The analyzing results show that the fault parameters have relatively big impact on the inversion results, and the calculated dislocation difference is up to 3mm. In the case of difficultly defining fault parameters, the
processing with scan line method could more accurately reflect the deformation of the fault, to a certain extent. -
. 2011, 31(2): 56-59.The Wenner and Diple devices of high-density resistivity method are used for exploring HuangzhuangGaoliying fault. Through data processing and analysis, the results show that the distribution, strike and dip of the fault are consistent with the results of shallow seismic exploration and trench. The study indicates that the application of highdensity resistivity method to explore the buried fault has a good prospect.
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. 2011, 31(2): 60-65.The GRACE Earth’s gravitational field complete up to degree and order 120 is
recovered using the improved energy conservation principle and on the basis of different intersatellite ranges. The simulative results are as follows: Firstly, based on the same accuracy indexes of GRACE key payloads, while recovering the longwavelength Earth’s gravitational field (L≤20), with the increase of intersatellite ranges (110 ~ 330 km) little by little, cumulative geoid height errors will be improved gradually. At degree 20, the accuracy of cumulative geoid height is at the level of 0.052 cm based on 110 km intersatellite range, and accuracies are 1.156 times and 1.209 times improved as using 220 km and 330 km intersatellite ranges. Secondly, while recovering the middlewavelength Earth’s gravitational field (100≤L≤120), at degree 120, the accuracy of cumulative geoid height comes to 13.052 cm based on 110 km intersatellite range, and accuracies are 1.327 times and 1.970 times degraded as using 220 km and 330 km intersatellite ranges. Lastly, intersatellite range designed as 220±50 km can effectively suppress the decrease of the accuracies of longwavelength and middlewavelength Earth’s gravitational field induced by improper range. -
. 2011, 31(2): 66-70.The dynamical method based on the precision orbits and rangerate data of GRACE for recovering gravity field model is discussed, and the gravitational potential coefficients and the satellite’s initial state error can be estimated simultaneously with this algorithm. The gravity field models are recovered with the combined observations with different orbits accuracy and different sampling rate
rangerate of GRACE, finally the accuracy of gravity field model recovery are analyzed. The simulated results show that the accuracy of accelerometer from (1.0×10 -10-1.0×10 -9 m/s 2 is suitable for the combined recovery algorithm,as the rangerate with 1 μm/s accuracy , satellite’s position with 2-3 cm accuracy, and satellite’s velocity with 0.1-0.5 mm/s accuracy. When the accuracy of rangrate is improved from 1 um/s to 0.1 um/s, the accuracy of recovered model is improved correspondingly; the accuracy of the recovered model based on same accuracy observations with sampling rate of 5 seconds is the hightest accurate. -
. 2011, 31(2): 71-75.High accuracy intersatellite microwave ranging system is one of the most important key loads of GRACE mission, and the technology of simulation is the necesary link for the study of GRACE mission. We simulated the base phase for ranging system, built the mathmatic model of twoway phase measurements, twoway range measurements and dualband twoway range measurements, accomplished the conversion from the base phase data to the baisedrange measurments, and the results of the simulation and preprocessing are showed.
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. 2011, 31(2): 76-79.The empirical mode decomposition method is applied to data processing of earth tide observations. FFT and Venedikov harmonic analysis are used to verificate the decomposition results. The conclusion is that five feature signals are found from the original signal, they are highfrequency signal, semidiurnal tide, diurnal tide,lowfrequency signal and the trend of the observation data.
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. 2011, 31(2): 80-83.By removing the typical interference signals and picking up the trend from the observations
the signals can be decomposed effectively with the EMD method.So the EMD method is an adaptive highpass filtering method without enacting bandwidth beforehand and fits for groundwater data decomposition and analysis. -
. 2011, 31(2): 84-88.On the texts of the vertical, horizontal rotary and torsional harmonic forced vibration by exciter, dynamic property of subsoil for petrochemical engineering project are measured under open and embedded conditions of concrete testing block. On the basis of testing data, the dynamic parameters of subsoil such as dynamic stiffness, dynamic stiffness coefficient, damping ratio of 1st vibration mode and mass of vibration soil are calculated. The experimental results show that the dynamic parameters under embedded condition are bigger than those under open condition. For resonance frequency of 1st vibration mode, the vertical is biggest, horizontal rotary is bigger and the torsional is smallest.It shouldn’t be ignored that the mass of vibration soil is more than total mass of testing concrete block and exciter.In the course of forced vibration, the vibration frequency of concrete testing block is not consistent with the running frequency of exciter.
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. 2011, 31(2): 89-93.Through the analysis of the geometric sense of vector algebra, vector crossproduct is used to determine the topological relationship between point and polygon. A horizontal vector is made based on the determination of point and then the cross multiplication between it and each vector of the polygon is made. Futhermore, the signal of kcomponent is employed to determine the spatial relationship between point and polygon. An appropriate weight value is given to a bare possibility. The parity of the weight sum is to decide the spatial relationship between point and polygon. The intersectant point is avoided to be computed, and some special cases are resolved with geometric equivalence. Software implementation verifies the high robustness and efficiency of this algorithm.
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. 2011, 31(2): 94-98.Double difference carrier phase observations have good smoothness, because they eliminate the common errors.After differencing between adjacent epochs in double difference observation sequences,cycle slips act as gross errors.When using Chebyshev polynomial for fitting double difference observations, taking into account of the thoughts of robust estimation,the order of Chebyshev polynomial fitting and the length of fitting arc, cycle slips detection and correction for singlefrequency GPS data based on sliding window of
Chebyshev polynomial fitting of robust estimation was proposed. L1frequency carrier phase data with sampling interval of 60 seconds and 15 seconds were applied for the test.Test results show that this algorithm can effectively detect multiepoch cycle slips and continuous cycle slips, and cycle slips can be accurately repaired. -
. 2011, 31(2): 99-101.On the sasis of AutoCAD 2008，the parametrization modeling system of pipe was realized by using the ObjectARX SDK 2008 in the environment of .NET 2005. The structure of the data files, the key technologies and basic functions of the system are introduced.
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. 2011, 31(2): 102-106.The coordinate transformation between different coordinate systems includes four parameters: two translations, one rotation, and one scale paramete.When there is illcondition transformation matrix, the common points’ little errors may cause big fluctuation of parameters’ results. Considering the unity between coordinate transformation model and centre of gravity datum of free net adjustment,
the two translation parameters may be elimineted under auxiliary condition. This method is validated with an example. -
. 2011, 31(2): 107-110.The method of zenith path delay (ZPD) estimation based on precise point positioning (PPP) is introduced. Besides,the effect of various factors on ZPD estimation’s accuracy is analyzed from the view of mapping function selection, satellite cutoff elevation angle setting, the use of precise ephemeris and clock errors. Accordingly, relatively better mode and data processing strategy are determined. Large amount of experiments and analysis show that ZPD with relatively high accuracy can be obtained by use of both NMF and GMF, and the difference between them is little. Moreover, 5° -10° in the cutoff elevation angle is more favorable to ZPD estimation. In addition, the ZPD calculated with rapid precise ephemeris and clock errors or with predicted precise ephemeris and rapid precise clock errors are of the similar accuracy as that derived from post precise ephemeris and clock errors. However, accuracy of ZPD obtained by adopting extrapolated ultrarapid precise ephemeris and rapid clock errors slightly decreases but is still relatively high.
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. 2011, 31(2): 111-116.Aiming at the accuracy of the GPS satellite clock bias service the realtime precise point positioning (PPP) currently, a method for realtime estimating the satellite clock bias based on the basis of IGU (IGS Ultrarapid) predicted orbits is put forward.
In this method the undifferenced carrier phase observations of global reference stations is used to estimate the realtime clock bias. Numerical calculation results show that most of deviations between the estimated satellite clock bias and the IGS final product are less than 0.3 ns, and the average accuracy is better than 0.2 ns; with the real-time estimated satellite clock bias, the static accuracy of PPP can achieve 1-2 cm, but also the accuracy of zenith tropospheric delay (ZTD),can reach to millimeter level. -
. 2011, 31(2): 117-120.The multipath error and the ionospheric delay are used as the evaluation indicators to analyze the GPS data of Amery Ice Shelf ,ice sheet, Nella fjord, Larsemann Hills and some IGS stations in Antarctic. The following conclusions can be drawn.1)At the same site, the multipath error of L2 is always larger than L1.2)Multipath error differs from each other according to the different circumstances in Antarctic area.3)Different latitudes and intensity of solar activity are the two main factors which influence the ionospheric delay.
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. 2011, 31(2): 121-124.In the field of surveying and mapping, the multipath effect is the main factors of reducing positioning accuracy. Following the the general principles of multipath effect model, the sea environment multipath effect model is established preliminarily, and the validity of the model is proved through the simulated data.
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. 2011, 31(2): 125-128.The necessity of sample data preprocessing for BP neutral networkbased GPS elevation fitting is analyzed, and three
preprocessing methods are given, which are normalization, centralization and standardization. In order to obtain an optimal model,
a data preprocessing layer is added in the network topology and then the three different methods are applied in training the neutral networks.
Through the comparative analysis of the results derived with different preprocessing methods and with quadratic surface model, it is found that the influence of three data preprocessing methods on BP neutral networkbased GPS elevation fitting is different, and the accuracy with BP neutral network method is higher than that with quadratic surface model. -
. 2011, 31(2): 129-132.The existence of point cloud registration error must cause error propagation of multi stations registration. Aiming at the closed error of point cloud registration of terrestrial 3D laser scanning, a distributing approach of closed error based on the theory of surveying error adjustment is proposed. Firstly, the parameters of coordinate transformation and their accuracy of each adjacent station are worked out
according to the indirect adjustment theory. Secondly, the closed error is adjusted to each station by variance proportion. Through the experiment of point cloud registration of multi stations, the results indicate that the approach improves the point cloud registration accuracy. -
. 2011, 31(2): 133-136.The stations constrained on international terrestrial reference frame (ITRF)
are usually chosen with some random and uncertainties, which directly affects the precision and reliability of ITRF. A system method to select stations on the rigid plate was summarized.Firstly, analysing the quality of data at each station,the second step is rigorous selection of the stations 7 parameters transformation. The third step is supervision clustering to eliminate some stations that is largely affected by local diastrophism and finally,we make stations wellproportioned spacial distribution. With by using the method, IGS frame station can be chosen in GNSS data processing to establish high precision terrestrial reference frame. -
. 2011, 31(2): 137-141.The cloud point registration is a peoblem of three dimensionaldatum transformation with big rotation angle.As the fitting coordinates of sphere target’s centers in the two sets of scanning coordinate systems are both influnenced by errors, we introduce constrained total leastsquares (CTLS) method for cloud point registration. We established the errorsinvariables(EIV) model with the constraints and revised the observed vector and the coefficient matrix.The calculated example has proved that the more reasonable transformation model and the more accurate parameter solution can be given with CTLS methods as compared with the CLS methods.
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. 2011, 31(2): 142-144.From the strong motion data at the first station which received seismic signal of a certain event downloaded from KIKnet of Japan, whose magnitude are more than 4 and epicentral distance range from 30 km to 100 km,we computed the epicentral diatance with the combined B-Δ method and Voronoi polygon method. The results show that with the combined method and
the calculated epicentral distance can be more accurately than with only B-Δ method as consune the same location time. -
. 2011, 31(2): 145-148.A highaccuracy horizontal benchmark standard installment is very important for verification of instrument of surveying and metering.At present， the debugging of highaccuracy horizontal benchmark installment is menmade，which wastes much time and with large error. A method of automatically debugging is presented，and the application of micronsized micro translation stages to leveling process and appraisal of measurement system precision have been elaborated.
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. 2011, 31(2): 149-152.The principle of the digital electrostatic feedback system developed with computer technology and control algorithm of digital PID(Proportion Integral Derivative) control is systematically introduced. In addition, it is the first time in China that this new system is successfully used in the update of LaCoste & Romberg (LCR) ET20 gravimeter. The experimental results of the LCR ET20 gravimeter with the new system installed show that problems of analog electrofeedback system, such as the difficulty to adjust linearity and the worse longterm stability, are basically resolved. Moreover, the precision of gravimeter has increased.
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. 2011, 31(2): 153-155.The Global positioning system (GPS) is the primary technology of The Crustal Movement Observation Network of China(CMONOC).
With the completion of the network project construction and the operation of unattended GPS station, we have designed the remote monitoring system of unattended GPS station for remote by monitoring and the management of GPS station.Managers can use the system for realtime monitoring station’s risks, identify and solve the problems in realtime. This system can be not only adapted to a single station, but also adapted to standard network, the regional network and other network environments. -
. 2011, 31(2): 156-159.The utilization of PC server in environment monitoring network faces some troublesomes, such as high cost, large size, difficult movement and annoying software installation. Seeing that, a ZigBee gateway server based on microprocessor STM32F101R8 and CGI technique is designed and implemented. The gateway server adopts module chip W5100 with hardware embedded TCP/IP protocols, and has a variety of hardware interfaces like UART/SPI/I\+2C/USB and a disassembled U disk with system application program. The gateway server has parameters of environmental monitoring issued by the embedded web, users can remotely control the sensor nodes via the web. The test results show that the server compared with the PC server, is of low cost, high reliability and easy operation. Therefore it can meet the requirements for environmental monitoring.
