15 April 2015, Volume 35 Issue 2
-
Select all|
-
jgg. 2015, 35(2): 183-185. https://doi.org/10.14075/j.jgg.2015.02.001
Bernese Software is modified in order to process the data received from the BeiDou Satellite. The BDS and GPS observations of 13 stations in the world from 23 to 29 July, 2013, are processed with Precise Point Positioning and relative positioning modes respectively, and then the results are analyzed. The results verify that there is a centimeter difference in Precise Point Positioning between GPS and BDS, and a millimeter difference in relative positioning mode.
-
jgg. 2015, 35(2): 186-189. https://doi.org/10.14075/j.jgg.2015.02.002
JASON\|2, which was launched on June 20, 2008, has been in operation for more than 5 years. As the processor of T/P and JASON\|1 satellite, the radial accuracy of the JASON\|2 orbit must be better than 1.5 cm, in order to continue the altimeter observations of T/P and JASON\|1 satellite. In this work, the antenna phase center variation of JASON\|2, based on residuals of GPS ionosphere\|free observations from January 1, 2012 to December 31, 2012, is modeled. The accuracy of the precise orbit of JASON\|2 achieved with the reduced dynamic method is assessed by comparison with the precise orbit ephemeris (POE) from JPL, orbit overlaps, and post\|fit residuals. Results show that strategies used by this paper can improve orbit accuracy and that the orbits achieved are stable and reliable. The 3D RMS of JASON\|2 orbit difference is about 2.5 cm and the RMS of radial direction of JASON\|2 reaches 1.0 cm.
-
jgg. 2015, 35(2): 190-193. https://doi.org/10.14075/j.jgg.2015.02.003
A high\|rate single\|epoch software using GPS double difference, WinTrack, is developed and used to analyze the precision of a dynamic differential positioning solution using high\|rate GPS data with short baselines of 10 Hz and medium baselines of 1 Hz.The single epoch GPS solution accuracy of broadcast ephemeris and three kinds of precise ephemeris (IGU, IGR and IGS) are compared. Experimental results show their accuracy is almost the same under the condition of a medium\|short baseline. A conservative estimation of the accuracy of high\|rate single epoch GPS solution is 1 cm. The accuracy is relative to observational condition, observational time and data quality.
-
jgg. 2015, 35(2): 194-198. https://doi.org/10.14075/j.jgg.2015.02.004
Fast and reliable ambiguity resolution (AR) is the key for high accuracy global navigation satellite system (GNSS) positioning. Due to the different characteristics of GPS and GLONASS in carrier phase frequencies, satellite geometry distribution and observation accuracy, the AR performance of GPS and GLONASS are not identical. This paper presents a GPS/GONASS single epoch AR method for short baseline and the receivers of the same type. Three short baselines are collected using GPS/GLONASS receivers of the same type. The results show that the ambiguity success fixing percentage of GPS is higher than that of GLONASS.
-
jgg. 2015, 35(2): 199-202. https://doi.org/10.14075/j.jgg.2015.02.005
This paper presents research on differences of sun and moon coordinates from astronomical almanac and JPL ephemeris and the effects of these differences on GNSS navigation and position. The maximum differences are 5×108 and 3×106 m of coordinates of sun and moon calculated with different ephemeris. The difference in angle can be up to 30′ in X direction of the satellite fixed coordinate system between astronomical almanac and DE421 (Y direction is similar to the X direction). Wind\|up correction difference and satellite antenna PCO correction difference can reach 0.3 mm and 3 mm respectively, caused by sun coordinate difference. Solid tidal correction difference can be up to 3 mm caused by coordinate differences of sun and moon. However, the designed PPP experiment has proved that the above\|mentioned influences on the PPP positioning can be ignored. The most efficient astronomical almanac is advised in PPP.
-
jgg. 2015, 35(2): 203-206. https://doi.org/10.14075/j.jgg.2015.02.006
Satellite clock offset prediction is a key technique in satellite navigation systems. The second\|order correlation function of the entangled photon pairs is investigated and a clock synchronization scheme is proposed based on the temporal correlation of the function. Furthermore, the effects of chromatic dispersion and attenuation factors in propagation are incorporated. The results indicate that the scheme can provide synchronization information and that its modeling error is 1 ns with an accuracy of 0.01 ns. The parameters in the clock offset model are estimated by Robust Kalman filtering, and the covariance is estimated by using total Hadamard variance along with the observed values provided by the synchronization scheme. The simulation indicates that the scheme can provide prediction accuracy equivalent to IGS ultra\|rapid products and that the initial value is close to IGS final products
-
jgg. 2015, 35(2): 207-210. https://doi.org/10.14075/j.jgg.2015.02.007
Locata is a new territorial radio positioning technology. It is a great break through because GNSS cannot offer high\|precision positioning results in the “difficult area” where visible satellites are less than 4, whereas Locata can. It has great practical prospect in fields such as deformation monitoring, machine automation, urban and indoor positioning. This paper introduces methods of pseudorange and carrier phase point positioning with Locata. Based on simulation data and experiments, the paper analyses the influence of reference station number on positioning accuracy, compares the accuracy of pseudorange positioning and observed value combination positioning. It testifies that results of carrier phase positioning are stable. Experimental results indicate that the accuracy of Locata static point positioning can reach the centimeter to millimeter level.
-
jgg. 2015, 35(2): 211-213. https://doi.org/10.14075/j.jgg.2015.02.008
Based on study of Fujian GPS network data in time series, baseline processing, velocity field, and high frequency GPS data, this paper discusses the relationship between GPS data and earthquake.The analysis shows that GPS data will play a very important role in earthquake prediction in the future.
-
jgg. 2015, 35(2): 214-218. https://doi.org/10.14075/j.jgg.2015.02.009
Displacement time series are calculated precisely at single epochs based on real\|time and dynamic monitoring for large buildings by GNSS. It is found that the displacement has some prominent law, and the principal component of the displacement series is extracted by the spectral analysis method. The displacement forecasting model is established by high order harmonic function. Taking Tongji mansion for example, the forecasting result is consistent with actual observation series. The Root Mean Square (RMS) is better than 3 mm in horizontal direction and 7 mm in the vertical direction. These results are significant for automatic deformation monitoring and issuing early warnings in the event of abnormal deformations of large buildings.
-
jgg. 2015, 35(2): 219-221. https://doi.org/10.14075/j.jgg.2015.02.010
With CGCS2000 widely used in China, it is necessary to transform previous WGS84 coordinates into CGCS2000 coordinates. Coordinate conversion first transforms WGS84 coordinates to ITRF coordinates and then switches to CGCS2000 coordinates. This paper will use the seven-parameter method and frame conversion to achieve coordinate conversions between WGS84 and CGCS2000. It also selects an example of calculation and analysis of data.
-
jgg. 2015, 35(2): 222-224. https://doi.org/10.14075/j.jgg.2015.02.011
〗This paper proposes an algorithm based on triangulation and directional line mosaic to construct a high precise coordinate transformation grid model, integrating graphics structure, data type and the requirement of grid mode precision, combining the graphics idea. Taking eastern and southern Chinese cities for comparison, the experiments show that the method takes the graphics structure effect on selected the known points, that the error propagation is effectively controlled, that good effects of grid model are achieved, that there is no influence among the sub triangle region, and that there is no mosaic gap. We test and verify the feasibility and reliability of this method.
-
jgg. 2015, 35(2): 225-227. https://doi.org/10.14075/j.jgg.2015.02.012
The traditional algorithm for coordinates system conversion applies a mathematical model for computation of control points’ coordinates in the target coordinate system. However, it needs to be pointed out that the traditional algorithm is irrational because the control points’ coordinates are made up of systematic and stochastic parts, and the traditional algorithm applies a conversion model to fit the systematic part of coordinates, ignoring the stochastic part of coordinates. In this paper, a new solution that establishes the covariance function based on Reilly function to fit the stochastic part of coordinates is presented. Furthermore, the detailed steps for establishment of the covariance function, which takes the residual error of known control points’ coordinates in the target coordinates system as its basis, are proposed. To prove the solution presented in this paper is feasible, an instance is cited, and the numerical results clearly demonstrate that computation control points’ coordinates based on an algorithm that applies covariance function to fit the value of the coordinates is more accurate.
-
jgg. 2015, 35(2): 228-231. https://doi.org/10.14075/j.jgg.2015.02.013
Based on comprehensive analysis of the nature and magnitude of the deformation of area caused by the Gauss projection, the article defends a method of correcting the area deformation by parabolic fitting to calculate the area, taking into account the curvature of the Earth. It can convert the Gauss plane area to the spherical area on the surface of the ellipsoid directly, according to the average abscissa of area. The results show that this new method is not only simple in calculating, but also maintains high and stable precision, with the relative errors of the revised area at less than a millionth throughout the projection zone.
-
jgg. 2015, 35(2): 232-234. https://doi.org/10.14075/j.jgg.2015.02.014
This paper is concerned with the gross error detection of leveling data, for example, the single detection method or the unclear detection level, etc. In order to improve the level of gross error detection, this paper proposes the joint use of loop closure network and the Baarda detection method. In the simulation experiments, the choice of tolerances in the Baarda detection method and different gross error were studied. We found that portfolio analysis method can effectively detect gross errors in levelling data, and improve the accuracy and reliability of the results, and provide a reference for gross error detection in actual projects
-
jgg. 2015, 35(2): 235-238. https://doi.org/10.14075/j.jgg.2015.02.015
To deal with the problem of improper selection of initial and critical values in robust estimation methods, an improved two-step M estimation method is proposed, based on the L1 estimation value and modified weight function of the Danish method.The proposed method is not only relatively robust, but also optimizes the least squares.The numerical experiments show that the estimated results of this method are basically consistent with those of LS estimation when there are no gross errors, and the method with conspicuous robust effect is much better than traditional other two-step robust estimation methods.
-
jgg. 2015, 35(2): 239-242. https://doi.org/10.14075/j.jgg.2015.02.016
Aiming at the situation that there are gross errors in the independent variable and dependent variable of the linear regression model，we propose the robust total least squares method.On the basis of the nonlinear adjustment model, we have deduced robust total least squares estimation calculation formula with selecting weight iteration through the equivalence transformation of the linear regression model. Finally, we apply the method to an example, and verify the feasibilities of the method.
-
jgg. 2015, 35(2): 243-247. https://doi.org/10.14075/j.jgg.2015.02.017
In this paper, to solve the seven-parameter model of the three-dimensional datum transformation, quaternion is introduced to construct rotation matrix. The spatial rotation axis, rotation direction and angle of quaternion are determined by using simple spatial geometric principles, resulting in more accurate initial rotation matrix. The matrix coupled with a more accurate approximation of the scale parameter and the translation parameters is substituted into the linearized observation equations, which can quickly and accurately determine the exact value of each parameter and then improve the reliability and stability of solution. Meanwhile Simulation results show that the algorithm is applicable to three-dimensional coordinate conversion about any angle.
-
jgg. 2015, 35(2): 248-252. https://doi.org/10.14075/j.jgg.2015.02.018
We use the scanning plane of the view instead of the common point to set up a corresponding mathematical model to complete point cloud registration. This paper proposes a method on point clouds registration using commonality single-plane. First, we do planes extraction, plane fitting, and calculate the plane normal accurately. Second, we use the plane normal information to calculate rotation angle and construct a rotation matrix. Finally,we do coordinate translation with the plane center to complete the point clouds registration. Experiments were carried out by simulated data and experimental data to verify the correctness of the algorithm.
-
jgg. 2015, 35(2): 253-257. https://doi.org/10.14075/j.jgg.2015.02.019
The displacement model of surface horizontal motion is calculated by using a multi-surface function based on the GPS data from the eastern Tibetan plateau from 2004 to 2007, and the strain field on the spherical coordinates is given. Through comparison of earthquakes that occurred in the observation periods and the fault distribution in the area, the relationship among horizontal motion, strain space distribution, strong earthquakes and regional tectonic deformation is discussed. The results indicated that EW trending crustal shortening is remarkable in Songpan block and the deformation in Sichuan-Yunnan block is dominated by left-lateral shear and rotation. Furthermore, before the Wenchuan earthquake, the Longmenshan fault displayed a secondary high value of strain energy, the surface strain showed a pressure property, with the strain increasing rapidly, and the middle segment of the Longmenshan fault has been locked. The crustal zone in the western segment of the Xianshuihe fault shows NE-SE shortening and in the eastern segment the crustal displays NW-SE shortening. Sichuan-Yunan diamond block is an area with high value of strain energy and surface strain gradient, the western region of Jinshajiang is dominated by strong strain energy, which is associated with the tectonic stress of Qiangtang block.
-
jgg. 2015, 35(2): 258-260. https://doi.org/10.14075/j.jgg.2015.02.020
With the fast rise in the number of GPS continuous operational reference system (CORS) stations in China, and geodesy and geodynamics subjects growing on the basis of geographic information needs, it is imperative to establish a high precision velocity model in China. China’s mainland is divided into five blocks: Northeast China, North China, South China, Qingzang (Tibet) and Northwest China.The study is performed on construction of the velocity field model in China’s mainland on the basis of three methods: Kriging interpolation, higher collocation precision in the blocks of Qingzang and North China, and the performance of the movable least squares collocation method.The latter is worse than other methods in all blocks.Finally, we apply configuration using Kriging interpolation and least squares collocation to estimate the 1°×1° center of grid velocity results.The resulting difference of the two methods is small.
-
jgg. 2015, 35(2): 261-266. https://doi.org/10.14075/j.jgg.2015.02.021
In this paper we introduce a method that rebuilds a layered earth model according to the real structures of the crustal and upper mantle around the epicenter. Further, we modify the computing codes for displacement Green functions (DGFs) based on the above newly-built layered earth model. The new codes can calculate more suitable DGFs for the objective earthquake, therefore providing us with higher-accuracy coseismic displacements. The case study of the Lushan Ms7.0 earthquake shows that the effects of earth model on vertical DGFs change with the variation of epicentral distance. Among the four independent dislocations, the effects of the earth model on the opening tensile at a horizontal plane are biggest, up to 40% of the DGF themselves in the near field. [JP2]After modifying the computing codes for DGFs according to the real structure in west Sichuan(call it “Lushan model” in this paper), we improve the accuracy of coseismic displacements in the near field by 20%-30% in total.
-
jgg. 2015, 35(2): 267-272. https://doi.org/10.14075/j.jgg.2015.02.022
Sounding data are first designed to be applicable to wide-angle refraction/reflection, and the 1D velocity structure linear inversion of iterative calculation is conducted by using travel time residual as the threshold. Then LIAE1D is programmed accordingly with the following characteristics: 1) the establishment of an adaptive preliminary model| 2) the solution of the linear equation by means of a broader inverse moment matrix. The method and program are later proved to be feasible and efficient in numerical simulation tests as well as in the application of the Huian-Datian-Ninghua profile of Fujian artificial earthquake sounding wide-angle refraction/reflection. Thus, these results could provide a suitable preliminary model for future 2D inversion.
-
jgg. 2015, 35(2): 273-277. https://doi.org/10.14075/j.jgg.2015.02.023
The northern margin fault zone of western Qinling is one of the principal tectonic boundaries in the northeastern margin of the Tibet plateau. The Zhangxian red bed basin is an important part of the Northern fault zone of western Qinling. The study of the paleostress field on the basin is essential to understanding the tectonic evolution of the fault belt of western Qinling in the Mesozoic and Cenozoic periods. Our method is, first, to match the joints of same period according to the structure characteristics of the joint that are observed and measured in the field. Second, we inversed the paleostress field by using the stereographic projection method. The result shows that the study area has underwent four stages of compressive stress after the Cretaceous period, i.e., N-W, S-W, E-W and N-S compressive stresses. The inversion results of Palaeostress field shows that the area is dominated by strike-slipping tectonics after the Cretaceous sedimentation.
-
jgg. 2015, 35(2): 278-282. https://doi.org/10.14075/j.jgg.2015.02.024
We examine the stream length-gradient SL index and gradient index SL/K for concavity studies, and analyze the tectonic activities in the head area of the Three Gorges reservoir based on DEM data and spatial analysis method. Consequent analysis reveals that the main factor causing the landform is tectonic uplifting. Tectonic fault exhibits a strong influence on river profile in the study area. However, the tectonic processes are distinct in different tributaries. The tectonic activities are very strong in the left bank and weak in the right bank. The differential lithology distribution is also anther aspect of the profile feature. In a general, the longitudinal profiles of the river tributaries are well controlled by neotectonic movement, tectonic faults and lithological difference.
-
jgg. 2015, 35(2): 283-286. https://doi.org/10.14075/j.jgg.2015.02.025
Tropospheric delay is one of the main errors affecting the accuracy of satellite navigation and positioning. In response to problems without meteorological conditions, a modeling and forecasting method of tropospheric delay is proposed using the measured value of zenith tropospheric delay (ZTD). Firstly, the cycle characteristics of the time series of ZTD are obtained using spectral analysis. On this basis, the ZTD model is created and the calculation method of model parameters is given. Secondly, the value of ZTD is fitted based on spectral analysis. A comparison is made between the fitting values and the actual data. The fitting residual is determined. Finally, the fitting residual is corrected and predicted using the Auto Regressive model (AR model). The results show that the corrected and predicted model of ZTD based on spectrum analysis and the AR compensation can meet the needs of different testing environments, with the accuracy reaching the centimeter level.
-
jgg. 2015, 35(2): 287-292. https://doi.org/10.14075/j.jgg.2015.02.026
In our paper, we use ionospheric tomography technology, which was proposed by Austen et al. in 1986, to detect a three-dimensional map of ionosphere over the epicenters of different magnitude earthquakes in Japan, Sumatra, Taiwan and Xinjiang China. We use the anomaly detection method to detect the electron density anomies and analyze earthquake ionospheric anomaly statistics. It is concluded that: 1) There are distinct ionospheric abnormalities in a few days or a few hours before the earthquake, especially in the 1-2 days before the earthquake near the epicenter. The earthquake accounts for the anomalies, with the exception of effects from solar activity and terrestrial magnetic field. 2) The abnormal ionospheric electron density area is generally near the epicenter, with a small offset from the epicenter. The closer to the epicenter, the greater the ionospheric anomaly. 3)The convincing functional relationship between negative or positive anomalies and earthquakes is not found yet.
-
jgg. 2015, 35(2): 293-297. https://doi.org/10.14075/j.jgg.2015.02.027
Based on 1999~2009 total electron content (TEC) data from IGS, we studied semiannual and seasonal variations of the global TEC in the daytime (Idc) and nighttime (Inc) as well as solar and geomagnetic effects on these variations. The main features are outlined as follows: the maximum values of Idc commonly appear in equinox seasons| in the northern ‘near-pole’ region and south America, the semiannual variation character of Idc is significant. Inc has only semiannual variation at low latitudes, and the semiannual variation of Idc and Inc change with the solar activity. At high solar activity years, in more than 85% area of the globe, the maximum value of Idc appears in equinox seasons. Seasonal variation of Idc and Inc change with latitude and longitude, and seasonal variation is apparent at high solar activity years. The variation of Idc and Inc correlates well with the solar P index, where the correlation coefficient reached 0.9. However, it poorly correlated with geomagnetic Dst, Kp, Ap index, where the correlation coefficient is less than 0.4. We further demonstrate that ionosphere photochemical production rate, which is controlled by solar zenith angle, plays a major role in the overall variation of TEC.
-
jgg. 2015, 35(2): 298-302. https://doi.org/10.14075/j.jgg.2015.02.028
Based on precipitable water vapor(PWV) data from GPS, the water vapor variation characteristics of two typhoons that hit Hong Kong in 2013 are compared. The results show that GPS/PWV data can vary with the intensity of the typhoon, particularly pressure changes. Far from the typhoon, PWV showed significant changes, shocks, stronger volatility. The degree of its shock has a good relationship with rainfall intensity. Close to the typhoon, PWV has a significant change in the structure of a single peak and its humidification process has a relationship with the time and distance from the typhoon. Also a short rapid change of PWV can better reflect rainfall intensity. In summary, GPS/PWV data have some value in monitoring and forecasting typhoons.
-
jgg. 2015, 35(2): 303-308. https://doi.org/10.14075/j.jgg.2015.02.029
Based on the GRACE data, we successfully extract the co-seismic and post-seismic gravity changes caused by the 2004 Sumatra Mw9.3 earthquake, using P3M6 de-correlation filtering, Gaussian smoothing with a 350 km radius, as well as the difference method. The peak co-seismic gravity changes in the uplift and subduction zones reach up to 4.6 and -8.3 μGal, respectively. Such results agree well in both magnitude and distribution with those calculated by the dislocation theory for a spherical earth model. The total post-seismic gravity changes of 7 years are up to 5.6 μGal in the uplift zone, which is bigger than the corresponding co-seismic gravity changes. On the other hand, the changes in the subduction zone are only 0.6 μGal, just about 11% of corresponding co-seismic gravity changes. Our results imply that the viscosity of the marine strata in the uplift zone is relatively lower than in the strata of the subduction zone. It is the low viscosity in marine area that caused the continuous deformation and relatively bigger gravity changes after the earthquake. The little post-seismic gravity changes in the subduction zone imply the high viscosity of the continental strata.
-
jgg. 2015, 35(2): 309-311. https://doi.org/10.14075/j.jgg.2015.02.030
〗In this paper, the Bouguer gravity anomaly computed from EGM2008 gravity data and the varying density contrast extracted from CRUST1.0 model are used to determine the Moho depth in mainland China using gravity inversion. The results are consistent with with previous studies of Moho depth in China.
-
jgg. 2015, 35(2): 312-317. https://doi.org/10.14075/j.jgg.2015.02.031
This paper attempts to achieve accurate results for the downward-continuation. In the paper the detailed characters of the standard Poisson kernel and the Molodensky-Poisson kernel are analyzed. The truncation error of the far-zone contribution is estimated. The relations of the height, the truncation radius and degree are analyzed in the downward-continuation of the gravity anomalies. The results suggest that the Molodensky-Poisson kernel can reduce the far-zone contribution. The height is less than 3 km and the truncation radius is more than 0.5°. The truncation error estimated at less than 1 mGal| when the truncation radius reaches 1°, the truncation error estimate achieves an accuracy of 10 μGal. Hence it ensures the accuracy of the geoid reach to the 1 cm level.
-
jgg. 2015, 35(2): 318-321. https://doi.org/10.14075/j.jgg.2015.02.032
We apply GPS data on gravity profiles to assess ASTER GDEM’s vertical accuracy, and then discuss its application in gravity terrain computation. The results show that standard deviations of ASTER GDEM compared to GPS data in the Guiyang-Weixi and Jinchuan-Qianwei gravity profiles are 14.93 m and 18.02 m respectively. The model data and the actual GPS measurements have good consistency. With the simulation, it can be concluded that the application of the ASTER GDEM is effective in computing middle and far zone gravity terrain corrections in small scale, as well as far zone corrections in large scale.
-
jgg. 2015, 35(2): 322-325. https://doi.org/10.14075/j.jgg.2015.02.033
Three kinds of GOCE-based gravity field models, i.e. time-wise models, space-wise models and direct approach models released by ESA, are evaluated from three schemes including accumulative geoid errors, geoid height differences and combination of the models in different spectral bands. Results from spectral analyses and GPS/leveling geoid difference in North America indicate that, the 4th generation model from direct approach satisfies the GOCE mission objective of achieving ±1 cm geoid accuracy at a spatial resolution of approximately 100 km. The direct approach models have the better performance compared to time-wise models and space-wise models. GOCE data products can improve the accuracy of middle to high spectral band signals of gravity fields.
-
jgg. 2015, 35(2): 326-330. https://doi.org/10.14075/j.jgg.2015.02.034
Wide-area polynomial approximation can be used to fit the disturbing gravity of a given region. This can reach high accuracy with great efficiency. However, 24 nodes’ value of the vice domains, which are connected to main domain, must be used when we calculate with this method. If the main domain is located on particular places, such as the vertices of the area, not all the nodes’ value of vice domains can be used. As a result, fitting accuracy is dragged down. This circumstance is researched in the paper, in which the accuracy and efficiency between wide-area polynomial approximation and inverse distance weighting are compared. Finally, an improved project is put forward, which made the fitting effect better
-
jgg. 2015, 35(2): 331-335. https://doi.org/10.14075/j.jgg.2015.02.035
By using gravity data in the area of the scientific expedition of the Lushan earthquake, we have systematically obtained the gravity variation before and after earthquake. The results show that：1) before the earthquake, the area beside the Longmenshan fault shows an obvious anomaly, and some high gradient zones are parallel or vertical with the Longmenshan, Xianshuihe and Daliangshan faults| 2) after the earthquake, gravity variation was opposite in the area beside the Longmenshan fault| 3) heat and bulge of the material of middle and bottom crust probably cause the gravity variation and may be one important trigger factor of the Lushan earthquake.
-
jgg. 2015, 35(2): 336-341. https://doi.org/10.14075/j.jgg.2015.02.036
This article examines data reduction methods for airborne gravimetry, including reducing raw gravity observations along survey lines to average height level, compensating system errors by two-step crossover adjustment and gridding gravity data using weighted average (WA), and Shepard surface fitting (SSF) methods. Data block EN01, released by NGS (National Geodetic Survey), is processed according to the scheme, outputting 5′×5′ grid gravity disturbances covering a region of 2°×3°, with geodetic height 6 200 m. Compared to reference values computed by EGM2008 at the same locations, the accuracies of the output data from WA and SSF are ±1.59 mGal and ±1.36 mGal.
-
jgg. 2015, 35(2): 342-345. https://doi.org/10.14075/j.jgg.2015.02.037
Three gravity anomaly gridding methods are introduced and analyzed in this paper. The computation of the lag distance and the semi-variogram are studied in detail. Three methods are compared with different parameters using real gravity anomaly data gridding computation. Results show that there is no great difference in precision. Comparatively, the Kriging method shows the best precision in this area.
-
jgg. 2015, 35(2): 346-348. https://doi.org/10.14075/j.jgg.2015.02.038
In this paper, the complex heterodyne method is studied to analyze the fringe signal produced during free fall movement in an absolute gravimeter. Firstly, it is necessary to perform a series of complex heterodyne on the high-speed sampling signal in order to iteratively reduce the bandwidth and to move it to dc. Secondly, initial velocity and acceleration can be estimated and a nonlinear fit is used to obtain a acceleration of gravity g. Simulation results with MATLAB indicate that the fit residuals can reach 10－3 μGal level and this ensures accuracy of measurement.
-
jgg. 2015, 35(2): 349-352. https://doi.org/10.14075/j.jgg.2015.02.039
On the basis of ThinkPHP framework of MVC, integrated Smarty templates, and using the PHP +MySQL, PHP+Oralce double database link principle, we developed B/S structure seismic business database management software. For the administrator, it provides database information display and query operation, classification of accident treatment records, as well as inspection report generation. For general users, it provides the corresponding business data using status query. At the same time, we configured the business database real-time monitoring module in the Nagios open source network management platform to send fault alarms through mobile phone text messages. Together, they form a complete seismic business database automatic monitoring and management system.
-
jgg. 2015, 35(2): 353-355. https://doi.org/10.14075/j.jgg.2015.02.040
Longyan seismographic station vertical pendulum displays the obvious influence of rainfall. Based on topographical and geological conditions research, we use mori in-depth analysis to understand the causes of the influence of rainfall. Due to the vertical pendulum observation curve, there is strong correlation between rainfall accumulation and the value curve. We use the unary linear regression method to rule out of rainfall interference, and at the same time, probe into the reflect effect.
-
jgg. 2015, 35(2): 356-359. https://doi.org/10.14075/j.jgg.2015.02.041
Geological conditions, observation environment of geomagnetic field, background noise and other electromagnetic environment aspects are tested and analyzed at Yingcheng station. The results showed that Yingcheng geomagnetic station is located in the limestone area, and that the horizontal gradient of the magnetic field is less than or equal to 1 nT/m, and that the electromagnetic background noise is less than or equal to 1 nT.The test results show that, based on borehole lithology analysis, the electromagnetic environment is stable but the soil of the station is affected with strong magnetism. It is suggested the soil magnetism detection work should precede station construction.
-
jgg. 2015, 35(2): 360-364. https://doi.org/10.14075/j.jgg.2015.02.042
For problem of the laser beam not being perpendicular to the ground, ground point spacing calculation method was deduced. With the field observation, the accuracy and feasibility of the calculation results were tested and the best scanner scanning radius was obtained. The result shows that by comparing the elevation of point clouds model and the 16 homonymy point using level monitoring measurements,the difference of corresponding point elevation and level measurement point is not obvious. It is stated that the 3D laser scanning technology has high accurate and can be used for deformation monitoring of the subsidence zone.
