16 July 2018, Volume 38 Issue 7
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jgg. 2018, 38(7): 661-667.
In this paper, we use empirical mode decomposition (EMD) and ensemble empirical mode decomposition (EEMD) to analyze BJFS height time series, spanning from 2000 to 2015. Results show that not only the signals at well-known periods (annual, semi-annual, 3-month, 2-month and 1 month), but also quasi-biennial signals, which were difficult to detect previously, are found. Compared with EMD, it is proven that the EEMD approach can weaken the mode mixing phenomenon significantly. The decomposed intrinsic mode function (IMF) is transformed with a Hilbert algorithm, from which we observe that the annual and quasi-biennial oscillations are the major contributors to the height variations. Compared with wavelet analysis, the RMS of the difference between EEMD reconstruction signal and elevation sequence is smaller, showing the effectiveness of the HHT-EEMD method in data analysis. The annual and semi-annual variations in the height are mainly attributed to the surface mass loading by integrating geophysical models, and the existence of the quasi-biennial signals are verified by GRACE data.
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jgg. 2018, 38(7): 668-672.
We first present a mathematical model of medium-long baseline kinematic positioning based on BDS triple frequency observations. Several baselines from CORS in Tianjin, Wuhan and Guangdong are adopted to evaluate and analyze the TTFF and the accuracy of BDS medium-long baseline kinematic positioning. In terms of the present BDS constellation, the TTFF shows strong correlation with the latitude and observation period. The TTFF in the north of China is about 2 h, while it is about 1.5 h to less than 1 h in the middle and south of China. With the right fixed ambiguity, the east and north accuracies of the baseline are 2.5 and 2.1 cm respectively, while the vertical accuracy is 61 cm.
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jgg. 2018, 38(7): 673-678.
The number and distribution of ground stations affects the accuracy and reliability of real-time satellite clock estimation. As current BDS mainly provides services to the Asia-Pacific region, the article selects 8, 12, 18 and 24 real-time ground monitoring stations distributed equally in the China region to analyze the relationship between the number of regional stations and the accuracy of BDS real-time satellite clock. The results show that, when the number of stations is less than 16, the arc length of IGSO/MEO satellite is observed in the Chinese region is not complete, and that real-time clock accuracy and positioning accuracy is poor. When the number of stations reaches 16, the observable BDS satellite arc length is covered in the China region. When the number of stations reaches more than 17, real-time clock accuracy is 0.15 ns, and positioning accuracy is 0.3 m or more in the horizontal direction and 0.4 m or more in the vertical direction; further, real-time clock estimation accuracy and positioning accuracy no longer significantly increases with the number of stations.
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jgg. 2018, 38(7): 679-683.
This paper attempts to solve the problem that, due to the loss of visible satellites in signal shadowed regions, GPS or BDS single system cannot meet the minimum requirements of relative positioning. We first discuss the mathematical model of the GPS/BDS single epoch baseline solution. It compares GPS/BDS combined solution results with GPS and BDS single system solution results with respect to satellite visibility, ambiguity resolution success rate, and positioning accuracy in multiple simulative masking environment. The numerical results show that: compared with the single epoch baseline resolution of a single system, GPS/BDS greatly increases the number of visible satellites, improves the success rate of ambiguity, and effectively improves the positioning accuracy under extreme observation conditions. In addition, the dual-frequency single epoch accuracy can reach cm-level or even mm-level in signal shadowed regions.
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jgg. 2018, 38(7): 684-688.
There are disadvantages of the BDS Navigation Satellite System (BDS), such as complicated constellation structure and large differences in residual errors of observed values from different types of satellites. In order to precisely determine the weight matrices of observed values between different systems, this paper studies the observed values from IGSO, MEO and GEO satellites in the BDS system through classification and weighting. It proposes an exponential weighting Helmert variance component estimation method that takes historical weight ratios into account. Static and dynamic navigation tests are carried out through a point positioning model to verify the effectiveness of this improved method in GPS/BDS combined positioning, and the results of this improved method are then compared with those of the equal weighting model, as well as of the Helmert variance component estimation method without exponential weighting. Results show that with the improved method, positioning precision in east, north and zenith directions is improved significantly. Under static conditions, compared with the equal weighting model, this improved method results in 50.0%, 51.0% and 420% improvement in positioning precision in the above three directions respectively; under dynamic conditions, relevant positioning precision is improved by 10.0%, 8.0% and 9.0% respectively. Especially under situations of fewer satellites and weaker intensity of satellite geometry, improvement in positioning results is even more significant.
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jgg. 2018, 38(7): 689-694.
According to the non-linearity, volatility characteristics and real-time dynamic data processing of deformation monitoring data, the auto-regressive and moving average model (ARMA) is used to construct the trend, based on the selection of variance compensation adaptive Kalman filter for stochastic disturbance rejection and model error weakening analysis. The error compensation and correction ARMA model is obtained by using particle swarm optimization (PSO) parameter optimization support vector machine (SVM). The method is used to predict the deformation monitoring engineering. The prediction results show that the method can describe the actual deformation of engineering under complex environmental factors and play a certain reference value in forecasting the project.
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jgg. 2018, 38(7): 689-694.
The traditional evaluation index cannot meet the requirements of wavelet de-noising quality evaluation if the truth value is unknown. Using rate-change characteristics, this paper proposes a new evaluation index that reconstructs the root mean square error variation evaluation index and smoothness variation evaluation index. We use the normalized entropy weight method to linearly combine the two normalized evaluation indices. This new index is the composite evaluation index. The method decides the optimal de-noising layer by means of the obvious change of the rate of change of the index as the number of decomposition layers increases. Experimental data analysis shows that this method can guide wavelet decomposition accurately, and accurately determines the optimal de-noising layer to achieve the optimal de-noising effect when the truth value is unknown.
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jgg. 2018, 38(7): 695-697.
Generally, there are many calculations of about zero in the traditional adjustment algorithm, which is useless and decreases the calculation efficiency, especially when the data quantity is very large. The new adjustment algorithm avoids the problem above effectively, and the new algorithm is further improved using a variable-loop-and-renumber-method. Finally, the new adjustment algorithm is used to adjust the precise leveling data in Tianjin, and the results show that new algorithm is more effective.
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jgg. 2018, 38(7): 703-706.
According to the CORS observation and meteorological data of Hebei Province in 2014, we analyze the characteristics of water vapor transport in Hebei using GNSS PWV. We compare the relation between GNSS PWV, ΔPWV and precipitation. We find that water vapor transport path is consistent with the spatial distribution of PWV. It is concluded that there are two water vapor transport paths in Hebei province.
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jgg. 2018, 38(7): 707-713.
Atmospheric precipitable water vapor (PWV) over the station can be estimated using ground-based GPS technology. The variation characteristics of PWV have very good indicators to the predict precipitation time and falling area. Along with the atmospheric thermodynamic conditions such as temperature and pressure, we analyze the variation characteristics of timeseries and plane dynamic distribution of PWV during the rainstorm that occurred May 22-23, 2017 in Hunan province. The results show that the formation of precipitation requires strong convergence ascending of water vapor. The precipitation time and intensity can be predicted by combining thermal dynamic conditions in the case of sufficient water vapor conditions. The contrastive analysis of plane distribution maps of PWV and actual precipitation shows that the high value region of PWV basically coincides with the falling area of the rainstorm. It means that GPS-PWV has certain indicating significance to forecast the falling area of the rainstorm.
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jgg. 2018, 38(7): 714-718.
Meteorological factors change dramatically and contain a lot of water vapor and particulate matter, causing the propagation path of satellite signal to be prone to change, further leading to changes of tropospheric delay. Therefore, this paper focuses on the correlation between meteorological factors and haze. The atmospheric pollutant concentration data and tropospheric delay data for 62d (doy 153-214) in 2016 in Shanghai are studied. The study finds that concentrations of each pollutant in the atmosphere shows a similar trend, and the tropospheric delay values increase with increasing PM2.5 content. At the same time, the content of PM2.5 in Shanghai is positively correlated with air pressure, air temperature and relative humidity, and is negatively correlated with wind velocity and precipitation.
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jgg. 2018, 38(7): 719-722.
In this paper, a submarine tunnel in Xiamen is selected as the target area. Using electromagnetic bubble source system seismic wave excitation and the seismic imaging test of igneous rocks, we better identify the water depth of the sea mud (sand) interface, and the bedrock surface boundary. Under the geological background of granite weathering in the igneous rock development area, the bedrock surface has been greatly undulating, and the single drilling method has great limitations. The results show that the seismic image method is an effective geophysical prospecting method for igneous rocks in marine areas, and can provide a reliable geological reference for marine geological exploration. The use of water seismic imaging exploration not only can better compensate for drilling defects, but may also greatly save economic costs. Further, it has higher application value and scientific research value.
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jgg. 2018, 38(7): 723-728.
In this paper, we study the crust-mantle transition zone structure of the south and north Songpan-Ganzi and the Yangtze plate (SSGT, BY-SG, YZB). The thickness and velocity structure of the crust-mantle transition zone of three different tectonic blocks are obtained by the receiver function method. It shows that the thickness of the transition zone of the SSGT block is 1.79-3.4 km, with an alternating velocity structure. The transition zone of the crust-mantle is getting thicker, breaking the original crust-mantle transition zone temperature and pressure conditions. Besides, it has a strong tectonic activity in the southeastern northeast, resulting in an alternating velocity structure. The thickness of the transition zone of the BY-SG block is 2.22-3.72 km, and the velocity structure is a gradual velocity structure. This block has been suffering the effects of continuous compression, gradually changing the temperature and pressure conditions of the transitional zone of the crust and mantle, forming the velocity gradient structure. The YZB block crust-mantle transition zone is 0.86-1.58 km, and the velocity structure is the velocity instantaneous structure. The crust-mantle transition zone in Sichuan basin (YZB) is a good first-order discontinuity, and the transition zone is thinner and the structure is a velocity instantaneous structure.
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jgg. 2018, 38(7): 729-733.
The research,using large tonnage vibroseis excitation and multiple coverage seismic reflection techniques, complets the 14 km middle-deep seismic reflection profile across the Taizhou fault. In this paper, we combine geological data from the study area and the characteristics of the obtained reflection wave group, establish a fine stratigraphic frame along the quaternary to the Paleozoic, and study the structural morphology, cutting depth and structural combination of the Taizhou fault and its two sides. The results show that there are many reflective interfaces with strong reflection energy in the upper crust of the area. Two important structural planes of the upper crust structure in this area are the ancient hidden hill surface and the top interface of crystalline basement TG. The Taizhou fault is generally shown as a fault tectonic zone consisting of two faults. Its upper part disconnects the bottom of the Quaternary, and lower part disconnects the Neogene, Paleogene and other sedimentary layers and crystalline basement. It has an important control effect on the formation of the uplift and depression in this area.
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jgg. 2018, 38(7): 734-737.
Based on previous work, this paper uses a stacking technique with 12 scenes and 27 interferograms to obtain the deformation rate in 2015-2016. The results demonstrate main subsidence area is distributed between Luoyunshan and Emei-Zijinshan fault zones. The value is greater than 40mm in the subsidence center, which is assembled with the underground contour. The deformation is caused by excessive pumping and the active fault zone.
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jgg. 2018, 38(7): 738-742.
We determine the coseismic displacement of the Qinghai Zadoi MS6.2 earthquake that occurred on October 17, 2016 using ascending InSAR data from the ESA’s Sentinel-1A satellite, and we obtain the fault distribution of the earthquake using the SDM method. The results show that there is large dip-slip in the fault concentrating in the depth between 8 km and 12 km, with a little strike-slip component. The maximum slip of 0.17 m is observed at a depth of 9 km and is located near 32.85°N, 94.86°E. The obtained focal depth is consistent with the aftershock and the inverted seismic magnitude is MW5.9, which is consistent with the USGS and CENC.
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jgg. 2018, 38(7): 743-747.
Satellite thermal infrared remote sensing applications and a large number of earthquake cases show that there are different degrees of brightness temperature anomalies around the epicenter before the occurrence of strong earthquakes. Over time the anomalies appear as warming bands or a large area of irregular distribution. In this paper, we focus on the relationship between the thermal infrared anomalies related to earthquake magnitude in the prediction of earthquake appearance. We linearly fit the thermal anomalies over 151 magnitude MS5.0 earthquakes that occurred in China from 2010 to 2014 to magnitude. The expression of the binary relationship between the magnitude, MS, and the average area of the thermal infrared anomaly area three days before the earthquake is obtained. The relationship between magnitude and thermal infrared anomaly area is analyzed quantitatively for the first time. It is better to connect the satellite thermal infrared with the earthquake magnitude.
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jgg. 2018, 38(7): 748-753.
Based on continuous observation data of GNSS in Yunnan since 2014, the velocity and strain parameters are solved by least squares configuration and the Kriging interpolation method. The velocity field and strain field results are used to analyze recent crust activity features of Yunnan region, as well as the resulting influences on strong earthquakes. The results show that the velocity field, based on Wenshan measurement point, show a whole clockwise motion characteristic, and the direction of motion is different. The maximum shear strain accumulation in the whole area of Yunnan is fastest and strongest in northwestern Yunnan, and the squeezing strain accumulates in south and southwestern Yunnan. In the year 2014, the strong earthquakes of magnitude 6 and above have maintained a good consistency with the maximum shear strain in the macroscopic direction, and the occurrence of the earthquake does not change the stress and strain distribution pattern and growth trend of the whole area in Yunnan.
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jgg. 2018, 38(7): 754-759.
In order to explore the characteristics of air-gun source, we deploy two circular arrays with portable seismographs around Binchuan Air-Gun Source Transmitting Seismic Station in February 2017. To get the radiation pattern of air-gun’s signals, we use the data received by circular arrays to get the signal’s duration, energy, and the area of S transform image. We get a preliminary result: 1) Differences can be seen obviously between signals from different azimuth. 2) Air-gun array formed by four air-guns shows a period of 90° and its main directions are NE, SE, SW and NW; single air-gun shows no clear periodicity and its main directions are NE, SW and NW. 3) The main cause of the radiation pattern is high-pressure-gas injection, which has strong directionality, and there is coupling between bubble and borehole wall. 4) If the air-gun signal ray path goes through a certain scale of water, its energy attenuation is smaller and time-frequency spectrum is smooth.
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jgg. 2018, 38(7): 765-770.
The high performance of the mechanical force balance accelerometer, supplemented by the 24 bit data acquisition, with a dynamic range more than 90 dB of the industrial MEMS intensity observation system, is used in the construction of high density network intensity Shanxi reservoir area. This makes a regional strong motion observation system to achieve high density, digital, network coverage, improves the dynamic range of seismic intensity quick report and earthquake observations in the region. The network makes full use of MEMS intensity meter, with low cost, easy expansion, good management, and network flexibility. The first successful application of seismic monitoring in our province will promote the development of seismic observation technology.
