15; revision: 2002-06-27 fund project: National Natural Science Foundation of China (40074002) funded 15 lung lung female benefit product annual volume, Tongji University milk 1 %% now mainly M geodetic survey data processing 1GPS network data processing At present, many GPS monitoring networks have been installed in coastal areas of China, and processing the measurement data is an important content of GPS monitoring crustal movement. At present, the main GPS processing software used at home and abroad are: GAMIT / GLOBK, SNAPS, GIPSY and so on. This article uses GAMIT software to comprehensively process GPS carrier phase observations. Post-processing uses a programming method to process all GPS phase observations, adding station drift and coordinate conversion parameters of each period to find the time for a certain epoch Drift speed of coordinates and station position.
In order to obtain the geocentric coordinates of the deformation network under strict benchmarks and determine the crustal deformation under a certain frame reference, the deformation network must be included in the ITRF framework. Therefore, when processing data, the known point coordinates (SHAO) under the ITRF2000 framework are introduced: to obtain the coordinates of the ground station, so that the station coordinate frame epoch and the satellite ephemeris are consistent. The data baseline processing of each issue takes the Shanghai station as the starting point, that is, the fixed Shanghai station.
When using GAMIT software, in order to obtain high-quality baseline processing results, the following settings are made to the measurement segment information control file (estbl.): Regular editing results for data editing; total volume, ambiguity resolution; cut-off height angle set to 15 * All weather observations are used for 30-second epoch interval, a total of 2880 epochs; 10-6, 9 radiation pressure is 0.01%. For GPS's main source of error, the satellite clock difference model is corrected by using the clock difference parameter in the satellite broadcast ephemeris; Correct the clock difference model of the receiver using the clock difference calculated by the pseudorange observations; use the LC observations to eliminate the ionospheric refraction and set the ionospheric constraint to 0.0mm + 106; use the standard atmospheric parameters for meter to correct the troposphere Refraction effect, and ensure that every station adds a deflection parameter in the zenith direction every 2 hours, a total of 13 delay parameters; for the correction of the satellite and receiver antenna phase center, use L1 set by GAMIT software The L2 phase center deviation value enables the satellite to switch from the mass center to the satellite antenna phase center, and the receiver from the station marker center to the receiver's antenna phase center.
Table 2 In 1998-2002, the error in each measurement segment was edited by the quick solution to obtain relatively clean data, and then the single-day baseline normal solution was performed on the measurement segment to obtain the result file Q file. The GAMIT baseline solution is good or bad, judged by the calculated medium error M (M 2 station drift mathematical model GPS observation data volume is very large, when using GPS positioning results to study global plate movement or regional crustal deformation "The general approach is to compare the baseline results of the GPS independent solutions in each period to obtain the relative changes between stations. This approach obviously ignores the comprehensive results of the period observations of the calculation results of each period, including a set of station coordinates for a certain epoch. , Drift velocity and accuracy, this article uses programming calculations, using the H file of the GAMIT software as an input to process the long-term observation of the GPS network to solve the global plate movement or regional crustal movement information, the adjustment model is: For the observation of the i-th measurement segment, the following error equations can be listed: the observation equation is rewritten into the normal equation form: where the normal equation coefficient Ni is the inverse of the covariance matrix Qi Qi is the coordinates of the i-th measurement segment and other parameters The co-factor matrix, Xi is the correction number. Both Qi and Xi can be read from the H file, and the constant term Ci can be obtained according to the formula (3). Pi represents the approximate value of the unknown parameter used in the measurement section. Read in the H file. Since the approximate value of the unknown quantity used each time is not uniform, for the overall adjustment, a consistent approximate value P must be used, but the approximate value used for each observation adjustment is relatively close, so the error equation coefficients can be omitted. Change, and the constant term of the normal equation is changed from Ci to Ci-Ni), the normal equation after the change is still expressed by (3).
Since the coordinates of each surveying site change during crustal movement, the value of the station coordinate at time T () is defined as P + S :, then the observation (time) coordinate of the i-th survey segment is household + 饫 + å«ã€‹ (linear Motion model, where = Ti-T0, is the drift velocity of the station, and its initial value is zero) After adding the drift velocity Z of the station, the error equation of the i-th segment is written in a matrix form as: a method composed of (4) The equations and the GPS deformation network are superimposed on each measurement section to obtain the final method equation of the deformation network: where: parameter c is the correction number of the station coordinates and non-coordinate parameters of the adjustment of each measurement section at a certain time, and c is the station Movement speed parameter. Since the total normal equation is formed by the superposition of each single-day solution, and the weights between each single-day solution can be considered equal, that is, the prior weights are equivalent, so the weight matrix of the total normal equation is considered to be unit weight. It is worth noting that the normal equation of (5) is rank-deficient. If a solution is required, one or a combination of the following conditions must be added to the equation: fix the coordinates and speed of certain points to a selected value; give parameters Certain a priori accuracy, in which the sum of squares of the first corrected numbers of some points is the smallest; the limiting conditions determined according to the geological conditions.
In this calculation example, the coordinates of the Shanghai station are fixed, that is, the drift amount and drift speed of the station are zero.
3 Calculation example analysis Obtain the phase observations of each measurement segment from the IGS station, use GAMIT software to perform baseline processing, obtain the result file H file, and calculate the baseline repetition rate according to (1) formula to evaluate the quality of the baseline solution. The listed Shanghai-Wuhan baseline repetition rate also confirms that the GAMIT software has a high baseline resolution accuracy. Taking the H file as input data, the comprehensive solution of all measurement segments is calculated by formula (6) and the station drift amount (1998 to 2002) and station drift speed (SHA) of each point relative to the Shanghai station (SHAO) are calculated. Per year).
However, the station drift amount and station drift velocity obtained from this are in the direction of the earth's longitude drop and radial direction. In order to better describe the movement and change of the station, it is necessary to convert it to coordinate The performance is north, east, and vertical (N, E, U) directions. The conversion steps are: first convert it to rectangular coordinates of the earth (X, Y, Z) and then convert the rectangular coordinates of the earth to the horizontal coordinates of the center of the station (N, E, U-one, B, L are the ground of the center of the station i In this example, the station center is Shanghai Station (SHAO).
According to formula (8), the drift velocity in X, Y, and Z directions under the coordinate frame of ITRF2000 can be obtained. Compared with the known velocity in X, Y, and Z directions under ITRF2000 provided by IGS, the comparison results are shown in Table 3. Table 3 Comparison of calculated values ​​of Y and Z directions with known values ​​Stations occupy X direction (cm / a) Y direction (cm / a) Z direction (cm / a) Station calculated value Known value Calculated value Known value Calculated value Known value one: Because the Shanghai station is fixed during the solution, the drift velocity of the station obtained by the solution is relative to the SHA0 station. For comparison, the drift velocity of the Shanghai station (SHAO) in the ITRF2000 coordinate frame is introduced: Vx = * 3.07cm / a, Vy = * 1.12cm / aVz = * 1.34cm / a By adding the drift speed of SHAO to each station, you can get the drift speed of each station under the ITRF2000 framework, as shown in Table 3. By comparing the calculated value with the known value, it can be seen that except for the large difference in the Y direction of the URUM station, the calculation results of the other points are good. The magnitude and direction of the drift velocity are basically the same as the speed provided by the IGS station. Consistent.
After obtaining the drift speed of each point in the ITRF2000 coordinate frame, then convert it to the N, E, U direction according to (9), and calculate the drift speed in the horizontal direction from the drift speeds in the N direction and the E direction (for details, see ) The drift velocity in the vertical direction (U), except that there is no obvious settlement at the Shanghai station, the other stations have a tendency to move upward and uplift.
There is a tendency to drift eastward, where the drift velocity in the west is faster, and the drift velocity in the east gradually decreases, which is basically consistent with the velocity and direction in the horizontal deformation speed table of the GPS station under the ITRF96 framework provided by the Shanghai Observatory; There is a tendency for upward movement and uplift in the direction, indicating that mainland China is affected by the interaction of the Pacific Plate, Indian Ocean Plate, and Philippine Plate.
4 Conclusion (1) GAMIT precision orbit determination software can eliminate or correct the main GPS errors: satellite clock error, receiver clock error, ionospheric refraction effect, tropospheric refraction effect, satellite and receiver antenna phase center deviation. In order to obtain high-quality baseline processing results, the parameter settings for GAMIT solution are introduced. The Quick solution is used to obtain cleaner data, and then the Regular solution is used to obtain the baseline single-day solution. The baseline repetition rate is solved to obtain no more than 2 The accuracy of 3mm and the vertical direction does not exceed 7mm, indicating that the accuracy of the baseline solution can meet the requirements of deformation monitoring.
(2) Using the station drift calculation model, the results of the single-day solution of multiple measurement sections simultaneously participate in the comprehensive adjustment, which not only considers the correlation between the calculation results of each period, but also considers the correlation between the stations.
Calculate the drift speed of each station under the ITRF2000 framework compared with the speed provided by IGS, except that the Y direction of the URUM station is poor, the calculation results of the other stations are basically consistent with the known speed; convert the drift speed to N, E , U direction, the drift speed of each station in the N and EU directions is basically the same as the drift speed and direction of the GPS station provided by the Shanghai Observatory under the ITRF96 framework.
Researcher Lu Chongwu, Institute of Seismology, China Earthquake Administration, visited Vietnam, invited by Professor NguyenNgocThuy, Director of the Institute of Geophysics, National Natural Science and Technology Center of Vietnam, from July 21 to August 1, 2002, Researcher Lu Chongwu, our institute A group of 6 people visited Vietnam. During Vietnam, Professor NguyenNgocThuy, Director of the Institute of Geophysics, Dr. LeHuyMinh, Deputy Director, Dr. HaDuyenChau, Deputy Director, and Dr. CaoDinhTrieu, Director of the Geodynamics Laboratory, received the delegation. The director of the Institute of Physics extended greetings and invited him to visit our institute in 2003. The delegation also made researches on the development of science and technology of the Institute of Seismology, China Earthquake Administration, the development of the China Crustal Movement Observation Network, the development of the SS * Y extensometer, gravity and solid tide observations, the China Crustal Deformation Observation Network, and the very wideband digital seismometer. A special report. After that, they visited the Vietnam National Natural Science and Technology Center and the HoaBinh Hydropower Plant Fault Observation Station 80km away from Hanoi. The Vietnamese side expressed satisfaction with the operation of the SS * Y type extensometer installed in my station.
During the visit, the two sides conducted detailed discussions on future bilateral cooperation. The two sides believe that between 2003 and 2005, the theme of bilateral cooperation between China and Vietnam was crustal deformation monitoring. In order to monitor the crustal deformation of Vietnam, the Vietnam Geophysical Institute will continue to install SS * Y extensometers in Vietnam and plan to install water pipe inclinometers. At the same time, it will work with our institute to conduct GPS surveys near the Red River fault zone in Vietnam. . The two sides also agreed to send scholars to carry out cooperative research together. The two sides also discussed the possibility of establishing cooperative projects such as GPS permanent observation stations, gravity change measurement stations and the installation of very wideband digital seismometers in Vietnam in the next few years. The directors of the two sides signed a cooperation memorandum on the above cooperation.
The China-Vietnam border area is an area prone to earthquakes. In the past, due to the lack of overseas data, the accuracy of the calculation of deformation and other data in the border provinces of China was limited. Carrying out the above-mentioned cooperation content will be conducive to China's monitoring of crustal movement and seismic activity in the surrounding areas, and greatly improve the accuracy of crustal movement calculation in the border area between China and Vietnam.
Zhuoligetu, Science and Technology Development Division, Institute of Seismology, China Earthquake Administration
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