At present, GPS static positioning technology is widely used in geodesy, engineering survey, cadastral survey and deformation monitoring. In these applications, it is mainly used to establish control networks of different levels and uses. Compared with conventional measurement technology, it has the characteristics of all-weather, short observation time, flexible point selection, high measurement accuracy and automation of observation and data processing. In this paper, the simulated GPS static positioning technology is applied to the deformation monitoring experiment of modern bridges, and the conclusion is given, which is of guiding significance to practical projects.
1, experimental situation
The experiment was carried out on the roof of a building. The monitoring network * * * consists of nine points, eight of which are compulsory centering observation piers, numbered GP 1, GP2, ................................................................................................................................. In the experiment, 9 Leica 1230 GPS dual-frequency receivers were used for synchronous observation. The antenna type is Leicaax 1202, the data sampling rate is 15 seconds, and the satellite altitude angle is used. The experiment was carried out in one day, from 9: 30 a.m. to 16: 20 p.m. It was sunny and northerly.
Because the experiment is carried out on the roof, there are no obstacles around, and the field of vision is wide, which conforms to the characteristics around the bridge. In addition, although the length of the bridge varies from a few hundred meters to dozens of kilometers, it still belongs to the short baseline; From the distribution of monitoring points in the figure, four points are located on the center line of the bridge, and the other four points are located on both sides of the bridge. The distribution of measuring points is uniform, which accords with the distribution of measuring points in actual bridge monitoring. Therefore, the experiment has strong universality and the conclusion has universal significance.
2. Data processing
In the experiment, after the data is exported and converted into RENIX format, we use TGO software to process the data. First, create a new project, establish and select the corresponding coordinate system, import data, input the name of editing point, antenna height and antenna type, edit the cycle slip timeline and then process the GPS baseline; Then, firstly, the unconstrained adjustment of monitoring network is carried out under the framework of WGS-84. After passing, select the local coordinate system, add the datum coordinates, adjust the constraint of the network, and output the results. TGO solves the process of static monitoring network.
All the eight monitoring points changed slightly to the south (1~2mm), which may be caused by the north wind. However, from 12 to 15, it moved northward (up to 4~5mm at the maximum) and reached stability at 16, which may be the cause of sunshine. Because each monitoring point is an observation pier of cement pouring, and the south side is irradiated by the sun, the thermal expansion is greater than that of the north side, which leads to the northward movement of each point to varying degrees.
In the east direction Y, as can be seen from Figure 4, each monitoring point first changes slightly to the west (about 2mm), and then gradually moves to the east, but the change values in both directions are not large. This is also because of sunshine. In the morning, the sunshine in the east is strong, pointing to the west. After about 14, the sun shone westward, causing the point to move eastward again, but the changes in both directions were not great.
In addition, it can be seen from the adjustment report of TGO in the last period that the plane accuracy of the point is 0.003m and the elevation accuracy is 0.0 14m, that is, the plane observation accuracy of GPS static positioning technology can reach millimeter level and the elevation accuracy can reach centimeter level. Because the deformation of bridges often reaches several centimeters or even dozens of centimeters, GPS static positioning technology can be used for high-precision deformation monitoring of bridges and other construction projects.
In the experiment, because it is predicted that the deformation of each monitoring point will change in a small range of millimeters, in order to better see the deformation trend of each point, we only divide the data into six time periods, each of which lasts for one hour. This is undoubtedly too long for projects that often need real-time monitoring to get deformation. In fact, we can shorten this period to a certain length to meet the monitoring needs, and adopt certain methods to improve the accuracy and reliability of the observation results. For example, for a long-distance and long-span bridge, because the bridge is linear, the geometric strength of the network may deteriorate, and we can use pseudolite technology to improve it. According to the characteristics of deformation monitoring, we can explore the fast calculation method of integer ambiguity, such as DC algorithm [7], so as to quickly determine the integer ambiguity and get the real-time and reliable deformation value.
4. Conclusion
From the simulation experiment, it can be seen that the static positioning method similar to the establishment of hierarchical control network has high accuracy and reliable results, and can be used for deformation monitoring of bridges or other construction projects. With the development of GPS observation and data processing automation technology and multi-antenna array technology, GPS static positioning technology can not only obtain reliable deformation values in real time, but also greatly reduce operating costs, thus better serving national production.
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