A new method for mining deformation monitoring with GPS-RTKGAO Jing-xiang1, 2, LIU Chao2, WANG Jian1, 2, LI Zeng-ke2, MENG Xiang-chao21. Key Laboratory for Land Environment and Disaster Monitoring of State Bureau of Surveying and Mapping,China University of Mining and Technology, Xuzhou 221116, China;2. School of Environment and Spatial Informatics, China University of Mining and Technology, Xuzhou 221116, China Received 19 June 2011; accepted 10 November 2011Abstract: Based on ranging intersection theory, a new method which is simple and easy to operate was proposed for data collection in the mine surface deformation monitoring with GPS-RTK centering rod measurements. It can fully eliminate the inevitable shaking error and the vertical deflection, and to some extent weaken the multipath effect on the estimates of coordinates in a relatively short period of time, using high-frequency observations. The results show that three-dimensional coordinates with a height accuracy better than 1 cm, horizontal accuracy better than 24 cm can be achieved through only 1530 s continuous observation by 20 Hz high-frequency and effectively improve the measurement accuracy and efficiency of RTK, fully satisfying the high-speed and high-precision data acquisition in mine surface subsidence deformation monitoring.Key words: GPS; rover pole; multipath delay; deformation monitoring In order to develop, utilize and protect the coal resources rationally, and promote and ensure the development of the coal industry, the Chinese government has enacted and improved some rules and regulations. A key problem of the rules is that how to confirm the range of protecting coal column by different coal mining methods, burial depth, seam thickness, roof and floor lithologic characters, geologic structure 1.Typically, a series of observation stations arranged at regular intervals (1525 m), measuring relative displacements of the stations by the traditional techniques (leveling, total station, etc), were established to summarize the change law of parameters of surface movement for production and construction of mine 2.However, the surface deformation is expensive to carry out or cannot be measured by traditional techniques in some coal mine areas, especially in the mountain. Hence, it is necessary to employ effective techniques to obtain the deformation data. Recent years, interferometric synthetic aperture radar (In SAR) 34, three-dimensional (3D) laser scanner 56, digital close- range photogrammetry 78 have received increasingly great attentions and have achieved firstfruits. However, at present they have boundedness to be used for deformation monitoring of mine surface and related theories should be continuously perfected in future research. Recent advantages in GPS receivers, antennas and data processing softwares, have made GPS RTK technique a very effective tool for deformation monitoring in coal mining areas 9, but the data-acquired quality still needs to be improved. With the main error sources including rover pole deflection of the vertical, un-modeled systematic error (gross error, multipath error, etc) and the height transformation error, plane accuracy can only reach 510 cm, the height accuracy can only 35 cm, which restrict the further application of this technology. Using tripod instead of rover pole and with longer observation to take full advantage of the cyclical nature of multipath can effectively eliminate or reduce the system error, but for a large number of mining ground deformation observation stations, the method means a huge amount of tasks. In the present work, a simple high-precision GPS-RTK measurement was proposed with the rover pole. That is, the position of the station can be obtained by ranging intersection with the coordinate series collected by continuously shaking GPS antenna. The relevant theory was deduced, the accuracy factor in different directions was given, and the feasibility of increasing sampling frequency and reducing the observation time to weaken the effect of multipath was analyzed in this mode Two experiments were done to evaluate the precision and accuracy of the models. 2 Theoretical foundation Usually, rover pole is used instead of tripod to improve operational efficiency, but the deflection and the shaking errors will appear inevitably. While the length of the rover pole is 2 m and the deflection angle of the vertical is 3, the the horizontal and the vertical deflections can reach 104.7 and 2.8 mm, respectively, which are main restrictive factors of GPS RTK technique applicable to mining subsidence monitoring and should be corrected. Without consideration of observation errors, the coordinate series collected by continuously shaking GPS antenna were on a sphere as discrete points (Fig. 1). Therefore, the positions of the stations can be obtained by ranging intersection with the length of the rover pole as the side length. Fig