Research on the method of three-dimensional surface displacements of Tianjin area based on combined multi-source measurements

Combining multi-source measurements can improve the accuracy and the spatial resolution of the three-dimensional (3-D) displacements field. Few researches have been conducted to integrate InSAR, GPS and leveling data of Tianjin in the recent three years to get the 3-D large displacement velocity field. How to effectively combine multi-source measurements and obtain the accurate 3-D large displacement field in high spatial resolution is worth studying. In this paper, the optimal method for acquiring 3-D displacement field by combining InSAR, leveling and GPS measurements is obtained by comparing the different methods. Then we realize the combining InSAR, leveling and GPS measurements to obtain the high-precision 3-D displacement field in Tianjin (China) from 2016 to 2018. Compared with different methods, we integrate InSAR, GPS and leveling measurements and use the weighted least squares method to estimate the 3-D displacement field with the highest accuracy. Although the accuracy of the horizontal displacement field obtained by this method has not been greatly improved, the vertical accuracy is obviously better than the other methods. The introduction of leveling measurements is beneficial to improve the accuracy of the vertical displacement field. Compared with independent GPS measurements, the standard deviations of 3-D displacements velocity field estimated by optimal solution method is 2.6 mm/yr, 2.1 mm/yr and 2.7 mm/yr in the vertical, eastern and northern directions, respectively. These results indicate that this method effectively utilizes the advantages of GPS, InSAR and leveling measurements, and extends the limitations of a single technical in describing surface-time scale applications. And the 3-D displacements information with a large spatial scale and high spatial resolution provides a reliable data basis for studying the crustal movement and its dynamic mechanism in China.