Abstract:  To achieve highprecision docking and positioning of immersed tubes in deepwater, the measuringtower method for coordinatebottom calibration is proposed. The immersed tube is stably located on a gravel base bed to accurately calibrate the relative position between the measuring tower and the immersed tube by prelaying the gravel bed in a deep dock, thus improving the measuringtower positioning accuracy and realizing highprecision docking of the immersed tube. The accuracy and stability of the measuringtower floating calibration are difficult to be effectively guaranteed and improved owing to the influence of the floating of the immersed tube. Further, the immersed tube is located on the gravel base bed after the completion of the measuringtower calibration under the immersedtube floating condition. Additionally, the measuring instrument is installed at the land control point to calibrate the feature points at the top of the immersed tube and measuring tower and perform a coordinate transformation. Subsequently, the positioning parameters obtained using the two calibration methods are inputted into the positioning system and compared with each other. Finally, the accuracy of the positioning results obtained using the two methods is verified by measuring the immersedtube installation. It is proven that the positioning parameters obtained using the two methods are stable and reliable and can effectively improve the installation and docking accuracy of the immersed tubes.

Key words: immersed tube, measuring tower, coordinate-bottom calibration, floating calibration, feature points, coordinate transformation, accuracy comparison