This paper presents the post-processing method used for field measurement of mega jacket launch. The Liwan 3-1 mega jacket was successfully launched at a water depth of 190 meters in South China Sea on August 30, 2012. In order to study the influence between the jacket and the launch barge, the field measurement is designed to record the trajectory of both the jacket and the launch barge. Both Inertial Navigation System (INS) and Global Positioning System (GPS) are used to ensure the accuracy of the field measurement. The GPS has a higher accuracy but cannot work underwater. Therefore the INS is used to measure the trajectory motion of the launched jacket when the jacket completely goes into water. Since only INS can record the accelerations in 3 degrees in inertia coordinate system when the jacket is completely under water, a special method will be used to transfer the initial acceleration data to those in the geographic coordinate system, combined with the position data recorded by GPS when it works, we can get a relatively accurate launch trajectory of the jacket. In this paper, we focus on the method used for transferring the initial data recorded by INS and GPS to the trajectories of both jacket and barge.

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