Precise Point Positioning/Magnetic Compass Integrated Robust Wave Level Application for Long Period Wave Detection in Buoy's wind up

摘要

Recently, there are many applications for detection wave level on the buoy. However, accurate and precise determination of sea surface height and long term sustainability of the system are prerequisites for long period wave detection on the wave level buoy, and normally GPS (Global Positioning System) based system satisfies these conditions. Especially, wave level application using PPP (Precise Point Poisitioning) make up for RTK (Real-Time Kinematic) GPS disadvantages that the operating range of positioning is dependent on the existing atmospheric conditions and is usually limited to a distance of up to 10-20 km[1]. Wave level application developed by KRISO (Korea Research Institute of Ships & Ocean Engineering) can detect long period wave in the ocean, using GPS/magnetic compass integrated navigation system. However, depending on the weather conditions and state of sea, buoy moves the position and turn on a yaw axis. This adversely affect precise positioning navigation which uses carrier phase, because GPS satellites transmit L-band signals which are righthand circularly polarized (RHCP)[1]. The measured carrier phase, therefore, varies when the receiving and/or transmitting antennas change their relative orientation. This effect is known as carrier phase wind-up[2]. The receiver's wind-up affects carrier phase's range error and continues to remain until missed signals. Although one cycle of carrier phase is short, such as 19cm and 24cm in distance units on L1 and L2 respectively, wave level application which requires cm-level precise positioning for long period wave detection is remarkably influenced by receiver's wind-up. Simon Banvile and Gui Tang showed that measurements has a strong correlation with the rotations of receiver antenna. Additionally, to overcome this problem, the usefulness of the decoupled clock model has been demonstrated [3]. However, this experiment has been carried out in static position, but not in dynamic position. Wave level application developed by KRISO compensates receiver's wind-up using the magnetic compass on the dynamic buoy and outcomes precise positioning results using PPP. Eventually, it provides accurate wave level information. To validate wave level application for long period detection in the real sea, experiment had been carried out at one kilometer away from Jukbeon-port in South Korea. For comparison of wave level results, commercial wave level buoy of KMA (Korea Meteorological Administration) is used. On July 4th, 2014, beaufort scale recorded 4 that means moderate breeze and sea conditions are small waves with breaking crests and fairly frequent whitecaps, and average wave level is 1.2m, as well as maximum wave level is 2.4m respectively via KMA's. Rotations in yaw axis occurred up to 15 times during 30 minutes regardless directions and removed from measurement using magnetic compass. In the result, it seems like the resulted wave level of KRISO's buoy is approximately equal to the significant wave level and the maximum wave level in commercial buoy. In regards to small errors at the result, it considers that the errors include accelerometer errors from commercial buoy. As a means of experiment, long period wave over 300 seconds generated by a simulator was added to measure wave level. Accordingly, the long period waves can be detected by KRISO's wave level application. In conclusion, Recently, although the number of GNSS (Global Navigation Satellite System) based applications carrying long period wave detection are growing, most of them does not operate carrier phase error compensation from the receiver's wind-up. Before the compensation, measurement errors make big errors for precise detection of long period wave. In this reason, this paper proposed the receiver's wind-up compensation using magnetic compass. For the experiment, the application validates for detection of long period wave in the environment occurring frequent rotation of buoy. Because the long period waves did not