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Automatic Identification System Data Fusion93Marine Research of the National Academy of Marine ResearchDOI: 10.29677/MR.202406_4(1).0006Figure 14. Schematic diagram of abnormal course over ground.Figure 15. Schematic diagram of ship information with MMSI 413212680. To assess whether there were anomalies in the heading data of a vessel in a stationary state, we started by obtaining two consecutive AIS data entries, D1 and D2, for the same vessel. Subsequently, we calculated the difference in true heading (DT) between D1 and D2 to evaluate whether the true heading data was normal for a vessel without a significant rate of turn. The purpose of considering the true heading difference was to account for potential errors in sensor measurements. If the difference in vessel heading exceeded 45 degrees, indicating a significant change in the vessel's bow direction, the AIS data entry was classified as abnormal. The abnormal judgment process for ship's course data is illustrated in the left flowchart of Figure 9. Based on the AIS data from the NAMR, the AIS data entries for the vessel with MMSI 413212680 indicate that the vessel was in a stationary state, as the vessel's speed over ground (SOG) was consistently 0, as shown in Figure 15. However, upon examining the true heading values for this vessel, there was a significant and rapid change within a minute, as shown in the highlighted region in Figure 16. The true heading difference exceeded the threshold of 45 degrees, indicating an abnormal change in the vessel's heading. Therefore, this AIS data entry was classified as abnormal and was removed from the dataset.