# The Impact of Space-Based AIS Antenna Orientation on In-Orbit AIS Detection Performance
## Materials and Methods
### Analysis Method
#### 2.3.2 Individual Message Reception Performance  
Besides comparing the entire number of messages which existed on each dataset, in this paper, we have also observed the change in the number of received messages of a particular ship as different satellite maneuvering is performed. This step was performed in order to assess the effect of satellite maneuvering on individual message reception performances of a moving ship. The assessment of individual message reception performances was carried by tracking a particular ship continuously before the maneuvering, during the maneuvering, and after the maneuvering stage. Practically, this assessment can be carried out by extracting the messages of the desired ship specified by its MMSI on \"before\", \"maneuver\" and \"after\" datasets from corresponding maneuvering processes. The extracted messages are then ascendingly sorted based on acquisition time. By using these sorted messages, the ship's positions are then plotted and provided as a multi-temporal plot. For convenience, the number of messages received by a particular ship before the maneuvering, during the maneuvering, and after the maneuvering were also displayed on the plot. There are only a few ships which were assessed in terms of individual messages reception performance. These selected ships have been chosen since during the maneuvering period they were found in our area of interest. The area of interest has been assigned by employing the map of global tracking capability of LAPAN-A2 AIS receiver as the reference. The map was generated by employing the method proposed by [PERSON], which was used to estimate the global tracking capability of space-based AIS using Norwegian AISSat-1 receiver [20]. The results of this method are based only on the data recorded by the space-based AIS sensors themselves without involving any ground truth data. The tracking capability represents the probability of re-detecting ships as they move around the globe and is explained to represent an upper bound on a space-based AIS system performance. In this work, a probability of re-detection map has been used as the reference as provided in Figure 8. This map was generated by using 2 days of the LAPAN-A2 AIS which dataset consisted of 19,955 unique vessels, from 1 October 2018, 00:00:00 UTC to 2 October 2018, 23:59:56 UTC. This dataset has been filtered in order to exclude the messages transmitted by re-used MMSI identifiers which can be recognized by its calculated speed exceeding 60 knots [20]. Based on this map, it is confirmed that the LAPAN-A2 AIS receiver is capable of producing an identical global tracking capability map compared to the map generated by [PERSON], which is provided in his work. \begin{table}
\begin{tabular}{c c} \hline \hline
**Data Categorization** & **Message Type** \\ \hline CLASS A POSITION REPORT & 1,2,3 \\ CLASS A STATIC & 5 \\ CLASS B & 18,19,24 \\ LONG RANGE AIS & 27 \\ AIS ATON & 21 \\ AIS BASE STATION & 4,10,11,20,23 \\ OTHER MESAGES & 6,7,8,9,12,13,14,15,16,17,22,25,26 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Categorization of AIS message type. By using the map provided in Figure 8 above, the area of interest has been set to the area having 50-60% and 80-100% of re-detection probability. The areas having 80-100% of re-detection probability are located on low traffic density, such as the Pacific Ocean, Indian Ocean, Arabian Sea and South American Ocean. Furthermore, the areas having 50-60% of re-detection probability are located on the transition region of the 80-100% and the high ship traffic density region, such as the Gulf of Mexico, Gulf of Oman and the ocean near the Philippines. The higher the tracking capability of an area, the higher the possibility to receive an AIS message transmitted by a ship in that area. Based on this definition, the tracking capability map was employed in order to observe the impact of maneuvering the antenna orientation to the message reception performance of an individual ship located on the area having a certain probability of re-detection value.