# The Impact of Space-Based AIS Antenna Orientation on In-Orbit AIS Detection Performance
## 3 Results and Discussion
### AIS Messages Comparison  
This section describes the comparison of total message number and unique MMSI received under nadir and maneuvered conditions. For detailed comparisons, each dataset has been categorized based on the AIS type messages according to the ITU definition [18]. The collection of AIS messages is categorized in Table 2.  
The resulting activity of before, during, and after the 90\({}^{\circ}\)-maneuver and 45\({}^{\circ}\)-maneuver, respectively, is shown in Figures 9 and 10. Those figures consist of the comparison of total AIS messages and each categorized message according to Table 2 excluding Class A static and other messages. The exclusion of those types of messages is due to its low reception performance resulting in none of the received messages. In Figure 9, it is shown that the total number of messages received during the maneuvering, i.e., \(D_{90}\), (orange bar) are not significantly improved compared to before the maneuvering, i.e., \(D_{0}\) (dark-blue bar). This trend is almost consistent with other categorized AIS data. This phenomenon could be understood since the antenna coverage patterns are quite similar while performing nadir and 90\({}^{\circ}\)-maneuvered, as provided in Figure 4a,c. However, there is an interesting point that after the maneuvering (light-blue bar), the number of total received messages increases by about 29,07% on the average compared to during the maneuvering. We have investigated into the reason and found out that this condition is caused by the procedure used to set the satellite back to nadir after performing a certain maneuver. Before the maneuver, the current satellite flight configuration is nadir, as shown in Figure 4a. In case an operator wants to change the current configuration to 90\({}^{\circ}\)-maneuvered flight configuration, it just needs to perform a straight forward maneuver by rolling the satellite. Moreover, to achieve 45\({}^{\circ}\)-maneuvered from the current nadir flight configuration, the pitch and roll maneuver have to be performed. Changing satellite orientation from nadir to 45\({}^{\circ}\)-maneuvered or 90\({}^{\circ}\)-maneuvered flight configurations can be achieved during a single satellite pass period. However, based on satellite attitude information, bringing back the satellite attitude to precise nadir flight configuration from a maneuver condition needs several adjustments; hence, it can be completed for about two to three satellite pass periods due to the limited access of  
Figure 9: Comparison of AIS message acquired under the 90\({}^{\circ}\)-maneuvered flight configuration. a ground station. In this transition time, the AIS antenna orientation varies \(\pm\)10\({}^{\circ}\) towards its flight direction. As a consequence, after the maneuver, the satellite is not immediately set to its nadir flight configuration. Therefore, all of the AIS datasets acquired after the maneuvering consist of a higher number of AIS messages compared to the number of messages acquired before the maneuvering, since these datasets are acquired under the combination of nadir and maneuver flight configuration. Based on Figure 10, it is confirmed that the performance of an AIS receiver during the 45\({}^{\circ}\)-maneuvered increases significantly compared to before and after the maneuver, except for Long-Range AIS messages type. For Long Range AIS on Run-3, although the 45\({}^{\circ}\)-maneuvered is capable of receiving a higher number of messages than before the maneuvering, this reception is still lower compared to after the maneuvering. On Run-4, the message reception of Long-Range AIS before the 45\({}^{\circ}\)-maneuvered is similar to the message reception during the 45\({}^{\circ}\)-maneuvered. We believe that the exception for Long Range AIS is caused by the small order of the number of received messages. Therefore, there is not enough data to make a statistically relevant conclusion.