# The Impact of Space-Based AIS Antenna Orientation on In-Orbit AIS Detection Performance
## 3 Results and Discussion
### Individual Message Reception Performance  
As described in the previous section, according to IMO regulation, several types of ships should transmit their AIS signals containing the status of their ship every several minutes. By using this positive assumption, we have also performed the ship tracking in order to observe the individual message reception performance of particular ships as explained in Section 2.3.2 by using the \(D_{0}\), \(D_{45}\), and \(D_{90}\) datasets. The ship tracking is required to assess the impact of different antenna orientations specified by its flight configuration to the number of the message received by the space-based AIS system. The visualization of the ship tracking results are provided in several figures below.  
From Figure 15, it can be seen that a similar ship is detected in the South American Ocean having 100% re-detection probability. This ship has a different AIS message reception during the 45\({}^{\circ}\)-maneuvered and 90\({}^{\circ}\)-maneuvered observations. A ship with MMSI number 735058041, an Ecuador oil tanker ship, was detected 35 times before the maneuver, 22 times during the 90\({}^{\circ}\)-maneuver, and 43 times after the maneuver. At different times, this ship was detected 26 times before the maneuver, 35 times during the 45\({}^{\circ}\)-maneuvered and 27 times after the maneuver. From that data, the 45\({}^{\circ}\)-maneuvered is capable of providing higher message reception compared to the 90\({}^{\circ}\)-maneuvered and nadir flight configuration.  
In Figure 16, in an ocean near the Philippines that has 50-60% re-detection probability, we also made a tracking of a class A ship with MMSI 374131000. This bulk carrier ship with a Panama flag was detected one time before the maneuver, four times during the 45\({}^{\circ}\)-maneuvered, and three times after the maneuver. This ship was detected four times before the maneuver, one time during the 90\({}^{\circ}\)-maneuvered and four times after the maneuver. According to this ship reception data, in the area that only has 50-60% re-detection probability, the 45\({}^{\circ}\)-maneuvered is also better than the 90\({}^{\circ}\)-maneuvered in terms of message reception performance.  
Figure 14: Comparison of unique MMSI detection performance as 45\({}^{\circ}\)-maneuvered and 90\({}^{\circ}\)-maneuvered flight configuration applied on the satellite.  
We have also performed some sampling of class B ships in the area which has 100% re-detection probability around the Pacific Ocean, as provided in Figure 17. Class B ship usually uses small transmit RF power, around 2 watts, so detection of this type of ship from space is a challenge. In the area of the Pacific with 100% re-detection probability, class B could be detected quite well. One sample of Taiwanese fishing ship with MMSI 416004043 has been detected 26 times before maneuver, 50 times during 90\({}^{\circ}\)-maneuvered, and 51 times after maneuver. This fishing ship has also been detected 23 times before maneuver, 100 times during the 45\({}^{\circ}\)-maneuvered and 50 times after the maneuver. According to this message reception data, in this case, the 45\({}^{\circ}\)-maneuvered leads to better performance compared to the 90\({}^{\circ}\)-maneuvered. This result may be caused by the effect of Faraday rotation of the AIS signal  
Figure 16: Class A sample of ship tracking in an area of 50–60% re-detection probability.  
Figure 15: Class A sample of ship tracking in an area of 100% re-detection probability.  
received in space. Furthermore, radio wave reflection from the seawater surface; & radiation pattern of ship-borne VHF antenna may fully match its radiation pattern with the satellite's antenna [22]. The other way to increase the performance could be done by placing a directional antenna to narrow the coverage on a higher orbit satellite, especially in the equatorial region and also there is a study to develop 5-element dual-polarized array AIS antenna to provide full Earth coverage [23; 24].