## 4 Discussion  
Before beginning the discussion regarding the field results, a few things need to be noted:  
1. The graphical environment presented here is used just for the data visualization of the described integration process, not as the command and control software's GUI. 2. Since tests took over a year, the visualization environment underwent some changes during this time, hence there are some minor graphical differences between the figures presented in this chapter. Anyhow, the yellow vessel markers always represent MRFTPs, while white vessel markers always represent AIS data. Hexagonal encirclement around the vessel marker means that that marker is selected by an operator and details about the vessel are shown in a separate window. Trace colors behind vessel markers are random and thus don't have any particular significance. In order to demonstrate the algorithm's capabilities in a real working environment, several representative situations will be shown and described in this chapter. These situations are:  
1. A so called \"clear situation,\" that is, a single stable MRFT and corresponding single AIS dataflow with low latency. Here two cases will be examined: 1. Vessel is sailing in a straight line 2. Vessel is maneuvering 2. MRFT data inaccuracy 3. SAIS and/or LAIS data latency 4. Multiple MRFTs within single AIS data gating radius 5. Multiple AIS data with in single MRFT gating radius 6. AIS data absence, that is, only MRFT data and 7. MRFT data absence, that is, only AIS tracking  
Firstly, a so called \"clear situation\" will be discussed. A stable MRFT and low AIS data latency (latency is measured in minutes) are main characteristics of clear situations. Since there is no need to load data form history and/or extrapolate AIS data, the whole integration process is simplified. In Figure 4 a clear situation with a vessel sailing in a straight line is presented. The MRFT labelled with Id F_2033, originating from the radar 0, radar track ID No. 2720615, is a candidate for integration with its AIS source defined with MMSI 355194000 in its vicinity. Since the matching coefficient is very high (96.7%) both data points most likely originate from the same vessel and they will be fused into one track in further processing. Please note that AIS data latency in this case is barely a few minutes which makes integration process quite easy, since the tracked vessel moved only a few hundred meters. This movement is insignificant since the MRFT's gate radius is around 1 km (current MRFTP and the received AIS data is still within the same gate). Next, a maneuvering target will be considered and thus the implications of maneuvering on the integration process will be discussed. During maneuvering, the vessel changes its course and speed, the basic parameters used are matching factor calculations, which implies that matching factor value will drop accordingly. Here even a minute of AIS data latency stands out and has clearly visible implications on the integration process. In other words, due to the latency of the data, course and speed that are measured by HFSWR and reported by AIS can significantly differ. This leads to situations where the matching factor will drop temporarily, since the newly calculated matching factor will be quite low which will decrease the average value significantly. After the vessel stabilizes its course the matching factor will rise again. As an example, we may analyze the situation presented in Figure 5. The MRFT with ID number F_45894 abruptly changed its course by 90 degrees which lead to a fall of the matching factor. After the vessel stabilized its course, its speed and course that was reported by AIS and MRFT came to similar values and the matching factor came to 87.2%. It is important to note that during this temporary fall of the matching factor, the integration link was not broken and uniqueness of integration of the pair has been preserved. Figure 4: Resolving a “clear situation”—vessel is sailing in a straight line (light purple trace MRTF, light blue trace AIS).