Ship encounters model

29 Figure 27 – Density map of total ships with TSS.

Thus, it is confirmed that the highest traffic areas correspond to the TSS, which reveals the importance of these density maps in the assessment of maritime traffic. With this correlation, it can be confirmed that cargo ships and tankers (with hazardous cargo) that were in transit (between 10 and 15 knots) and were identified in the corridors of the trajectories plots (Figure 25 e Figure 24, Respectively), were navigating in the respective TSS corridors.

30 Figure 28 – Ship encounters detections (Jupyter Notebook)

While Jupyter Notebook allows to observe the results instantaneously when running the code, QGIS allows to analyse the attribute table and to understand which ships are involved in the detected encounters. Figure 29 allows visualizing which are the ships identified in the encounter situations under analysis. Their identification was omitted for security reasons, but it can be seen that each ship has been identified twice.

Figure 29 – Ship encounters detections (QGIS)

Based on the analysis of the previous figure, it appears that four ships are in the conditions specified by the algorithm, despite being marked with red circles four situations classified as encounters. It is noticeable that each pair of detected ships has two events considered as encounters.

31 In order to understand the behaviour of the ships identified in the encounters, an analysis of their total daily track within the study area was carried out.

Figure 30 – Tracks of detected ships

From Figure 30 it can be seen that QGIS allowed visualising the tracks of the 4 ships involved in the encounters, over a whole day. The encounters under analysis were found to be located along the north-eastern edge of the study area, not far from the coast (between 7 and 11,3 NM from the coast). In order to better visualize the tracks of the ships involved, Figure 31 and Figure 32 show, on a larger scale, the pairs of ships that have been identified. The first pair is the one that was identified further west and the second pair is the one that was further east. In both cases, it can be seen that the tracks are similar in each pair for a significant period of the route. More specifically, the timings and courses shown in the figures demonstrate that the ship pairs were in close proximity for an equivalent period of time and moving in the same direction. Additionally, they show similar reduced speeds. Such values may indicate transhipment actions.

32 Figure 31 – Tracks of detected ships (first pair)

Figure 32 – Tracks of detected ships (second pair) Ship B

11:03 – 11h30 Course 220

Speed 2.7

Ship A 11:00 – 11h22

Course 219 Speed 2.9

Ship C 07:58 – 08h03

Course 073 Speed 2.3

Ship D 07:54 – 08h02

Course 076 Speed 2.0

33 In a practical use, in which illegal transshipment activities would be under investigation, these ships would be subject to a more detailed investigation based on the results presented in Figure 31 and Figure 32. A technique that can significantly help to understand if there are potential illegal actions includes the integration of satellite images, especially optical and high-resolution ones.

Depending on the temporal resolution of the images, there may be records of the proximity of ships, in which possible exchanges of people or goods can be seen.

Additionally, the detected encounters were overlaid on the density maps, in order to identify the characteristics of maritime traffic in these areas. Thus, within the investigation and monitoring of illegal activities, there may be a focus on certain areas according to the traffic density where these situations are more likely to occur. In this way, the maritime surveillance effort can be better targeted by the competent authorities.

Figure 33 shows the overlapping of the encounters with the total density map, in which it appears that they occurred in areas with moderate traffic. The meetings were all located in yellow areas, away from the heavy traffic areas, symbolised in red.

Figure 33 – Density map of total ships with the detected encounters

Figure 34 shows the overlapping of the encounters with the density map of merchant vessels, in which it can be seen that they occurred in areas with reduced traffic. The meetings were located in blue areas, away from areas with moderate or high merchant ship traffic, symbolised in yellow or red respectively.

34 Figure 34 – Density map of merchant vessels with the detected encounters

Figure 35 shows the overlapping of the encounters with the density map of fishing vessels, in which it can be seen that they occurred in moderate and high traffic areas. The encounters were located in yellow or orange areas, which correspond to areas of moderate or high traffic density of fishing vessels. In parallel, they are far from the areas with the lowest density of this type of vessel, which are blue or green areas.

35 Figure 35 – Density map of fishing vessels with the detected encounters

Figure 36 shows the overlapping of the encounters with the density map of passenger ships, in which it can be seen that they occurred in areas with reduced traffic. All the encounters were detected in blue areas, where the lowest density of this type of vessel is recorded.

36 Figure 36 – Density map of passenger ships with the detected encounters

Based on the analysis of the previous images, it can be assumed that the probability of these encounters occurring is higher in areas where fishing vessels are present. On the other hand, in TSS areas, with greater maritime traffic, mainly from merchant ships, this probability is lower.

To understand this correlation, Table 4 shows the types of ships that were detected, as well as their nationality and length.

Ship number Type Flag Length

Ship A Fishing vessel Portuguese 15 m

Ship B Fishing vessel Portuguese 15 m

Ship C Fishing vessel Portuguese 25 m

Ship D Fishing vessel Portuguese 26 m

Table 4 – Types of ships detected in encounters

It can be observed that all the vessels detected are Portuguese fishing vessels, which may be an indication that they are engaged in fishing activity, like other vessels in the same area. However, the detected pairs may have also carried out an illegal transshipment of fish or other goods. It is verified that the length of the ships is similar within each detected pair, that is, between ships A and B, and between ships C and D. This similarity can also facilitate transshipment activities.

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