Port Visits Using Real-Time Shipping Data

The Automatic Identification System (AIS) is the international system for tracking ship movements. Ships of a certain size and type are required to carry a transponder which transmits their location and other key information regularly, and this is used for real-time ship monitoring. Stored AIS data is an example of Big Data due to the extremely large amount of signal data generated every minute by ships around the world. This data offers an alternative method for compiling statistics on maritime traffic. Ireland, as an island relying heavily on sea transportation for tourism and transport, is ideally placed to capitalise on the potential offered by faster AIS-based maritime indicators. AIS-based data could significantly reduce the time lag between the reference period and the publication of official statistics and even has the potential to produce maritime indicators on a weekly basis. This release aims to showcase how AIS data can be used to generate reliable and valid port call statistics by comparing AIS data with CSO official data sources.

Tables and Figures

In this release the AIS port call statistics are based on two methods developed by the CSO: The Boundary Crossing Method (BCM) and the Stationary Marine Broadcast Method (SMBM). Both are described in “Data Source, Methods and Quality”. These are compared with the CSO’s Statistics of Port Traffic which are published on a quarterly basis from returns made by Port Authorities.

Overall, on a national level, the AIS-based port calls follow closely CSO’s official number of port visits. Figure 1.1 compares the number of vessels that arrived at six Irish ports using AIS-based port calls and CSO’s official numbers from the first quarter of 2021 to the first quarter of 2022.

Based on the administrative data for 2021, a total of 11,552 vessels arrived in the six Irish ports. This number increased to 11,640 when using AIS data with the Boundary Crossing Method (BCM) and to 11,804 when using the Stationary Marine Broadcast Method (SMBM). While the AIS methodology produces a slightly higher number of port calls it is clear from Figure 1 that the AIS data mirrors the trends in port calls across 2021 very closely.

Similarly, when the AIS data is analysed across the individual ports (see Figures 1.2 to 1.7) it produces the same trend as the administrative data across the five quarters, and the results show that most vessels arrived in Dublin port followed by Rosslare, Cork, Waterford, Drogheda and Bantry Bay. While the overall trends are very similar, there are some differences between the AIS numbers and administrative data in some ports. The AIS-based port calls for Dublin, Waterford and Bantry Bay almost match the official figures exactly. Compared with data from CSO’s Statistics of Port Traffic, all vessels which arrived at Bantry Bay were correctly identified (100%) using AIS data (see Figure 1.4) and only small differences exist between the number of vessels that arrived in Dublin and Waterford using AIS and administrative data (see Figures 1.2 and 1.3).

In the other three ports there are more obvious differences between the AIS and administrative data sources and some volatility between the estimates across quarters. Using AIS data, significantly fewer port visits were detected in Drogheda (see Figure 1.5) than recorded in the administrative data. These differences will be further investigated, but preliminary examination suggests that due to invalid IMO or MMSI numbers it is not possible to match all vessels to the IHS Shipping Registry. This led to AIS data from some vessels not being included.

For Cork and Rosslare ports there are also some differences between the administrative and AIS numbers, with the administrative data generally lower than the AIS methods in Rosslare (see Figures 1.6 and 1.7).

The AIS data provides a very similar breakdown of ship classification when compared to administrative data. In 2021 cargo ships accounted for 79% of the total port calls in Ireland according to the administrative data. Similarly, both AIS-based port call methods show that cargo ships accounted for nearly 77% of visits. The smallest share of arrivals were dry bulk and specialised ships and Figure 1.8 highlights that AIS data also capture this breakdown correctly.

Overall, the findings of this project confirm that AIS data could be used to produce valid estimates of port calls and illustrates the potential of Big Data for official statistics.

However, the release also highlights some inconsistencies in the AIS methods and further work will be required to improve the accuracy of both methods. For example, the CSO will have to investigate why not all vessels in the administrative data were detected in the AIS methodologies and vice versa. This will help to understand why in some ports AIS-based port calls exceed official numbers and why in others (e.g. Drogheda) AIS-based port calls are below official numbers.    

This release confirms the potential of AIS data as a supplementary source to existing administrative data to enable timelier official maritime statistics going forward. The use of AIS data would allow the CSO to publish preliminary estimates of port call statistics and trends within days of the end of the reference period, with these estimates being revised or adjusted subsequently with administrative data.