MnrAq

Inventories of CO2 emissions from international shipping 2007–2012 65
shore-based stations. This difference can be seen by contrasting the first (2007) and last (2012) years’ AIS data
sets, depicted by geographical coverage in Figure 46.
Figure 46: Geographical coverage in 2007 (top) and 2012 (bottom), coloured according to the intensity
of messages received per unit area. This is a composite of both vessel activity and geographical coverage;
intensity is not solely indicative of vessel activity
The consequence of the change in coverage over time and the quality of the regional coverage can be
inferred from an analysis of the number of messages received in different sea regions. Two investigations were
carried out, on large oil tankers and large bulk carriers, both ship types that were anticipated to be engaged
in activity on routes that encompassed most of the world’s sea areas. Figure 47 displays the trend over time
in the number of messages received in different sea regions for a random sample of 300 large oil tankers.
The number of messages received is a composite of the number of ships in an area, the duration of time
they spend in an area and the geographical coverage of an area. This analysis cannot isolate the change in
geographical coverage alone. However, the marked contrast in open ocean regions (e.g. Indian Ocean, South
Atlantic Ocean and North Atlantic Ocean) over time shows increased quality of coverage on a regional level.
Importantly, by 2012, there are no sea areas for which no activity is observed, which implies that by the latter
years coverage quality has minimal regional bias. Greater detail and maps of both AIS and LRIT data for further
years is provided in Annex 3 (details for Section 1.4).