MnrAq

Inventories of CO2 emissions from international shipping 2007–2012 33
1.2.2 Summary of data and method input revisions
Data
Access to increasingly detailed data on ships’ activity was enabled by the advent of S-AIS, which began
providing significant coverage in 2010. These data enable the specifics of any ship’s operation to be identified
on an hourly basis, or even more frequently if required. S-AIS allows greater fidelity in the calculation of the
fleet’s aggregate operational characteristics. For the first time in global inventory calculations, the activity of
specific individual ships (e.g. actual vessel speed over ground) and consequent engine load and emissions can
be considered as a component of an overall inventory calculation. In the Second IMO GHG Study 2009, a
limited sample of terrestrial AIS data was used to calculate ship activity parameters (speeds, days at sea, etc.).
In that study, ship activity could only be observed for a subset of the fleet and only within approximately 50
nmi of available shore-based receivers (only partial coverage of coastal regions), which left the activity of
vessels in the open ocean unobserved. In this study, the consortium brings together a number of data sets
from both terrestrial and satellite receiver operators and merges the data to provide extensive spatial and
temporal coverage of shipping activity observations. A visualization of the merged AIS data for 2012 is shown
in Figure 24.
Figure 24: Chart showing the coverage of one of the merged AIS data sets used in this study (2012,
all sources, but no LRIT)
Observations in the merged AIS data set of ship activity (speeds, time spent in modes) are compared to similar
data derived from samples of the global fleet from LRIT. In all, data concerning approximately 8,000 ships
were put together (see Section 1.4 for details). LRIT data were not used in the Second IMO GHG Study 2009.
A visualization of the LRIT data for 2012 is shown in Figure 25. LRIT data are of lower temporal resolution than
AIS data but provide higher reliability and therefore enable important quality checks for the AIS data set and
the bottom-up calculations of average speeds and days at sea.