Third IMO Greenhouse Gas Study 2014

Annex 1 167
more random. The overall effect of the days at sea and the days at port can be seen in the histograms in the
third column.
Figure 8: Illustration of the extrapolation process
The application of the above method was considered acceptable for 2010 to 2012 AIS data sets. However, for
previous years no satellite data was available, which would inevitably lead to bias, notwithstanding the bias
correction within the extrapolation algorithm. The adopted extrapolation method discussed above or a linear
extrapolation would particularly affect larger ships that would be out of range for greater periods of the year.
Therefore, for the years 2007 to 2009, following the application of the extrapolation method, the data sets
were further adjusted to align with an external source for days at sea. This was applied using “best available”
data, as follows:
• In 2007 and 2008, the extrapolation algorithm is calibrated to the days at sea reported in the Second
IMO GHG Study 2009 for the year 2007 (it is assumed that 2007 and 2008 saw similar operation).
• In 2009, the extrapolation algorithm is calibrated to the days at sea as analysed from LRIT data in this
year (see Annex 3 for greater discussion).
This had the dual effect of correcting the bias towards days in port (observed if only shore-based AIS data is
used) but also provided comparability with the Second IMO GHG Study 2009 estimates for emissions for the
year 2007. Limited analysis of the quality of these assumptions is carried out in Section 1.4 (due to limitations in
the availability of noon report data in these earlier years of the study), but extensive analysis of the assumption
is carried out in Section 1.5 to test the consequence of missing AIS data on the uncertainty of the inventory.
Assumptions for auxiliary and boiler power demands
Ship technical data are required to estimate ship emissions in the bottom-up model. The primary source of
technical data used for this study is the IHSF ship registry database. Ship technical data utilized from the IHSF