Third IMO Greenhouse Gas Study 2014

Annex 1 165
Figure 6: Example plot of coverage indicated by source of data
Extrapolating ship annual profile to generate complete annual operational profiles
As discussed above, the coverage of activity reports varies temporally and spatially, with significant
improvements in later years. However, to determine the emissions for the global fleet over the whole year, a
complete hourly data set of speed and draught for each ship is required.
This is done by correcting for biases in each year of data. A linear extrapolation is not suitable in most cases
as the data is often biased towards shore-based data, particularly in years 2007 to 2009 which do not have
satellite data and are therefore naturally biased towards shore-based reports. Together with this, satellite data
will be bunched around the period that the ship is in range of the satellite.
As a result a method was developed that disaggregated the full year activity reports into discrete trips comprising
a port phase, a transition phase and a voyage phase. Each trip is considered discretely with infilling of missing
data drawn from in-phase samples.
The algorithm defines the phases as below:
• Port/anchor phase: Any activity report with a speed of less than 3 nm/hr. This is consistent with the
definition of days at port used throughout this report.
• Voyage phase: Characterized by a speed over ground above a calculated threshold and a standard
deviation of less than 2 nm/hr within a six-hour rolling window. This threshold is the 90% percentile
of speeds reported above 3 nm/hr.
• Transition phase: This is defined as the period when a ship is transiting in and out of port or anchor. It
consists of the remaining activity reports that have not been classified as port or voyage.
The phases are displayed visually in Figure 7 for an example ship.