Third IMO Greenhouse Gas Study 2014

200 Third IMO GHG Study 2014
Figure 14: The average volume of AIS activity reports for a region reported by a ship
for up to 300 randomly selected Capesize bulk carriers from 2007 to 2012
In summary, the coverage of AIS in 2011 and 2012 can be considered to be very rich. There are no areas
identified in this analysis for which there is no coverage available, although the volume of reports in some
areas has decreased with a drop in coverage in some coastal regions from 2009 to 2010, but this greatly
improves in the following years.
Activity estimates temporal coverage QA/QC
To test and verify the number of days at sea and the speed profiles derived from the AIS data, results are
compared to LRIT data. LRIT data complements AIS data by providing an independent data source against
which the quality of the AIS data can be tested. Under LRIT, ships must send position reports to their flag
administration at least four times a day, or every six hours. The transmission process is different to that of AIS
so that LRIT is not subject to the same constraints that can limit AIS coverage. In particular, recording of AIS
messages depends on the ship being located in the field of view of either a land- or a space-based AIS receiver
and the successful reception of the message by that receiver. LRIT messages are not recorded by the same
receivers and coverage by LRIT is therefore largely independent of coverage by AIS data.
The data sets hold LRIT messages from 6,441 distinct ships in 2009, from 8,716 ships in 2010, 8,127 in 2011,
and 8,838 in 2012 (see Table 5). If four position reports per day are considered full coverage, this would
correspond to 1,460 messages (1,464 in 2012) per year per ship. Table 11 shows the mean number of LRIT
reports per ship. In 2010–2012, most ships came close, with more than four reports per day from very few
ships and with fewer than four reports per day from some ships. In 2009, there were fewer reports per ship
as LRIT was still coming into operation during that year. There are different reasons why there may be fewer
than 1,460 (1,464) reports per year from a ship. For example, some reports might be lost and, of course, ships
entering into service in a given year would not have the full number of reports in that year. It could also be
the case that ships are laid up and inactive for some part of the year, and the LRIT signal is only transmitted at
times when the ship is active/in service.
Table 11 – Mean number of messages by ship for LRIT ships used in the analysis
2012 2011 2010 2009
Mean no. of messages 1,194 1,161 1,118 342