Third IMO Greenhouse Gas Study 2014

Annex 3 203
Figure 16: Plots of difference in fraction of time spent at sea for all ships, with increasing
high-confidence AIS count over the year. For each ship in one of these 5%-wide bins,
the difference between fraction of time at sea between AIS and LRIT is calculated.
The mean of this difference per bin is plotted in red, and the standard deviation
of the difference in each bin is plotted in blue
Speed is also compared from AIS-derived estimates to the LRIT estimates. During the processing and
extrapolating from AIS data, the AIS data are resampled to hourly bins. This introduces uncertainty into the
estimate of the speed of the ship, as the ship speed is not constant throughout the hour. To highlight this
uncertainty, Figure 17 shows the distribution of the difference between reported speed and resampled speed
for a ship travelling at its average speed.