Third IMO Greenhouse Gas Study 2014

64 Third IMO GHG Study 2014
increased numbers of satellites providing greater spatial and temporal coverage, and increased
experience in filtering and processing the raw data for use in modelling.
• A quality advantage in this work is that our approach for the bottom-up activity-based inventory
uses calculations for individual vessels. By maximizing vessel-specific activity characterization using
AIS data sources, this work quantifies the variability among vessels within a type and size category.
This eliminates the dominant uncertainties reported by the Second IMO GHG Study 2009 and most
published inventories.
• The AIS-informed bottom-up methodologies cannot directly distinguish between fuel type and voyage
type, which requires additional analyses and some expert judgement. Our QA/QC on allocation
of residual/distillate fuels (HFO/MDO) and international/domestic shipping provides transparent and
reproducible methodologies, with the opportunity to adjust these if and when better information
becomes available in the future.
At the time that this report was written, there were too few data sets of on-board measurements of CO 2
emissions for any statistically representative quality assurance investigation of the modelled CO 2 emission to
be carried out. The closest that the quality assurance can therefore get to the end product of this study is the
fuel consumption comparison (modelled estimate compared with operator data), carried out using noon report
data. This is done for a sample of approximately 500 ships (approximately 1% of all vessels) representing over
60,000 days of at-sea operation. This sample is described in detail in Annex 3. It should be noted that noon
report data are not infallible; their reliability and the implications for the comparative analysis undertaken here
are discussed in greater detail in Annex 3.
To provide further assurance of the inputs and assumptions of the bottom-up method, specifically the activity
estimate, the consortium also performed analysis with LRIT data (approximately 8,000 ships and 10% of the
global fleet) and third-party literature study.
Noon reports, LRIT data and the literature were used for the following components of quality assurance work:
• The activity estimation quality was assured using:
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spatial coverage analysis with information on the number of messages received in different geographical
locations and contrasting the AIS coverage with coverage maps obtained from alternative sources (e.g.
LRIT);
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temporal coverage analysis to test whether the derived profiles of time spent in different modes of
operation (e.g. in port, at sea) and at different speeds are representative;
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comparison of the AIS-derived activity parameters speed and draught against noon report data;
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description of coverage statistics for each year and each fleet (to evaluate AIS completeness and
facilitate imputed algorithms to estimate CO 2 emissions from periods when observations are missing).
• Fleet specifications and model assumption quality were assured using:
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investigations into the robustness of the IHSF database;
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comparative evaluation of prior work, independently produced and published by consortium
members, including peer-reviewed reports and scientific articles;
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consultation of third-party inventory and shipping literature (including the work of consortium partners)
providing substantial fleet data.
• Fuel consumption estimate quality was assured using:
––
comparison of calculated fuel consumption to operators’ data recorded in noon reports pooled from
data independently collected by several consortium partners.
It should be noted that noon report data are not infallible; their reliability and the implications for the
comparative analysis undertaken here are discussed in greater detail in Annex 3, along with detailed QA/QC
for the source data and other analyses.
Spatial coverage of activity estimates QA/QC
The AIS data coverage, in terms of both space and time, is not consistent year-on-year during the period
studied (2007–2012). For the first three years (2007–2009), no satellite AIS data were available, only data from