Since 2001, Automated Identification Systems (AIS) have been required for most commercial marine vessels – international transit ships with a gross tonnage of 300 or more and all passenger ships. Ship tracking with AIS not only provides continuous detailed location information, but also other factors are captured, such as vessel speed, navigation status, heading, name, type of cargo, ship size and draught, VHF call signs, and destination. Currently, more than 40,000 vessels worldwide are equipped with AIS.
A recent report by Eastern Research Group Inc. and the Texas Commission on Environmental Quality employed this archived ship tracking data to study marine vessel emissions. The report looked at coastal Texas vessel traffic patterns (with the exception of the Houston/Galveston/Bazoria port area). The coastline of Texas is over 600 miles long and vessel emissions information is important to proactive marine planning by the State of Texas.
The collected historical data was supplied by AIRSIS and developed from PortVision data. PortVision processes more than one million records a day along the Sabine-Neches ship channel alone, just one of the locations in the study. PortVision, an operating unit of AIRSIS, tracks and retains 64 data elements for each vessel transmission; seventeen were used for the emission report.
The vessel tracking report analyzed individual vessel movements as well as general traffic patterns within 9 nautical miles of the Texas tidewater coastline. 132 Points of Interest (POI) were identified where AIRSIS maintains vessel monitoring stations in Texas state waters. Each POI covers a radius of 40 miles, and, depending upon conditions, may include reliable coverage up to 60 miles. The total data included more than 80,000 ship transits in 2007-8 for every vessel type. All departures, arrivals and passings in the target area were included in the study.
ERG linked this AIS data to vessel and engine characteristics (e.g., vessel speed, cylinder displacement, and power rating) from the Lloyd's Register of Ships, the American Bureau of Shipping, and Bureau Veritas. Using this cross-referenced data, quantifiable emissions estimates were possible. Emissions of interest included carbon monoxide, volatile organic compounds, nitrogen oxides, sulfur oxides as well as inorganic compounds such as metals, ammonia, biphenyls and hexachlorobenzene. These were evaluated by quantity, county, and vessel type.
One conclusion of the report indicates that being able to access historical AIS data, like that supplied by PortVision, is promising when studies such as these are necessary. Being automatic and electronic, reporting consistency and ease of manipulation are maximized -- far easier and more accurately than manual logs. However, a lack of POIs in some areas, as well as the fact that AIS equipment is not required of some vessels, such as tugs and fishing boats, makes any data collection for studies such as this challenging.
The report will be utilized by Texas to determine where adjustments are needed in refining their ship channel and port vessel emission requirements.