|Density map based on Ter AIS, for all vessel types, using a resolution of 10km, for the month of December 2021||blue and purple colours indicate areas where Sat AIS have larger density values; yellow and red point to larger Ter AIS densities, while green indicates equal values from both sources (December 2021)||Density map based on Sat AIS, for all vessel types, using a resolution of 10km, for the month of December 2021.|
Maps of vessel density can be derived from the GPS-based Automatic Identification System (AIS) used by ships to signal the position of nearby ships and thus avoid collisions. These are transmitted by FM radio signals and can be picked up by shore stations provided the ships are within about 40 nautical miles of the coast and thus above the horizon and also by earth-orbiting satellites. The signals can identify the type of vessel (fishing, tanker etc.) and the vessel density maps derived from these signals are available through the European Marine Observation and Data Network (EMODnet) for European waters and on other platforms for specific purposes such as identification of illegal fishing.
A study carried out by MarineTraffic, the ship tracking and maritime intelligence company, has analysed the accuracy of these density maps and concluded:
Marinetraffic.com have produced digital map-layers indicating the reliability of the vessel density maps that will be made available through EMODnet and an improved open-source toolbox for producing the maps that is fully-documented and publicly available on GitHub