The Enhancement of SAR-Based Iceberg Surveillance using Space-Based Automated Identification System Data
Power, Desmond; English, Jerry; Hewitt, Robert
There is a long history of the use of satellite Synthetic Aperture Radar (SAR) for ship detection and surveillance dating back to the launch of the ESA ERS satellites in 1992. Satellite SARís large swath and ease of data collection regardless of geography makes it particularly attractive for maritime surveillance. At present, there are a large number of service companies offering ship detection services on an operational basis and there have been a number of projects that have funded capacity building to support large scale surveillance programs. SAR is also used for iceberg surveillance to support mapping of maritime hazards. Compared with ship detection, this is a more recent SAR application, with the first operational program implemented within Polar View in 2003. Today, maritime surveillance with SAR is mature and its use is prevalent throughout the world.
Automated Identification System (AIS) is used by ships and Vessel Traffic Services (VTS) to identify and locate ships, primarily for the purpose of collision avoidance. AIS involves the use of VHF transponders aboard vessels to report ship identification, tonnage, position, course and speed. The use of AIS transponder is mandated by the International Maritime Organization (IMO)'s International Convention for the Safety of Life at Sea (SOLAS) on ships with gross tonnage of 300 tons or more. In addition to collision avoidance, AIS is also used for vessel surveillance. However, shore based AIS receiver have a range that is limited to the horizon, and a network of range-overlapped shore based receivers will only provide surveillance along the coast. The use of AIS receivers onboard satellite systems in an emerging technology for global monitoring of SOLAS class ships. Satellite-based systems eliminate the horizon limitation to provide global coverage. However, there are some inherent limitations on the exploitation of this technology, particularly in regions of high ship densities. In spite of these limitations, Space-based AIS (S-AIS) promises to offer added value to companies and agencies responsible for maritime surveillance.
This presentation demonstrates the combined use of S-AIS data and satellite SAR to improve monitoring of transportation in iceberg-prone waters. One of the challenges in using satellite SAR for monitoring icebergs is in discriminating between ship and iceberg targets. To this end, C CORE has developed discrimination algorithms for use on SAR-derived targets; discrimination rates are highly accurate, particularly for high resolution SAR data. Nonetheless, the algorithms are never 100% effective and any additional information to assist in discrimination rates is valuable. The use of S-AIS vessel detections improves the accuracy of a SAR-based discrimination algorithm by reducing confusion. This is accomplished by correlating S-AIS detections with SAR detections and positively identifying these targets as vessels.