Satellite Imaging for Maritime Surveillance of the European Seas

Surveillance of ships at sea poses particular challenges for spaceborne sensors: small targets need to be detected, wide areas need to be surveyed, and both targets and background are anything but stationary. Incidental, snap-shot images find their application niches – among the existing technologies for ship monitoring – mostly in alerting to the presence of unknown targets and in surveying outlying areas. The main applications in the European seas cover fisheries control, pollution control and maritime border security, although operational use is still sporadic. The sensor of choice is SAR, because it allows ship detection over wide swaths and under many conditions. High-resolution optical sensors can provide additional information on ship classification, which is still difficult for SAR. Their narrow swaths, however, mostly limit their use to predetermined locations. Clutter from the sea surface hinders detection of the smallest ships, especially at high sea state, leading to false alarms and to less than 100% detection probability. For many applications these drawbacks can be kept within acceptable limits by proper choice of the swath width/reso- lution combination. Satellite sensors may also image ship wakes, from which information on ship speed and heading can be gleaned. Crucial to operational use is the ability for automatic analysis. This is relatively well developed for ship detection, and less well for classification and wake analysis, in SAR images, and quite immature for optical images.