Adaptation to the clutter environment by airborne maritime surveillance radars

Airborne maritime surveillance radars must detect small targets against a background of sea clutter whilst maintaining surveillance over a large area of sea. This task is very demanding and requires the radar to dynamically adapt to the local environment in order to obtain the best possible detection sensitivity. An aircraft flying at, say 3000 ft would be able to observe an area of sea of about 49,000 km, with a range to the horizon of about 124 km. Over this area, the clutter characteristics observed the radar will be continuously changing as a function of range and look direction. These characteristics will vary in a manner dependent on the prevailing conditions, the radar characteristics and the viewing geometry. In practice, the radar must cope with a very wide dynamic range of signal amplitude, with amplitude statistics varying from those of thermal noise to very spiky sea clutter and land. Continuous adaptation to this environment is required as a function of range and bearing. The dynamic behaviour of the radar as it adapts in this way is often a much more relevant measure of performance than more traditional static measures such as detection range. Methods used to adapt to the environment are surveyed in this paper, together with indications of how their dynamic behaviour can influence performance.