Abstract
Unmanned air systems are becoming ever more important in modern societies but raise a number of unresolved problems. There are legal issues with the operation of these vehicles in nonsegregated airspace, and a pressing requirement to solve these issues is the development and testing of reliable and safe mechanisms to avoid collision in flight. In this article, we describe a sense and avoid subsystem developed for a maritime patrol unmanned air system. The article starts with a description of the unmanned air system, that was developed specifically for maritime patrol operations, and proceeds with a discussion of possible ways to guarantee that the unmanned air system does not collide with other flying objects. In the system developed, the position of the unmanned air system is obtained by the global positioning system and that of other flying objects is reported via a data link with a ground control station. This assumes that the detection of those flying objects is done by a radar in the ground or by self-reporting via a traffic monitoring system (such as automatic identification system). The algorithm developed is based on game theory. The approach is to handle both the procedures, threat detection phase and collision avoidance maneuver, in a unified fashion, where the optimal command for each possible relative attitude of the obstacle is computed off-line, therefore requiring low processing power for real-time operation. This work was done under the research project named SEAGULL that aims to improve maritime situational awareness using fleets of unmanned air system, where collision avoidance becomes a major concern.
Highlights
IntroductionIntroduction and motivationMost coastal states have a problem with monitoring maritime activities in their waters, since it is necessary to patrol vast areas and resources are always scarce
Introduction and motivationMost coastal states have a problem with monitoring maritime activities in their waters, since it is necessary to patrol vast areas and resources are always scarce
Self-reporting systems such as automatic identification system (AIS). These systems tend, to be quite expensive to maintain, especially since there is usually a need to keep manned systems available to check the situation in loco
Summary
Introduction and motivationMost coastal states have a problem with monitoring maritime activities in their waters, since it is necessary to patrol vast areas and resources are always scarce. It is important to develop and test reliable and safe methods to avoid collision, and a lot of work has been done in this area.[2] For maritime patrol, and in the SEAGULL project in particular, the main risk of collision is between different UASs,[3] since a fleet of vehicles will be used This problem is easier to tackle since all vehicles will be using the same collision avoidance methods, and in some cases the vehicles will be flying in formations, where this problem has been studied.[4] According to Schaeffer,[5] in the United States, there are approximately 0.5 midair collisions per 1 million flight hours. Most of these collisions happen in uncontrolled airspace where there is no coordinating entity, and a decentralized approach, where each vehicle must act independently, is essential.[6]
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