The problem of directional sensors and effectors: Dwell time and aiming errors

The effectiveness of directional sensors like video and IR cameras, and of directional effectors like acoustic devices and dazzlers, depends of course one's ability to aim the device onto its target. Aiming inaccuracies reduce the dwell time on a target and degrade expected performance. Aiming inaccuracies in turn depend on the velocity of the target, the sensor by which it is tracked (possibly human vision), and the aiming control system (possibly human or automatic). The effectiveness metrics for directional devices are usually assessed assuming static conditions-by the field of view and resolution for a camera, for instance, or the sound pressure level at beam centre for acoustic devices-without considering the dynamics that may arise in realistic engagements. Aiming inaccuracies enter into dynamics engagements to bad effect, especially in close engagements such as arise in merchant ship self-protection in counter piracy. It is shown how aiming errors generally increase in dynamic close engagements, and how the expected effectiveness of a directional device decreases accordingly. Where static performance metrics suggest ever-increasing effectiveness at decreasing range, the average dwell time or exposure can dramatically decrease at close range, completely ruining close-range effectiveness. A straightforward method is given to assess the aiming accuracy of an existing system (loop from sighting to aiming) accuracy. The results for an experimental port protection system (assembled at NURC PROVEx 09) are reported for illustration of aiming limitations. On the other hand, when given a particular aiming device and scenario, the allowable aiming uncertainties can be derived as system requirements.