The present invention relates to a method for tracking a maneuvering target with a slow scan rate sensor, and, more particularly, to tracking a highly maneuvering target without overburdening the target processing capabilities of a tracking system using such a sensor.
By "slow scan rate" is meant a scan rate, wherein a target monitoring or sensor system, such as a radar antenna or sonar hydrophone, examines a predetermined volume in space and returns to the same volume relative to the sensor in a time interval which is long relative to the anticipated or maximum velocity acceleration and maneuvering capability of a potential target. By way of example and not of limitation, a known radar system employs an antenna which is rotated or slewed through 360.degree. in about ten seconds. Thus for a stationary target, the sensor would return to the subject detection volume nominally every 10 seconds depending on the sensor platform or own ship motion, if any.
For certain current jet aircraft or missiles which may be desired to be detected and tracked, an interval as long as ten seconds between obtaining updated actual target position information may permit the target to maneuver far enough away from its previous historical position and path so that a next interval detection using a conventional system cannot be reliably correlated or determined to be the same target.
Tracking targets through their maneuvers is a classical tracking problem solved by conventional tracking algorithms. Successful target track is typically the result of frequent updates of target position during any maneuver. Slow scanning sensors do not provide the required frequent target updates for conventional trackers to maintain track on maneuvering targets. Within one scan interval of a slow scanning sensor, a maneuvering target, like a cruise missile, can initiate, perform, and terminate a large acceleration or high g turning maneuver away from its previous position and course. The term g is used to refer to acceleration in terms of a multiple of the acceleration due to gravity which is nominally 9.8 m/sec.sup.2 On the next scan, the target location may be a significant distance from the location predicted by the tracker from historical data of a predetermined number of prior scans and the target may be headed on a drastically different course from the one derived from such historical data. Either or both of these events may defeat the performance of conventional target correlation and tracking algorithms when employed in conjunction with a slow scanning sensor.
Previously developed scan-to-scan correlation methods for use with slow scanning sensors have exhibited a number of deficiencies such as excessive false alarms, target tracking limitations and/or intermittent target tracking. Some slow scan tracking methods employ small correlation gates to restrict the probability of false correlation,thereby limiting the false track report rate. These trackers do not have the capability to track maneuvering targets because of the insufficient size of the gates. Other tracker developments for use with such sensors have utilized large, non-optimally shaped correlation gates which can track maneuvering targets but which permit an excessive number of false correlations and false target reports. Further, use of such large gates inefficiently consumes target processing resources of the overall system, such as a radar or sonar by examining portions of a spatial volume where there is a low probability of finding the historically tracked target.