The invention relates to a method for passive determination of target data associated with a target from measured and estimated bearing angles of the type mentioned in the precharacterizing clause of claim 1, to an apparatus for carrying out the method according to claim 10, and to a computer program which has suitable program code means for carrying out the method.
In order to determine the range, velocity and course of a target, for example of a surface vessel, a submarine or of a torpedo, as target data associated with the target from a carrier vehicle, for example a surface vessel or a submarine, without giving itself away, a sonar receiving installation is used to receive sound waves of the target noise, and to measure bearing angles to the target. These bearing angles are used to estimate a position of the target as a function of the carrier vehicle's own position, and to calculate an associated estimated bearing angle. This is dependent on the target moving uniformly, that is to say on a constant course without acceleration.
DE 34 46 658 C2 discloses a method which iteratively reduces the difference between measured and estimated bearing angles over a plurality of processing cycles, until an error limit is undershot. When this error limit is undershot, the estimated position on which this is based is identified as the target position. The target data associated with this target position is therefore optimized on the basis of a predetermined optimization criterion, depending on the iteration method that is used. These include an optimized solution, which is updated with every new bearing angle measurement during each processing cycle. In uniform conditions, in particular without any target manoeuvre or change in the sound propagation, the optimized solution will evermore closely approach the actual solution as the observation time increases, because the solution which is in each case defined as the best solution, that is to say the optimized solution, converges with the actually correct solution at an earlier or later stage depending on the optimization method that is used and the current scenario.
One such method, which is also referred to as target motion analysis (TMA), has the disadvantage, however, that the calculated solution may be unrealistic because of unknown disturbances in the received signals. If the input data is received with major errors, the TMA method sometimes estimates unrealistic or illogical target data, such as a velocity of 80 knots or a departing course, even though the target is on an approaching course.
WO 2009/156337 A1 discloses a method in which the reliability of the optimized solution is indicated in addition to this solution. For this purpose, a multiplicity of different target tracks and a quality measure for each of these assumed target tracks are calculated during each processing cycle. The reliability of the optimized solution can be deduced from the distribution of the quality measure.
A further method is disclosed in DE 10 2007 019 444 B3, in which bearing angle measurements from a second transducer arrangement, which is arranged at a distance from a first transducer arrangement, are used for estimation of the target data when a parallax value, which is determined between the bearing angle measurements from the two transducer arrangements, is greater than a predeterminable parallax limit value and the range estimated for the target data estimate is less than a comparison range determined from the parallax limit value.
EP 1 531 339 A2 describes a method in which limit values are predetermined for the target data, thus resulting in the iterative estimation process producing only physically and technically sensible target data. Completely unrealistic or illogical results, such as a range of 1000 kilometers, which can invariably occur in the iteration process when the received signals are subject to heavy noise, are excluded from the start.
An optimization method such as this, in which limit values are taken into account for the target data during the optimization process, is referred to as constraint TMA (CTMA). By way of example, the limit values are entered manually by an operator or else are determined from geographic characteristics. Even coarse presets make it possible to exclude estimates of target positions which could not possibly be detected by the sonar receiving installation.
However, the known CTMA method has the disadvantage that its optimized solution cannot converge with the actually correct solution if the limit values are chosen incorrectly. Since the CTMA solution corresponds to the global minimum of an optimization criterion within the defined limit values, this does not produce the actually correct solution when the actual solution is outside the solution space defined by the limit values. After a convergence phase, the simple TMA method would therefore produce more accurate results than the CTMA method if the limit values had been chosen incorrectly.
The invention is therefore based on the problem of identifying and correcting incorrectly chosen limit values when using an optimization method for determination of target data.