IL201612A - Method for passive determination of target data - Google Patents

Description

METHOD FOR PASSIVE DETERMINATION OF TARGET DATA The invention relates to a method for passive determination of target data by directionally selective reception of soundwaves, of the type mentioned in the precharacterizing clause of claim 1.

In order to determine the position, speed and course of a target, for example of a surface vessel, submarine or torpedo as target data without giving away one's own carrier vehicle, for example a surface vessel or submarine, soundwaves of the target noise are received, and bearing angles to the target are measured, using a sonar receiving installation. The position of the target is estimated, and an associated estimated bearing angle is calculated, from these bearing angles together with the own positions of the carrier vehicle. The difference between the measured and the estimated bearing angles is reduced iteratively until an error limit is undershot. The fundamental estimated position is identified as the target position.

Starting from an initial position of the target which, for example, is chosen' arbitrarily as a start position on a first bearing ray, or is known by other sensors located on board, positions are calculated from estimated x-y components for the target, and bearing angles estimated therefrom are determined. When carrying out bearing angle measurements, the carrier vehicle travels on a constant course and at a constant speed for a predetermined time period and travels over a distance which is referred to as own leg. For an initial determination of the target data, it is necessary for the carrier vehicle to carry out a maneuver and to change its course or its speed, and therefore carry out a new own leg. The next bearing angle measurements then allow a first target data determination .

It is already known from EP 1 410 060 for target data to be determined without any maneuver of the carrier vehicle, in that the received signals, which are combined on a directionally selective basis to form array signals, from the electroacoustic transducer arrangement are subjected to Fourier transformation, and the frequencies of spectral lines are determined in the frequency spectrum of the array signals . The frequency of one or more combined spectral lines as a received frequency is used together with the measured bearing angle for target data estimation. Target positions are estimated, and estimated bearing angles relating to them are determined. A bearing angle difference is determined between the measured and the estimated bearing angles. In addition, a Doppler shift and a transmission frequency emitted or transmitted by the target are estimated from the same estimated target positions and their rates of change. The estimated transmission frequency is f equency-shif ed corresponding to the estimated Doppler shift and forms the estimated Doppler frequency, from which the received frequency is subtracted. The difference between the received frequency and the estimated Doppler frequency is used as a difference frequency together with the bearing angle difference in order to determine the target data, using the least squares algorithm .

The object of the present invention is to provide a method of the type mentioned in the precharacterizing clause of claim 1, in which the target data can be determined reliably and matched in time to the tactical requirements, without any own maneuver and without frequency evaluation.

According to the invention, this object is achieved the features in the characterizing part of claim 1.

The bearing angles of two transducer arrangements on board a carrier vehicle, which are at a distance from one another, are combined with one another, with the distance between the transducer arrangements being very much less than the ranges of the associated sonar receiving installations, as a result of which the bearing angles to the target differ only insignificantly from one another. The first transducer arrangement is, for example, a cylindrical base of a passive panorama installation, such as that described by way of example in German patent specification 2 136 780. Soundwaves are received over a broadband width by means of adjacent directional characteristics and a target is detected, and the bearing angle to the target is determined, by comparison of array signals of the directional characteristics. The transducer installation is located in the bow of the carrier vehicle, for example of a submarine.

In addition, receiving antennas of a so-called PRS (passive range sonar) system, for example as known from US-PS 4 910 719 are installed along the flanks of a submarine for broadband reception of soundwaves, or a flank array system is installed at a distance from the cylindrical base, and is likewise used to find the bearing of a target. By way of example, the same carrier vehicle additionally tows a towed array antenna, for example as described in DE 4 341 364 C2. There, the various transducer arrangements are used to identify which side that the bearing results from the towed array antenna are on.

In the present invention, the bearing angles of two transducer arrangements and the distance between them are combined to form a bearing triangle with respect to the target, whose base line is this distance. When a target is detected by both transducer arrangements, then the range to the target is several orders of magnitude greater than the distance between the transducer arrangements. The acute angle at the target location is very small at long ranges, since the two main reception directions of the directional characteristics run virtually parallel. The parallax which results from the distance between the transducer arrangements is used, according to the invention, for estimation of the range to the target, by determining the parallax value and comparing it with a predeterminable parallax limit value. A worthwhile cross-bearing for determination of a target data record exists only when the parallax limit value is exceeded, thus allowing estimation of target track, range to the target and target speed by means of the bearing angles of the second transducer arrangement. This cross-bearing means there is no need for an own maneuver, the knowledge of a start position of the target, and frequency evaluation of the received signals which are combined to form array signals. The second transducer arrangement that is required is fitted on board the carrier vehicle in any case, and its received signals are likewise subjected to signal processing in order to find the bearing of the target.

The parallax limit value covers a location area to the side of the carrier vehicle which is bounded on the one hand by the vessel-relative, maximum possible bearing angle rays of the main receiving directions of the two transducer arrangements, and on the other hand by a maximum permissible range or limit range, limited by the parallax limit value. The parallax limit value corresponds to a limit angle of a bearing triangle which is formed by the bearing angle, the distance between the transducer arrangements and the limit range to the target. This limit range is used as a comparison range, in order to make it possible to preclude estimated ranges to the target which are not in the location area.

The presetting of the parallax limit value and of the comparison range result in target data records being output which converge without any own maneuver and in particular can be assessed as being reliable in the close-range of the submarine. The closer the target is, the greater is the parallax value and the greater is the accuracy of the range estimates.

Expedient embodiments of the method according to the invention and advantageous developments and refinements are specified in the further claims.

The parallax value between the bearings of the two transducer arrangements involved is determined by forming a sliding mean value of the differences between the bearing angles measured by the two transducer arrangements . This compensates for scatters in the measurement of the bearing angles.

In order to calculate the parallax limit value, the standard deviations of the bearing angle measurements of each transducer arrangement are continuously determined, squared, added, square-rooted and multiplied by a factor c, and are divided by the root of the number of bearing angle measurements per processing cycle of the target data estimation process. The factor c is preferably c = 1.8. The processing cycle is, for example, 20 seconds. The dynamic determination of the parallax limit value takes account of the dependency of the accuracy of the estimation of the target data on the scatters of the bearing angle measurements .

A new target data record is estimated with every new bearing angle measurement of the transducer arrangements involved. A comparison with the target ranges estimated in the previous processing cycles provides information about the stability of the estimate. For comparison, a straight line is placed through a predeterminable member of estimated ranges, and the range differences of the estimated ranges from the straight line are determined. In addition, a stability criterion is obtained for the estimation of the target data and the confidence level in this by comparison of the mean value of the range differences with a predeterminable limit value or determination of the standard deviation of the estimated ranges and comparison with a predeterminable stability measure.

During the bearing angle measurements, the parallax value, the range to the target and its stability are estimated continuously. Furthermore, the parallax limit value and the associated comparison range are determined. As soon as the parallax value exceeds the parallax limit value, the estimated range is less than the comparison range and the estimated ranges to the target have a certain stability, the further associated target data record, specifically the course, speed and the range to the target, are also output, in addition to the bearing, which is always output.

If the estimated range is equal to or less than a predeterminable minimum range, the target is in the immediate close area of the submarine as a carrier vehicle. In this case, an additional warning of the output of the target data is a major advantage for the operation and protection of the carrier vehicle.

If the standard deviation of the estimated range is low, indicating a stable estimate, the number of bearing angle measurements to be considered for target data estimation is reduced. The advantage is that the target data of targets which are not traveling on a straight course at the same speed can also be estimated reliably, since the measurement sections and therefore the processing cycles for a target data estimation are correspondingly short, and the target is moving in a straight line at a constant speed in these short sections. This applies in particular in the case of a target maneuver or in the case of a target which is approaching at high speed. When the number of bearing angle measurements to be considered is reduced, the parallax limit value also becomes correspondingly higher, and the comparison range is reduced. These measures allow robust target data determination in hazard situations.

The advantage of the method according to the invention is the respective matching of the determination of the parallax value, of the parallax limit value and of the comparison range to the target data determination and its stability.

The invention will be described in more detail with reference to one exemplary embodiment of a method for passive determination of target data. In the figures: Fig. 1 shows a bearing triangle, Fig. 2 shows a block diagram with two transducer arrangements, Fig. 3 shows a scenario with bearings from one carrier vehicle to a target, Fig. 4 shows a time profile of the parallax value associated with the scenario shown in figure 3, Fig. 5 shows a timing diagram of the range estimation process for a scenario as shown in figure 3, and Fig. 6 shows a functional relationship between the comparison range and the bearing angle.

On board a submarine, a first transducer arrangement with electroacoustic transducers in the form of a cylindrical base 11, as is shown in figures 1 and 2, is located in the bow. The signals received by the cylindrical base 11 are combined in a sonar receiving installation in the form of a passive panorama installation to form array signals with adjacent directional characteristics in a beamformer 12 which receive sound omnidirectionally on a directionally selective basis, corresponding to the main reception directions of the directional characteristics. The main reception directions point at right angles to respective cords, which are offset around a transducer, of a circular arc, which is fitted with transducers, of the cylindrical base 11, in that the signals received by the electroacoustic transducers are subjected to a propagation time delay or phase delay, corresponding to their distance from the circular arc to the cords, and are added to form array signals . Using the cylindrical base 11 as shown in figure 1, a target Z is detected at a vessel-related bearing angle (pca- The longitudinal axis L of the submarine is the reference axis for the bearing angles (pca.

The bearing of the same target Z is found at a bearing angle (pfa by a second transducer arrangement, which is arranged at the distance D from the transducer position of the first transducer arrangement, and is in the form of a flank array 13. The signals received by the flank array 13 are delayed for this purpose in a second beamformer 14, corresponding to the different virtual scan angles of the flank array 13, and are added to form array signals, thus creating a fan of directional characteristics, whose adjacent main reception directions cover a sector at the side of the submarine.

The flank array 13 finds the bearing of the target Z at a bearing angle (pfa, with respect to the longitudinal direction L. Together with the distance D, the bearing angles cpca and cpfa form a bearing triangle, at whose apex the target Z is located. The range R to the target Z is very much greater than the distance D between the two transducer arrangements, the bearing angles (pca and cpfa are virtually the same, and differ only by a parallax value P.

The sonar receiving installation of the cylindrical base 11 on board the submarine contains an estimation filter 15 for passive determination of target data from bearing angles (pCai> 9ca2/ -■■/ < can/ which are measured along a so-called own leg at own positions of the submarine E0, Ei, En to the target Z with the submarine travelling at a constant velocity, while the target Z is moving at a constant speed v on a target track γ from the target position Zo to the target position Zn, as is shown in figure 3 in a right-angled north-east coordinate system with a kilometer subdivision, whose origin is the own position, Eo- The ranges to the target R0, Ri, ... Rn are likewise shown in figure 3.

In the estimation filter 15, which is described by way of example in DE-PS 3 446 658, first target data can be determined from bearing angles (pca only when the submarine is carrying out a maneuver itself and is continuing on its second own leg at an angle to the first own leg, or at a different speed. The bearing angles measured on the second own leg are now linked to the bearing angles measured on the first own leg, making it possible to estimate the range to the target, by iteratively minimizing the bearing angle differences, based on the principle of least square errors. For this purpose, the estimated bearing angles are determined in the estimation filter 15 from the respective next estimated position of the target, which is assumed by presetting an estimated speed and an estimated course of the target as the next target position. When the sum of the bearing errors between the estimated and measured bearing angles is less than a predeterminable error, the best possible estimate of the target parameters range, course and speed is identified.

In order to estimate the target data for each bearing measurement of a transducer arrangement, the estimation filter 15 uses the corresponding transducer location position relating to the time at which the bearing angle was measured. These transducer location positions are determined in a position computer 151 from the own position of the submarine, as calculated by an integrated navigation installation 152, with the aid of an inertial platform, from the longitudinal direction L of the submarine as determined at that time by a compass 153 and from the distances between the installation locations of the transducer arrangements and the installation location of the inertial platform. The exact installation locations are stored as distances relating to the longitudinal direction and lateral direction of the submarine, in the form of tables in a memory 154, with these tables being created and supplied by the dockyard.

Instead of a maneuver by the carrier vehicle, bearing angles (fa of a second transducer arrangement and an estimated parallax value are taken into account, according to the invention, in order to determine the target data in the estimation filter 15. The parallax value P, as shown in figure 1, is estimated by subtraction of the two measured bearing angles tpca and >fa. For this purpose, a sliding mean-value window is placed over a predeterminable set M of subtractions in a parallax computer 16, that is to say 60 differences are used, by way of example, for a data rate of 1 Hz: The estimated parallax value P is compared with a parallax limit value Pumit calculated in a parallax limit value computer 17. The parallax limit value Pumit defines a bearing triangle, whose apex angle clearly shows that the bearing rays from the cylindrical base 11 and the flank array 13 are not parallel, as shown in figure 1. This parallax limit value Pumit is determined from the estimated scatters acpa, afa of the bearing angle measurements using the cylindrical base 11 and the flank array 13 of a number Nca or fa of bearing angles measured during one processing cycle for estimation of a target data record: By way of example, one processing cycle lasts for 20 seconds .

The estimated parallax value P is compared in a downstream comparison circuit 18 with the calculated parallax limit value Piimif When the parallax value P is equal to or greater than the parallax limit value Pumit r the bearing angle measurements Figure 4 shows the time profile of the parallax value when the carrier vehicle is travelling from the start point E0 along its own leg as shown in figure 3. If the distance between the two transducer arrangements is D=30m, and there are a total of N=20 bearing angle measurements from each transducer arrangement and a respective scatter in the bearing angle measurements of o"ca = Using the bearing triangle as shown in figure 1, the time profile of a limit range or comparison range Rum t is calculated taking into account the measured bearing angle The comparison range Rnmit is calculated in a range computer 30: Ri|mjt . D ..Si!l& (3) > The bearing angle cpca from the beamformer 12 and the parallax limit value Piimit from the parallax limit value computer 17 are applied to the input side of the range computer 30. The comparison range Rumit is compared in a range comparison stage 31 "with the estimated range Rest from the estimation filter 15. When Reat ≥ Riimit/ a logic circuit 40 is operated, whose input side is likewise connected to the comparison circuit 18. The estimated target data record, comprising the range to the target Z, the speed v of the target Z and the course γ of the target Z, is released to be displayed on a situation display 21, by means of a control signal at the output of the logic circuit 20, when the logic circuit 40 simultaneously receives controlling signals from the outputs of the comparison circuit 18 and the range comparison circuit 31.

This time for releasing the display corresponds to the own position Eg of the submarine and position Z9 of the target in figure 3. In somewhat more than 8 minutes, the target Z has travelled in a straight line on a course γ from its start position Zo at the speed v to the target position Zg. At this time, the range between the submarine and the target Z is Rest = 2.2 km. The profile of the parallax value P in figure 4 and the comparison range Riimit n figure 5 show that all the subsequent target data estimates can be supported by the bearing angles < fa of the second transducer arrangement, and there is no need to carry out any own maneuver .

By way of example, the target data is re-estimated every 20 seconds. If Monte Carlo simulation runs are carried out for the scenario illustrated in figure 3, then the transient behavior of the target data estimate for the range R to the target Z is obtained, as illustrated in figure 5. The true range Rcrue to the target Z is shown by the curve represented by a solid line in figure 5. At the time t=0, the true range Rtrue = 5 km. The curve Rest in figure 5 shows the mean value of the respective range estimates produced in this time. The dashed curves Re3t + σκ and Re3t - aR above and below the profile Re3t indicate the standard deviations of the range estimates from the various Monte Carlo runs. After 0.8 minutes, the first range value is estimated in each Monte Carlo run, as a result of which the first mean value of the estimated range Rest s then also available. As time passes, the curve for Reat approaches the curve for the true range Rtruef with a scatter that becomes less all the time.

The range differences ARi of the estimated ranges Re3t with respect to a straight line placed through the estimated ranges Rest are determined in a regression circuit 32, are averaged in an averager 33, and are compared with a limit value Am, which can be predetermined in a transmitter 34. The output of the averager 33 is likewise connected to one input of the logic circuit 40. When the range differences are less than the limit value Am, the logic circuit 40 is operated .

Range standard deviations aR of the range estimate are determined selectively in a computer circuit 36 via a switch 35 and are compared with a stability measure SR from a preset circuit 37, which is likewise connected to one input of the logic circuit 40. When the range standard deviation aR is less than or equal to the stability measure SR, the logic circuit 40 is operated. For the scenario illustrated in figure 3, the stability measure SR is reached after 9 minutes, and the estimated range Re3t is then 2 km (see figure 5) .

For an additional warning indication, the logic circuit 40 is connected on the output side to a further comparison stage 41, whose input side is connected to the range comparison stage 31. As soon as the output of the logic circuit 40 emits a signal for indication of the target data record to the situation display 21, the comparison stage 41 is activated. The estimated range Rest is compared with a minimum range Rmj.n which can be preset in a transmitter 42. If the estimated range Rest is less than the minimum range Rrain/ the warning indication on the situation display 21 is activated by the output signal from the comparison stage 41, since a target is in a surrounding area with a radius which is less than the minimum range Rmin to the own vessel, and this can indicate a hazard to vessel safety. This situation occurs, as shown in figure 5, at a predetermined minimum range Rrain = 2.0 km after 10.8 minutes, with the target being located at an estimated range of Rest = 1.8 km from the submarine. From this point on, the range standard deviation oR is always less than the stability measure SR.

The averager 33 and the computer circuit 16 are followed by a threshold circuit 43 which, when the stability measure SR is undershot in the computer circuit 36, or when the limit value Am is undershot in the averager 33, operates a preset circuit 44 to preset the number Nca and Fca of the bearing angle measurements used for the bearing angle measurement in each processing cycle, and sets them to lower values. The output side of the preset circuit 44 is connected to the estimation filter 15 and to the parallax limit value computer 1 . The parallax limit value Pumit is then increased in accordance with equation (2), and the time of the processing cycle in the estimation filter 15 is shortened.

Figure 6 shows the relationship between the vessel-related bearing angle (pca and the comparison range Rnmit for a parallax limit value Pumit of 0.2° and a distance D = 30 m between the two transducer arrangements. In the scenario shown in figure 3, the target is at the start of a measurement run at a range of ¾ = 5 km. In the first six minutes, the vessl-related bearing angle cpca changes from 20° to 0°, the range becomes shorter and the comparison range Rnmit decreases in this angle range from 3 km to 0 km.

Thereafter the vessel-related bearing angle cpca then rises from 0° to 90°, while the range R to the target Z becomes ever shorter. The comparison range R mit rises to values up to 8.5 km for these bearing angles.

After a good 8 minutes, the bearing angle (pca = 17° (figure 3) , the parallax value P is greater than the parallax limit value Pumit = 0.2° (figure 4), the estimated range Re3t to the target Z is equal to the limit range Riimit = 2.5 km (figure 5), and the stability of the range estimate is adequate (figure 5) . The target data record is displayed on the situation display 21, even though the own boat has still not carried out any own maneuver.

Claims (9)

PATENT CLAIMS

1. A method for passive determination of target data by directionally selective reception of soundwaves which are emitted or sent by a target, having a first electroacoustic transducer arrangement of a sonar receiving installation, in particular a passive panorama installation, on a carrier vehicle from estimated bearing angles which are determined from estimated positions of the target, and measured bearing angles, with the bearing angle difference between measured and estimated bearing angles being minimized iteratively, characterized in that bearing angles (

2. The method as claimed in claim 1, characterized in that the parallax value (P) is determined by averaging a predeterrainable set ( ) of differences between the bearings {

3. The method as claimed in claim 1 or 2, characterized in that the own position (E) of the carrie ' vehicle is determined by means of a navigation installation (>, its longitudinal direction (L) is determined by means of a compass (), and the distance (D) between the transducer arrangements is determined from the transducer location positions, with the transducer location positions being determined via the known installation locations thereof with reference to the longitudinal axis and lateral axis, and forming the basis for an indication of the target data as a target data record.

4. The method as claimed in one or more of claims 1 to 3, characterized in that the scatter (acpca, a

5. The method as claimed in one or more of claims 1 to 4, characterized in that the range standard deviation (aR) of the estimated ranges (Rest) to the target (Z) is determined and is compared with a predeterminable stability measure (SR) , in that the output of the target data record is allowed if the stability measure (SR) is undershot.

6. The method as claimed in claim 5, characterized in that a straight line is placed through a predeterminable number of estimated ranges (Rest) to the target (Z) , and range differences (AR) of the estimated ranges (Rest) from the straight line are determined, in that the range standard deviation ( oR ) of the range is determined from the range differences (AR) .

7. The method as claimed in one of claims 1 to 4, characterized in that a straight line is placed through a predeterminable number of estimated ranges (Res ) to the target (Z), and range differences (AR) of the estimated ranges (Re3t) from the straight line are determined, and in that the mean value of the range differences (AR) is compared with a predeterminable limit value (Am) for the output of the target data record, and the output of the target data record is allowed if the limit value (Am) is undershot.

8. The method as claimed in one of claims 1 to 7, characterized in that the estimated range (Re3t) of the output target data record is compared with a predeterminable minimum range (Rmin) and a warning is indicated if the minimum range (Rmin) is undershot, because there is a hazard to the vessel safety.

9. The method as claimed in one of claims 4 to 8, characterized in that, if the stability measure (SR) is undershot or the limit value (Am) falls below a predeterminable threshold, the number (Nca, Nfa) of the bearing angle measurements which are used for the determination of the target data is reduced, with the parallax limit value (Pumit) being increased corresponding to the chosen smaller number.