I PROCESS FOR LOCATING SOUND PROJECTING TARGETS The invention relates to a process for locating sound-projecting targets. 5 In such a process, which is described, for example, in DE 100 27 538, direction-forming with "preformed beams" or directional patterns in the time domain of the received signals is produced for a sonar system by combining the 10 received signals, which are time delayed and/or phase shifted on a common time reference plane, to form group signals. The preformed beam having the greatest received level, that is to say the directional pattern formed by the group signal having the greatest received level, 15 indicates the target bearing. This known locating process is based on the fact that the receiving antenna with its transducers is built up in ideal manner without restrictions in free space and 20 without the unavoidable spreads in transducer sensitivities or transducer efficiencies. However, production tolerances in the installation of the transducers in the receiving antenna and/or of the receiving antenna at the antenna carrier, e.g. ship or 25 submarine, lead to mismatches of the time delays for the direction-forming. The installation is carried out e.g. in or on the ship's side of a surface craft or the side of a submarine. In many cases, the transducers assembled to form transducer arrangements are protected by enveloping 30 bodies. Due to this installation, the 2 incident sound waves are additionally unforeseeably distorted on unavoidable holders for the enveloping bodies and/or by the shaping of the ship's hull or of the keel or by underwater structures on the carrier craft which leads to systematic, 5 spatially variable bearing errors. During the operational testing of sonar system also used for locating as part of sea trials, these bearing errors are determined and subsequently compensated for by elaborate error calculations. The corrected bearing values obtained from targets are then forwarded to a 10 subsequent position display. Without this error compensation, a detection panorama is also displayed to the operator on board which is generated from the raw data for the locating and is distorted by the abovementioned imperfections. If the operator wishes to manually calibrate a suspected target in the 15 detection panorama, he cannot take into consideration systematic bearing errors which leads to discrepancies in the assessment of the position. Any discussion of documents, acts, materials, devices, articles 20 or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field 25 relevant to the present invention as it existed before the priority date of each claim of this application. Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be 30 understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. 35 In accordance with the present invention there is provided a process for locating sound-projecting targets by using a 2A receiving antenna, fixed on an antenna carrier, with a multiplicity of electroacoustic transducers for receiving sound waves and generating electrical received signals, in which - for forming equal-phase received signals, time delay 5 coefficients are applied to the received signals and the equal phase received signals are added to form group signals which specify bearing directions defined by bearing angles, - the levels of the group signals are detected in correlation with the bearing angles, and 10 - in the resultant level characteristic over the bearing angles, bearing angles which belong to level peaks are output as target bearings, characterized in that, by means of carrier-related locating of targets in the sea area which are located in predeterminable 15 bearing directions rotated by angular steps, a set of time delay coefficients allocated to the transducers is empirically determined and stored for each carrier-related bearing angle, and in that, for north-related bearing angles with the heading of the antenna carrier, carrier-related bearing angles are 20 calculated and the stored sets of time delay coefficients belonging to the calculated, carrier-related bearing angles are applied to the received signals. In a preferred feature, the invention may provide a locating 25 process of the type initially mentioned so that system-related errors are already compensated for in the delayed received signals used for forming group signals of the directional patterns or preformed beams, thus producing from the group signals a detection panorama and a position display without 30 systematic bearing errors. The process may have the advantage that by means of the empirically determined time delay coefficients, an installation-generated and vehicle-associated distortion of the 35 preformed beams or directional patterns, formed by the group signals, is WO 2007/124797 - 3 - PCT/EP2007/001349 taken into consideration and the latter are thus virtually pre-equalized compared with preformed beams which are calculated for undistorted sound wave reception. The empirical determination is preferably 5 carried out during the sea trials for the operational test of the locating system by locating an artificial target which moves around the carrier vehicle of the locating system with known positions. For each tilted main direction of the directional pattern, the time 10 delay coefficients are iteratively optimized by the stationary carrier vehicle. As a result, the target bearings determined after the detection of targets are thus freed of systematic bearing errors in use. The detection panorama is displayed undistorted and manual 15 target tracking operates basically with appropriate "true" bearing values so that bearing data on the displays, e.g. in the detection panorama and in the position display, match and are determined everywhere with the same accuracy. In the case of automatic target 20 tracking, this is freed of installation-generated angular accelerations, which, after losing the target, improves the automatic restarting of target acquisitions and relieves the operator. The target data obtained by means of the process according to the 25 invention correspond to target data obtained via other locating systems so that they can be compared with one another without correction measures. Suitable embodiments of the process according to the 30 invention with advantageous developments and embodiments of the inventions are obtained from the other claims. In the text which follows, the invention is described 35 in greater detail by means of an exemplary embodiment illustrated in the drawing, in which: WO 2007/124797 - 4 - PCT/EP2007/001349 figure 1 shows a perspective view of a submarine representing an antenna carrier with a side antenna; 5 figure 2 shows a diagrammatic representation of the incidence of sound on the side antenna to illustrate time delay coefficients; 10 figure 3 shows a block diagram of a circuit arrangement for illustrating the process; and figures 4 in each case show the locating of two 15 and 5 targets Z and Z* with allocation of the bearing angles at a different heading of the antenna carrier. In the process, described in the text which follows, 20 for locating sound-projecting i.e. sound-generating or sound-reflecting targets, an underwater receiving antenna 11 is used which is fixed on an antenna carrier 12. In the exemplary embodiment shown in figure 1, the antenna carrier 12 is a submarine which 25 carries one receiving antenna 11 each on the starboard and port side, which is called flank array or side antenna. Of the two receiving antennas 11, only the receiving antenna 11 on the starboard side can be seen in figure 1. As is indicated diagrammatically in 30 figures 2 and 3, the receiving antenna 11 has a multiplicity n of electroacoustic transducers 13 which are equidistantly placed behind one another at a distance d (figure 2) from one another. As is not shown in greater detail here, the transducer arrangement 35 composed of the electroacoustic transducers 13 is completely covered by an enveloping body 14 which is transparent to sound and which is attached to the side WO 2007/124797 - 5 - PCT/EP2007/001349 wall of the submarine by means of a carrier structure, not shown here. The receiving antenna 11 spans a receiving sector within which incident sound, which is emitted by sound sources forming targets and spreads 5 out in water, is received by the transducers 11. The transducers 11 are connected in a conventional manner to a locating system 15 in which the direction of incidence of the sound, and thus the bearing direction to the targets, is determined by means of the 10 electrical output signals of the transducers 13, called received signals in the text which follows. The locating system 15 comprises, in a familiar manner, a direction-forming unit 16, also called a beam former, 15 a signal processing block 17 and a peak detector 18. In the direction-forming unit 16, the received signals of the transducers 11 are time-delayed in a familiar manner by the application of time delay coefficients in such a manner that they are in phase in a time 20 reference plane 21 at right angles to the direction of incidence of the sound. In figure 2, a planar sound wave front 20 incident at the angle a is shown as an example. The angle of incidence x is measured with respect to the normal 19 of the receiving antenna 11 25 which, in the case of the side antenna shown in the example of figure 1 is oriented at right angles to the longitudinal axis of the antenna carrier 12. If the orientation of the antenna carrier 12 changes in 30 the sea area, the angle of incidence a of the sound wave front 20 at the receiving antenna 11 also changes, with the direction of sound propagation of the sound wave front 20 being unchanged. 35 As is shown diagrammatically in figure 2, the received signals of the individual transducers 13 must be time delayed differently so that they are in phase with one WO 2007/124797 - 6 - PCT/EP2007/001349 another in the time reference plane 21. The required time delay coefficients c*1,, for the i transducers 13 with i = 1, 2 ... n, are obtained from the sound propagation times from the sound wave front 20 passing 5 over the first transducer 13 (i = n) until the sound wave front 20 passes over the last transducer 13 (i = 1) . The required time coefficients T*i,j are usually calculated for each ith transducer 13 and each jth direction of incidence of the sound wave with angles of 10 incidence aj, according to T*i, = (n - 1)d- sin cj (1) where i =1, 2 ... n and 15 j = 1, 2 ... k and stored. This calculation of the time delay coefficients T*i,j is based on the assumption that the electroacoustic transducers 13 of the receiving 20 antenna 11 are built up in free space and ideally without the unavoidable dispersions of the transducer sensitivities and/or the location of installation of the transducers. However, such ideal conditions are not present in the case of a receiving antenna 11 fixed to 25 an antenna carrier 12. In addition, the sound wave fronts 20 incident on the receiving antenna 11 are subjected to not inconsiderable distortions due to the shape of the submarine representing the antenna carrier 12, the enveloping body 14 covering the transducers 13 30 and the unavoidable enveloping-body holders, so that the ideal assumption of a planar wave front 20 also does not apply any longer. At the end of signal processing, this leads to unavoidable bearing errors which must subsequently be corrected. 35 To eliminate such bearing errors, the time delay coefficients T 1 ,j are empirically determined by WO 2007/124797 - 7 - PCT/EP2007/001349 carrier-related locating of targets in the sea are a in the process presented here, the targets lying in known bearing directions, swiveled by equidistant angular steps, e.g. 10, with respect to the stationary antenna 5 carrier 12. The carrier-related bearing angles ax obtained in this process are the angles of incidence x, specified in figure 2, of the sound wave fronts 20 and are measured with respect to the normal 19 of the receiving antenna 11. For each carrier-related bearing 10 angle aj, that is to say each angle of incidence of a sound wave front 20 measured with respect to the normal 19, a set of time delay coefficients Ti,j in each case allocated by the transducers 13 is determined and stored in a memory 22 (figure 3). 15 The time delay coefficients Ti,j are advantageously determined in such a manner that, in the locating system 15, the theoretical time coefficients T*i,j for ideal installation conditions for undisturbed sound 20 incidence according to equation (1) are applied to the received signals of the transducers 13 and the correspondingly time delayed received signals are added in the signal processing block 17 to form group signals. The levels of the group signals are plotted 25 over the bearing angles aj. The theoretical time delay coefficients T* 1 ,j are changed until peaks occur in the level characteristic under the known bearing directions. The set of "calibrated" time delay coefficients ri,j set for each peak obtained is stored 30 in the memory 22 under the carrier-related bearing angle ai,j belonging to the level peak. The known bearing directions are obtained e.g. in that a ship representing a sound source moves around the antenna carrier 12 at a constant radial distance and the 35 bearing directions are calculated from the respective ship positions and the unchanged position of the antenna carrier 12.
WO 2007/124797 - 8 - PCT/EP2007/001349 For the detection and locating of targets, a fan of preformed beams or directional patterns is generated over the receiving sector in correlation with a 5 multiplicity of north-related bearing angles S which are rotated with respect to one another by a constant bearing angle difference, e.g. 10. The multiplicity of north-related bearing angles 4j is recalculated into an equal multiplicity of carrier-related bearing angles aj 10 in a computing unit 23 (figure 3), according to as = 9Q 0 + & - ( (2), where p is the angle of the longitudinal axis of the 15 antenna carrier 12 (of the submarine in figure 1) with respect to the geographic north direction, the so-called heading. The relationship of heading p, north-related bearing angle 3 and carrier-related bearing angle a can be seen in figures 4 and 5. The 20 vehicle-related bearing angle a corresponds to the angle of incidence, mentioned initially and measured with respect to the normal 19 of the receiving antenna 11, of the planar sound wave front 20 in figure 2. Starting from the normal 19, a positive carrier-related 25 bearing angle a is plotted in the clockwise direction and a negative carrier-related bearing angle a plotted in the counterclockwise direction. In the same manner, a positive north-related bearing angle 9 is measured in the clockwise direction and a negative north-related 30 bearing angle & is measured in the counterclockwise direction, starting from the geographic north direction. The heading p, too, is measured clockwise starting from the north direction. 35 With the carrier-related bearing angle ax calculated with respect to the respective north-related bearing angle S3, the set of "calibrated" time delay WO 2007/124797 - 9 - PCT/EP2007/001349 coefficients T 1 ,j belonging to this carrier-related bearing angle ax is read out from the memory 22 (figure 3) and supplied to the direction former 16. In the direction former 16, the respective sets of 5 "calibrated" time delay coefficients Ti,j are applied to the received signals from the transducers 13 and the correspondingly time delayed received signals are added in the signal processing block 17 to form group signals. The levels of the group signals are stored in 10 correlation with the north-related bearing angless 9j. From the multiplicity of stored levels, a level characteristic P(4j) over the north-related bearing angle aj is obtained which is displayed on a display 24. By means of the peak detector 18, level peaks are 15 determined in the level characteristic P(83) and the bearing angles &z belonging to the level peaks are displayed as the target bearing. Figures 4 and 5 show two examples of target bearings of 20 two targets Z and Z* with a different orientation of the antenna carrier 12. In each exemplary embodiment, a target Z is detected at a north-related bearing angle 4 = 30" and a target Z* is detected at a north-related bearing angle & = -30'. The heading p of 25 the antenna carrier 12 is p = 980 in figure 4 and p = 143' in figure 5. In the locating of target Z in figure 4, the set of "calibrated" time delay coefficients ai,j was applied to 30 the received signals from the transducers 13, which set is stored for a carrier-related bearing angle of x = 220. These time delay coefficients Ti,j already compensate for a carrier-associated bearing error at the carrier-related bearing angle a = -22' so that the 35 north-related bearing angle & = 30* does not contain any bearing errors and corresponds to the true bearing. In the locating of target Z* at the north-related WO 2007/124797 - 10 - PCT/EP2007/001349 bearing angle a* = -300, the set of "calibrated" time delay coefficients rit, which is stored in the memory 22 under the carrier-related bearing angle ax* = -38', was applied to the received signals from the 5 transducers 13. This set of time delay coefficients Ti,j again compensates for a bearing error which is produced installation-generated at a carrier-related bearing angle of a = -38' so that the north-related bearing of the target Z* does not exhibit any bearing errors. 10 In the exemplary embodiment of figure 5, the heading p of the antenna carrier 12 has changed. Accordingly, the "calibrated" time delay coefficients Tij, which are stored in the memory 22 under the carrier-related 15 bearing angle a = -23' and a = -83', respectively, were then applied to the received signals of the transducers 13 in the locating of the spatially unchanged targets Z and Z*. The installation-generated bearing errors occurring at these carrier-related bearing angles are 20 taken into consideration in the "calibrated" time delay coefficients Tj,j so that the north-related bearing angles & and q* are again free of bearing errors for the targets Z and Z*.