GB1605225A - Arrangement for the determination of the direction and/or distance of objects by means of water-borne sound waves - Google Patents

Description

(54) ARRANGEMENT FOR THE DETERMINATION OF THE DIRECTION AND/OR DISTANCE OF OBJECTS BY MEANS OF WATER-BORNE SOUND WAVES We, FRIED KRUPP GmbH ATLAS ELEKTRONIK BREMEN, a German Company of 28 Bremen, Sebaldsbrucker Heerstr. 235, Germany, do hereby declare the invention, for which we pray that a patent may be granted us, and the method by which it is to be performed, to be particularly described in and by the following statement:: The invention relates to an arrangement for the determination of the direction and/or distance of objects, especially of watercraft, by means of water-borne sound waves of an active or passive sonar equipment forming a means of communication of limited band width between a ship and a dirigible projectile such as a torpedo carrying part of said sonar equipment, the indicating device of which contains at least one cathode ray tube for indicating the direction of sound waves and/or the distance of objects.

In known equipment of the kind described above, a wire unwinding after launching of the torpedo or the torpedo-like projectile is used as a means of communication by which signals from an electroacoustic device within the head of said projectile which is part of a searchbeam-sonar equipment are transmitted to the ship. The distance over which the dirigible torpedo may be controlled from the ship is limited by the total length of the unwinded wire which in turn is limited by the frequency band width of the communication. Said frequency band width is narrowed down with growing length of wire. The torpedo carries the electroacoustic transducer of the searchbeam-sonar equipment and part of the associated electronic means. One or more cathode ray tubes are set in the ship for the indication of bearing and/or distance of Objects located within the seach-beam.

It is an object of the present invention to minimize the frequency band width as far as possible in order to cover distances as large as possible by using a corresponding great length of wire and nevertheless to transmit all informations necessary for detection, identification and pursuit of objects especially of watercraft and especially information relating to bearing and/or distance of objects within a large horizontal sector.

According to the present invention there is provided an arrangement for the determination of the direction and/or distance of objects, especially of watercraft, by means of water-borne sound waves of an active or passive sonar equipment forming a means of communication of limited band width between a ship and a dirigible projectile such as a torpedo carrying part of said sonar equipment, the indicating device of which contains at least one cathode ray tube for indicating the direction of sound waves and/or the distance of objects, which comprises a) a cathode ray tube at the ship for a display of adjacent sectors in plan position indication (PPI) or partial plan position indication, b) at least one storage means at the projectile, especially an output storage means for storage and delivery of sound location data as bearing (y) and/or distance or range (r) of targets, which storage means is connected to said communication means for transmitting stored location data to the ship, c) a controllable threshold value discriminator connected to said storage means, d) means limiting the frequency band width of data signals transmitted by said communication means to an order of magnitude of 500 Hz.

Such an arrangement has the advantage that location data from all adjacent sectors may be transmitted in a very short time.

Another important advantage is an effective protection against acoustic means intended to deceive direction/distance detecting means.

The invention may be better understood by consideration of its background as follows: Another location information of sonar equipment consists of signals of relatively small band width, it is nevertheless impossible to transmit the complete location information from only a single sector of the search beam sonar equipment on the torpedo through a long wire to the ship, which would be necessary for a display at a plan position indicator on the ship. Now, such a plan position indicator is a preferred means to detect and observe targets by echo sounding.

To obtain an image for detection and identification of targets like watercraft it would be useful to avoid quick changes of said image. Therefore, the amount of information required to produce an image can be small compared with the band width of the original location information of the sonar equipment.

These circumstances make it possible to reduce the band width by said storage means and threshold value discriminator. The threshold value discriminator offers the advantage of an even distributed response function to disturbances; furthermore the indication of reverberation zones which is typical at conventional plan position indicators can be avoided by using a threshold value discriminator according to the invention. It is not usually desirable to indicate such reverberation zones because the torpedo can scarcely be steered in a manner to avoid such zones without the risk of loosing the target.

Therefore, it is preferred to transmit location information in reverberation zones only if the echoes from targets especially a watercraft will reach a magnitude above the threshold of the threshold value discriminator which threshold is adjusted by the effective magnitude of the reverberation signals.

The output storage may be combined with a programme transmitter for restriction of the reading-in data especially from the signal treatment stage relating to the distance (r) and/or bearing (y) of received sonar signals.

The storage capacity of the output storage is adapted to the minimum of the expected volume of information. It may be considered that generally only one, eventually two or three and in any case only few objects are to be observed which, however, may appear in any sector. In order to avoid said minimum being exceeded by unrequired signals, it is preferred to increase the threshold of said threshold value discriminator as the contents of the output storage grow in order to avoid a volume of information higher than the capacity of the output storage.

The location information from the output storage may be transmitted to a first transmitter, a branching stage, said communication connection, a second branching stage and a second receiver amplifier to a computer for conversion of the transmitted relative bearing information related to the course of the torpedo in a true bearing information related to north-direction which then is stored in a second storage means which in turn is connected through a digital analogue transducer and a demultiplexer to the first cathode ray tube.

Information concerning true bearings may be added without an essential increase in the band width for transmission. The use of true bearings has the advantage that changes of course do not appear on the plan position indicator.

The transmission of location information and additional data as mentioned above from the output storage at the torpedo or torpedolike dirigible projectile by said first transmitter may be performed in a regular sequence which is slower than the sequence of echo sounding without losing relevant location information. This sequence of transmission is chosen so that for example of the order of 1000 bit/sec can be transmitted.

This reading-out frequency which is relative slow as compared with the frequency possible with respect to the sequence of obtained location data offers the important advantage to reduce the frequency band width for the signal communication from the torpedo to the ship.

The capacity of the second storage on the ship can be made high enough to store the true location date from the computer over a relatively long time interval, i.e. equal to several echo sounding periods.

The storage means makes it possible to form average values of directions and/or distances obtained from several succeeding echo sounding periods; the comparison of the latest location information with the information from foregoing echo sounding periods results in a flickerfree image at the screen of the PPI-cathode ray tube.

Another advantage of the storage across a longer time interval is that the computer can be switched to perform the calculation which area is dependent on the repetition of location information within preselected limits of values of location data.

The computer evaluates the area of expected values of distance and bearing from those location information which exceed the threshold of the threshold value discriminator which in turn is controlled by the programme transmitter.

The calculation of area of expected values overmore is utilized to mark these areas at the screen of the cathode ray tube by symbols or color. Conventional means may be used for this purpose. Within the computer an evaluation of the location information stored by the second storage may be performed according to the rules of long time correlation.

Preferrably signals corresponding to the area of expected signals (ie sectors in which signals had been received from one or more foregoing echo sounding periods) from an output of the computer may selectively be switched on a second transmitter and second branch stage through said communication connection, the first branch stage, a second receiver amplifier on three intermediate storages in the torpedo, a first intermediate storage for change-over information from PPI to enlarged target view, a second intermediate storage for an expected distance value (r') and a third intermediate storage for an expected bvearing value (y').

The introduction of these intermediate storage means in connection with the output storage and the comparison of expected values with incoming location information has the advantage that only those location information are transmitted to the output storage which are lying within the area of expected values. Thereby it is possible to further reduce the frequency band width of communication. Moreover only data of location information will be transmitted to the output storage which in all probability originate from watercraft, wrecks, large floating objects, propeller wash or shoals of fish the identification of which especially in a true plan position indication at the screen of the PPI-cathode ray tube can relatively easily be performed.

In order to facilitate this identification a second cathode ray tube for a convential enlarged target view may be provided which is connected to said second branch stage through a separate second storage, digital/ analogue transducer, demultiplexer and signal treatment stage. Such an enlarged target view requires only all location information from a timely as well as angularly reduced area stored during foregoing echo sounding periods and therefore can be obtained with said small frequency band width of communication.

Automatic change-over switches may be provided for alternating operation of the two cathode ray tubes.

The intermediate storage means at the torpedo in which the expected values 6,,, of distances (r) and bearing (y) are stored can be utilized for selection of the area to be indicated at the second cathod ray tube.

Preferably means for periodically readingout the location information from said first and second storage means are provided with a frequency of reading-out is high compared with the frequency of echo sounding periods.

The storage means at the ship connected to the two cathode ray tubes are arranged so that the information data stored in them are alternately transmitted to the cathode ray tubes with a periodic sequence which is small compared with the echo sounding period.

Thereby a stationary pattern of images is obtained also at echo sounding periods of a length of several seconds which are much more adapted for identification and observation of targets as are the images of conventional sonar equipment with PPI or enlarged target indication.

In order to make the invention clearly understood, reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 is a block diagram of an arrangement according to the present invention and Figure 2 is a block diagram of that part of the sonar equipment which is arranged at the torpedo or torpedo-like dirigible projectile, in an arrangement according to the invention.

An electroacoustic transducer 1 for waterborne sound consisting of an array of strips is arranged within the head-part of the torpedo or torpedo-like dirigible projectile the observation area of which is directed ahead.

The transducer serves for receipt during passive sound location and serves for transmission and receipt during active sound location.

First of all the receipt function which is most important for the present invention will be illustrated.

The transducer 1 is connected through a signal treatment stage 2 to a controllable threshold value discriminator 3. A compensating network system 33 is connected to the strips of transducer 1 to attain eight angularly separated over-lapping receiving directional characteristics or beams 1A+B, 2A+B .... 8A+B each covering sectors of about 15". Each beam does exist twice, as an A-beam and a B-beam whereby the acoustic centres of each corresponding A-beam and B-beam are arranged at a distance of the order of half a wave length of the sound wave in water, that is the two different beams are employed in each sector in known manner in order to obtain a phase difference between the A-signal and the B-signal which is dependent on the distance of the A-and B receiver and on the direction of the received sound wave.

The signals SA and Sg of said A- and B-beams are amplified by amplifiers 341A and 341B to 348A and 348B, respectively. These amplifiers include conventional AVC/TVCadjustment. The signals SA of the A-beams are rectified by rectifiers 351 to 358. Phase difference evaluating networks 361 to 368 are fed by the signals SA and Sg to produce output signals the values of which are dependent on the phase differences between corresponding A- and B-signals. The signals SA from the A-beam after rectification in the rectifiers 35.1 to 35.8 are scanned by a scanner 37 and then fed to the input of said threshold value discriminator 3.

The signals from the phase evaluating networks 361 to 368 are fed to a second scanner 38. The outputs of said two scanners 37,38 are connected to a multiplexer 4. The rectified signals from amplifiers 341A to 348A and the signals from the phase difference evaluating networks 361 to 368 are transmitted by a switch 5 and a change over switch 6 to an analog-digital transducer 7 which in turn is connected to an output storage 8. The output storage 8 is connected to a programme transmitter 8a which is provided for restriction of feeding-in of location data per sector. The feeding-in of location data especially the feeding-in of the distances r which are proportional to the echo transit times and the feeding-in of the bearing characterized by the corresponding phase differences takes place periodically.A first transmitter 9 is connected to the output of the output storage 8 for reading-out the contents of the output storage 8 in a regular sequence.

On the assumption that the echo sounding period be 4 sec, that twenty location data may be stored per sector and that additionally beats of the propeller of a located ship which has been located by passive location may be stored with 40 bits per echo sounding period, then the maximum of location data to be transmitted to the control ship will amount to 200 per period of echo sounding. With a requirement of accuracy in the range of 1% (10 bit), an accuracy of bearing of % at 120 total angular area (8 bit), an indication of high amplitude (amplitude above the prescribed threshold) by fourstages (2 bit) each location information will result in a word of at least 10+ 8 + 2 = 20 bit per echo sounding period.

In order to avoid overflow of the output storage 8 in this case, it is necessary to transmit the location data with a maximum of frequency equal to 4000 = 500 Hz.

2x4 The digital values are fed-out through a branch stage 10 by frequency shift keying. No high signal-/noise ratio is necessary when transmitting the location data through a wire 17 from the torpedo to the ship by digital values.

Thus it is possible to have a wire of great length with a frequency of transmission of 500 Hz. When using the conventional direct transmission without an output storage 210 28 = 2,6x 105 image points must be transmitted in each echo sounding period. This would require a band width of 2,6x105 = 32 2x4 kHz without taking into account the four degrees of brightness.

The restriction of the necessary band width from 32 to 0,5 kHz is an important advantage of the invention regarding the fact that the length of a wire used as communication means may be increased by a similar magnitude.

The location data transmitted through the wire 17 or by water soundwaves from the torpedo to the ship after passing a branch stage 18, a receiver amplifier 19 and a second change-over switch 32 the function of which will be described in connection with the function of the aforesaid change-over switch 6, is fed to a computer 30.

Also data relating to the run for example speed of the torpedo is transmitted simultaneously through the wire 17 and fed to the computer 30. This can be done without a remarkable increase of the band width and the means for measuring and transmitting the values relating to the run of the torpedo are not shown in the drawing because they are not part of the sonar equipment.

The computer 30 translates firstly the location data from relative bearing, i.e.

bearing related to the course of the torpedo to north-bearing of true bearing, i.e. bearing related to the north-direction. The true location data is stored within a second storage 20 which is connected through a digital/analog transducer 21 and a demultiplexer 22 to a first cathode ray tube 23. The cathode ray tube 23 in a conventional manner is arranged for a display of location data relating to direction y and distance r in a plan position indication (PPI) whereby the PPI-synchronisation is coupled with that of the demultiplexer. The information SA relating to the amplitude of the incoming sound signals controls the brightness of the luminous spot.

The capacity of the second storage 20 is made high enough to store the true location data from the computer 30 over a relatively long time interval, i.e. equal to several echo sounding periods.

The reading-out of the second storage 20 is performed in such a manner that approximately twenty images or displays per second are transmitted to the cathode ray tube. Thereby is obtained a flickerfree display as hereinbefore described that in the case of a moving watercraft located by the sonar equipment the movement of the watercraft during the immediate past is displayed at the plan position indicator.

Marking signals for located watercraft or other objects may be added in the image from a symbol-signal transmitter 39 by a control panel 29. The symbol-signal transmitter 39 is connected to the computer 30 and may be controlled by the control panel in such a manner that computer 30 will pick up especially the marked objects and will figure out areas of expected values of distance r and direction y corresponding to the marked objects.

Controlled by a command signal from the control panel 29, the computer 30 will transmit values of said areas of expected values through a second transmitter 31, the second branch stage 18 and the wire 17 from the ship back to the torpedo and through the branch stage 10 at the torpedo via amplifier II to an intermediate storage 12 for the changeover information from PPI to an enlargedscale observation of the marked objects and to two intermediate storages 13 and 14 for corresponding expected center values r' and y'. Thereby the marked object can be represented in an enlarged view at a second cathode ray tube 28 on the ship r' and y' are center values of said areas of expected values.

Change-over switch 6 is controlled by the output of intermediate storage 12 for changing over from PPI at cathode ray tube 23 to enlarged target view at cathode ray tube 28.

The signal treatment stage 2 is controlled by the output value y' in such a manner that by actuating a double change-over switch in the following called target switch 45 only the signals SA and SB corresponding to said center value y' are selected and transmitted through a multiplexer 16 and a range switch 15 to the analog/digital transducer 7. The range switch 15 is controlled by the center value r' at the output of the intermediate storage 13 in such a manner that the digitized signals SA and Sg are passed to the output storage 8 only within the range r'+ 100 meters.

Depending on the position of intermediate storage 12 and change-over switch 6 controlled by the computer 30 the output storage 8 is fed by the information data for PPI from the total angular area of eight sectors or by the information data from a selected enlarged view including a selected target The reading-out of the output storage 8 takes place dependent on the stored data slowly and steadily. The change-over switch 32 on the ship is operated simultaneously with the change-over switch 6 on the torpedo so that the PPI-signals will be transmitted to the second storage 20 whereas the signals for said enlarged view are transmitted to a further storage 24.If the signals SA and 513 are scanned by the multiplexer 16 with a frequency f16 at equidistant times then the original signals may be regenerated by corresponding rapid reading-out of the storage 24 through a digital/analog transducer 25, a demultiplexer 26 and a filtering within a second signal treatment stage 27.

If the non-destructive reading-out from the storage 24 and the demultiplexing by demultiplexer 26 is operated with a frequency which is higher by a factor n compared with the frequency of multiplexer 16, then the signals SA and SB with n-times greater band width could be indicated n times per echo sounding period at the cathode ray tube 28.

By a sufficient high n a flickerfree image is produced at the cathode ray tube 28, which may change once per echo sounding period. If informations from several (m) echo sounding periods are stored within the storage 24 then it is necessry to increase the frequency of reading out from n to m n in order to display the complete contents of the storage 24 n-times at the cathode ray tube 28.

In a similar manner the PPI-information is displayed in a flickerfree manner at the cathode ray tube 23 with the second storage 20, digital/analog transducer 21 and demultiplexer 26, whereby the frequency of reading-out of the second storage is n m higher than the scanning frequency of multiplexer 4.

Within the second signal treatment stage 27 preferably a frequency multiplication may be applicated by using in a conventional manner an evaluation of doppler frequency with high resolution within a fraction of time needed with original frequency.

The range of distance r is determined in a conventional manner after beginning of an echo sounding period by a trigger input from a synchronizing stage 44 by a time measuring stage 40. An oscillator 41 is simultaneously controlled by said synchronizing stage 44 which is connected through a delay-line network 42 to a transmitter 43 with eight stages connected to said eight strips of transducer 1.

The invention is applicable not only at torpedoes or torpedo-like dirigible projectiles which are connected to the ship by a wire but it may be used as well in connection with a communication by radio. Thus, a torpedo-like projectile could cover a first part of its travel as a rocket and submerge only after approach to the target whereby location information is transmitted by a relatively short drag antenna.

The invention is useful also for civil purposes to solve the problem of location of shoals of fish and especially shoals of fish above the sea-bed, by using a sonar equipment part of which is arranged on the submerged fishing net. The small band width which can be used by the present invention is useful also in such fishing equipment especially if the transmission of location data shall be made through the water instead of the aforesaid means of communication. In this case the problem is less to reach a communication over a large distance rather than to obtain an elimination of interference inspite of high noise level.

WHAT WE CLAIM IS: 1. An arrangement for the determination of the direction and/or distance of objects, especially of watercraft, by means of waterborne sound waves of an active or passive sonar equipment forming a means of communication of limited band width between a ship and a dirigible projectile such as a torpedo carrying part of said sonar equipment, the indicating device of which contains at least one cathode ray tube for indicating the direction of sound waves and/or the distance of objects, which comprises.

a) a cathode ray tube at the ship for a display of adjacent sectors in plan position indication (PPI) or partial plan position indication, b) at least one storage means at the projectile, especially an output storage for storage and delivery of sound location data as bearing (y) and/or distance or range (r) of targets, which storage means is connected to said communication means for transmitting stored location data to the ship.

c) a controllable threshold value discriminator connected to said storage means, d) means limiting the frequency band width of data signals transmitted by said

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (17)

**WARNING** start of CLMS field may overlap end of DESC **. enlarged target view at cathode ray tube 28. The signal treatment stage 2 is controlled by the output value y' in such a manner that by actuating a double change-over switch in the following called target switch 45 only the signals SA and SB corresponding to said center value y' are selected and transmitted through a multiplexer 16 and a range switch 15 to the analog/digital transducer 7. The range switch 15 is controlled by the center value r' at the output of the intermediate storage 13 in such a manner that the digitized signals SA and Sg are passed to the output storage 8 only within the range r'+ 100 meters. Depending on the position of intermediate storage 12 and change-over switch 6 controlled by the computer 30 the output storage 8 is fed by the information data for PPI from the total angular area of eight sectors or by the information data from a selected enlarged view including a selected target The reading-out of the output storage 8 takes place dependent on the stored data slowly and steadily. The change-over switch 32 on the ship is operated simultaneously with the change-over switch 6 on the torpedo so that the PPI-signals will be transmitted to the second storage 20 whereas the signals for said enlarged view are transmitted to a further storage 24.If the signals SA and 513 are scanned by the multiplexer 16 with a frequency f16 at equidistant times then the original signals may be regenerated by corresponding rapid reading-out of the storage 24 through a digital/analog transducer 25, a demultiplexer 26 and a filtering within a second signal treatment stage 27. If the non-destructive reading-out from the storage 24 and the demultiplexing by demultiplexer 26 is operated with a frequency which is higher by a factor n compared with the frequency of multiplexer 16, then the signals SA and SB with n-times greater band width could be indicated n times per echo sounding period at the cathode ray tube 28. By a sufficient high n a flickerfree image is produced at the cathode ray tube 28, which may change once per echo sounding period. If informations from several (m) echo sounding periods are stored within the storage 24 then it is necessry to increase the frequency of reading out from n to m n in order to display the complete contents of the storage 24 n-times at the cathode ray tube 28. In a similar manner the PPI-information is displayed in a flickerfree manner at the cathode ray tube 23 with the second storage 20, digital/analog transducer 21 and demultiplexer 26, whereby the frequency of reading-out of the second storage is n m higher than the scanning frequency of multiplexer 4. Within the second signal treatment stage 27 preferably a frequency multiplication may be applicated by using in a conventional manner an evaluation of doppler frequency with high resolution within a fraction of time needed with original frequency. The range of distance r is determined in a conventional manner after beginning of an echo sounding period by a trigger input from a synchronizing stage 44 by a time measuring stage 40. An oscillator 41 is simultaneously controlled by said synchronizing stage 44 which is connected through a delay-line network 42 to a transmitter 43 with eight stages connected to said eight strips of transducer 1. The invention is applicable not only at torpedoes or torpedo-like dirigible projectiles which are connected to the ship by a wire but it may be used as well in connection with a communication by radio. Thus, a torpedo-like projectile could cover a first part of its travel as a rocket and submerge only after approach to the target whereby location information is transmitted by a relatively short drag antenna. The invention is useful also for civil purposes to solve the problem of location of shoals of fish and especially shoals of fish above the sea-bed, by using a sonar equipment part of which is arranged on the submerged fishing net. The small band width which can be used by the present invention is useful also in such fishing equipment especially if the transmission of location data shall be made through the water instead of the aforesaid means of communication. In this case the problem is less to reach a communication over a large distance rather than to obtain an elimination of interference inspite of high noise level. WHAT WE CLAIM IS:

1. An arrangement for the determination of the direction and/or distance of objects, especially of watercraft, by means of waterborne sound waves of an active or passive sonar equipment forming a means of communication of limited band width between a ship and a dirigible projectile such as a torpedo carrying part of said sonar equipment, the indicating device of which contains at least one cathode ray tube for indicating the direction of sound waves and/or the distance of objects, which comprises.

a) a cathode ray tube at the ship for a display of adjacent sectors in plan position indication (PPI) or partial plan position indication, b) at least one storage means at the projectile, especially an output storage for storage and delivery of sound location data as bearing (y) and/or distance or range (r) of targets, which storage means is connected to said communication means for transmitting stored location data to the ship.

c) a controllable threshold value discriminator connected to said storage means, d) means limiting the frequency band width of data signals transmitted by said

communication means to an order of magnitude of 500 Hz.

2. Arrangement as claimed in Claim 1, wherein the output storage is combined with a programme transmitter for restriction of the readin-in data especially from said signal treatment stage relating to the distance (r) and/or bearing (y) of received sonar signals.

3. Arrangement as claimed in Claim 1 or 2, wherein the storage capacity of the output storage is adapted to the minimum of the expected volume of information

4. Arrangement as claimed in any one of Claims 1 to 3, wherein the threshold of said threshold value discriminator is increased as the contents of the output storage grow.

5. Arrangement as claimed in any one of Claims 1 to 4, wherein the location information from the output storage are transmitted through a transmitter, a first branching stage and a communication means and through a second branching stage and a receiver amplifier to a computer for conversion of the relative bearing information related to the course of the projectile in a true bearing information related to north-direction which is stored in a second storage means which in turn is connected through a digital/ analog transducer and a demultiplexer to the cathode ray tube.

6. Arrangement as claimed in Claim 5, wherein the location information from said transmitter are transmitted in a regular sequence which is slower than the sequence of echo sounding without losing relevant location information, so that of the order of 1000 bit sec may be transmitted.

7. Arrangement as claimed in Claim 5, wherein the capacity of the second storage is high enough to store the true location data from the computer over a relatively longer time interval, i.e. equal to several echo sounding periods.

8. Arrangement as claimed in any one of Claims 5 to 7, wherein the computer is switchable to computing of areas of expected location data within several echo sounding periods.

9. Arrangement as claimed in Claims 1 and 8, wherein only signals above the threshold of said threshold value discriminator will control the computer for computing corresponding areas of expected values of location data (r,y).

10. Arrangement as claimed in Claim 1 and 8, wherein the areas of expected values are indicated at the cathode ray tube by symbols or by color.

11. Arrangement as claimed in Claims 5 and 7, wherein the true location information at the output of said computer are stored in the second storage from several echo sounding periods and are evaluated by the computer by correlation over long time periods.

12. Arrangement as claimed in any one of Claims 8 to 10, wherein signals corresponding to the areas of expected values from an output of said computer may selectively be switched on a second transmitter and second branch stage through said communication connection the first branch stage a second receiver amplifier on three intermediate storages, a first intermediate storage for change-over information from PPI to enlarged target view, a second intermediate storage for an expected distance value (r') and a third intermediate storage for an expected bearing value (').

13. Arrangement as claimed in Claim 1, wherein a second cathode ray tube is arranged on the ship for indication of an enlarged target view.

14. Arrangement as claimed in Claim 13, wherein said second branch stage is connected to the second cathode ray tube through a separate second storage, digital/analog trandsucer, demultiplexer and signal treatment stage.

15. Arrangement as claimed in Claim 14, wherein automatic change-over switches are provided for alternating operation of the two cathode ray tubes.

16. Arrangement as claimed in any one of the foregoing claims, wherein means for periodically reading-out the location information from said first and second storages are provided with a frequency of reading-out which is high compared with the frequency of echo sounding periods.

17. An arrangement for the determination of the direction and/or distance of objects, substantially as hereinbefore described with reference to, the accompanying drawings.