United States Patent 3792194

A video magnetic disk is utilized in the conversion of side looking sonar or slow scan TV data into a form suitable for displaying as a flicker-free picture on a conventional TV monitor. In the side looking sonar mode of operation, provision is made for displaying the sonar information as a moving window display.

Wood, Kenneth E. (Annapolis, MD)
Parrish, William F. (Baltimore, MD)
Kennedy, Paul G. (Monroeville, PA)
Application Number:
Publication Date:
Filing Date:
Primary Class:
Other Classes:
348/163, 367/11, 367/88, 379/93.17
International Classes:
G01S7/62; G01S7/531; G01S7/533; H04N7/01; H04N7/12; (IPC1-7): H04N5/02; H04N5/78; H04N7/18
Field of Search:
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Primary Examiner:
Britton, Howard W.
Attorney, Agent or Firm:
Schron D.
We claim as our invention

1. Scan conversion apparatus comprising

2. Apparatus according to claim 1 which additionally includes:

3. Apparatus according to claim 1 wherein:

4. Apparatus according to claim 3 which includes:

5. Apparatus according to claim 1 wherein:

6. Apparatus according to claim 5 wherein:

7. A system for displaying multiple sonar return signals, comprising:

8. Apparatus according to claim 7 wherein said time compression means includes:

9. Apparatus according to claim 7 which includes:

10. Apparatus according to claim 7 which includes:

11. Apparatus according to claim 7 which includes:

12. Apparatus according to claim 11 which includes:

13. A system for displaying slow scan TV signals on a conventional TV monitor comprising:

14. A system for transmitting information comprising:


1. Field of the Invention

The invention in general relates to scan conversion apparatus, and particularly to such apparatus which utilizes a rotating storage medium such as a magnetic disk.

2. Description of the Prior Art

In the operation of many sensor systems it would be desirable to display sensed information on a conventional display such as a TV monitor. For example, side looking sonar information is produced at a very low data rate and is generally displayed on a paper recorder. For displaying the same information on a TV monitor it is necessary to assemble the return sonar signal on an electronic scan converter as a one line at a time picture. Due to the relatively slow speeds of the sonar apparatus through the water, it may take several minutes to assemble a complete picture and electronic scan conversion registration becomes a major problem. For broader sonar coverage a plurality of system may be utilized necessitating the use of separate electronic tube scan converters.

These electronic tube scan converters are also used for slow scan TV systems wherein a television picture may be transmitted at a reduced data rate over a reduced channel bandwidth. This system may be utilized where a reduced number of transmitted pictures can be tolerated such as in the transmission of stationary pictures or slow moving scene information. For example, for a 60 to one time difference between the slow scan TV picture and the conventional TV picture, a 60 to one bandwidth compression is achieved, however, only one scene is transmitted for every 60 scenes of the conventional TV. The electronic tube scan conversion utilized in conjunction with this arrangement is complicated and registration of the recorded and readout signal is a problem because of drifting of the scan circuits and alignment.

Another method of performing the conversion is to write the slow scan TV signals on a long persistence phosphor tube. This method is objectionable however as the picture at the beginning is decaying in brilliance as the final portion of the picture is being written.


A sensor system provides multiple sequential signals indicative of a condition to be portrayed on a display means which displays multiple lines of information. The system signals are converted to respective display signals each having a time duration compatible with the line time of the display means. The display signals are stored, preferably on a magnetic disk, and are read out and provided to the display means at the proper time for displaying.

In the case where the sensor system is a side looking sonar system, means are provided for moving the information displayed as movement through the water of the side looking sonar system takes place.


FIG. 1 is a block diagram illustrating, generally, the concept of scan conversion;

FIG. 2 is a view of one type of side looking sonar apparatus which may be utilized as the system of FIG. 1;

FIG. 3 is a plan view of the side looking sonar apparatus of FIG. 2 showing the starboard beam only;

FIG. 4 is a block diagram illustrating an embodiment of the present invention with respect to a sonar system;

FIG. 5 are curves illustrating various signal time occurrences in the arrangement of FIG. 4;

FIG. 6 illustrates a sonar return signal, and the compression thereof with respect to time;

FIG. 7 is a block diagram which illustrates one way of obtaining the sampling pulses illustrated in FIG. 5;

FIG. 8 is a timing diagram illustrating the operation of FIG. 7;

FIG. 9 illustrates a conventional TV display;

FIGS. 10 and 11 illustrate waveforms utilized in obtaining the display of FIG. 9;

FIG. 12 is a plan view of a magnetic disk with storage locations thereon;

FIG. 13 is a portion of the disk of FIG. 12 illustrating the relative storage of a particular signal;

FIGS. 14A, B, and C are charts illustrating the storage of information in particular address locations of the disk of FIG. 12 in relation to a typical display;

FIG. 15 is a plan view illustrating side looking sonar apparatus as it proceeds over a target;

FIGS. 16A through G illustrate the appearance on a TV display of the situation depicted in FIG. 15;

FIG. 17 is a block diagram illustrating in more detail the arrangement of FIG. 4;

FIGS. 18A, 18B and 18C illustrate the target of FIG. 15 as presented on the TV display for three different velocity conditions of the sonar system;

FIG. 19 is a block diagram illustrating a possible correction for the condition of FIG. 18C;

FIG. 20 is a block diagram illustrating a portion of typical synchronizing generator which may be utilized herein;

FIG. 21 is a block diagram illustrating a driving arrangement for the magnetic disk;

FIG. 22 illustrates a magnetic disk having two recording tracks for the storage of information to be displayed;

FIGS. 23A, 23B, 23C, and 23D serve to illustrate the writing of information on a magnetic disk such as illustrated in FIG. 22;

FIG. 24 is a block diagram of a slow scan TV system utilized in conjunction with the magnetic disk of FIG. 22; and

FIG. 25 is a block diagram illustrating a typical use of the present invention for transmission of information over conventional telephone lines.


In FIG. 1 illustrating the concept of scan conversion utilized herein, a sensing system 10 provides multiple sequential signals containing information and which are to be presented on a display 12. The display 12 is of the type which displays multiple lines of information, with each line being presented on the display in a certain line time.

In order to insure that the system signals are compatible and can be displayed in the proper line time of the display 12, there is provided a signal time conversion means 14 which is responsive to the system signals and is operable to expand or compress them in time depending upon whether the particular system signals are of a shorter or longer time duration than the line time of the display 12. System signals which are converted to respective display signals are provided to a storage means 16 where they are maintained and thereafter read out to build up a display picture.

FIG. 2 illustrates one of many uses of the present invention, the use being in the side looking sonar field although the invention may be utilized with various sonar systems. Side looking sonar transducers mounted on carrier vehicle 20 transmit acoustic energy pulses in a certain pattern such that the sound energy impinges on the bottom 22 and scans, or sweeps out elongated narrow insonified strips such as 24 and 25 produced by starboard and port transducers respectively. Reflected acoustic energy containing information relative to the bottom, or targets on the bottom, is picked up by receiving transducers and then processed and displayed. The carrier 20 is towed by means of a vessel 27 and cable 28, and as it proceeds along a course line multiple sequential acoustic transmissions take place such that, as illustrated in the plan view of FIG. 3, multiple adjacent areas 30, 31, 32 . . . on the bottom are insonified. Although not illustrated, bottom strips on the port side of the carrier would also be insonified. Each return signal contains information and collectively the return signals are indicative of a sound picture of the target area over which the apparatus is towed.

For various operations it would be desirable to portray the return signals indicative of target information on a conventional TV monitor. The present invention is capable of performing this function and to this end reference is made to FIG. 4.

A sonar system 35 provides, on line 36, multiple sequential return signals indicative of a condition to be displayed on a display means in the form of a conventional TV display 39. With the system 35 being of the side looking sonar type, the return or echo signals received from the target area are each to be presented on a separate line of the TV display, however, their time duration far exceeds the time it takes to scan one TV line. Accordingly, each sonar return signal is compressed for displaying as a TV line.

The compression of the signals appearing on line 36 can be accomplished in a number of ways. FIG. 4 illustrates one such compression method and includes an analog to digital converter 41, shift register means 43 and a digital to analog converter 45. With proper signals from the timing and control circuits 49, the analog to digital converter 41 including sample and hold circuits will sample, at a predetermined sampling rate, each sonar signal presented to it and convert it into digital form. The digital data is then presented bit by bit to the shift register means 43. For example, if each sample is converted to a six bit equivalent digital signal, there could be provided six parallel shift registers which shift the digital information down at the sampling rate. The stored signal is then read out, as governed by the timing and control circuits 49, at a much faster rate than the sampling rate and chosen such that the resulting signal will be of a time duration suitable for a one-line display. The signal from the shift registers 43 is converted back to analog form by means of the digital to analog converter and is then stored for future display presentation.

The storage means is preferably in the form of magnetic disk 53, such disks being well known in the TV industry for the recording of TV signals for subsequent replay. The basic disk and drive assemblies have been advanced to a point where signal registration is mechanically insured and the cost of the apparatus is relatively inexpensive. In addition, several hundred tracks of information can be stored on one disk.

The sonar signals, each of a time duration too great for a TV line display are presented to the analog to digital converter 41 and emerge from the digital to analog converter 45 as display signals each of a time duration equal, or substantially equal, to the time for displaying one TV line.

Prior to storage on the magnetic disk 53, the display signals are processed in signal conditioning apparatus 56 which may include for example, such circuitry as preamplifiers, limiters, modulators, filters, etc.

The recorded signals on the magnetic disk 53 are then presented to the TV 39 by way of other signal conditioning apparatus 58 which may include such circuits as preamplifiers, limiters, demodulators, filters, etc.

Since the display signals are to be presented on the TV 39 there must be provided certain synchronizing and blanking signals to make up the complete TV signal. In the embodiment illustrated these signals are provided by the synchronizing generator 62 and may be combined with the display signals in the signal conditioning apparatus 58.

Each time a sonar transmission takes place, this information is communicated to the timing and control circuitry 49 as a sonar pulse. In the embodiment of the moving window display, to be described, the timing and control circuits 49 in response to the transmissions readjusts the output of the synchronizing generator 62.

By way of example FIG. 5 illustrates a timing diagram for various events occurring in the operation of FIG. 4. Suppose, by way of Example, that the pulse repetition frequency (PRF) is 3 hertz (Hz). FIG. 5 illustrates a first sonar pulse at time equal to zero and the next pulse 333.33 milliseconds later. At a predictable time after transmission, a meaningful sonar return is received. Sampling pulses are continuously provided at a predetermined rate and for each sampling pulse during the sampling period, the amplitude of the sonar return is converted to digital form by the analog to digital converter 41 and provided to the shift registers 43 (See FIG. 1). Assuming that the disk rotates at a constant 1,800 rpm, FIG. 5 illustrates that a complete revolution takes place every 33.33 milliseconds and that after 10 revolutions the compressed signal to be subsequently displayed, is written at a particular location on the magnetic disk and at a time prior to the next sonar pulse.

FIG. 6 illustrates the sonar return and the compressed signal in somewhat more detail. At T0 an acoustic pulse is transmitted by the sonar system and at a predictable time later, T1, the return signal indicative of target information is initially received and continues to be received until time T2, dependent upon system design. During the time from T1 to T2, the sonar return is sampled at the sampling rate and placed into the shift registers. At time T3 the shift registers are read out at a rate such that the entire sonar signal is presented to the magnetic disk in the time from T3 to T4.

One arrangement for obtaining the sampling pulses is illustrated in FIG. 7. Let is be assumed for the example that it is desired to sample each sonar return signal 512 times. The sonar pulse indication is provided to a delay circuit 66 which provides, after a predetermined time delay δ , an output signal to the S input of flip-flop 67. Flip-flop 67 provides an output signal when a signal is presented to the S input, and provides no output signal when a signal is presented to its R input. The output from the delay circuit 66 therefore causes the flip-flop 67 to provide an output signal to start oscillator 69 which then provides the load pulses. Each pulse output from oscillator 69 is provided to a counter 71 which provides an output signal when its count reaches 512 at which time the flip-flop 67 is turned off and oscillator 69 ceases to provide pulses. Counter 71 then reverts back to its initial setting. The timing relationship for this operation is illustrated in the curves of FIG. 8.

At time T0 a sonar transmit pulse occurs. The effect of such pulse is delayed from time T0 to time T1 and from time T1 to T2 loading of the shift registers is accomplished, the time T1 to T2 representing the output signal of flip-flop 67. For various operations the delay may be modified or eliminated so that sampling of the sonar return signal takes place during the deadtime from T0 to T1.

Since the display signals are presented to a TV monitor, the operation of a conventional TV display will be briefly discussed. For a cathode ray tube TV, the electron beam scans the picture or display area at repeating intervals giving rise to a series of single pictures with the repetition rate of successive pictures detemining the apparent continuity of a moving scene. This rate is referred to as the frame rate. Most practical TV systems resort to linear scanning starting at the top of the tube and tracing successive lines till the bottom of the picture is reached, after which the beam is returned to the top and the process is repeated. In order to reduce flicker there is generally utilized an interlace scanning method wherein two scanning fields are produced for each complete picture frame. Depending upon the system circuitry and resolutions desired, any number of scanning lines may be chosen and by way of example the present invention will be described with a TV system utilizing 525 lines per frame with 489 of these lines being actually displayed. The remaining 36 lines are utilized in the retrace or return of the beam to the top of the screen from the bottom. With a 2:1 interlace scanning, 18 of the lines are taken up for each field retrace. With 489 lines being displayed for each frame, there will be 244 1/2 lines displayed for each field. This is illustrated in FIG. 9.

If one were to look at the display and consider a single picture, that is, a single frame, the first line is actually a half line at the top, the second line is the first full line across the display, and the lines would continue in numerical order until the last line 490, which is actually half a line. The frame line numbers are designated under the title Display Line No. The picture, or frame, however, is made up of two interlaced fields. In FIG. 9 the dotted lines are the lines of the odd field and the solid lines are the lines of the even field. The field line numbers are designated under the title Field Line No. The first line written is the odd field line number 1. The second line written is the field line number 2 which in actuality is the third line of the overall display or frame. After the 245th line in the field is written, corresponding to the 489th line of the display, the beam is brought to the top of the screen to begin the display of the even field. The retrace time takes, for the example illustrated, 18 line periods so that the first line displayed in the even field is numbered 264. Again, line No, 264 is actually the second line of the display. The last line of the even field, line 508 is equivalent to display line 490 and the remainder of the 525 line display is taken up in the vertical retrace.

The display of FIG. 9 is accomplished with the provision of the waveforms of FIGS. 10 and 11. In FIG. 10 the saw tooth horizontal scanning waveform is presented to the cathode ray deflection plates or coils and has the effect of scanning the electron beam across the face of the tube after which it is quickly returned. Thus, for the portion 74 of the horizontal scanning waveform the cathode ray beam will scan across the face of the tube in 55 microseconds (μs), and for the portion 75 will quickly retrace in 8.5 μs. The horizontal synchronizing pulses serve to initiate each saw tooth of the scanning waveform and each pulse is illustrated as occurring coincident with the peak of the saw tooth. During the portion 74 of the entire 63.5 μs period, information may be displayed and the horizontal blanking pulses encompass a period just prior and subsequent to the retrace portion 75. During the provision of the horizontal blanking pulses the cathode ray beam is blanked e.g., for 10 μs so that no information is written on the screen, while the unblanked portion of 53.5 μs is the actual line display time.

In FIG. 11 there is illustrated the vertical scanning waveform having a much longer period than the horizontal scanning waveform and wherein during the portion 78 the scanning beam is moved down the screen, and during the portion 79 the beam is retraced back to the top. As was the case with FIG. 10, the vertical synchronizing pulses occur coincident with the peak of the saw tooth waveform and the vertical blanking pulses which blank the beam during the vertical retrace encompass a period prior, and subsequent to the retrace portion.

If the vertical synchronizing and blanking pulses are made to occur at a time prior to their normal occurrence, as illustrated by the dotted line portions of these waveforms, they will have the effect of starting the vertical scanning waveform at a corresponding earlier point in time as indicated by the dotted portion of that waveform. The purpose of this operation will be subsequently explained with respect to FIGS. 14A, B and C.

In the present invention each sonar signal is compressed to an equivalent line display time, for example, approximately 53.5 μ s, and is stored on a magnetic disk at a certain address or location. As the disk rotates the information contained in the storage locations is read out and displayed on the TV monitor. An example of a typical disk and the storage locations is illustrated in FIG. 12.

The disk 90 includes a recording track T for recording display signals. Each display signal is recorded at a particular location on the track and these locations are herein termed slots and are designated by a slot number with the prefix S. Accordingly, for a 525 line TV system, there are 525 slot locations S1 to S525. A magnetic recording/reading head H is positioned over the track T and will write in and read out information as the disk 90 rotates in the direction of the arrow at a constant speed of 1,800 rpm.

The slot numbers correspond to the field line numbers shown in FIG. 9 and into these slot locations will be written the corresponding display lines, each of which is designated by a number preceded by the letter L. According to FIG. 9 display line 1 is written into the first slot location, display line 3 written into the second slot location... and display line 525 is written into the 263rd slot location. The very next slot location 264 will contain the second display line, slot 265 the fourth display line... and slot 525 will contain the 524th display line. In one complete revolution of the disk 90 with head H in the read out mode, the odd field will be displayed starting with line 1 and after the vertical blanking period the even field will be displayed starting with line 2 and after the second vertical blanking period the process is repeated.

At the rotational speed designated, a slot location, as illustrated in FIG. 13, occupies the equivalent of 63.5 μs. Within this slot location is the display signal 93 recorded in FM form and occupying an equivalent of approximately 53.5 μs with the remaining 10 μs being for blanking and retrace.

FIG. 14A illustrates, in linear form, the circular slot and line arrangement on disk 90 of FIG. 12. The line number is the top most series of numbers designed L and the numbers directly below them are the slot numbers designated S. As mentioned, one complete rotation of the disk with the head H in the read out mode will present a display as in FIG. 9. Thus, in FIG. 14A, the displayed odd field starts in the middle of line 1 and continues for 244 1/2 lines up to line 491. Vertical blanking takes place for 18 lines after which the 244 1/2 lines of the even field are displayed starting with line 2 and ending in the middle of line 490. The even vertical blanking for 18 lines then brings the system around to its initial starting point. Waveform 95 illustrates the vertical scanning in relation to the displayed fields.

As the side looking sonar apparatus proceeds over a target it is desirable that an observer see a picture on the TV display moving as if he were facing the direction of motion of the apparatus. In FIG. 15 there is illustrated a vessel 99 at position P1. FIG. 15 also illustrates an alternate embodiment wherein the side looking sonar apparatus is carried by the vessel which also includes a TV display 100. As the vessel 99 proceeds to position P2, the insonified area 102 proceeds over a target 104. The present invention provides means for moving displayed information on the screen as the apparatus proceeds over a target area. Thus, for the situation depicted in FIG. 15, the TV display 100 will portray the target 104 as illustrated in A through G of FIG. 16. One way of accomplishing this moving window display is to slip the sync and advance the vertical synchronizing pulse by one line time as described previously with respect to FIG. 11. For example, and with reference again to FIG. 14A, let it be assumed that no information has been recorded in any of the slot locations and accordingly, no meaningful information is presented on the TV display. The first and second sonar returns converted to display signals are stored respectively in slots 263 and 525. When the sync is slipped one line time early, as indicated by arrow 107, the information contained in the particular slot locations will be displayed as the respective lines indicated in FIG. 14B. In other words, information previously stored in unviewed slot 263 will now, in FIG. 14B, be displayed as line 2 and information stored in slot 525 previously unviewed will be seen as line 1, more particularly, one half of line 1. The second and third returns, converted to display signals, are stored respectively in slots 262 and 524. When the sync is slipped one line time as indicated by arrow 108, the situation will be as depicted in FIG. 14C wherein the initial information received and stored in slot 263 is now displayed as line 4, the second piece of information in slot 525 now appears as line 3, information in slot 262 appears as line 2 and the information in slot 524 appears as line 1. By continuing this process of slipping the sync after each two returns the display picture will move down the screen as in FIG. 16.

There are various methods of accomplishing this recording, display and movement operation and FIG. 17 illustrates one embodiment. In order to insure synchronism of operation, it is preferable that the disk contain synchronizing information in the form of synchronizing pulses. Accordingly, the disk 110 includes a first clock track CT1 which provides an output for each revolution of the disk, a second clock track CT2 for providing an output signal for each slot location, and a third clock track CT3 for providing clocking pulses utilized for reading out the shift registers, in addition to being utilized in the generation of the synchronizing waveforms. For ease of understanding, these clock tracks are illustrated as being individual tracks however, it is to be understood that the information could be incorporated into a single track with a certain number of clock pulses being equal to one slot location and a certain number of slot locations being equal to one revolution.

The clock tracks are read by respective heads 113, 114, and 115. In the exemplary embodiment being described, with the occurrence of a sonar pulse there are 10 disk revolutions until a return is to be written. (e.g., See FIG. 5). Accordingly, a sonar pulse indication on line 118 is utilized to reset a counter 120 which receives a signal from head 113 for each revolution of the disk 110, and provides an output signal on line 121 when the count of ten is attained.

Counter 124 is of the type which receives the signals from head 114 and in response thereto provides a unique output signal on output line 125 indicative of the particular slot count. It is to be noted that the use of the term line herein is meant to include one or more signal conducting wires. At the beginning of each disk revolution, counter 124 is reset by means of the signal on line 127.

The actual slot location is compared with a desired slot location into which information is to be recorded and if the two are alike, and if the correct number of revolutions has taken place, then the writing of the information into the disk at the proper slot location can take place. For this purpose, there is provided comparison means 130 which receives the actual slot indication on line 125 from counter 124, and a desired slot indication on line 133 from encoding means 134 to provide an enabling output signal on line 136 when the two are identical.

Gating means such as AND gate 139 receives, at one input, the indication that the two slot locations are identical, and at its other input, an indication that the correct revolution has been attained, to provide an enabling output signal on line 140. This enabling signal may be utilized as a write command to the signal conditioning apparatus 143 and may be additionally utilized to enable AND gate 145 to pass the clock pulses being provided to it from head 115. These pulses passed through OR gate 148 serve to shift the information out of the shift registers 150, after which a conversion takes place by the digital to analog converter 153, which also receives the clock pulses via line 155. Since the signal conditioning apparatus 143 is receiving a write command, the analog information will then be written into track T by means of head 157.

Upon the occurrence of the very next slot, the output of counter 124 will no longer be equal to the desired slot indication on line 133 and the enabling signal on line 136 will be removed. With AND gate 139 disabled, the write command is removed and information is no longer shifted out of the shift registers 150. The head 157, however, provides signals indicative of the information stored on track T to the signal conditioning apparatus 160 which combines the output from the disk with the synchronizing information, to present a TV signal to the TV display 163.

When the next sonar return is received it is also fed to the analog to digital converter 166 on line 167, which also receives the sampling pulses, from FIG. 7, as does the shift registers 150 through OR gate 148, to load a new return.

Each sonar return is to be written into a different slot location as predetermined by the encoding means 134. One way of providing the moving window display, as previously discussed, is to write the first two returns in slots 263 and 525, respectively, the next two in slots 262 and 524, etc. This may be accomplished with the provision of counters 178 and 179 each being responsive to count input signals to in turn provide, on respective output lines 182 and 183, signals indicative of the number of inputs counted. Both counters can count up to 525, however, a reset signal on line 185 provided at the start of operations, will set counter 178 to the number 264 and will set counter 179 to the number 1. The reset signal also resets flip-flop 189 so that upon the receipt of a first sonar pulse it will provide an output on line 191 to counter 178, and upon receipt of the next sonar pulse will provide an output signal on line 192 to counter 179. The output signals are thereafter alternated between these two lines with subsequent inputs to flip-flop 189. The first sonar pulse, therefore, will have the effect of triggering counter 178 to the next count below 264, such that counter 178 provides the number 263 to enable gate 193. The enable gate 193 is enabled by virtue of an enabling signal on line 191 and OR gate 196 passes this number to the comparison means 130 as the desired slot location. The sonar return is then written into that slot location as previously described. The next sonar return is to be written into slot 525. When the next sonar pulse is received, line 192 provides the output signal to counter 179 which assumes its next count of 525. This count is passed through enable gate 198, enabled from line 192, through the OR gate 196, and presented to the comparison means 130 as the desired slot location. The counters continue to count down until the last number in sequence is reached, after which the counting sequence will repeat.

Starting with the first input signal to the counters, the counting sequence will be as indicated in the following chart:

Counter 178 Counter 179 263 525 262 524 261 523 . . . . . . 3 265 2 264 1 263 525 262 524 261 523 260 . . . . . . 266 3 265 2 264 1

Since the vertical synchronizing will be slipped by one line after two entries have been made, such indication may be obtained from line 192 to provide the slip sync signal indicated on line 200.

If the sonar apparatus is proceeding over the target area at a certain velocity, then the target on the moving window display will appear geometrically correct, as in FIG. 18A. If the velocity is relatively slower, with the same pulse repetition frequency, there will be a greater number of returns for the same area thus giving a distorted picture, as in FIG. 18B. Similarly, if the relative velocity is faster, fewer returns will be obtained, information will be missing, and the target will appear as in FIG. 18C. Accordingly, the present apparatus includes means for eliminating, or reducing, these geometric incongruities due to variations in velocity over the target area.

With reference again to FIG. 17, this can be accomplished with the provision of the pulse selector means 204 which receives each sonar pulse on line 206 and will provide an enabling signal on line 207 to the enabling gating means 209 as follows: Let it be assumed for example that the sonar speed is such that a normal picture as in FIG. 18A is presented. In such instance the pulse selector 204 provides an output for each pulse input, which is then passed through the enable 209, and through OR gate 212 to appear as a sonar signal on line 118.

If the apparatus is proceeding too slowly, certain ones of the returns are not to be written and displayed. Accordingly, with the proper setting, the pulse selector 204 will provide an enabling signal on line 207 only after a predetermined number of pulses has occurred on line 206 such that the sonar pulses on line 118 will be the result of one out of every two, one out of every three, seven out of twelve, or any other desired selection. As indicated, the pulse selection may be made manually or it may be made automatically in accordance with the actual velocity of the apparatus by means of a velocity indication signal on line 217.

If the apparatus is proceeding too rapidly, then information will have to be added to the picture to prevent the distortion shown in FIG. 18C. This information, to a good approximation, can be obtained from previously written information and in such mode of operation, the pulse selector 204 will provide a plurality of pulses on line 218 for each input pulse received on line 206. These plurality of pulses then appear on line 118 as the sonar pulses as though they emanated directly from line 206. In order to rewrite previously received target information, the pulse on line 218 is additionally utilized to recirculate the shift registers as indicated in FIG. 19. FIG. 19 shows the analog to digital converter, the shift registers, and the digital to analog converter shown at the lower portion of FIG. 17. If it is desired to have the capabilities to rewrite information, then gating means can be added to take the information as it comes out of the shift register and put it back in. For example, the output of the shift registers is provided through an AND gate 220 the output of which is fed to OR gate 221. For normal operation the Recirculate Shift Registers signal to the AND gate is not provided and the apparatus operates as previously described. When an output signal is provided on line 218 of FIG. 17, the AND gate 220 will be enabled and the information will not only be provided to the digital to analog converter for subsequent recording on the disk but will additionally be provided to the input of the shift registers and will be read out again when all the conditions for writing are met.

The synchronizing generator 62 illustrated in FIG. 4 may be of the well known variety which utilizes a series of counters for providing the synchronizing and blanking waveforms. FIG. 20 illustrates a portion of the generator and includes counter circuitry 224 which is normally responsive to pulse input signals on line 225 to in turn provide output signals to the vertical synchronizing and blanking circuits 227 and 228. Similar circuits can be provided for the horizontal synchronizing and blanking waveforms. To insure synchronism with the information on the rotating disk, the input pulses to the counter circuitry 224 preferably are derived from a clock track on the disk. The slip sync circuit 230 is provided to add a count to the counter circuitry 224 at the precise time to achieve the advanced condition described in FIG. 11. This pulse, which may be adjusted with respect to time, is added in response to the slip sync signal (FIG. 17), coupled with information relative to revolution and slot count. For displaying port sonar information similar apparatus may be utilized with a reversal of scanning of the TV horizontal sweep.

Although it is possible to provide a track on the disk to trigger the sonar system, it is preferable that the sonar pulse repetition rate be the controlling factor in driving the disk. FIG. 21 shows an arrangement wherein the sonar pulse repetition frequency is compared with the disk rotation frequency and any error is utilized to correct the disk speed. A phase comparison means 233 receives as one input each sonar pulse from the sonar system 234. Another input is provided by the division circuit 236 which provides an output signal after a certain number of disk rotations. In the present example, there are 10 disk revolutions for each sonar pulse. If the sonar pulse occurs at the same instant of time as the tenth revolution then no corrective output signal is provided to the amplifier 238 to correct the speed of the motor 240 driving the disk 242. Should the rotational speed vary from the desired speed, the resultant out of phase signals applied to the phase comparison means 233 will provide an error signal to the amplifier 238 to correct the condition.

FIG. 12 illustrated a disk containing a single information storage track for the TV display and rotatable at 1,800 rpm. Various other track arrangements and rotational speeds are possible, one such other arrangement being illustrated in FIG. 22.

Disk 248 is rotatable at 3,600 rpm and contains two information tracks T1 and T2 for the recording of the display signals. All of the even field lines may be recorded in slot locations on track T1 and all of the odd field lines may be recorded in slot locations on track T2. A few of the even field lines are illustrated around head 250, and a few of the odd lines are illustrated around head 252, and since there are an odd number of lines, 525, half of line L1 is in track T1 and half in T2. This arrangement may be utilized not only in conjunction with sonar systems but may be utilized with other information generating systems. For example, in the arrangement of FIG. 2, the carrier vehicle 20 in addition to the sonar apparatus may also carry television viewing equipment. In order to transmit television pictures up the cable 28 to the vessel 27 to be processed, it is necessary to utilize a cable 28 of a particular design capable of handling the bandwidth requirements for such signal. In instances where the cable 28 is extremely long, its cost becomes excessive. A slow scan TV system, however, can be utilized in conjunction with the normal towing cable, although the information rate is slower. A typical slow scan TV camera will not have the scanning interlace and will produce approximately 4 camera scan lines in a time that disk 248 of FIG. 22 makes one revolution. Accordingly, 4 writing heads are provided as in FIG. 23A with heads 1 and 3 being for writing on track T1 and heads 2 and 4, positioned at 90° from the other two heads, being for writing on track T2. When all of the necessary information for display has been recorded in the slot locations or during the recording process, heads 1 and 5 are operable for alternately reading out their respective tracks.

In FIG. 23A head 1 is dark indicating that it is writing into a particular slot location. Arrow 254 is utilized as a reference mark for comparison with the subsequent FIG. 23B where head 2, shown dark, is writing into the next slot location on the opposite track one quarter of a revolution plus one half a slot distance later. The next information is written by head 3, FIG. 23C, wherein the reference mark 254 has rotated through another 90° plus one half a slot. In FIG. 23D head 4 is writing and the reference mark 254 has rotated another 90° plus another half slot distance. With reference back to FIG. 22 suppose that head 250, equivalent to head 1 of FIG. 23A, proceeds to write line 2 information in its correct slot location. After the information has been written, the beginning of the line 2 slot location will have proceeded 90° in the direction of the arrow and one half slot later line 3 will be written by head 2, and so on.

An arrangement for a slow scan TV system is illustrated in FIG. 24. The two track 3,600 rpm disk is not illustrated, however, it would include clock tracks as described with respect to the disk in FIG. 17. Clock pulses from a clock pulse track will appear on line 260, pulses indicative of each half slot rotation appear on line 261 and pulses indicative of each revolution of the disk appear on line 262.

The slow scan TV signal is presented on line 264 and is fed via line 265 to the analog to digital converter 267, the digital output signal of which is placed into the shift registers 269 at a rate determined by the output of oscillator 271.

The stored signal is compressed by the increased read out rate determined by the clock pulses and after conversion to analog form in the digital to analog converter 273 and after passage through the signal conditioning apparatus 275 (where it is combined with synchronizing and blanking information from generator 277,) is presented to respective power amplifiers of heads 1 through 4. These power amplifiers are enabled in sequential order as described in FIGS. 23A through D by means of an enabling signal from AND gates 283 to 286. These AND gates are enabled in sequence by the output of ring counter 289, which, in response to each new slow scan TV line will provide an enabling signal on a different one of its output lines 292 through 295, in sequence.

Since the slow scan TV signal on line 264 contains synchronizing signals, information relative to the occurrence of each line may be obtained by separating the synchronizing signal by means of the sync separator 298 which will provide a signal H on line 300 at the start of each new line and will provide a signal V on line 302 at the start of each new field. In the slow scan TV case each slow scan TV line can be stored in the exact same slot location, for each new picture. The mechanization for designating the slot location includes counter 305, encoding means 307 and comparator means 309. The V signal on line 302 is utilized to reset the counter 305, encoder 307 and ring counter 289. Each new slow scan TV line is designated by the H signal on line 300 and counter 305 counts these signals to provide an indication thereof to the encoder 307 operable to supply a unique slot location designation to the comparator 309. The other input to the comparator is an indication of the actual slot location, to a half slot accuracy, provided by counter 112 which is resettable by the output of OR gate 113 each time that the disk makes a revolution or each time that a new V signal is supplied.

When the actual location is equal to the desired location, the comparator 309 provides an output signal on line 316 to enable the AND gates 283 to 286 and signals via line 318, the generator 277 to supply the necessary signals to the signal conditioning apparatus 275.

The generator 277 provides these signals in response to the H and V information of the slow scan TV sync signals and the disk revolution, so that there is stored at a particular slot location for read out not only the desired information signal but also the desired synchronizing signals.

When the heads aren't enabled for writing, they are operable for reading information. However, in the embodiment illustrated, only two of the heads, head 1 and head 5 will do the reading function. The output signal from head 1 is fed to a read preamplifier 322 and the output of head 5 is fed to read preamplifier 323. Since one field is stored on one track and the other field is stored on the other track, the first track can be read out in its entirety for a revolution and thereafter the second track can be read out in its entirety for a revolution. The alternate selection of head 1 and head 5 is accomplished by select gating means 225 which alternately passes the signal from read preamplifier 322 and 323 to its output 327, in response to each revolution of the disk as indicated on line 262. The signal to be displayed is processed by the signal conditioning apparatus 330 and presented to the TV display 332.

As an added feature, it would be desirable, for many operations, to be able to look at a past picture. For this purpose there is included a storage system 335 which receives the TV signals and stores them whereby they may be recalled by a select circuit 337 under control of an operator. The storage system 335 may if desired include another magnetic disk arrangement or the signals may be stored on unused tracks of the same disk.

The present invention additionally allows the transmission of high quality pictures over reduced bandwidth channels. FIG. 25 illustrates an arrangement whereby slow moving scene information or pictures may be transmitted over conventional telephone lines. Although pictures can be transmitted over telephone lines by means of facsimile apparatus the resolution of the pictures received nowhere would approach the resolution utilizing the present invention which makes it particularly useful in the medical field for example for diagnosing transmitted X-rays or in the industrial field for transmitting precise picture information.

At the transmitting end a conventional television camera 350 views the information to be transmitted but provides video signals which cannot be accommodated over conventional telephone lines. The video signals therefore are expanded in time to be equal to, for example, a slow scan TV signal, in the down conversion apparatus 352. The down conversion apparatus can be similar to the apparatus described herein in that each video line signal can be recorded in a separate slot location on a magnetic disk and thereafter each slot may be read out into an analog to digital converter where the signal may then be stored in a plurality of shift registers and read out at a slow rate for telephone transmission. The signal conditioning apparatus 355 conditions the signal for transmission and presents it to an acoustic coupler 357. Such couplers are well known and are sometimes called modems, short for modulator-demodulator. The transmitting telephone apparatus 360 sends the signal via the telephone exchange to a receiving telephone apparatus 362 where the signal is converted by acoustic coupler 364 and is provided to the signal conditioning apparatus 366. The remainder of the apparatus at the receiving end is the same as that illustrated in FIG. 1 and includes a signal time conversion means 368 for compressing the received signal to place it into storage 370, such as a magnetic disk, whereby it can be presented to display 372, preferably a conventional television monitor.

In the instance where a slow scan TV camera 374 is utilized at the transmitting end, its output signals may be fed directly to the signal conditioning apparatus 355 since there is no requirement for the down conversion.