Portable Sonar System

Abstract

The patent disclosure presented herewith is directed to an improved sonar stem to be worn by swimmer-diver personnel having as its salient features an improved transducer assembly for establishing a plurality of investigative beam patterns; a phase detector arrangement for eliminating spurious echo returns; and a high resolution visual display adapted to be worn by the swimmer diver user of the system.

Description

STATEMENT OF GOVERNMENT INTEREST

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION

This invention pertains to an echo type ranging and detection system. More particularly, the invention pertains to an underwater acoustic ranging and detection system. By way of further description, but not by way of limitation, the invention is characterized as a swimmer carried sonar system.

There are few sonar systems which may be carried by a swimmer. The most successful prior art type of sonar for swimmer use has a narrow investigative beam pattern which is aimed by the user to obtain azimuth information. The range of the target is determined by judging the frequency of an aural tone. In this system, there is no visual display.

A system such as the aforedescribed prior art system, without visual display, is difficult to use because most swimmers depend upon visual stimuli in their underwater activities. In areas where the swimmer-divers work about marine ordinance or sunken structures, there has been a need for a system with a higher resolution that has been available heretofore and, thus, there has been a need for a visual display to effect such resolution.

SUMMARY OF THE INVENTION

As will be more completely explained, the invention provides a high resolution sonar system of compact dimensional parameters suitable for use by swimmer personnel engaged in underwater activities. The sonar system of the invention provides a "B" scan visual presentation and is useful in orienting the swimmer with respect to underwater objects, other swimmer personnel, and the sea floor; therefore, it obviously constitutes a meritorious advance in the art.

Accordingly, it is an object of this invention to provide an improved swimmer carried sonar system.

A further object of this invention is the provision of side scanning type of sonar system of compact dimensions.

A further object of this invention is to provide a sonar system with a readout for selection of sonar readout and visual perception combined or sonar readout only.

A further object of this invention is the provision of a swimmer carried sonar system with a viewing mask readout.

Another object of this invention is the provision of an improved sonar system employing a staggered beam transducer assembly.

A further object of this invention is the provision of a compact sonar system employing an improved phase detection means.

Other objects and many of the attendant advantages will be readily appreciated as the subject invention becomes better understood by reference to the following detailed description, when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing the system of the invention in use;

FIG. 2 is an illustration of the preferred form of a control unit, a component part of the invention;

FIG. 3 is an elevation view of the transducer assembly used in the invention;

FIG. 4 is a diagrammatic showing of the hydrophone orientation used in the invention;

FIG. 5 is a diagrammatic showing of the projector transducer orientation used in the invention;

FIG. 6 is a diagrammatic showing of a single projector pattern in relation to adjacent hydrophone patterns, as used in the invention;

FIG. 7 is a diagrammatic showing of how a plurality of hydrophone and projector patterns cooperate to provide a composite scanning arrangement;

FIG. 8 is a plan view showing the relation of ensonified zones of the sea bottom and a target object lying thereon;

FIG. 9 illustrates a preferred hydrophone transducer arrangement;

FIG. 10 is a front view of the viewing mask assembly according to the invention, as it is worn by personnel using the system of the invention;

FIG. 11 is a sectional view taken along line 11--11 of FIG. 10 and illustrates the optical portion of the readout according to the invention;

FIG. 12 is a block diagram of the circuitry of the sonar of the invention;

FIG. 13 is a schematic representation of an alternate circuit arrangement for the visual readout of the instant invention;

FIG. 14 is a diagrammatic illustration of the transmit multiplex and power amplifier circuit component of the instant invention;

FIG. 15 is a diagrammatic showing of an alternate arrangement for the transmit multiplex and power amplifier circuit component of the invention;

FIG. 16 is a showing in block diagram form of the receiver multiplex circuit componet of Applicant's invention;

FIG. 17 is a block diagram showing a preferred embodiment of the counter-programmer circuit of Applicant's invention;

FIG. 18 is a circuit diagram of the bistable delay and phase detector circuits of the system of the invention;

FIG. 19 is an illustration of electrical waveforms taken from indicated points shown in FIG. 18;

FIG. 20 is a schematic showing of a monostable multivibrator circuit component according to invention;

FIG. 21 is a block diagram showing of a quadruple NAND component used in the system of the invention; and

FIG. 22 is a schematic showing of the circuit arrangement of one of the NAND gates used in the quadruple NAND gate shown in FIG. 21.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1 there is shown an underwater diver 21 approaching a submerged object 22. A conventional back mounted life support system 23 provides a mounting for an electronics and battery package 24, a component of the invention. Diver 21 wears a viewing mask 25 which has provisions for a visual sonar display. Mask 25 is connected to instrument package 24 by a suitable connecting cable 26, which may comprise a fibre optic light transmission device. Diver 11 controls the sonar system from a hand held control unit 27 which is, likewise, joined to battery electronics package 24 by suitable cable means 28.

Referring to FIG. 2, hand held control unit 27 is seen to comprise a cylindrical body portion 29. Switch panel 31 on the upper surface of body portion 29 is positioned to be accessible to the thumb of hand of diver 21 grasping control unit 27. Switches 32, 33, and 34 are mounted in switch panel 31 for the control of the various functions of the system, as will be explained herein. A control ring 35 may be rotated to provide continuous adjustability for some functions such as gain or display intensity. One such control is shown, but it should be understood that more may be provided, if desired. A plate 36 at the foreward end of body portion 29 mounts a transducer assembly 37.

It will be observed that plate 36 is angularly mounted relative to the axis of body portion 29 of control unit 27. This arrangement permits a diver swimming horizontally to scan the bottom beneath him and determine his height thereabove. In this application, the system of the invention is especially useful in swimmer navigation, in turbid waters, or in darkness. Further, it should be noted that a fastening means, not shown, may be provided to attach control unit 27 to the clothing of diver 21 and thereby free both hands for swimming.

Referring to FIG. 3, it will be seen that transducer assembly 37 comprises both receiving hydrophone array 38 and projector transducer array 39. Hydrophone array 38 comprises eleven electroacoustic transducers 31, to be more completely described herein, which are mounted on angularly faced mounting pedestal 42. Similarly, transducer array 39 comprises 10 electroacoustic transducers 43 mounted on angularly faced mounting pedestal 44. Pedestals 42 and 44 are attached to a common base support 45 so as to extend perpendicularly upwardly therefrom. As shown in FIG. 3, arrays 38 and 39 are located adjacent to one another and may be encapsulated in a suitable material to form an enclosure 46 thereabout. Pedestals 42 and 44 are hollow and provide housing means for some of the circuitry of the invention.

Such an encapsulation constitutes only one type of housing arrangement for transducer arrays 38 and 39. Other constructions may be employed, if desired. One type of housing considered useful in swimmer carried sonar systems employs a fluid filled enclosure to surround transducer arrays. It should also be noted that the fluid filled enclosure may, if desired, comprise an acoustic lens.

As may be better understood with reference to FIGS. 4 and 5, the individual hydrophone transducers 41 are angularly displaced from one another by an angle .alpha.. The projector transducers 43 are similarly angularly oriented with respect to one another and are separated by the same angle .alpha.. However, the transducers are arranged such that a given projector transducer 43 makes an angle with respect to base support 45 to bisect the angle made by two adjacent hydrophone transducers 41 located in the hydrophone array 38.

The resulting transmission and reception patterns for a projector transducer and associated hydrophone are shown at FIG. 6. Projector pattern 47, shown by the solid line, is typical of the pattern produced by a linear array. Hydrophone patterns 48, shown by broken lines, are located on either side of projector pattern 47 and are equally spaced therefrom. The directivity patterns cooperate, when used together, to produce a narrow directivity with respect to the reference axis 49 corresponding to the linear direction of the pair.

Referring to FIG. 7, there is shown diagrammatically how a plurality of transducer combinations found in transducer assembly 37 are combined to form a sector scan. As may be seen, projector patterns 47 are positioned between two receiver patterns 48. From the figure, it is readily apparent that N projectors and N+1 transducers may be switched to produce a sector scan of 2N sectors. Of course, the greater the number and the smaller the beamwidth of the sectors, the higher will be the resolution of the system.

For the device of the invention, ten projector transducers 43 are used in combination with eleven hydrophone transducers 41. These arrangements are switched by means of suitable circuitry, to be more fully described herein, to provide twenty composite transmit and receive channels to be established using but 10 projectors. Each pattern is a composite of the patterns generated by one projector pattern 47 and one hydrophone pattern 48. The two patterns combine in the well understood fashion to produce a composite pattern which is the product of the individual patterns. This resultant pattern has a narrow, highly directive pattern with greatly reduced side lobes in comparison with the patterns of the projector or the hydrophone.

Referring to FIG. 7, it may be seen how the respective patterns cooperate to produce the desired scan area. Projector pattern 47 first cooperates with hydrophone pattern 48 to produce a first scan, and then with hydrophone pattern 48' to produce a second scan. Next, projector pattern 47' cooperates with hydrophone pattern 48' to produce a third scan, and then with hydrophone pattern 48" to produce a fourth scan. The process is carried on with the following projector and hydrophone patterns until the sequence is complete with projector pattern 47.sup.n cooperating with hydrophone pattern 48.sup.n.sup.+1 to produce the final scan. In the developmental studies of the invention, each individual pattern is assumed to be .beta. degrees wide so that the resulting composite pattern is 2.beta./3 degrees wide. The entire sector covered is 4n.beta./3 degrees wide. Practical values for .beta.are in the range of 1.degree. to 5.degree. and n may be between 10 and 40. It should be noted that the angular spacing of the patterns preferably results in an angular redundancy in the total composite scan pattern.

The angular overlap of adjacent composite patterns permits the ranging system of the invention to provide a more accurate relative bearing and range information than prior art systems having the same number of transducers. That is, to obtain the narrow composite beamwidth the same transducer had to be used for transmitting as well as receiving or elaborate shading arrangements were required. This improvment is particularly useful in determining the relative range and position of an object having an angular size which is relatively large in comparison to the composite pattern employed by the system, and having a relatively large surface lying at an angle to the acoustic axis of the composite sector. Such a target is presented by object 22 in FIG. 1.

Referring to FIG. 8, the parameters involved in detection and ranging of object 22 with an angularly disposed leading edge 54 are more clearly shown. The figure illustrates a single composite pattern with the divergence thereof exaggerated for purposes of explanation. At any instant, the target returns may be considered to originate from a strip which is .DELTA.R wide and of a length which is a function .delta. of the range R. The three strips 51, 52, and 53 illustrated may be considered portions of the bottom ensonified by successive pulses directed along a common acoustic axis 55, or by a single pulse at three separate instants of time. When the ensonified zone encounters a solid object, such as object 22, a shadow zone is formed which limits the length of the strip 53 at ranges greater than the range of edge 54.

If the ranging sonar is only equipped to process amplitude information, the reverberation echo from strip 53 will be displayed on a bearing corresponding to acoustic axis 55. In the illustrated instance, the return would be displayed in the shadow zone where no returns actually originate. In the device of the invention this would result in a bright line, of a length corresponding to the 2.degree. composite radiation pattern of the preferred embodiment of the invention, displayed as centered on acoustic axis 55. A detection system which would display the echo return from strips 51, 52, and 53 on their respective centers would improve the resolution of the edge 54.

A sonar system that measures the difference in time of arrival of the return signal at two spaced hydrophones located in a side-by-side relationship will display the return centered on the bearing azimuth to the center of reflection of the particular strip from which the reflected signal originates. A phase detector is capable of providing this type of signal processing, and, for this reason, is incorporated in the circuit arrangement of the invention. It should be made clear that the exact position of the display is dependent upon the number and distribution of the scattering elements in the strip from which the echo originates. The echo return is displayed centered on the bearing of the apparent acoustic center of gravity -- i.e., the mean energy distribution of the strip. It should not be supposed, however, that the phase detection is able to resolve individual ones of these scatters which are not resolved in range.

FIG. 9 illustrates how the individual hydrophone transducer may be configured to produce the aforesaid highly desirable results. It will be observed that hydrophone transducer 41 comprises a piezoelectric plate 56. An electrode 56 is attached to one side thereof and is coextensive therewith. Conductor 58 makes electrical contact with electrode 57 and provides electrical connection to the transducer from the remainder of the circuitry. A plurality of grooves 59 are cut into plate 56 to effectively form thereon a plurality of posts 61 extending upwardly from the uncut portion of plate 56. In the example shown there are 44 posts 61. Electrodes 62 are affixed to the upper face of each post 61 for electrical contact therewith. Electrical conductor 63 joins eighteen alternate posts 61 starting at the right end of transducer 41, and conductor 64 joins an identical number of alternate posts 61 starting at the left end thereof. The two groups of posts comprise, in effect, two transducer arrays. The two arrays are separated acoustically by the distance between their centers, represented by the broken lines shown in FIG. 9. Conductors 63 and 64 may be routed downwardly between the posts in a known fashion, if desired.

An important design parameter for the purposes of the instant invention is that the hydrophone transducer 41 be configured to have a resonant frequency which is higher than the operational frequency of the ensonifying projector transducers 43. This is because a phase shift occurs within a hydrophone transducer for operational frequencies in the region of electrical resonance. Since a phase detection system is to be used as an important component in the signal processing channel of the system of the invention, such internal phase alterations within the hydrophone itself are to be avoided. Configuring the transducer to resonate well above the operational frequency of the system effectively prevents these phase alterations from occurring.

Before proceeding to the description of the electronic circuitry of Applicant's invention, some particular features of the novel information readout arrangement will be explained. In murky waters or after nightfall swimmer-diver personnel have no useful visual information. This lack of visual contact is especially acute where an element of secrecy is desired, such as in Naval operations, and the use of lighting is precluded. Under such conditions underwater swimmer-diver personnel frequently become disoriented and experience difficulties in navigating. The visual readout of the invention provides a choice between the visual presentation of the ranging system, the normal visual perception of the surroundings, and a composite presentation of the two presented superimposed one on the other.

Referring to FIG. 10, the viewing mask assembly 25 of the invention is shown as it is worn by swimmer-diver 21. A conventionally constructed face mask 65 has an optical unit 66 mounted on the upper wall 67 thereof. Optical unit 66 is joined to the battery and electronics package by a fibre optic image transmission cable 26 (see also FIG. 1). Face mask 65 is shaped at the side portion 68 to receive the optical unit 66 when it is pivoted to one side, so as to permit an unobstructed vision through viewing plate 61. When in viewing position, the optical unit 66 is positioned over one eye of diver 21 and lens 71 is aligned therewith.

It should be made clear that, although the invention is described as a monocular arrangement, the invention may be configured as a binocular viewing device. In such instances the optical viewing unit would provide for both eyes to view the presentation and may pivot vertically to a position above or foreward of upper wall 67 of viewing mask 25.

Referring to FIG. 11, the details of construction of the optical unit 66 are shown in greater detail. The optics are contained in a housing 72 which supports lens 71 on the front surface thereof. A rubber, or other flexible material, bellows 73 extends from the rear surface of housing 72 to resiliently abut viewing plate 69 and provide a glare free viewing path from the divers eye, shown schematically at 74, through housing 72.

Within housing 72 is an image forming bundle 75 which terminates in an image display surface 76. A lens 77 relays the image to prism 78 in such a fashion as to appear to be at a distance of approximately 15 to 20 meters. Prism 78 has a lower, semi-reflecting surface 79 which permits the visual superposition of the display image from surface 76 and the view of the surrounding transmitted via lens 71.

It is sometimes desirable to exclude the view from lens 71 to permit examination of the sonar image displayed on surface 76 alone. For this purpose, a reflector 81 is pivotably supported below prism 78. Reflector 81 may be moved into contact with semireflecting surface 79 by pusher arm 82. Pusher arm 82 is actuated by suitable means, not shown, on the exterior of housing 72, or by solenoid means, not shown, located within housing 72. Ordinarily, the viewing of the sonar display alone is performed for short periods, and, accordingly, reflector 81 is spring biased to the position shown. Should longer periods of exclusively sonar readout display be desired, suitable catch means, not shown, may be employed to hold reflector 81 against prism 78.

The circuitry, shown in FIG. 12 in block diagram form, provides for the operation of the invention. A clock circuit 83 produces a series of predetermined pulses which are used to produce the timed and synchronous operation of the individual circuit arrangements comprising the system. The output signal pulses from clock 83 are connected by suitable circuitry to a ring counter-programmer circuit 84, a staircase generator 85, a sawtooth generator 86, and a gated oscillator 87.

Staircase generator 85 is also connected to 20 bit ring counter-programmer 84 to receive an output therefrom. Staircase generator 85 is configured to produce a twenty step staircase voltage waveform in response to the signals supplied it from clock 83 and ring counter-programmmer 84. Clock 83, staircase generator 85, sawtooth generator 86, and gated oscillator 87 comprises a timing means which controls the timed relationships of the other components of the system.

The ring counter-programmer 84, to be more fully described herein, is connected to multiplexer circuit 88 and multiplexer and power amplifer circuit 89. The output of gated oscillator circuit 87 is also connected to multiplexer and power amplifier circuit 89. Multiplexer and power amplifer circuit 89 is connected so as to provide a timed actuation of particular transducer in projector array 39. Multiplexer 88 provides a signal transfer path from the hydrophone array portion 38 of transducer assembly 37 to left and right preamplifers 91 and 92, respectively. The function and construction of multiplexer 88 and multiplexer and power amplifer 89 will be more completely described herein.

Preamplifiers 91 and 92 are connected to filters 93 and 94, respectively. As indicated, filters 93 and 94 are designed to pass a select band of frequencies and reject, i.e., block the passage of, frequencies above and below said select band. Filters 93 and 94 are electrically identical and, accordingly, limit the frequency content of the two channels to the same spectrum. A limiter 95 is connected to filter 93 to effectively remove the amplitude variations from the output thereof.

A similar limiter 96 and a time varied gain amplifier 97 are connected to filter 94. The output of filter 94 supplies the highlight information, as will be more fully explained herein, and this accounts to its output being connected to TVG amplifier 97 prior to having the amplitude variations removed.

Limiter 96 is connected in circuit with a bistable delay 98 so as to apply its output thereto. Bistable delay 98, as its name implies, delays in time the transmission of the output of limiter 96 for one of two fixed time intervals. The time interval that is used is determined by the output of twenty bit ring counter 84 which is connected to bistable delay 98 via appropriate circuit connection means.

A phase detector 99 of a novel construction is connected to limiter 95 so as to receive the output therefrom, and is connected to bistable delay 98 so as to receive the time delayed output of limiter 96 therefrom. One output of phase detector 99 is a function of the difference in arrival time of the two input signals, and is connected to the input of summing amplifier 101. Preamplifiers 91 and 92, filters 93 and 94, limiters 95 and 96, bistable delay 98 and phase detector 99 comprise the dual channel receiver means of the invention.

Summing amplifier 101 is also connected to staircase generator 85 to receive the 20 step waveform therefrom. Amplifier 101 combines these two signals into a composite sum signal of an amplitude of a predetermined value corresponding to the bearing of the center of reflection. Amplifier 101 is connected to the x axis input circuit 102 of a visual readout 103.

Phase detector 99 produces a second output signal which indicates whether or not the arrival times of the input signals thereto were within a predetermined time interval. A transmission gate 104 is connected to phase detector 99 so as to receive this second signal therefrom. This second signal, as will be readily apparent to those familiar with electronic ranging circuitry of the type described herein, determines if the signals originally impinged the hydrophone array 38 from a predetermined angular sector. This angular sector is chosen so as to exclude returns from composite patterns produced by adjacent projector transducer and hydrophone transducer pairs. Transmission gate 104 controls the highlight display.

As previously noted, the highlight signals are derived from the unlimited output of filter 94 which is connected to time varied gain amplifer 97. The gain of amplifier 97 is controlled by the output of sawtooth generator 86 which is connected to a slope modification preamplifier 105. The slope of the sawtooth is adjusted, in the well understood manner, to compensate the gain for signal loss due to attenuation by the medium over the expected range of the system. Slope preamplifier 105 is connected to time varied gain amplifier 97 to control the time-gain function thereof.

The amplitude variations in the output of TVG amplifier 97 are detected by detector 106 to which it is connected. Detector 106 is effectively electrically connected to a low pass filter 107. Filter 107 removes the high frequency amplitude variations from the detected video signal prior to display.

Filter 107 is connected to the previously mentioned transmission gate 104. Transmission gate 104 is connected in circuit with Z axis input circuit 108 for display of target highlights as intensity variations. Gate 104 prevents a display when the signal is from a sector outside the predetermined acceptance angle as explained in description of phase detector 99, supra, and to be more completely described herein.

The remaining input to visual readout 103 comes from sawtooth generator 86. Sawtooth generator 86 is connected to Y axis input circuit 109 so as to provide a time varying signal to provide a range generating sweep on which the highlight and bearing information are displayed. As illustrated schematically, X axis input circuit 102, Y axis input circuit 109, and Z axis input circuit are all effectively connected to supply cathode ray tube 111 with operational signals.

As previously noted, the cathode ray tube 111 is physically located within battery and electronics package 24 located on the life support system 23 (FIG. 1). In some developmental units cathode ray tube 111 has been located on the viewing mask 25 and may be so mounted in the invention, if desired. However, such an arrangement requires high voltage conductors to lead externally around the head of swimmer-diver 21, a system with obvious dangers to operating personnel.

It is difficult at the present state-of-the-art to obtain a cathode ray tube to meet the requirements of compactness, persistency, and brightness imposed by the operational parameters in which the system is to be used. For example, in some waters the visibility is low despite a relatively high light level. In such circumstances, the brightness of the video display produced by cathode tube 111 must exceed that of the ambient light to be seen by diver 21. As pointed out above, the present state-of-the-art cathode ray tube of dimensions sufficiently small to mount in battery and electronics package 24 and of the persistency to be used in sonar applications requires a light intensifier 112 to be placed between cathode ray tube 111 and fibre optics input bundle 113.

When performing duties under water, the personnel using the sonar are quite occupied, and duties that are not essential are often neglected. It is for this reason the device of the invention may be equipped with a brightness adjustment circuit to free the diver from making control adjustments and to automatically keep the display at an optimum brightness.

The brightness control circuit comprises a light collector 114. The ambient light falling on light collector 114, shown as a positive lens, is directed to suitable photoelectric transducer means 115. An automatic gain control amplifier 116 is electrically connected to photoelectric transducer 115. The output of photoelectric transducer 115 causes the gain of A.G.C. amplifier 116 to be adjusted to attain a predetermined value with respect thereto. AGC amplifier 116 is connected to light intensifier 112 to control the optical gain thereof.

Should a suitably dimensioned cathode ray tube with sufficient brightness become available, or should operation only in low light levels be expected, the circuit arrangement of FIG. 13 could be employed for an automatic brightness controlled readout arrangement. Visual readout 103 employs such a bright cathode ray tube 117 coupled directly to fibre optic bundle 113 without an intermediate light intensifier. The light sensing arrangement of light collector 114 and photoelectric transducer 115 function as in the arrangement in FIG. 12. Automatic gain control amplifier 116 is connected to Z axis input circuit 108 to vary the gain thereof and to effectively alter the brightness of the display in accordance with the ambient light level. In such an arrangement X axis input circuit 102 and Y axis input circuit 109 function as in the circuit of FIG. 12.

As will be obvious to persons versed in the electroacoustic ranging arts, some of the circuits identified as blocks in FIG. 12 are themselves rather complex circuit arrangements, but are so well known as not to require further description. Similarly it should be recognized that a variety of circuits are well known which will perform the design functions satisfactorily in the system of the invention. Accordingly, the selection as between different ones of these well known prior art circuit arrangements is regarded as a matter of design choice to a proficient artisan.

However, certain ones of the circuit blocks, to be more fully identified and described herein, are departures from standard prior art circuitry. In certain ones thereof the departures from known circuit arrangements are for the purpose of optimizing the circuit arrangement for use in the system of the invention. In other circuits, innovations are presented herein which are meritorious advances in the electroacoustic circuitry arts per se. These circuits, although capable of independent and separate application, are described with sufficient detail to enable a skilled artisan to make and use the acoustic ranging system of the invention.

Referring to FIG. 14, projector multiplexer-power amplifier circuit 89 is shown in block diagram form. Each projector transducer 43 is driven by a power amplifier 118. Each of the power amplifiers 118 are identical and raise the power level of the pulse of acoustic energy pulse supplied by gated oscillator 87, a unijunction oscillator in the developmental model of the invention, to a level sufficient to ensonify the desired projection pattern. Each of power amplifiers 118 is fed the input from gated oscillator 87 by a transmission gage 119. Transmission gates 119 are energized sequentially by twenty bit counter 84, to be described in greater detail herein. The reason for having an individual power amplifier 118 for each projector channel is based on the reliability of gates 119 when repeatedly switching high level acoustic power pulses. If reliable switching circuitry of compact dimensions could be developed, a more direct circuit arrangement would be possible.

FIG. 15 shows such an alternative arrangement. As is shown therein, amplifiers 118 have been replaced with a single amplifier 121. Similarly, gates 119 of FIG. 14 have been replaced by high power gates 122. The two circuits function in the same fashion, and, for the purposes of the invention, may be used interchangeably.

In both of FIGS. 14 and 15, only four channels are shown for purposes of illustration, but it should be understood that each circuit has ten channels in the preferred embodiment.

FIG. 16 illustrates the multiplex circuit 88 in a more complete, but still diagrammatic, fashion. As previously explained, each hydrophone transducer 41 has a right and a left array. Each of the right arrays are connected, via conductor 63 to a right received signal gate 123. Similarly, each hydrophone has its left array connected, via conductor 64, to a left received signal gate 124. Each hydrophone transducer 41 has its associated right received signal gate 123 and its left received signal gate 124 have their trigger inputs connected in parallel to be triggered simultaneously by the ring counter-programmer circuit 84. The eleven individual channels in the receiving channel each comprise a hydrophone transducer 41, a right received signal gate 123, and a left received channel gate 124. The eleven channels are triggered in a predetermined sequence by the ring counter circuit 84, which serves as a programmer for the combined operation of the hydrophone transducers 41 and the projector transducers 43. The terms left and right are used in this discussion are understood as being only mutually exclusive, and, in some orientations, may actually correspond to other interrelations such as up and down.

The construction of the ring counter-programmer circuit 84 is diagrammatically illustrated in FIG. 17. The principal component in the circuit is a twenty bit ring counter 125. The counter functions in a conventional manner for circuits of its kind, i.e., conduction advances one stage for each pulse input received from clock circuit 83. The ring counter 125 is illustrated foreshortened with only nine of its twenty stages shown. Each of the stages are numbered to correspond to the sequence in which it is activated.

The output of each stage of ring counter 125 are illustrated as two terminals so as to agree with the illustration of circuit 84 in FIG. 12 and to simplify explanation thereof, but, in fact, the outputs may be taken from a common point. As illustrated, one set of outputs are ultimately associated with the eleven receiving hydrophone channels and these outputs are labeled H.sub.1, H.sub.2, etc. The other set of outputs are ultimately used to trigger the ten gates 119 or 122 in multiplexer and power amplifier circuit 89, and are labeled P.sub.1, P.sub.2, etc. It will be noted that the first and last stages of ring counter 125 are used to trigger the associated hydrophone gate pairs directly. The remaining stages are processed by a plurality of identical "or" gates 126. There are nine "or" gates 126 for the hydrophone channels and they accept inputs from adjacent stages of ring counter 125 starting with the second and third states. Ten similar "or" gates 126 receive inputs from adjacent stages of ring counter 125, starting with stages one and two, and are used to trigger the gates 119 or 122 in the projector channels.

A monostable multivibrator 127 is triggered by the last, i.e., twentieth stage. The output of this stage is connected to, and provides for the reset pulse for, staircase generator 86, as previously noted in connection with FIG. 12.

It may be seen from inspection of FIG. 17 that, upon receipt of the first clock pulse, stage one of counter 125 is energized. This energizes the first hydrophone channel and the first projector channel. A second clock pulse energizes the second stage of counter 125, and, accordingly, triggers the second hydrophone and the first projector channels. The third clock pulse energizes the third stage of ring counter 125, and triggers the second hydrophone channel and the second projector channel. Subsequent clock pulses trigger succeeding stages of counter 125 into conduction to advance the triggering of subsequent projector and receiver channels that each one, except for the first and last receiver channels, is used twice in succession. This sequential switching action together with the relative positioning of the transducers as shown at FIGS. 3, 4 and 5, and discussed above, produce the radiation and reception patterns 47 and 48 shown in FIG. 7 and described above.

An output is taken from alternate stages of ring counter 125 starting witn the first stage. These outputs, labeled x in FIG. 17, are connected as inputs to 10 input "or" gate 128. The output from "or" is connected to bistable delay 89, as will be presently described, for the purpose of synchronous triggering thereof.

The construction of the bistable delay circuit 98 and the cooperating phase detector circuit 99 is explained with reference to FIG. 18. Because circuits 98 and 99, like most circuits in modern electronic systems, employ micro or integrated circuits the block diagram like illustration is actually the wiring diagram of the circuit. The particular circuit configuration of the electrical circuitry encompassed within the blocks is illustrated separately and the appropriate figures will be referred to from time-to-time in the course of the following description. In practice, however, these circuits are commercially available units and are connected in circuit as if they were single active elements.

When employed by itself as a receiver, a given hydrophone transducer 41 has an acoustic axis centered between the axis of the two arrays of posts. However, as discussed above, each hydrophone transducer 41 is paired with two projector transducers 43 spaced on either side thereof. For one ping-listen cycle the hydrophone is used in conjunction with the projector transducer 43 on one side thereof, and on the next ping-listen cycle it is used in conjunction with the projector transducer 43 on the opposite side thereof. As a result of this alternate use to establish a sector scanning arrangement, the acoustic axis of the composite pattern will be shifted to one side of the normal axis of hydrophone transducer 41. In the instant invention this shift corresponds to an angular shift of .+-.2.beta./6.degree.. As a result of this, a difference in time of arrival, termed .DELTA.t, occurs for an echo return on the axis of the composite beam when one projector transducer 43 is used as compared to .alpha. return of the same range and relative bearing when the other projector transducer 43 is used.

Assuming the beamwidth of the composite pattern for the device of the invention is approximately 2.degree. at the half power points, the phase detector circuit 99 is designed to determine the incident angle of wavefronts received within this composite pattern beamwidth an accuracy of 0.25.degree.. Phase detector circuit 99 also prohibits the amplitude information of wavefronts received from directions outside of the desired angular response beam from reaching the cathode-ray tube display 103. The system is, in such a hypothetical system, only responsive to echoes having bearing angles of .+-.1.degree.. A bearing of 1.degree. relative to the acoustic axis of the hydrophones corresponds to an arrival time difference of 192 nanoseconds (ns) in the system of the example. An accuracy of 0.25.degree. corresponds to detecting an arrival time difference of 48 ns.

A wavefront incident 1.degree. to the left of the acoustic axis was assigned at t = 0 for proper display orientation. Then an axis return in one pattern corresponds to a .DELTA.t of 192 ns and for the adjacent composite pattern to a .DELTA.t of 384 ns. Thus the signal output of the right hydrophone will always lag the signal from the left. The bistable delay 98 mentioned previously and located in the right channel (FIG. 12), must add a delay T when the acoustic axis of the composite pattern is displayed -0.75.degree., and a delay T.sub.2 when it is displayed .+-.0.75.degree.. .DELTA.t for 0.75.degree. is 144 ns; therefore, for one complex pattern this delay corresponds to 192 ns - 144 ns, or 48 ns, and for the adjacent pattern the delay corresponds to 192 ns + 155 ns, or 336 ns.

Bistable delay circuit 89 comprises a monostable multivibrator 129 which is triggered by the amplitude limited waveform, shown at A in FIG. 19, from right channel limiter 96. This waveform is a square wave of the operating frequency. As shown at FIG. 20, monostable multivibrator 129 comprises a five transistor, seven diode circuit. A variety of integrated circuits which are commercially available may be, with small circuit modifications, used for monostable multivibrator 129. However. for purposes of completeness of disclosure, it should be noted that the circuit marketed under the designation SE106 by the Signetics Corporation of Sunnyvale, California, has proven satisfactory in developmental models of the invention.

The bistable delay operation of monostable multivibrator circuit 129 is accomplished by feeding the voltage output of circuit 128, via diode 131, to pin number three of the integrated circuit. The pulse width of monostable multivibrator 129 may be controlled with respect to designed value by applying a voltage at pin 3, as is done in this instance, and by connecting a capacitor between pins three and four. As may be seen from the circuit configuration of FIG. 20, an external capacitor between pins three and four shunts capacitor 132 to alter the pulse width. A change in voltage at pin 3 alters the voltage drop across resistor 133 to produce a similar alteration in pulse width. In the device of the invention, capacitor 134 causes monostable multivibrator 129, abbreviated MSMV 129, to produce the 336 ns delay and the voltage output of "or" gate 128 is regulated to produce the 48 ns delay. The frequency of the switching of delays is very slow since it is at the ping-listen cycle rate, in comparision to the other pulses, which are at the operating frequency rate.

Phase detector 99 comprises monostable multivibrators, abbreviated MSMV, 135, 136, 137, 138, and 139. Each of these circuits is identical with MSMV 129 with the exception of external connections. Quadruple NAND gate 141, power supply 142, and integrate and hold output circuit 143 are connected in circuit with the aforementioned MSMV circuits as shown in FIG. 18. Waveforms illustrated in FIG. 19, and circuit details illustrated in FIGS. 21 and 22 will be referred to from time-to-time to more clearly explain the operational details of phase detector 99, illustrated at FIG. 18.

Power supply 142 comprises a regulating transistor 144 which is biased to regulate the output voltage to a predetermined value with respect to a reference potential established by zener diode 145. The regulated voltage is distributed by the illustrated circuitry to all component stages of bistable delay 89 and phase detector 99.

MSMV 135 is connected to receive the delayed output of bistable delay 89, waveform B. The pulse width of waveform B establishes the desired delay in accordance with the value of capacitor 134 and the voltage applied via diode 131 as discussed previously. The negative going edge of waveform B triggers MSMV 135 to produce a positive pulse output shown at waveform C, and having a pulse width regulated by capacitor 146. The pulse width of waveform C is chosen to be of a time duration corresponding to twice the desired angular resolving power as discussed above.

MSMV 136 is connected to receive the output of limiter 95, waveform D, and produces a positive pulsed waveform E in response thereto. MSMV 136 is configured to be electrically identical to MSMV 135.

The outputs of MSMV's 135 and 136, waveforms C and E, respectively, are fed to quadruple "NAND" gate 141. As shown at FIG. 21, quadruple gate 141 comprises four "NAND" gates 147, 148, 149, and 151. Each of the gates is configured as shown at FIG. 22. A variety of circuits may be used for quadruple NAND gate 141. The unit marketed by Signetics Corporation of Sunnyvale, California, under the designation SE480J has proven satisfactory, and is cited as an example of a type which may be used successfully for the purposes of the invention.

The individual circuit arrangement shown at FIG. 22 reveals that the circuit comprises a transistor 152 with dual emitters. When an input of the proper characteristics appears on each of the two emitters simultaneously, transistor 152 conducts. Transistor 152 and associated circuitry form an "AND" gate 153. The output of AND gate 153 is inverted by the action of transistors 154 and 155 to produce the "NAND," or "NOT AND," logic function.

In phase detector 98, FIG. 18, quadruple gate 141 is wired such that "NAND" gate 151 has its output connected to one input of "NAND" gate 149. The other imput of gate 149 is connected to a fixed voltage source such that gate 149 merely inverts the output of "NAND" gate 151 to produce an "AND" function of the inputs thereof. This output, waveform F, is connected to integrate and hold circuit 143 and to MSMV 137.

MSMV 137, which has its pulse width unmodified by external capacitors, produces a spike pulse output, waveform G.

As previously noted, the waveform F is also applied to integrate and hold circuit 143. The pulse width of waveform F has been processed, as noted above, such that it is a function of the difference in arrival time of the same cycle of returned echo to the left and right arrays of the hydrophone transducer 41 then in use. This time difference, as previously explained, is a function of the bearing within a composite beam pattern of the center of reflection. Integrate and hold circuit 143 charges capacitor 156 to a value dependent upon the duration of the pulse of waveform F.

The output of integrate and hold circuit 143, waveform H, is connected to summing amplifier 101 (FIG. 12) where it is combined with the output of staircase generator 85 to position the beam in a horizontal direction. The beam position is held until the next cycle of the returned echo or reverberation signal when the integrate and hold circuit 143 again indicates the center of reflection.

Integrate and hold circuit 143 is reset by transistor 157 which, when energized, discharges hold capacitor 156.

Transistor 157 is triggered by a spike pulse output of MSMV 138, shown at J in FIG. 19. MSMV 138 is, in turn, triggered by the delayed output of bistable delay 129, waveform B.

The output of MSMV 135, waveform C, and the output of MSMV 137, waveform C, are connected to quadruple NAND gate 141 where they are combined in NAND gate 148. The output of NAND gate 148, waveform K.

MSMV 139 is connected to receive the output of NAND gate 148 and be triggered thereby. The output pulse width of MSMV 139, waveform L, is determined by capacitor 158, and is chosen to permit gate 104 (FIG. 12) to pass the amplitude information contained in the echo return so as to be displayed by visual readout 103. Should the echo return impinge from a direction outside the predetermined angular bandwidth, there will be no output from NAND gate 148 and transmission gate 104 will block amplitude information from being displayed.

NAND gate 147, although contained in integrated quadruple NAND gate 141, is not used in the circuitry of the invention.

PREFERRED MODE OF OPERATION

The operation of the device of the instant invention is considered straightforward, and differs from other acoustic ranging and detection systems only in its compactness and special environmental aspects. Accordingly, this description will deal primarily to the operational manipulation performed by a swimmer-user of the system. FIGS. 4, 10, and 11 illustrate the controls normally used in operating the system.

The swimmer enters the water with the system turned off and the optical unit 66 in its inoperative position, shown by broken lines in FIG. 10. Upon reaching an area where his vision is obscurred, the system is energized by pressing control switch 34. Optical unit 66 is positioned before the eye, or eyes in the event a binocular presentation is employed, and reflector 84 adjusted to provide the presentation desired. Control ring 35 is then adjusted to set the slope of the slope preamplifier 105 to cause time varied gain circuit 97 to fill the presentation to the optimum range. Practical experience has shown a twenty meter range for a swimmer height of three and one half meters from the bottom is optimum. Control ring may effect a continuous adjustment or select one of a plurality of set TVG slopes for different bottom conditions.

The swimmer-diver 21 traverses the area with the control unit 27 either hand held, as illustrated in FIG. 1, or clipped to his person. Head mounting may be used if desired, but has proven somewhat troublesome as swimming and performing underwater tasks causes head movements resulting in blurred images and optical distraction. Perhaps because swimming-diving personnel have grown accustomed to hand held electric lights, or some other psychological reason, the hand held operation seems preferred.

The acoustic energy is projected from, and returned to, control unit 27 which, in addition to supporting the electroacoustic energy converters, provides a mounting for the electrical controls and houses the ring counter-programmer 84, receive-multiplex circuit 88, multiplex-power amplifier 89, as well as some component circuits of the dual channel receiver means. The signal from hydrophone means 41 in use is processed, amplitude and phase detected as previously explained in connection with FIG. 12.

If the signal is transmitted by gate 104, i.e., if the return is within predetermined limits, a visual light image is produced by visual readout 103. The display produced by visual readout 103, which is physically located in battery and electronics package 24, is transferred via fibre optical bundle 75, to optical unit 66.

If it is desired to study the sonar image in detail, reflector 81 (FIG. 11) is positioned against prism 78. This may be accomplished either with a manual control of pusher arm 84 or electrically by use of switch 32 to control a solenoid, not shown, mounted within optical unit 21.

Switch 33 may be connected to gate circuit 104 to cause interruption of the sonar display. In such an operation swimmer-diver 21 sees only the visually preceived details of his environment.

The phase-detector action, previously described, presents an improved image resolution not heretofore obtainable. This presentation, together with the compact scanning arrangement made possible by the aforedescribed construction and circuitry details, provides an improved sonar system for swimmer-diver use. The advantages offered by this system ove the proper art systems are so marked as to constitute an unobvious advance in the art.

Obviously, other embodiments and modifications of the subject invention will readily come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing description and the drawings. It is, therefore, to be understood that this invention is not to be limited thereto and that said modifications and embodiments are intended to be included within the scope of the appended claims.

Claims

What is claimed is:

1. A portable sonar system comprising in combination:

a plurality of angularly oriented linear transducer means for converting electrical energy supplied thereto into acoustical energy;

a plurality of angularly oriented hydrophone means adjacent to said plurality of angularly oriented linear transducer means for converting acoustic energy impinging thereon into electrical signals, each of said hydrophone means comprising left and right linear arrays of hydrophone elements and having a predetermined angular orientation with respect to individual ones of said transducer means;

control unit means effectively attached to said plurality of transducer means and to said plurality of hydrophone means, so as to provide cooperative relationship therebetween and configured so as to facilitate manual positioning thereof for directing the investigative beam pattern of said sonar system;

a receive-multiplex circuit means effectively electrically connected to said plurality of hydrophone means for selectively transmitting signals from a single one thereof into left and right channels corresponding to said left and right arrays of hydrophone elements;

multiplex-power amplifier circuit means effectively connected to said plurality of transducer means for selectively applying a pulse of electrical energy to one thereof;

ring counter-programmer means effectively connected to said receive-multiplex circuit means and effectively connected to said multiplex-power amplifier circuit means for the actuation thereof in a predetermined programmed sequence;

dual channel receiver means effectively connected to said receive multiplex circuit means for processing the signals from the left and right channels thereof;

amplitude detection circuit means effectively connected to one channel of said dual channel receiver means for detecting the amplitude variations in the signals processed thereby and for producing an output signal which is a direct function thereof;

phase detection circuit means effectively connected to said dual channel receiver means and responsive to the phase difference between the left and right channel signals thereof for producing a first output signal which is a function of the phase difference of said left and right signals and a second output signal if the phase of said left and right signals is within predetermined limits;

signal transmission gate circuit means effectively connected to said amplitude detection circuit means to receive the output signal therefrom and effectively connected to said phase detection circuit means to receive said second output signal therefrom for effecting the passage of said first output signal from said amplitude detection circuit when said second output signal from said phase detection circuit means corresponds to a phase relationship within said predetermined limits;

visual readout means effectively connected to said signal transmission gate for displaying the signals passed thereby as light intensity variations and effectively connected to said phase detector circuit means to receive said first signal therefrom for positioning said displayed light intensity signals in response thereto;

timing circuit means effectively connected to said ring-counter-programmer circuit means, said multiplex-power amplifier circuit means, and said visual readout means for supplying electrical signals corresponding to predetermined time functions thereto; and

optical means operatively associated with said visual readout means for transmitting the light output thereof to a position remote therefrom for visual readout thereof.

2. A portable sonar system according to claim 1 in which said left and right arrays of hydrophone elements spatially overlap such that individual elements of one array are placed between adjacent individual elements of the other array.

3. A portable sonar system according to claim 1 in which said dual channel receiver means includes, in one channel thereof, a bistable delay circuit means for delaying pulses passed therethrough for one of two predetermined time intervals in response to control signals applied thereto.

4. A portable sonar system according to claim 3 in which said ring counter-programmer means further comprises in combination:

ring counter circuit means electrically connected to said timing circuit means for receipt of signals therefrom, and having outputs from the first and last stages thereof electrically connected to said receive multiplex circuit means;

a first series of binary input "or" gates electrically connected to successive stages of said ring counter circuit means such that successive ones of said "or" gates receive inputs from successive, nonoverlapping pairs of the stages of said ring counter circuit means starting with the first stage thereof, the outputs of said first series of "or" gates being connected to said multiplex-power amplifier circuit means;

a second series of binary input "or" gates electrically connected to successive stages of said ring counter circuit means such that successive ones of said second series of "or" gates receive inputs from successive, nonoverlapping pairs of the stages of said ring counter circuit means starting with the second stage thereof, and having outputs therefrom connected to said receive-multiplex circuit means; and

multiinput "or" circuit means connected so as to receive inputs from the outputs from alternate ones of the stages of said ring counter circuit means starting with said first stage thereof and having its output connected to said bistable delay means.

5. A portable sonar system according to clam 1 in which said phase detection circuit means further comprises in combination:

a pulse generator circuit means for generating a pulse having a width which is a function of the difference in time of arrival of acoustic energy which is impinging said left and right hydrophone element arrays; and

integrate and hold circuit means electrically connected to said pulse generator circuit means for generating and holding a voltage which is a function of the length of the pulse generated thereby.

6. A portable sonar system according to claim 5 in which said phase detection circuit means further comprises in combination:

logic circuit means electrically connected to said pulse generator circuit means for comparing said pulse width to a predetermined time duration; and

second pulse generator circuit means electrically connected to said logic circuit so as to receive the output thereof for generating a control pulse in response thereto.

7. A portable sonar system according to claim 5 in which said phase detection circuit means further comprises in combination, a trigger pulse generator means connected in electrical circuit so as to receive the output of one channel of aforesaid dual channel receiver means for resetting said integrate and hold circuit means.

8. A portable sonar system according to claim 1 in which said visual readout means further comprises in combination:

cathode ray tube means electrically connected to said signal transmission gate circuit means for converting electrical signals received therefrom to visual signals; and

light intensifier means fixedly positioned so as to be effectively operatively associated with said cathode ray tube means for increasing the light intensity of the output thereof prior to transmission to aforesaid optical means.

9. A portable sonar system according to claim 8 in which said visual readout means further comprises in combination:

gain control means electrically connected to said light intensifier means for control of the light intensity of the output thereof; and

light sensing means positioned to be illuminated by the ambient light surrounding said sonar system and electrically connected to said gain control for the regulation thereof in response to the level of ambient illumination.

10. A portable sonar system according to claim 9 in which said visual readout means further comprises an optical light collector means fixedly positioned to collect the ambient light in the region of said sonar system and to transmit said ambient light to said light sensing means for the electrical control thereof.