United States Patent 19 11, 3,944,967 Acks et al. (45) Mar. 16, 1976 (54) UPDATED DIVER NAWGATON DEVICE (75) Inventors: Robert S. Acks; Stanley J. Watson, Primary Examiner-Richard A. Farley both of San Diego; Howard B. Attorney, Agent, or Firm-Richard S. Sciascia, Ervin McCracken, Poway, all of Calif. F. Johnston; William T. Skeer (73) Assignee: The United States of America as represented by the Secretary of the Navy, Washington, D.C. (57) ABSTRACT 22 Filed: Dec. 23, 1974 (21) Appl. No.: 535,542 In a diver's navigation system employing a receiver having three equal, angularly disposed hydrophone lo cations, a digital signal processing circuit is employed 52 U.S. Cli................................................. 34016 R which receives frequency shift keyed digital data from 5 i Int. C.’.......... G01S 3/80 remote beacons. Circuitry is provided to process this 58) Field of Search........................... 34016 R, 16 R data to derive a bearing indication to the beacon. 56 References Cited UNITED STATES PATENTS 4 Claims, 5 Drawing Figures 3,475,72 10/1969 Cappel, Jr. et al.................. 34016 R ASA StGat HYOROAHowe AAOCESSoap 7 OGAa Asia HYOROPHONEHA;ig; 2:34 65.8%Eotomy 254 £3 2:#2% comparror Giéthis rose; "5:2% AS SIGWat AAOCESSOP Distrazy 65;; stgivrsala Afoovatives GAAaroA aayadow Stefaa Aa WOMSE FSA) awcrow stw FUWCTOW SEZAOT/OW A a 7OA/ /WSA/MALE Au?vcrow cos AU/voc77OW SELEC//OW a 7 CA/ WSA/MALE --------------------------------- FG.5 af UPDATED DIVER NAVIGATION DEVICE STATEMENT OF THE OBJECTS OF INVENTION It is an object of this invention to provide an im STATEMENT OF GOVERNMENT INTEREST proved diver navigation system. The invention described herein may be manufac 5 Another object of this invention is to provide an tured by or for the Government of the United States of improved underwater navigational beacon. America for navigational purposes without the pay Still another object of this invention is to provide an improved diver carried homing system. ment of any royalties thereon or therefor. Another object of this invention is the provision of FIELD OF THE INVENTION 10 frequency shift keyed navigational processing circuitry. This invention pertains to the field of underwater These and other objects of the invention will become navigation. More particularly, this invention pertains to more readily apparent from the ensuing specification the field of portable navigation instruments used by when taken together with the drawings. swimmer-divers. In still greater particularity, this inven tion pertains to a diver navigation system employing 15 BRIEF DESCRIPTION OF THE DRAWINGS frequency shift keyed digital beacons. By way of fur FIG. 1 is a perspective view showing the system of the ther characterization this invention pertains to a three invention in an operational environment; hydrophone bearing receiver employing frequency FIG. 2 is a diagrammatic representation of the navi gational beacon in the system of the invention; shift keyed navigational information. By way of further 20 FIG. 3 is a diagrammatic representation of the diver characterization, this invention pertains to an underwa carried beacon receiver illustrated in FIG. 1; ter navigational system employing a frequency shift FIG. 4 is a diagrammatic representation of the FSK keyed acoustic beacon, together with a swimmer-diver signal processor circuit of FIG. 3; and carried beacon receiver. FIG. 5 is a diagrammatic representation of the digital DESCRIPTION OF THE PRIOR ART 25 error rejection circuitry shown in FIG. 3. Present diver navigation system for use with small, DESCRIPTION OF THE PREFERRED underwater beacons employs a noise-modulated, FM, EMBODIMENTS acoustic signal as the navigational signal. Each beacon Referring to FIG. 1, an oceanographic research ves transmitting the navigational signal has an assigned 30 sel 11 provides a working station for a swimmer-diver frequency band on which it continually transmits. 12 who is shown approaching an underwater object 13. The cooperating receiver assembly consists of three Swimmer-diver 12 is guided in his approach to object acoustic receiver channels, each of which receives 13 by means of an underwater beacon 14 situated information from one of three triangularly disposed nearby. Beacon 14 may have been placed in a proxim hydropphones mounted in a plane on the receiver 35 ity of underwater object 13 by a variety of means such housing. Because the receiving hydrophones are posi as, for example, ejection from oceanographic vessel 11 tioned at the vertices of an equilateral triangle and the to mark a previously received sonar contact. Diver 12 wave fronts are essentially plane wave signals, the re navigates between oceanographic vessel 11 and under ceiver may process the time of arrival of the wave front 40 water object 13 by means of a diver navigation instru at each hydrophone to obtain sine and cosine values of ment, indicated generally at 15, which responds to the bearing to the transmitter by conventional tech sonic pulsed energy emanating from oceanographic niques. Of course, these trigometric functions may be, vessel 11 or beacon 14. These energy pulses, indicated in turn, solved to obtain the bearing angle. at 16 and 60' respectively, are propagated through the The use of linear FM as a modulation system requires 45 water and impinge a triad of hydrophones indicated at an analog noise source for the modulating signal in the 17, 18, and 19 respectively. The parameters of this beacon which is band limited by the output of the system, thus far described, are conventional in the noise-diode used in the generation of the noise signal diver and oceanographic instrumentation arts. and the frequency characteristics of the associated In the past, navigational beacon systems for divers amplifier circuitry. The power consumption, physical 50 have employed noise modulated FM signal sources size, and electronic complexity of the beacon assembly which transmit continuously over their assigned por used in this system have made the beacons expensive, tion of the acoustic spectrum and are selected by fre troublesome to maintain, to have relatively high power quency discriminating circuits within diver navigation consumption, and to be of short operational life. It is receiver 15. the solution of these unresolved shortcomings of the 55 Such systems while being satisfactory for their in prior art to which this invention addresses itself. tended purpose and range of utilization suffer from a low battery life, in case of remote beacons 14, and ease SUMMARY OF THE INVENTION of detection by unauthorized or undesirable monitoring The invention provides a diver navigation system in stations. In these prior art systems the use of linear FM which the marker beacon and receiver processing cir 60 as a modulation scheme requires an analog noise cuitry employs frequency shift keyed acoustic energy. source for modulating this signal to be transmitted by The marker beacon circuit employs a timed power the beacon and requires detection and filtering cir supply to each of the component circuits in order to cuitry in the receiver. The analog noise for the modu prolong operational life. Further, the receiver circuitry lating signal is provided by band limiting the output of employs a voltage and signal comparison system which 65 a noise diode and associated amplifier circuitry. The materially reduces the erroneous bearing angle indica band limiting is conventionally accomplished by means tions caused by bottom reverberation and other envi of low pass filters. Additionally, circuitry is required for ronmental phenomenea. the frequency modulation of a carrier signal. s 4. As may be readily seen the consumption and cir by E. A. Granfors et al. in U.S. Pat. No. 3,444,508 cuitry size and complexion of the beacon assembly as a granted on May 13, 1969 for "Directional sonar Sys result of the choice of FM is unnecessarily excessive for tem. remote instrumentation. Likewise, the complexity of Thus, it may be seen that by employing conventional the detection and filtering circuitry in the receiver 5 circuitry and packaging techniques, an improved un causes power consumption problems. derwater marker beacon is provided which transmits A fixed package size for the use of beacon 14 is de timed bursts of frequency shift keyed acoustic energy termined by beacon handling equipment aboard vessel to be used as a digital signal source in the diver naviga 1. Thus, an improvement in beacon life may be ob tion system of the invention. Each burst, of course, tained if a portion of the beacon housing previously 10 contains sufficient redundancy to permit determining required for circuitry is given over to the storage of a the bearing angle. battery power supply. It is in this fashion that the inven It is well understood in the electronic navigation arts, tion provides an improved navigation system for use of the triangular spacing configuration of the receiving Swimmer-divers without redesign of beacon handling hydrophones 17, 18, and 19 in conjunction with the and storage equipment or basic detection circuitry 5 essentially plain wave front signal beacons transmitted redesign of the swimmer-diver carried reception equip either from beacon 14 or surface vessel 11 may be ment. conveniently processed to indicate a sine and cosine Referring to FIG. 2, a diagrammatic representation relation between the hydrophone array and the signal of the beacon transmitter is illustrated. As shown, a source. Such an arrangement and the trigonometric timer 21 receives from the enlarged conventional bat 20 consideration thereof are discussed in U.S. Pat. No. tery package the electrical energy for operation of the 3,383,651 granted on May 14, 1968 to S. N. Koblick transmitter and supplies all active elements in the trans for “Plane Coordinate Computing System' and are mitter beacon. In this fashion, no power is consumed incorporated herein. Although the inventors make no during shut down periods, except for the operation of claim of originality of this arrangement and since it is timer 21 itself.