Abstract: A technique for a vibration isolation module (VIM) used for towed arrays is disclosed. The VIM has a stretchable cable on which is mounted one or more rigid spacers which make contact with an outer hose formed of a flexible material having a selected vibration attenuation characteristic. The spacer transmits energy between the parts of the VIM which contact the spacer for attenuation purposes. The spacer is "soft mounted" on the stretchable cable so that it may be moved by a limited amount along the cable in response to forces of a specified minimum magnitude. This ability to move allows adjustment of the internal parts of the VIM during use to avoid concentrating stress at any one particular contacting area. Disclosed is an embodiment where two sleeves are used to abut the spacer at opposing ends thereof.

Abstract: A method and apparatus for remotely activating and analyzing fiber optic ed and conformal sensor arrays using fiber optic transmission and reception with multiplexed input and output signals using optical wavelength division, electronic frequency division, or both.

Abstract: A novel configuration of a low-frequency lightweight sonar system is described comprising a coaxial assembly of a transmitting transducer and a directional receiving array contained within a cigar-shaped streamlined cylindrical housing less than 1 ft. diameter which operates in the 3 to 4 kHz frequency region and achieves submarine target detection ranges in the order of 20,000 meters with a bearing accuracy within 2.degree.. The small cylindrical streamlined structural assembly results in a very great reduction in drag resistance while it is being towed underwater at high speeds as compared to conventional sonar domes which must be an order of magnitude larger in diameter to accommodate the larger conventional scanning sonar transducers which are several wavelengths in diameter at the operating frequency.

Abstract: An elongated retaining and electromagnetic shielding member for a towed underwater acoustic array which includes a plurality of interconnected hydrophones and circuit modules protected by a plastic foam cushioning sheath, covered with a tough, essentially acoustically transparent hose-like jacket and containing a plurality of aramid fiber ropes as strength members to carry the tensile loads on the array, wherein the retaining and shielding member consists of an an elongated tube-like electrically conductive fabric member interposed between the sheath and the exterior hose jacket which is longitudinally stitched to provide a plurality of spaced parallel tubes, some of which are of just sufficient diameter to contain said strength members and a larger central tube for containing the hydrophones, circuit modules and interconnecting wires.

Abstract: Method and means are provided for determining the position of a submerged marine streamer towed behind an exploration vessel. An array of sets of at least three transponders secured to the ocean floor generate distinguishable acoustic pulses upon a command signal. These signals are received by receivers housed in the streamer. The position to each receiver may be triangulated from the data generated.

Abstract: A method for maintaining a substantially constant tension on a towed seismic cable, wherein the instantaneous towing force and the instantaneous cable displacement relative to a fixed shipboard reference are continously measured and sampled. A microprocessor associated with a servo controlled capstan device, uses those measurements to pay out cable or to retrieve cable in response to an increase or decrease in the instantaneous towing force. The microprocessor also tries to minimize the average cable displacement.

Abstract: A system for maintaining a substantially constant tension on a towed seismic cable, wherein the instantaneous towing force and the instantaneous cable displacement relative to a fixed shipboard reference are continuously measured and sampled. A microprocessor associated with a servo controlled capstan device, uses those measurements to pay out cable or to retrieve cable in response to an increase or decrease in the instantaneous towing force. The microprocessor also tries to minimize the average cable displacement.

Abstract: The position of a submerged object towed at great depth from a ship is determined, with respect to the ship, from measured values of the travel time of acoustic pulses between the ship and the object. These pulses are emitted at different locations of the ship and received at a point of the object. The values of the travel times of the pulses are measured and digitized on the object and transmitted by cable to the ship where they are processed, in combination with values representing the distances between the emission locations, to determine the coordinates of the object with respect to a system of axes associated with the ship.

Abstract: Method and means are provided for determining the position of a submerged marine streamer towed behind an exploration vessel. An array of at least three transponders secured to the ocean floor generate distinguishable acoustic pulses upon a command signal from the ship. These signals are received by hydrophones housed in the streamer and by the ship. The distance to each hydrophone may be triangulated from the data generated including accounting for changes in velocity between the vessel and the seismic streamer and the bottom transponders during the taking of such data.

Abstract: A hydrophone streamer that includes several arrays of optical fiber pressure sensors. Each array consists of at least three sensors symmetrically disposed around the inside of the streamer skin to form a vertically-disposed array. Each sensor modulates a coherent light beam in accordance with the instantaneous ambient water pressure. The output signals of the sensors include an AC component due to seismic waves and a DC component due to hydrostatic pressure difference between the sensors of an array. Means are provided to resolve the AC and DC components to determine the arrival direction of the received seismic waves.

Abstract: Selected sections of a seismic streamer cable are provided with an acoustically-triggered compressed gas supply. The acoustic triggering devices associated with each compressed gas supply may be individually addressed by a coded signal. In the event that the streamer cable is severed, the gas supplies of the severed sections of the streamer are used to inflate the jackets of those severed sections so that they will float to the water surface for salvage.

Abstract: A construction and method of producing an elongated underwater acoustic array includes a plurality of interconnected hydrophones and circuit modules protected by a plastic foam cushioning sheath, covered with a tough, essentially acoustically transparent hose-like jacket and containing a plurality of aramid fiber ropes as strength members to carry the tensile loads on the array. An elongated tube-like fabric retaining member is interposed between the sheath and the exterior hose jacket which is longitudinally stitched to provide a plurality of spaced parallel tubes, each of which is of just sufficient diameter to contain one of said strength members. The strength members are terminated at a connector at each end of the array, and a spacer member is placed near each connector to spread the strength member ropes to the desired diameter. The spacer members and the adjacent ends of the retaining members are each cemented to the strength member ropes.

Abstract: A thin-line heading sensor is disclosed having an outside diameter of less than an inch which is accurate to within 1.degree. of arc. The invention includes a magnetic wheel having a reflective multifaceted perimeter. The facets are optically coded for identification. When the wheel is illuminated by a collimated beam of light, a beam is reflected onto an array of photodetectors. The photodetectors are coupled with an electronic circuit which decodes the position and pattern of illumination to determine the position of the magnetic wheel.

Abstract: An apparatus for locating, classifying and identifying underwater marine animals by means of the sounds they make includes an elongated submersible array adapted to be towed in various directions. The array is made up of subarrays of multiple hydrophones which are arranged along the length of each subarray in groups. By changing the combinations of groups, the frequency response and the directional sensitivity of the array can be varied. The outputs of the groups can be selectively analyzed both visually and audibly for characteristic fish sounds. The received sounds are classified and used for the identification of newly found fish.

Abstract: A marine seismic survey is disclosed in which a plurality of steerage centers are selected for circular traversal thereabout by a marine vessel towing a streamer cable. While the vessel and the streamer are following a circular track about a steerage center, the feathering of the cable creates a separate concentric track line for each of the mid-points between the receivers included in the cable and the source. In this manner an areal coverage is assured which requires no reliance on unpredictable and uncontrollable currents for the desired feathering. An additional important feature of the current disclosure is that there is little wasted time in which the survey vessel moves outside of the overall surveyed area. A preferred course tracking for the vessel is to move from the arc of one steerage course line to another in tangential fashion.

Abstract: A Tactical Expendable Device (TED) adapted to be ejected into the water f a variety of launch platforms and to achieve and remain substantially stationary at a predetermined operating depth for a predetermined time interval or to sink at a predetermined rate for sensing acoustic signals and transmitting such signals to the launch platform through a long, small diameter connecting cable such as a fiber optic filament. The TED system comprises the TED cannister, a long connecting cable, deployment means on the launch platform including a launch tube with integral dereeler, a buffer and onboard signal processing/display equipment. The TED cannister further comprises a sensing element, a buffer, a power source and a dereeling device.

Abstract: A system for detecting and identifying acoustic sound sources using a pluity of identical data acquisition modules spaced at preselected intervals along a line array. Two small diameter coaxial cables provide intermodular connections for power, timing control and sequential data transmission to a remote receiver. A control clock waveform leading edge simultaneously triggers sampling and holding of sensor data at each module of the array while the waveform trailing edge is delayed for a preselected interval at each module to provide squential data output.

Abstract: An acoustic envelope is provided which may include a tubular sheath which mounted about a conducting element. The tubular sheath has inner and outer tubular portions which are integral with respect to one another. The acoustic envelope further includes a plurality of non-elastic strands which extend longitudinally along the sheath between the inner and outer tubular portions and which are bonded thereto. The tubular sheath is constructed of a material which optimally minimizes vibration induced noise and flow induced noise when the line array is towed through the water.

Abstract: An apparatus for rejection of turbulence induced flow noise for towed hydhone arrays. Two adjacent hydrophones in the array are spaced less than flow noise coherence distance apart forming a flow noise cancelling module. The inverted acoustic/flow noise signal from the lead hydrophone of the pair is split, one side passing to the final stage of signal processing while the other side, filtered, amplified and inverted, is added to the combined signal from the lag hydrophone which has been filtered and amplified. The acoustic signal components cancel leaving only the lead hydrophone flow noise plus the lag hydrophone flow noise which has been shifted by a factor dependent upon tow vessel speed and hydrophone spacing.

Abstract: Marine seismic data is gathered by a single vessel beyond the range of a conventional towed seismic sensor cable through the use of expendable sensors and hard wire transmission cables. The vessel tows a submerged platform adapted to carry several inexpensive seismic sensors and very small diameter multiconductor cables which are controllably released from the platform by appropriate equipment on the towing vessel. Signals generated by each sensor are transmitted back to the towed, submerged platform through the small diameter cable connected to each sensor and are transmitted by other means from the platform to the towing vessel for retransmission, recording and/or display. Each sensor transmits a signal back to the platform until its small diameter cable is completely deployed at which time the cable breaks and is abandoned together with the sensor.

Abstract: Method and means are provided for determining the position of a submerged marine streamer towed behind an exploration vessel. A sonic ring around feedback system is employed to redundantly ascertain the distance to various hydrophones housed in the streamer from an outboard mounted transponder capable of generating high frequency sound pulses of short duration.

Abstract: A hydrophone deployment apparatus is provided for an underwater vehicle, rein the apparatus includes an annular drum releasably mounted about the tail portion of the vehicle. A plurality of arms are pivotally connected to the aft portion of the drum and are capable of swinging from forward positions flush with the vehicle to aft positions behind the drum. A device is provided for enabling retention and selective releasing of the arms from the forward flush positions. A hydrophone is releasably mounted on the inside of one of the arms, and a cable is connected between the hydrophone and the vehicle with an intermediate portion wound on the drum. With this arrangement a release of the arms during travel of the vehicle will cause the drum to be released and the vehicle will swim away from the drum pulling the cable until it is completely off the drum, at which time the hydrophone is pulled from its mounting in the arm. At this time the drum is jettisoned and the hydrophone becomes operational.

Abstract: A towing link consists of spaced-apart head and tailpieces. The headpiece includes a towing eye and a pair of lugs for receiving the stress members of a streamer and a lead-in cable. The tailpiece defines a pair of bores through which the stress member and electrical conductors of the two cables are inserted and sealed. A pair of mating connector plugs are provided to interconnect corresponding conductors of the two cables. The assembly is enclosed in a watertight plastic boot.

Abstract: A hydraulically-powered yo-yo reel for handling a marine seismic cable in shallow water. At the beginning of a recording episode, a partially reeled-in seismic cable is released to drift to a standstill behind a ship. Data are recorded. The cable is then accelerated to match the ships's velocity. Following the initial acceleration, the cable is superaccelerated as it is partially reeled in. A microprocessor adjusts a dwell time between recording episodes to compensate for small variations in the ship's velocity.

Abstract: 1. Apparatus for protecting a vessel from a waterborne missile launched urwater by air pressure, comprising means for continuously listening to port and to starboard at three spaced locations at predetermined progressive distances astern of the vessel for any waterborne wavefront radiated as a consequence of a waterborne missile launching, and for detecting the passage of such wavefront across each of said spaced locations, means for signalling aboard the vessel the passage of such wavefront across any of said locations, and means for recording on a time base the instants that such wavefront crosses each of said locations and the approximate arrival direction of the wavefront in terms of port or starboard, whereby proper evasive action for the vessel may be determined and taken.

Abstract: A seismic survey apparatus comprises circuit arrangements for providing a train of first signals each corresponding to a sound wave transmitted towards the sea bed, and circuit arrangements for providing associated trains of second signals each corresponding to sound waves reflected from the sea bed. Signal storage means are provided for storing the trains of associated second signals. A filter is provided for deriving from the first and associated second signals a control signal indicative of the apparent vertical movement of the surface of the sea bed due to wave motion or swell. The read out from the signal storage means is then controlled in accordance with the control signal to compensate for the apparent vertical movement of the sea bed due to wave motion or swell. Preferably the read out from the signal storage means is controlled by delaying or advancing the read out of the second signal in accordance with the control signal.

Abstract: Apparatus for determining the bearing of an acoustic source from a selected ocation in an acoustic environment includes a plurality of discrete acoustic sensor elements and a flexible member, having first and second ends, which may be deployed in a linear configuration in the environment. The sensor elements are attached along the flexible member in spaced apart relationship, one of the elements, comprising a lead element, being closer to the first end than any of the other elements. A motion measuring device is coupled to the lead element when the flexible member is deployed in the environment to generate signals which indicate the velocity of the lead sensor element in the environment.

Abstract: A device is structured to pass along a towed array of hydrophones, from the orward end thereof to the rearward end thereof. The device carries a small acoustic projector to project test signals to respective hydrophones as the device passes them by. The responses of respective individual hydrophones to the test signals are recorded to enable calibration of the array in situ, and additionally, or alternatively, are recorded to determine the departure of the array from the ideal straight, (generally) horizontal line.

Abstract: A hydrophone deployment apparatus is provided for an underwater vehicle, rein the apparatus includes an annular drum releasably mounted about the tail portion of the vehicle. A plurality of arms are pivotally connected to the aft portion of the drum and are capable of swinging from forward positions flush with the vehicle to aft positions behind the drum. A device is provided for enabling retention and selective releasing of the arms from the forward flush positions. A hydrophone is releasably mounted on the inside of one of the arms, and a cable is connected between the hydrophone and the vehicle with an intermediate portion wound on the drum. With this arrangement a release of the arms during travel of the vehicle will cause the drum to be released and the vehicle will swim away from the drum pulling the cable until it is completely off the drum, at which time the hydrophone is pulled from its mounting in the arm. At this time the drum is jettisoned and the hydrophone becomes operational.

Abstract: A device is described for determining the characteristic configuration of long, towed underwater structures such as tubes or cables. The device is a collar which fits around the structure and has sufficient hydrodynamic drag that it remains essentially stationary relative to the linear configuration of the structure as the structure is drawn through it. The device, however, has relatively low mass and assumes the horizontal and vertical position of the structure as the structure is drawn through it. Instrumentation within the device registers the position assumed by the collar and either records it or transmits it to an external receiving station. This information gives a characteristic profile of the elongated structure as it passes through the water.

Abstract: A marine cable location system includes a plurality of magnetic compasses located at known spaced intervals along a cable being towed by a marine vessel. These compass readings are recorded along with an onboard magnetic compass reading, an onboard gyrocompass reading, and satellite navigational information. From these recordings, the X-Y coordinates of cable compasses with respect to vessel heading are determined. These X-Y coordinates are recorded along with the vessel's position and heading on magnetic tape and a cathode-ray tube so as to provide a visual display of the cable position with respect to the vessel.

Abstract: A filter for use in determining the vertical displacement of a body travelling through water relative to a datum such as mean sea level, and having specific application to underwater seismic systems in which a towed body forms a part of equipment for producing profiles of the terrain beneath bodies of water. A vertical displacement signal is produced from a signal, generated by an accelerometer, indicative of the vertical acceleration of the body and a position signal, generated by a pressure transducer, indicative of the vertical displacement of the body, the position signal being corrupted by pressure transducer noise. The filter comprises a first filter portion for receiving the position signal, the first filter portion having a transfer function which is substantially the product of a predetermined gain divided by the pressure transducer gain and a first real rational polynomial function of the form P.sub.1 (s)/Q(s).

Abstract: An electronic filter for use in determining the position of a body travelling through water relative to a datum such as mean sea level, and having specific application to underwater seismic systems that produce profiles of the terrain beneath bodies of water. The filter is connected to an accelerometer and a pressure transducer, physically located within the body, that respectively produce an acceleration signal indicative of the body's vertical acceleration and a pressure signal indicative of the body's vertical displacement with respect to the datum. The filter combines the acceleration and pressure signals to effectively isolate a signal proportional to noise generated by the pressure transducer. The filter then combines the signal so isolated with the pressure transducer signal to produce a vertical displacement signal relatively free from noise.

Abstract: A suspension system for an air-dropped sonobuoy includes a transducer housing wherein the upper portion is emptied upon deployment of a float. The weight distribution of the transducer and housing provides for a center of mass and a center of buoyancy at a location beneath a pivot in the upper portion of the housing. A suspension line connects the pivot with the float, and a pair of opposed extensible fins at the top of the housing locate the center of hydrodynamic pressure at the pivot. Thereby, the housing is maintained in a stabilized vertical attitude during descent through the water and during deployment at a predetermined depth independently of a difference in velocity of fluid movement at the float and at the sonobuoy.

Abstract: A marine seismic streamer-cable section includes a plastic tubular jacket reinforced by tough, braided-fiber tapes embedded in the jacket wall. A termination fixture is fastened to each end of the cable section. The termination fixture includes a bulkhead, an untapered end of which fits snugly into the plastic jacket. The other end of the bulkhead is tapered and protrudes from the end of the jacket. Short lengths of the reinforcing tapes are exposed by stripping away some of the jacket wall. A cylindrical wedge grips the exposed tapes between the inner wall of the wedge and the tapered portion of the bulkhead. The tapes are doubled back over the outside of the wedge and are bound to the jacket and to the untapered end of the bulkhead by bands.