Abstract: An improvement for an apparatus for calibrating or otherwise determining low frequency operational parameters of an elongate hose-like array is compact enough to be mounted on a cart-like member which is free to travel the length of the array. The improvement is in the form of a pair of oppositely extending tubes each having a reciprocating element for ensonifying selective portions of the elongate array with low frequency energy. Having the reciprocating elements 180.degree. moving out of phase with respect to one another to exhibit mirror image excursions and at least one flexible radiating surface proximately located to the array assures that performance compromising vibrations are nullified and that low frequency energy is responsively received by the individual transducer elements along the array's length.

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: Apparatus and method for calibrating a hydrophone array comprising a plurty of electrically interconnected hydrophones over a range of acoustic signal frequencies having a lower limit on the order of 1 Hz. Apparatus includes a container having a sealed cavity for sealing the hydrophone array in a selected fluid, an electro-acoustic projector for projecting acoustic signals of frequencies selected from the frequency range into the sealed cavity, and a reference hydrophone contained within the sealed cavity for generating a reference signal in response to each projected acoustic signal. Apparatus further includes monitoring equipment coupled to the reference hydrophone and to the hydrophone array for enabling a selected characteristic of one of the reference signals to be compared with the same characteristic of a signal generated by the hydrophone array when an acoustic signal is projected into the sealed cavity.

Abstract: In an apparatus for projecting low-frequency acoustic waves in a liquid ma, a chamber adapted to be immersed in the media contains gaseous material to provide a compliance and is provided with an aperture. A piston of selected mass is sealably mounted in the aperture, having one end adapted to displace a selected mass of the liquid media and the other end adapted to displace the gaseous material in the chamber. An actuating device is coupled to the piston for reciprocating it at the resonant frequency of a mechanical system which substantially comprises the compliance provided by the contained gaseous material, the mass of the piston, and the mass of the displaced liquid media.

Abstract: A tensioning device for submarine oceanographic structures includes a sure float having a pendent line suspended therebeneath and a vertical rod support attached to the distal end of the pendent line. An electrical motor attached to the lower end of the support provides ballast to hold the rod in a substantially vertical position and also provides mechanical motive power to turn two coaxially mounted hydrodynamic screws. These screws are attached to the support so as to provide a propulsive force for the support and surface float system. A hitch employing standard marine hardware connects the tensioning system to an underwater structure such that this propulsive force is used to tension the structure. Power for the electrical motor is provided by a source of electrical power housed in a small surface vessel and effectively connected to the surface float and pendent line.