USA As Represented by Secretary of the Navy

Steven E Crocker

Ronald R Smalley

Daniel Casimiro

Robert F Cutler, Iii

William H Slater

Jason R Bernier

Michael A Bergeron

Joseph A Carreiro

Daniel R Nashold

Mark R Grden

Ryan Amaral

Brian W Duarte

Amarilis Blankenship

Ernest J Briggs

A method is provided to measure the complex sensitivity of hydrophone data channels across a range of frequencies by using a water-filled tank with proximate boundaries. A hydrophone array and reference hydrophone are helically affixed to a test fixture resting on a rotation platform. When the test fixture is submerged in the tank; the platform rotates about a contour of the platform in intervals for a predetermined time interval before indexing to the next angle. Signals transmitted by an acoustic projector in the tank are received on the hydrophones of the line array and the calibrated reference hydrophone. Electrical signals from the reference hydrophone are transmitted over an electrical cable and received by the acoustic data processor for use in calibrating the hydrophone line array. Electrical signals from the hydrophones of the hydrophone line array are also transmitted to the data processor.

System and method for the calibration of a hydrophone line array in a water-filled tank

A method is provided to measure a modulus of complex sensitivity of hydrophone data channels using a quasi-diffuse sound field. In the method, a radiation pattern representing shallow water sources directs to a location as a direct acoustic path and sound reflects to the location from the water bottom as a reflected acoustic path. At least one hydrophone receives the sounds at the location as acoustic signals with an acoustic intensity being the sound intensities along the acoustic paths. The sound intensity at the hydrophones also relates to a zenith angle and a bottom intensity reflection coefficient. The modulus of the frequency dependent sensitivity of the hydrophone is computed from measurements of the voltage output and voltages of reference hydrophones with the sound intensity as factor and with uncertainty reduced by averaging hydrophone sensitivities.

System and method for the calibration of a hydrophone line array in a quasi-diffuse ambient sound field

A method is disclosed for calibration of a towed line array. In a low frequency band, calibration is performed using an acoustic field observed by reference standard hydrophones. The observations form a model of a complex acoustic field throughout a space occupied by a measurement apparatus. The array sensitivities are computed by comparing output voltages of the array with the acoustic field estimated at the locations occupied by hydrophones of the array. Variations in the acoustic field that cannot be accounted for by free field propagation theory are included in the calculation of array channel sensitivities. The method extends the low frequency limit for the calibration to less than the minimum frequency at which free field propagation conditions can be approximated. Boundary reflections and spatial variations in the acoustic field are recognized. The spatial distribution of acoustic energy is used to provide low frequency calibration with improved precision.

System and method for the calibration of a hydrophone line array

A method using a tow body and sensor array for locating an underwater location beacon is provided. The steps of the method are moving the body and array in a direction of motion; orientating the array orthogonal to the direction of motion; beamforming acoustic conical beams from the array onto a seafloor; detecting a time series of acoustic data channels from the beacon; converting the data channels into spatial beams of acoustic frequency; determining if a signal of the underwater location beacon is present from each spatial beam; calculating likelihood functions for locations of the beacon to represent an area of the seafloor from which the signal of the underwater location beacon is to have originated; accumulating likelihood functions for the location of the underwater location beacon over the course of a search pattern; and producing a grid for a beacon location based on the likelihood functions.

Underwater acoustic beacon location system

A method is disclosed for acoustic calibration of a towed hydrophone line array. In a very low frequency band, calibration is performed using a surrounding ambient acoustic noise environment observed by one or more calibrated reference standard hydrophones and hydrophone channels of the array being calibrated. The array hydrophone sensitivities are computed by comparing output voltages of the array hydrophones with the output voltages of one or more calibrated reference hydrophones. The method extends the low frequency limit for the calibration of a towed hydrophone line array to substantially less than the minimum frequency at which the acoustic projectors commonly used for acoustic calibrations can transmit a useful acoustic signal.

Measurement of complex sensitivity of data channels in hydrophone line array at very low frequency

A system, processor and method of use for calibration processing is provided to calibrate acoustic vector sensor data collected at comparatively close range. Vector sensor data collected at close range includes data collected with source-to-receiver separations ranging from a one-tenth to approximately two acoustic wavelengths. The calculations substantially account for the acoustic impedance of a spherically diverging wave front, where the curvature is sufficiently pronounced to cause errors in resulting measurements in the calculations. The processing uses information contained within the vector sensor data to increase the accuracy of the vector sensor data.

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Bristol, RI, United States of America

Steven E Crocker