Abstract: A sonar array for forming multiple transmit and/or receive acoustic beams by a frequency beamforming technique. In frequency division beamforming, beam steering direction is made a function of frequency by driving (receiving) each element of a uniformly spaced line array by a signal which leads or lags its nearest neighbor by a fixed phase shift, &Dgr;&phgr;. This permits scanning a transmit and/or receive beam through a range of angles by changing its frequency. The same principle can be used to form multiple simultaneous transmit and/or receive beams. This is accomplished by transmitting a wide bandwidth signal and receiving the echoes through a spectrum analyzer. Each frequency bin of the spectrum analyzer then corresponds to a beam pointing in its own unique direction. Advantages of such a sonar system include improved cost, weight, and size versus performance for a variety of systems including ahead looking sonars and bottom mapping sonars.

Abstract: A system and method for measuring the directional spectrum of one or more waves in a fluid medium using a multi-beam sonar system. In an exemplary embodiment, range cells located within a plurality of acoustic beams are sampled to provide current velocity data. Optionally, wave surface height and pressure data is obtained as well. This velocity, wave height, and pressure data is Fourier-transformed by one or more signal processors within the system, and a surface height spectrum produced. A cross-spectral coefficient matrix at each observed frequency is also generated from this data. A sensitivity vector specifically related to the ADCP's transducer array geometry is used in conjunction with maximum likelihood method (MLM), iterative maximum likelihood method (IMLM), or other similar methods to solve a the wave equation at each frequency and produce a frequency-specific wave directional spectrum.

Abstract: An acoustic transducer array in which the transducer elements project a plurality of acoustic beams which are not coplanar. In a first embodiment, a cylindrical transducer array housing has each of four transducer elements skewed at an angle relative to the longitudinal axis of the housing. Each acoustic beam formed by the array lies in a unique plane (e.g., in a "pinwheel" configuration), thereby effectively eliminating overlap of the beams throughout the entire profiling range of the array. In another aspect of the invention, acoustic damping material is incorporated throughout selected portions of the transducer housing to mitigate the effects of echoes and undesirable acoustic propagation within the array.

Abstract: A system and method for measuring the directional spectrum of one or more waves in a fluid medium using a multi-beam sonar system. In an exemplary embodiment, range cells located within a plurality of acoustic beams are sampled to provide current velocity data. Optionally, wave surface height and pressure data is obtained as well. This velocity, wave height, and pressure data is Fourier-transformed by one or more signal processors within the system, and a surface height spectrum produced. A cross-spectral coefficient matrix at each observed frequency is also generated from this data. A sensitivity vector specifically related to the ADCP's transducer array geometry is used in conjunction with maximum likelihood method (MLM), iterative maximum likelihood method (IMLM), or other similar methods to solve a the wave equation at each frequency and produce a frequency-specific wave directional spectrum.

Abstract: An acoustic array transducer capable of forming narrow dispersion, broadband or narrowband acoustic beam sets in two dimensions with a minimum aperture size. Concurrent yet independent electrical interfacing with array transducer elements allows simultaneous formation of multiple transmit and receive beams inclined within two planar orientations normal to the array face, while requiring a minimum amount of supporting circuitry. A method of economically and accurately fabricating the aforementioned transducer array by incrementally dicing bonded layers of solid discs of transducer materials being rigidly held together is also disclosed.

Abstract: An electronic heading and attitude sensing subsystem which is fully integrated with the existing hardware of an acoustic Doppler current profiler (ADCP) oceanographic sonar suite to reduce the size and complexity of the apparatus. The subsystem uses a tri-state drive signal with relaxation periods and integration windows to synchronously drive the fluxgate magnetic sensors while reducing the effects of non-linearities and higher order harmonics which may result in heading errors. The present invention includes an electrolytic tilt sensor device and driving circuit which allow measurement of system vertical orientation without the effects of electrolyte conductivity are described. The present invention further includes methods of system calibration, magnetic perturbation modeling, and heading calculation.

Abstract: A system and method for measuring current velocities using coded-pulse broadband acoustic signals. Autocorrelation of two phase coded pulses which are in the water during a single transmission cycle is used to calculate a Doppler frequency. The effective result is current profilers having improved profiling range and spatio-temporal resolution.

Abstract: A system and method for measuring current velocities using coded-pulse broadband acoustic signals. Autocorrelation of two phase coded pulses which are in the water during a single transmission cycle is used to calculate a Doppler frequency. The effective result is current profilers having improved profiling range and spatio-temporal resolution.

Abstract: In a correlation device, a system and method for measuring velocities using a single coded pulse generator. The correlation device may also include maximum likelihood estimation techniques for processing the echo signals received from a plurality of transducers. The presently preferred embodiment of the device is as a current profiler having a bottom tracking capability for providing vessel velocity.

Abstract: An acoustic transducer having impedance matched layers that can be deployed in environments having wide temperature variations. An anisotropic layer provides a low coefficient of thermal expansion orthogonally to the direction of sound wave propagation. The anisotropic layer may be a solid matrix embedded with fibers, such as glass, arranged in a common orientation.

Abstract: In a correlation device, a system and method for measuring velocities using a single coded pulse generator. The correlation device may also include maximum likelihood estimation techniques for processing the echo signals received from a plurality of transducers. The presently preferred embodiment of the device is as a current profiler having a bottom tracking capability for providing vessel velocity.

Abstract: A system and method for measuring current velocities using coded-pulse broadband acoustic signals. Autocorrelation of two phase coded pulses which are in the water during a single transmission cycle is used to calculate a Doppler frequency. The effective result is current profilers having improved profiling range and spatio-temporal resolution.

Abstract: A system and method for bottom tracking in a sonar system. The present invention provides for convolving the received signal with the second derivative, or an approximation thereof, of the matched transmitted pulse. In another aspect of the invention, the received signal is convolved with the matching transmitter pulse and the result is evaluated by summing the differences between a central peak and its neighboring left and right values. The filtering of the present invention removes the effect of water absorption on signal amplitude. The invention also includes compensating for spreading loss in the received signal.

Abstract: A system and method for measuring current velocities using coded-pulse broadband acoustic signals. Autocorrelation of two phase coded pulses which are in the water during a single transmission cycle is used to calculate a Doppler frequency. The effective result is current profilers having improved profiling range and spatio-temporal resolution.