H.A. DeFerrari

Bio: H.A. DeFerrari is an academic researcher from Miami University. The author has contributed to research in topics: Signal processing & Underwater acoustics. The author has an hindex of 2, co-authored 3 publications receiving 17 citations.

Ocean acoustic sensor installation at the South Florida Ocean Measurement Center

Abstract: A tri-axial array of acoustic hydrophones has been installed off the South Florida coast in 145 m of water. The installation is one of a number of projects that have begun making use of the new South Florida Ocean Measurement Center facilities in Dania, FL. The arrays are linked to shore via a fiber-optic cable and powered from shore with a separate insulated copper cable. Two of the arms of the array are deployed on the bottom to the east and south of the origin. The third array is a sub-surface vertical mooring which includes a pressure sensor to monitor the depth of the top buoy. Each axis contains 32 hydrophones spaced in a nonlinear distribution to facilitate acoustic coherence measurements. Other sensor configurations are possible, including the replacement of hydrophones with other instruments such as current meters or temperature, pressure, or conductivity sensors. Small projectors are placed at the base of the vertical array and at the ends of the horizontal arrays, making it possible to determine the location of each sensor in real time via time-of-flight measurements. Computers running the Linux operating system control the projectors and process data from each leg of the array. Each of the three computers is connected via fiber-optic lines to a Fast Ethernet switch box and networked to shore. The computers can be accessed via TCP/IP connections and programmed from shore to suit new missions. A wireless link to the Nova Southeastern University network and the Internet makes it possible to access the system and conduct experiments from anywhere in the world. The current mission of this system is to study the coherence of shallow-water acoustic propagation. However, knowledge gained here will facilitate a variety of future projects-which include active and passive sonars, ambient noise study, high-frequency acoustic monitoring of fish migration, and acoustic tomographic monitoring of the Gulf Stream. Excellent data were obtained from several experiments. At the present time, only the vertical array is working but plans to restore the two horizontal arrays are actively pursued.

A general purpose autonomous transmitter and receiver system for underwater acoustic experiments

Abstract: A versatile multifrequency, multi-purpose acoustic transmitter and receiver system has been developed and used to measure low frequency acoustic backscatter from the ocean surface. The instrumentation is general purpose in that all signal and sample parameters are selected by software and a variety of transmission, scattering and reverberation experiments are possible without hardware modification. The system is battery-powered and self-contained for remote and unattended operation for periods of months, depending upon the experimental parameters that affect power and tape consumption. The main features of the system are: a high-powered broadband set of acoustic sources-with center frequencies of 100, 200, 400, and 800 Hz, programmable output signal types, a 64-element vertical hydrophone array, fifty gigabytes of data storage capacity, dynamically-tuneable band pass filters and variable sampling rates, high power microprocessors for in situ signal processing and independent subsystems for recording mooring depth and inclination. The system has been used in surface backscattering experiments at sea and results that demonstrate the capability of the system are presented and discussed.

A synthetic bandwidth measurement system for acoustic remote sensing of geoacoustic properties of bottom sediments

Abstract: A series of narrowband acoustic transmissions may be combined into an equivalent broadband signal - with a corresponding increase in resolution in the time domain. This procedure is called synthetic bandwidth processing. If ray methods are used in combination with inverse theory to determine the otacoustic properties of bottom sediments, the increased time resolution aids in the identification of arrivals which are closely spaced in time. This, in turn, permits improved estimates of the spatial distribution of properties and more accurate otacoustic models. Signal processing techniques and guidelines for synthesizing multioctave broadband pulse-like signals are presented. Also described is the instrumentation used to implement the technique in real ocean environments. >

A Comprehensive Study of Optical Fiber Acoustic Sensing

Abstract: The optical fiber acoustic sensing system is suitable for long-distance monitoring of the acoustic signals generated by the external disturbances. According to the continuity of sensing units, quasi-distributed and distributed optical fiber acoustic sensing technologies are differentiated to meet different application requirements. On the one hand, the recent progress of Fabry-Perot interferometer (FPI) focusing on the diaphragm material, and the research hotspots in the field of the continuous Fiber Bragg grating (FBG) array are firstly reviewed. On the other hand, Mach-Zehnder interferometry (MZI), Michelson interferometry (MI), and Sagnac interferometry (SI) have rapidly developed in the aspect of the demodulation algorithm optimization with the purpose of the sensing performance improvement. Moreover, the current primary research works of the phase-sensitive optical time-domain reflectometer ( $\varphi $ -OTDR) are the signal-to-noise ratio improvement and the mixed optical structure design. Finally, this paper presents an overview of the recent advances of optical fiber acoustic sensing system in the application domains of military defense, structural health monitoring, petroleum exploration, and development.

Geoacoustic inversion of broadband data by matched beam processing

Abstract: This paper describes results of geoacoustic inversion using broadband signals from an experiment carried out at a site near the South Florida Ocean Measurement Centre in the Florida Straits. M-sequence coded pulse trains at different center carrier frequencies from 100to3200Hz were recorded at a vertical line array at a distance around 10km. Geoacoustic inversion was carried out to determine the feasibility of inverting the environmental parameters from this long-range propagation experiment. The received signal at lower frequencies below 400Hz consisted of a dominant water column signal and a secondary arrival delayed by 0.4s. The secondary signal was spatially filtered by beamforming the array data, and the beam data were inverted by matched beam processing in the time domain, combined with an adaptive simplex simulated annealing algorithm. The estimated values of compressional wave speed and density were in good agreement with ground truth values from sediment cores. The inverted shear wave speed appea...

Long-range acoustical positioning system on continental shelf regions

Abstract: Methods and systems for determining a geophysical position of an object in an underwater channel are provided. Acoustic signals from at least two sources are received by a receiver of the object. The acoustic signals have a frequency corresponding to at least one waveguide mode associated with the underwater channel, where the acoustic signals are transmitted at predetermined transmission times. An arrival time for the at least one waveguide mode is determined from the received signals, based on the predetermined transmission times. The geophysical position is determined based on the arrival time and a modal group velocity for the at least one waveguide mode.

Numerical investigation of out-of-plane sound propagation in a shallow water experiment.

Abstract: In an experiment in the Florida Straits, broadband pulses were transmitted over a range of 10 km and received by a vertical hydrophone ar- ray. For pulses with center frequency below 400 Hz, the received signal con- sisted of a dominant arrival followed by a secondary one delayed by about 0.4 s.A hypothesis that the secondary arrival was caused by 3D out-of-plane propagation is investigated here numerically with a 3D parabolic equation model (3DWAPE) and a 3D ray model (MOC3D). Both models clearly pre- dict a secondary arrival caused by 3D horizontal refraction from the sloping bottom in the shoreward direction.