Hydrophone Units Research Articles

ENGINEERING OF ACOUSTIC TECHNOLOGY FOR UNDERWATER POSITIONING OBJECT

Underwater Positioning System (UPS) is a system to track the existence of the position of an object by utilizing the arrival time of the signal measurement. On land, the system uses an electromagnetic signal called GPS. However, because it cannot penetrate water effectively, an acoustic signal is used as an alternative. The purpose of this research is to engineer the control system of data acquisition and underwater acoustic device to measure arrival time (TOA) and apply equation model for underwater sound source positioning system. the effective frequency resonance of the transducer and the hydrophone is at a frequency of 6 kHz. The acquisition control device is able to measure the TOA signal with an error on a digital channel smaller than an analog channel. The difference between the TOA values measured by oscilloscope and acquisition control system is caused by inaccuracy of threshold estimates at the receiver's peak detector circuit. The position of the sound source coordinates obtained from the equation model shows the highest difference in depth point (z) compared to points (x) and (y), caused by the equation model used is limited to four hydrophone units forming a horizontal baseline.

Comparison of shallow water mode transport theory with acoustic transmissions during Shallow Water Experiment 2006

Coupled-mode transport theory appears to have put on solid theoretical ground acoustical scattering by internal waves in both deep and shallow water, over a range of low, medium, and high frequencies [Raghukumar and Colosi (2014) and Colosi and Morozov (2009)]. Here, full-field theoretical calculations of the acoustic field moments are compared against experimental data gathered during the Shallow Water Experiment 2006. Transport theory at low frequency is validated using data gathered by the WHOI Shark array at 175 Hz with a source towed by R/V Sharp at several different speeds over distances of 1.5–5.5 km. At high frequencies, comparisons are made at 1.2 kHz using data received by a WHOI bottom-mounted single hydrophone unit with a source towed by CFAV Quest over distances of 0–20 km. Acoustic observables include the mean and variance of intensity. The effect of a range dependent stochastic internal wave field is examined in the context of data-model comparison, along with the effect of random surface waves. In addition, further insights into mode coupling are presented using the shallow water hybrid transport theory.

Intensity fluctuations of mid‐frequency sound signals passing through moving nonlinear internal wave in experiment sw06

Fluctuations of an intensity of the broadband pulses are studied in mid‐frequency area (2 ‐ 4.5 kHz) propagating in the shallow water in the presence of intensive internal waves (IW) moving approximately along an acoustic track. Theory elaborated earlier predicts that in this case specific features of fluctuations are provided by modes coupling (for low frequency sound) or ray scattering (high frequency area) and depend on direction of propagation of signals relative wave front of IW. The corresponding research was carried out during multi‐institutional experiment sw06 in New Jersey shelf. We analyze temporal dependence of intensity for the sequence of the sound pulses radiated from the R/V Knorr during approximately one hour ‐ 15:31 ‐16:20 GMT (August 13, 2006) and received by two separate single hydrophone units (SHRUs) placed at different distance from the source (4 km and 12 km). The corresponding acoustic tracks had a little different directions relative wave front of IW. Properties of IW were established using temperature records of sensors in different locations. It is shown that frequency spectra of fluctuations for these SHRUs have different predominating frequencies in accordance with mentioned directions of acoustic tracks. Results of measurements are compared with theoretical estimations and demonstrate good consistency.

Guided underwater object

A guided underwater object (GUO) ( 100 ) comprises steering means, an on-board guidance system ( 200 ) for controlling the steering means, and a hydrophone unit or units ( 104 A, 104 B, 104 C, 104 D, 104 E, 104 F, 104 G, 104 H) arranged to pass signals induced therein by an acoustic guiding beam to the on-board guidance system to effect directional control of the self-propelled underwater object. The GUO is guided by a remote guidance system characterised by a plurality of transmitter arrays ( 402 A, 402 B, 402 C, 402 D; 412 A, 412 B, 412 C, 412 D; 422 P, 422 Q, 422 R) arranged to transmit a plurality of contiguous acoustic beams ( 302 A, 302 B, 302 C, 302 D) each having a different frequency or frequency chirp (or other acoustic signal coding) and enclosing a guidance corridor of lower sound level (‘null’) ( 304 ) extending approximately in the direction of propagation of the acoustic beams and defining a flight path of the object. The GUO requires no on-board search sensors, no communications link with the guidance system and is of low cost.

Using calls to estimate the abundance of inshore dolphins: a case study with Pacific humpback dolphins Sousa chinensis

1 Assessing the number of animals in a population is a fundamental requirement for effective wildlife management. Determining this information for cetaceans can be logistically difficult, and the abundance of inshore cetaceans along most of the world's coastline is unknown. 2 In this study we illustrate the potential of using sound as a tool for estimating the abundance of inshore cetaceans, using Pacific humpback dolphins Sousa chinensis . 3 Acoustic recordings of humpback dolphins were made in conjunction with visual observations of school size from a land-based platform on Stradbroke Island, Australia. 4 The mean number of calls recorded per 3-min sample period was regressed against the number of dolphins observed using schools for which more than three sample periods were recorded. The relationship estimated number of dolphins = 2·39 × the mean number of calls per 3-min sample was used to estimate the number of dolphins in schools for which fewer than four samples were recorded. Comparing these results against known group sizes indicated that this estimation technique is acceptable. 5 Recordings could be made using remotely deployed hydrophone units or submerged autonomous units to provide information on the occurrence and group size of inshore delphinids within an area. 6 Inexperienced personnel could deploy and retrieve recording units. Analysis would require training to recognize sound types from different species, or computer-based sound recognition programs. 7 We conclude that simple techniques using phonations can provide estimates of relative abundance for one species of inshore cetacean. The technique is acceptable for groups of fewer than nine individuals and should be developed to assess its usefulness for studying other species.

Underwater sonar array

A sonar array connected to a data unit includes a substantial number of hydrophone units distributed along a small diameter cable having a substantial number of connecting wires, a center strength member and a tough polyurethane jacket. The hydrophone units each include a strong metal bracket bifurcated at each end and fastened to the strength member. A generally cylindrical hydrophone member is fastened to the bracket as is a circuit board including a preamplifier and the entire unit is sealed with paraxylene resin and then molded into a smooth generally cylindrical unit which is tapered at the ends and sealed to adjacent parts of the cable jacket. To minimize the cross-sectional area and the effects of cross currents, the cable is composed of a plurality of interconnected sections, each of which is of smaller cross-section and carries fewer conductors than the section next closer to the data unit. To assure that the array extends substantially vertically from the data unit, either a weight or a float is fastened to the cable at the end remote from the data unit.

A Hydrophone System for Very Low Frequencies

The Acoustic System Mark 1 was developed by the Naval Ordnance Laboratory for measuring and recording pressure variations in the frequency band between 0 and 200 c.p.s. It has had numerous applications including a seismic investigation of Bikini Atoll as a part of Operation Crossroads. A 1000-c.p.s. carrier is modulated by pressure variations applied to the hydrophone which comprises a variable inductance in one arm of a bridge. The diaphragm is resonant at about 1800 c.p.s. and can be used at depths up to 200 feet without pressure compensation. Although the hydrophone unit contains no amplifiers it may be used at distances exceeding 3 miles from the amplifying and recording system. Amplification of a million between motion of the diaphragm and motion of the recording pen are easily obtained. At a lower amplification the instrument may be used to follow changes in pressure caused by tides. Problems encountered in the development of the system included the mechanical design of an extremely rugged hydrophone and the electrical design of an oscillator of unusual amplitude stability and a circuit permitting easy and rapid balance of the bridge.