Passive acoustic bearing estimation via ultra short baseline wideband methods

In various embodiments, a passive bearing detector is disclosed. The passive bearing detector comprises a plurality of hydrophones. The plurality of hydrophones is arranged in a three-dimensional geometry. The three-dimensional geometry exposes each of the plurality of hydrophones to an ambient aquatic acoustic environment. The passive bearing detector further comprises a processor electrically coupled to the plurality of hydrophones. The processor is configured to determine a direction of arrival of an unknown broadband acoustic signal received by the plurality of hydrophones based on the phase difference of the unknown broadband acoustic signal at each of the plurality of hydrophones.

BACKGROUND

Locating and tracking surface, near-surface, and underwater platforms continues to be a concern of government and private organizations. Traditional methods of sea-going platform tracking rely on active signals or known information about a received signal. For example, sonar tracking relies on an active signal sent from a known location. The active signal is reflected off one or more sea-going platforms, such as a ship, and returned to the source of the active signal. Although sonar tracking provides accurate location information, sonar tracking relies on an active pulse that can be easily detected by sea-going platforms and which provides location information on the signal source.

Ultra-short baseline (USBL) positioning allows underwater acoustic positioning for known acoustic signals. A transceiver is mounted on ship and transmits a known signal. The known signal is received by a remote device, such as an underwater remotely-operated vehicle (ROV). The remote device responds with a return signal which is detected by the transceiver on the ship. The return time and the return angle are calculated for the received signal and the position of the remote device determined. Traditional USBL requires a known signal transmitted from a known location. U.S. Pat. No. 7,362,653, issued on Apr. 22, 2008, and entitled “Underwater Geopositioning Methods and Apparatus” is incorporated herein by reference in its entirety. Because a known signal must be sent and received, USBL does not provide tracking capabilities for unknown signals or uncooperative sea-going platforms.

What is needed is a system for passively tracking sea-going platforms based on unknown broadband acoustic signals generated by the sea-going platform.

SUMMARY

In various embodiments, a passive bearing detector is disclosed. The passive bearing detector comprises a plurality of hydrophones. The plurality of hydrophones are arranged in a three-dimensional geometry. The three-dimensional geometry exposes each of the plurality of hydrophones to an ambient aquatic acoustic environment. The passive bearing detector further comprises a processor electrically coupled to the plurality of hydrophones. The processor is configured to determine at least one direction of arrival of an unknown broadband acoustic signal received by the plurality of hydrophones based on the phase difference of the unknown broadband acoustic signal at each of the plurality of hydrophones.

In various embodiments, a method for passive bearing tracking of sea-going platforms is disclosed. The method comprises arranging a plurality of hydrophones in a three-dimensional geometry configured to expose each of the plurality of hydrophones to an aquatic ambient acoustic environment. The method further comprises receiving an unknown broadband acoustic signal at a plurality of hydrophones. A processor calculates at least one direction of arrival of the unknown broadband acoustic signal. The calculation is based on a phase difference of the unknown broadband acoustic signal received by the plurality of hydrophones.

In various embodiments, an apparatus for passive direction of arrival estimation of sea-going platforms is disclosed. The apparatus comprises a plurality of hydrophones arranged in a three-dimensional geometry configured to expose each of the plurality of hydrophones to an ambient aquatic acoustic environment. The apparatus further comprises a processor electrically coupled to the plurality of hydrophones and a memory unit coupled to the processor. The memory unit is configured to store a plurality of instructions. When loaded by the processor, the instructions control the processor to determine at least one direction of arrival of an unknown broadband acoustic signal received by the plurality of hydrophones. The determination is based on a phase difference of the unknown broadband acoustic signal received by the plurality of hydrophones.

DESCRIPTION

In various embodiments, a passive bearing detector is disclosed. The passive bearing detector comprises a plurality of hydrophones. The plurality of hydrophones are arranged in a three-dimensional geometry. The three-dimensional geometry exposes each of the plurality of hydrophones to an ambient aquatic acoustic environment. The passive bearing detector further comprises a processor electrically coupled to the plurality of hydrophones. The processor is configured to determine at least one direction of arrival of an unknown broadband acoustic signal received by the plurality of hydrophones based on the phase difference of the unknown broadband acoustic signal at each of the plurality of hydrophones.

In various embodiments, a method for passive bearing tracking of sea-going platforms is disclosed. The method comprises arranging a plurality of hydrophones in a three-dimensional geometry configured to expose each of the plurality of hydrophones to an aquatic ambient acoustic environment. The method further comprises receiving an unknown broadband acoustic signal at a plurality of hydrophones. A processor calculates at least one direction of arrival of the unknown broadband acoustic signal. The calculation is based on a phase difference of the unknown broadband acoustic signal received by the plurality of hydrophones.

In various embodiments, an apparatus for passive direction of arrival estimation of sea-going platforms is disclosed. The apparatus comprises a plurality of hydrophones arranged in a three-dimensional geometry configured to expose each of the plurality of hydrophones to an ambient aquatic acoustic environment. The apparatus further comprises a processor electrically coupled to the plurality of hydrophones and a memory unit coupled to the processor. The memory unit is configured to store a plurality of instructions. When loaded by the processor, the instructions control the processor to determine at least one direction of arrival of an unknown broadband acoustic signal received by the plurality of hydrophones. The determination is based on a phase difference of the unknown broadband acoustic signal received by the plurality of hydrophones.

Reference will now be made in detail to several embodiments, including embodiments showing example implementations of systems and methods for passive acoustic bearing estimation. Wherever practicable similar or like reference numbers may be used in the figures and may indicate similar or like functionality. The figures depict example embodiments of the disclosed systems and/or methods of use for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative example embodiments of the structures and methods illustrated herein may be employed without departing from the principles described herein.

FIG. 1illustrates one embodiment of a passive bearing detector2. The passive bearing detector2comprises a plurality of hydrophones configured to receive an arbitrary, random, or otherwise unknown underwater broadband acoustic signal6. The broadband acoustic signal6may be generated by a sea going platform, such as, for example, a passing ship20, an underwater autonomous vehicle22, or other sea-going platform. The sea-going platform20,22may passively radiate the unknown broadband acoustic signal6or may actively transmit the unknown broadband acoustic signal6. The unknown broadband acoustic signal6may be received by the passive bearing detector2without any foreknowledge of the source of the unknown broadband acoustic signal6. The passive bearing detector2may be configured to determine at least one direction of arrival for the received unknown broadband acoustic signal6. In some embodiments, an azimuthal direction of arrival and a vertical direction of arrival may be determined by the passive bearing detector2. Those skilled in the art may recognize that any number of suitable directions of arrival may be calculated.

FIG. 2illustrates one embodiment of the plurality of hydrophones. The plurality of hydrophones4a-4dmay be arranged in a three-dimensional geometry to allow each of the plurality of hydrophones4a-4dto receive the unknown broadband acoustic signal6. The plurality of hydrophones4a-4dmay be equally spaced or arbitrarily spaced within the three-dimensional geometry. In the embodiment shown inFIG. 2, the plurality of hydrophones4a-4dare arranged in a tetrahedral configuration. Those skilled in the art will recognize that any suitable geometric arrangement and spacing may be employed based on the number of hydrophones present in the passive bearing detector2. The geometric arrangement allows each of the hydrophones4a-4dto receive the unknown broadband acoustic signal6. Each hydrophone4a-4dmay receive the broadband acoustic signal6at a different phase. The passive bearing detector2may utilize the phase difference between the plurality of hydrophones4a-4dto calculate the at least one direction of arrival for the unknown broadband acoustic signal6.

FIG. 3illustrates one embodiment of a block-diagram of the passive bearing detector2shown inFIGS. 1 and 2. In some embodiments, the plurality of hydrophones4a-4dmay be configured to receive an unknown broadband acoustic signal6. The unknown broadband acoustic signal6may be processed through individual bandpass filters8a-8dassociated with each of the individual hydrophones4a-4d. The bandpass filters8a-8dmay be electrically coupled to a processor10. In some embodiments, the processor10may be configured to calculate one or more directions of arrival for the unknown broadband acoustic signal6. The processor10may calculate the one or more directions of arrival for the unknown broadband acoustic signal6based on the phase difference between the unknown broadband acoustic signal6received at each of the hydrophones4a-4d.

In some embodiments, the passive bearing detector2may comprise a transmitter12. The one or more directions of arrival (or other measurements performed on the unknown broadband acoustic signal6) may be transmitted to a remote device or entity capable of acting on the direction of arrival information. The processor10may be configured to generate a message14indicative of the one or more directions of arrival calculated for the unknown broadband acoustic signal6. The message14may be provided to the transmitter12for transmission to a remote device. The remote device may comprise, for example, one or more additional passive bearing detectors, a communication buoy, a sea-based platform, one or more undersea or near-surface sensors, a land-based monitoring station, or any other suitable remote device. In some embodiments, the transmitter12may be configured as an acoustic transmitter and may transmit the message using one or more acoustic signals. In some embodiments, the transmitter12may be configured as a transceiver configured to transmit and receive acoustic signals. For example, the transmitter12may comprise an acoustic modem. In some embodiments, the transmitter12may comprise the same signal acquisition structure and signal processing structure as the direction of arrival calculation. For example, in one embodiment, the plurality of hydrophones4a-4dmay be configured to receive an unknown broadband signal6and may also be configured as an acoustic modem for transmitting or receiving one or more messages14comprising the at least one direction of arrival. In some embodiments, the transmitter12may transmit the message14as an acoustic signal to an acoustic receiver, such as, for example, an acoustic modem, connected to a communication buoy. The communication buoy may be configured to transmit the received message14to a remote location, such as, for example, a land-based or ship-based monitoring station.

FIG. 4illustrates one embodiment of a two-hydrophone passive bearing detector102. The passive bearing detector102may comprise a first hydrophone104aand a second hydrophone104b. The first hydrophone104aand the second hydrophone104bmay be formed on a backing103. The backing may support the first hydrophone104aand the second hydrophone104bin a linear arrangement.FIG. 5illustrates one embodiment of a planar representation100of the two-hydrophone passive bearing detector102. As can be seen in bothFIGS. 4 and 5, the unknown broadband acoustic signal106is received at the passive bearing detector102from a reference angle Θ126.

FIG. 6illustrates one embodiment of a process200for determining a direction of arrival of unknown broadband acoustic signal106received by the passive bearing detector, such as, for example, the passive bearing detector102. Although the process200for determining direction of arrival of an unknown broadband acoustic signal is discussed with respect to the passive bearing detector102, those skilled in the art will recognize that the process may be applied by any passive bearing detector comprising any number of hydrophones, such as, for example, the passive bearing detector2shown inFIGS. 1-3. The direction of arrival of the broadband acoustic signal106may be determined based on the phase difference of the broadband acoustic signal106received at each of the plurality of hydrophones104a-104b. A temporally-restricted second order function may be utilized to derive a phase measurement from the broadband acoustic signal6received at each of the plurality of hydrophones104a-104b.

An unknown broadband acoustic signal106may be received at a reference hydrophone comprising one of the plurality of hydrophones, such as, for example, the first hydrophone104a. In some embodiments, the unknown broadband acoustic signal106, r(t), may be represented by the equation:
r(t)=X(t)ej2πFct+noise  (1)
wherein X(t) is the complex envelope of the signal and Fcis the center frequency of the broadband acoustic signal106. In some embodiments, the noise is assumed to be independent of the broadband acoustic signal106and the noise bandwidth is assumed to be the same as the signal bandwidth. The broadband acoustic signal106arrives at all of the N hydrophones in the plurality of hydrophones from an angle θ126relative to a reference angle. In some embodiments, the passive bearing detector comprises at least two hydrophones104a,104b. In some embodiments, three or more hydrophones, such as, for example, the four hydrophone arrangement shown inFIG. 2, may be employed to eliminate forward-backward and up-down ambiguities that may arise in a two hydrophone passive bearing detector102.

The unknown broadband acoustic signal106may be received202by each of the plurality of hydrophones104a,104band may be filtered204through individual bandpass filters associated with each of the plurality of hydrophones104a,104b. In some embodiments, an autocorrelation R11(τ) at the first hydrophone104aand a cross-correlation R12(τ) between the first hydrophone104aand the second hydrophone104bis performed106. The autocorrelation R11(τ) and the cross-correlation R12(τ) are used to determine the approximate arrival time from the correlator output R1(τ). The correlations may be calculated according to the equation:

R1⁢⁢k⁡(τ)=1T⁢∫τ-T/2τ+T/2⁢[X1⁡(t+τ)⁢ⅇ-j2π⁢⁢Fc⁡(t+τ)+noise1*⁡(t+τ)]⁢[Xk⁡(t)⁢ⅇj2π⁢⁢Fc⁢t+noisek⁡(t)]⁢ⅆt⁢⁢⁢⁢k=1,2(2)
wherein T is the arbitrary signal duration. As the plurality of hydrophones104a,104bare physically close relative to the half wavelength at the signal center frequency, the autocorrelation R11(τ) and the cross-correlation R12(τ) may be considered essentially the same function, with the exception of the presence of noise and a slight variation in phase as discussed in more detail blow. Assuming that WT>>1, wherein W is the signal bandwidth, it can be shown that:
R1(τ)≈RX(τ)+RN(τ)  (3)
R1k(τ)≈exp(−i2πFc(τ+L))RX(τ+L)+RN1k(τ+L)  (4)
wherein RN1kreflects the correlation between the noise at the two receiving hydrophones. In one embodiment, as identified in equation (4), a low noise or strong signal to noise ratio (SNR) is required. Because a low noise or strong SNR is assumed, the noise term (RN1k) may be dropped from equation (4).

In some embodiments, the peak of |R1(τ)| is found. The lag time of the system, τ, is set 14 to τ≡0 at the peak of |R1(τ)|. At τ≡0, the relationship between the correlation R1kand R12may be reduced to:
R1k(τ)≈R12(L)≈(constant)·e−j2πFcL(5)

FIG. 7illustrates one embodiment of a plot300aof a phase304aof an unknown broadband acoustic signal6plotted relative to the autocorrelation function302aof the unknown broadband acoustic signal. As can be seen inFIG. 7, the phase304ais nearly constant under the main lobe of the autocorrelation function302a. Because the phase304ais nearly constant, those skilled in the art will recognize that the assumptions of equation (5) are justified in broadband acoustic signals, such as the unknown broadband acoustic signal106.

With reference again toFIGS. 4 and 5, The phase of R1(0) and R2(L) can be compared108. Let D=R*11(0)R12(L) and note that R11(0)≈1 (real). The phase angle between the two complex correlations is:
Φ=arctan(imag(D),real(D))  (6)
wherein the arc tangent is the 4-quadrant version of its arguments. But in the vicinity of the peak, which is assumed to be nearly constant, D=e−j2πFcL, therefore

Φ=2⁢π⁢⁢Fc⁢L(7)Φ=2⁢π⁢⁢Fc⁡(dc)⁢cos⁡(Θ)(8)
wherein c is the sonic speed (which is assumed known) and d is the spacing between the reference hydrophone and each of the remaining hydrophones. Therefore, the desired direction of arrival, θ, for the unknown broadband signal may be calculated210using the relationship:

Θ=cos-1⁡(λΦ2⁢π⁢⁢d)(9)
wherein λ=c/Fcis the wavelength at the upper band edge frequency.

The requirement that |R(τ)| be a constant value is equivalent to the requirement that 1/W>d/c which means that W<c/d. For example, if W=5 kHz and c=1500 m/s, then the spacing between the plurality of hydrophones104a,104bin the passive bearing detector is constrained to d<30 cm. However, in some embodiments, a tighter restriction requiring d<λ/2 may be imposed. Assuming this restriction, for Fc=11,000 Hz, the maximum spacing between the plurality of hydrophones104a,104bmay be approximately 6.5 cm. In some embodiments, the passive bearing detector102may comprise three or more hydrophones4a-4d. The phase estimates for each of the plurality of hydrophones4a-4dmay be compared112to produce a three dimensional (3D), unambiguous estimate of the vertical and horizontal directions of arrival for the unknown broadband acoustic signal106.

FIGS. 8A-8Cshow graphs300b,300c,300dof signal phase plotted relative to the autocorrelation function for three distinct waveforms: a linear frequency modulated (LFM) signal shown inFIG. 8A, a hyperbolic frequency modulated (HFM) signal shown inFIG. 8B, and a pseudo-random frequency hopping signal shown inFIG. 8C. As can be seen inFIGS. 8A-8C, the phase of each of the distinct signals is constant (or nearly constant) under the main lobe of the autocorrelation function. The waveforms shown inFIGS. 8A-8Coffer further support for the assumptions present in the process200for determining a direction of arrival.

FIG. 9illustrates one embodiment of a multiple passive bearing detector system400. The multiple passive bearing detector system400comprises a plurality of passive bearing detectors402a,402b. Each of the plurality of passive bearing detectors402a,402bis configured to determine a direction of arrival for an unknown broadband acoustic signal406received at each of the plurality of passive bearing detectors402a,402b. The plurality of passive bearing detectors402a,402bmay each comprise a plurality of hydrophones in a geometric configuration, such as, for example, the four-hydrophone tetrahedral configuration shown inFIG. 2. An unknown broadband acoustic signal406is generated by a sea-going platform420, such as, for example, a surface ship or a submersible. Each of the passive bearing detectors402a,402bmay generate one or more directions of arrival for the unknown broadband acoustic signal406, such as, for example, an azimuthal (or horizontal) direction of arrival and a vertical direction of arrival. The one or more directions of arrival calculated by the passive bearing detector402a,402bmay be transmitted to a communication buoy424.

In some embodiments, each of the passive bearing detectors402a,402bmay comprise a transmitter, such as, for example, an acoustic modem, for transmitting a message comprising the one or more directions of arrival calculated by the passive bearing detector402a,402b. The multiple passive bearing detector system400may be configured for autonomously coordinated observation among the distributed multiple passive bearing detectors402a,402b. For example, in some embodiments, a first passive bearing detector402amay transmit one or more directions of arrival calculated by the first passive bearing detector402ato a second passive bearing detector402busing acoustic communication. The second passive bearing detector402bmay receive the one or more directions of arrival calculated by the first passive bearing detector402a. The second passive bearing detector402bmay transmit the one or more directions of arrival calculated by the first passive bearing detector402aand one or more directions of arrival calculated by the second passive bearing detector402bto a communications buoy424. The communications buoy424may receive the one or more directions of arrival and may transmit the received information to a remote location, such as, for example, a land-based or ship-based monitoring station.

In some embodiments, a distributed passive bearing detector, such as passive bearing detector2or multiple passive bearing detector system400may be used to track one or more sea-going platforms, such as, for example, surface, near-surface, or sub-surface vessels. For example, tracking of sea-going platforms may be required in military operations, anti-smuggling operations, anti-piracy operations, or marine preservation operations. In one embodiment, the multiple passive bearing detector system400may provide autonomously coordinated observation among the distributed multiple passive bearing detector system400. For example, in one embodiment, a sea-going platform, such as, for example, a ship420, may radiate one or more unknown broadband acoustic signals406. The unknown broadband acoustic signal406may be received by a first passive bearing detector402a. The first passive bearing detector402amay comprise a plurality of hydrophones arranged in a three-dimensional geometric configuration, such as, for example, the tetrahedral configuration shown inFIG. 2. The first passive bearing detector402amay comprise a processor configured to determine at least one direction of arrival at one or more of the hydrophones. For example, the first passive bearing detector402amay be configured to determine an azimuthal (or horizontal) direction of arrival and a vertical direction of arrival for the unknown broadband acoustic signal406at each of the hydrophones in the geometric configuration. The first passive bearing detector402amay be configured to determine an average azimuthal and vertical direction of arrival for the unknown broadband acoustic signal406at the first passive bearing detector402a. The first passive bearing detector402amay comprise a transmitter configured to transmit a message comprising the at least one direction of arrival determined by the first passive bearing detector402ato a second passive bearing detector402b.

In some embodiments, the second passive bearing detector402bmay comprise a plurality of hydrophones arranged in a three-dimensional geometric configuration, such as, for example, the tetrahedral configuration shown inFIG. 2. The second passive bearing detector402amay receive the unknown broadband acoustic signal406at each of the hydrophones. The second passive bearing detector402bmay comprise a processor configured to determine at least one direction of arrival at one or more of the hydrophones of the second passive bearing detector402b. For example, the second passive bearing detector402bmay be configured to determine an azimuthal (or horizontal) direction of arrival ad a vertical direction of arrival for the unknown broadband acoustic signal406at each of the hydrophones of the second passive bearing detector402b. The second passive bearing detector may comprise a transceiver, such as, for example, an acoustic modem, configured to send and receive acoustic signals.

In some embodiments, the first passive bearing detector402amay transmit the one or more directions of arrival calculated by the first passive bearing detector402ato the second passive bearing detector402b, for example, through acoustic communication. The second passive bearing detector402bmay transmit the one or more directions of arrival calculated at the first passive bearing detector402aand the one or more directions of arrival calculated by the second passive bearing detector402bto a remote location, such as, for example, a communication buoy424. The second passive bearing detector402bmay be in signal communication with the communication buoy, for example, through acoustic communication. The communication buoy424may transmit the received directions of arrival to a remote monitoring station, such as a land-based or ship-based monitoring station. The monitoring station may use the received directions of arrival of the unknown broadband acoustic signal406to calculate the position of the sea-going platform420. Based on the calculated position, the monitoring station may dispatch sea-going platforms to intercept the sea-going platform420or to aim munitions at the sea-going platform, for example.

In some embodiments, a passive bearing detector is disclosed. The passive bearing detector may comprise a plurality of hydrophones arranged in a three-dimensional geometry configured to expose each of the plurality of hydrophones to an ambient aquatic acoustic environment. The passive bearing detector may further comprise a processor electrically coupled to the plurality of hydrophones. The processor may be configured to determine at least one direction of arrival of an unknown broadband acoustic signal received by the plurality of hydrophones based on the phase difference of the unknown broadband acoustic signal at each of the plurality of hydrophones. In some embodiments, the plurality of hydrophones may be equally spaced.

In some embodiments, the processor may be configured to determine the at least one direction of arrival, Θk, of the unknown broadband acoustic signal at one pair of the plurality of hydrophones in accordance with the following relationship:

Θk=cos-1⁡(λ⁢⁢Φk2⁢π⁢⁢dk)
wherein λ is the wavelength of the upper edge of the frequency band of the unknown broadband acoustic signal, k is a reference hydrophone selected from the plurality of hydrophones, Φkis the phase angle arising from a cross-correlation of the unknown broadband acoustic signal between the reference hydrophone and each one of the remaining plurality of hydrophones, and dkis the distance between each of the plurality of hydrophones.

In some embodiments, the processor may be configured to determine the at least one direction of arrival of the unknown broadband acoustic signal at each pair of the plurality of hydrophones. The passive bearing detector may comprise a transmitter configured to generate a message comprising the at least one direction of arrival calculated by the processor. The transmitter may be configured to transmit the message to a remote device. The transmitter may comprise an acoustic modem. The acoustic modem may provide acoustic communication to one or more additional passive bearing detectors and one or more associated undersea or near-surface sensors.

In various embodiments, a method for passive bearing tracking of sea-going platforms is disclosed. The method may comprise arranging a first plurality of hydrophones in a three-dimensional geometry configured to expose each of the plurality of hydrophones to an aquatic ambient acoustic environment. The first plurality of hydrophones may receive an unknown broadband acoustic signal. A first processor may be configured to calculate at least one first direction of arrival of the unknown broadband acoustic signal. The calculation is based on a phase difference of the unknown broadband acoustic signal received by the plurality of hydrophones. In some embodiments, the first plurality of hydrophones is arranged in an equally-spaced three-dimensional geometry.

In some embodiments, the first processor may be configured to calculate the at least one first direction of arrival of the unknown broadband acoustic signal, Θk, in according with the following relationship:

Θk=cos-1⁡(λ⁢⁢Φk2⁢π⁢⁢dk)
wherein λ is the wavelength of the upper edge of the frequency band of the unknown broadband acoustic signal, k is a reference hydrophone selected from the plurality of hydrophones, Φkis the phase angle arising from a cross-correlation of the unknown broadband acoustic signal between the reference hydrophone and each one of the remaining plurality of hydrophones, and dkis the distance between each of the plurality of hydrophones. In some embodiments, the method for passive bearing detection may comprise generating, by the first processor, a first message indicative of the at least one first direction of arrival of the unknown broadband acoustic signal. A first transmitter, such as, for example, an acoustic modem, may transmit the first message indicative of the at least one first direction of arrival of the unknown broadband acoustic signal through acoustic communication.

In some embodiments, a second plurality of hydrophones may be arranged in a three-dimensional configuration configured to expose each of the plurality of hydrophones to an ambient aquatic acoustic environment. The second plurality of hydrophones may be spaced apart from the plurality of hydrophones. The second plurality of hydrophones may receive the unknown broadband acoustic signal. A second processor coupled to the second plurality of hydrophones may calculate at least one second direction of arrival for the unknown broadband acoustic signal at the second plurality of hydrophones. In some embodiments, the second processor may generate a second message indicative of the at least one second direction of arrival for the unknown broadband acoustic signal. A second transmitter may transmit the second message indicative of the at least one second direction of arrival to a remote location. The second transmitter may transmit the second message indicative of the at least one second direction of arrival using acoustic communications. In some embodiments, a remote location may calculate the position of a sea-going platform using the first message and the second message

In various embodiments, an apparatus for passive direction of arrival estimation of sea-going platforms is disclosed. The apparatus may comprise a plurality of hydrophones arranged in a three-dimensional geometry configured to expose each of the plurality of hydrophones to an ambient aquatic acoustic environment. The apparatus may further comprise a processor electrically coupled to the plurality of hydrophones and a memory unit coupled to the processor. The memory unit may be configured to store a plurality of instructions which when loaded by the processor control the processor to determine at least one direction of arrival of an unknown broadband acoustic signal received by the plurality of hydrophones based on a phase difference of the unknown broadband acoustic signal received by the plurality of hydrophones. In some embodiments, the plurality of hydrophones may be equally spaced.

In some embodiments, the plurality of instructions may control the processor to determine the at least one direction of arrival of the unknown broadband acoustic signal by calculating:

Θk=cos-1⁡(λ⁢⁢Φk2⁢π⁢⁢dk)
wherein λ is the wavelength of the upper edge of the frequency band of the unknown broadband acoustic signal, k is a reference hydrophone selected from the plurality of hydrophones, Φkis the phase angle arising from a cross-correlation of the unknown broadband acoustic signal between the reference hydrophone and each one of the remaining plurality of hydrophones, and dkis the distance between each of the plurality of hydrophones.

In some embodiments, the apparatus for passive direction of arrival estimation may comprise a transmitter. The transmitter may be configured to generate a message comprising the at least one direction of arrival. The transmitter may be configured to transmit the message a remote device. In some embodiments, the transmitter may comprise an acoustic modem. The acoustic modem may provide acoustic communications to one or more additional passive bearing detectors and one or more associated undersea or near-surface sensors.

While various details have been set forth in the foregoing description, it will be appreciated that the various aspects of the systems and method for passive bearing detection may be practiced without these specific details. For example, for conciseness and clarity selected aspects have been shown in block diagram form rather than in detail. Some portions of the detailed descriptions provided herein may be presented in terms of instructions that operate on data that is stored in a computer memory. Such descriptions and representations are used by those skilled in the art to describe and convey the substance of their work to others skilled in the art. In general, an algorithm refers to a self-consistent sequence of steps leading to a desired result, where a “step” refers to a manipulation of physical quantities which may, though need not necessarily, take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It is common usage to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like. These and similar terms may be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities.

Unless specifically stated otherwise as apparent from the foregoing discussion, it is appreciated that, throughout the foregoing description, discussions using terms such as “processing” or “computing” or “calculating” or “determining” or “displaying” or the like, refer to the action and processes of a processor, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices.

It is worthy to note that any reference to “one aspect,” “an aspect,” “one embodiment,” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the aspect is included in at least one aspect. Thus, appearances of the phrases “in one aspect,” “in an aspect,” “in one embodiment,” or “in an embodiment” in various places throughout the specification are not necessarily all referring to the same aspect. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner in one or more aspects.

Although various embodiments have been described herein, many modifications, variations, substitutions, changes, and equivalents to those embodiments may be implemented and will occur to those skilled in the art. Also, where materials are disclosed for certain components, other materials may be used. It is therefore to be understood that the foregoing description and the appended claims are intended to cover all such modifications and variations as falling within the scope of the disclosed embodiments. The following claims are intended to cover all such modification and variations.

All of the above-mentioned U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications, non-patent publications referred to in this specification and/or listed in any Application Data Sheet, or any other disclosure material are incorporated herein by reference, to the extent not inconsistent herewith. As such, and to the extent necessary, the disclosure as explicitly set forth herein supersedes any conflicting material incorporated herein by reference. Any material, or portion thereof, that is said to be incorporated by reference herein, but which conflicts with existing definitions, statements, or other disclosure material set forth herein will only be incorporated to the extent that no conflict arises between that incorporated material and the existing disclosure material.

In certain cases, use of a system or method may occur in a territory even if components are located outside the territory. For example, in a distributed computing context, use of a distributed computing system may occur in a territory even though parts of the system may be located outside of the territory (e.g., relay, server, processor, signal-bearing medium, transmitting computer, receiving computer, etc. located outside the territory).

A sale of a system or method may likewise occur in a territory even if components of the system or method are located and/or used outside the territory. Further, implementation of at least part of a system for performing a method in one territory does not preclude use of the system in another territory.

Although various embodiments have been described herein, many modifications, variations, substitutions, changes, and equivalents to those embodiments may be implemented and will occur to those skilled in the art. Also, where materials are disclosed for certain components, other materials may be used. It is therefore to be understood that the foregoing description and the appended claims are intended to cover all such modifications and variations as falling within the scope of the disclosed embodiments. The following claims are intended to cover all such modification and variations.

In summary, numerous benefits have been described which result from employing the concepts described herein. The foregoing description of the one or more embodiments has been presented for purposes of illustration and description. It is not intended to be exhaustive or limiting to the precise form disclosed. Modifications or variations are possible in light of the above teachings. The one or more embodiments were chosen and described in order to illustrate principles and practical application to thereby enable one of ordinary skill in the art to utilize the various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the claims submitted herewith define the overall scope.