Patent Description:
Noise sources may be analyzed to understand the physics behind noise generated by the noise sources. For example, arrays of microphones may be positioned proximate a noise source, such as an aircraft engine, to collect noise data from a noise source. The arrays of microphones are sometimes referred to as acoustic arrays or acoustic phased arrays. The noise data collected by the arrays of microphones may be analyzed using specialized software to determine what components within, and exterior to the engine contribute to the noise. Information extracted from the analysis may be useful in design and/or operation of devices which include noise sources. For example, aircraft manufacturers may use such information in the design of aircraft components which generate noise.

<CIT>, according to its abstract, states a technique for acquiring wide azimuth seismic data using simultaneous shooting in which a plurality of seismic sources are positioned to achieve a desired crossline sampling as a function of the number of passes. This is accomplished by "interleaving" sources as deployed in the spread, as positioned in multiple passes, or some combination of these things, to achieve an effective shotline interval during acquisition or an effective crossline sampling less than their crossline source separation.

<CIT>, according to its abstract, states a computer implemented method and apparatus for identifying a component breakdown of noise sources. Noise data is received from a noise source from an array of sound sensors. Measurement points of interest, candidate sound source points along an axis, and array aperture angles are identified. Sets of first and second bounding traces are identified from ray traces extending from the candidate noise source points towards the measurement points of interest using the array aperture angles. The bounding ray traces are rotated around the axis to form sets of first and second surfaces. Sets of first and second curves are identified from an intersection of the sets of first and second surfaces with the ground plane. Sound sensors are selected from the array using the curves to form subarrays. The component breakdown of noise generated by the noise source is identified using noise data from sound sensors in the subarrays.

<CIT>, according to its abstract, states an oceanographic sampling system includes two or more underwater vehicles disposed in an array and an array controller for controlling the array of underwater vehicles as data is acquired. Each underwater vehicle includes a propulsion system for moving the underwater vehicle independently of the other underwater vehicles, a sensor for sensing an ocean parameter and providing sensor data representative of the ocean parameter as the underwater vehicle moves, a navigation subsystem for determining position data representative of the position of the underwater vehicle as the sensor data is acquired and a synchronizing subsystem for time synchronizing the sensor data and the position data acquired by the underwater vehicle with sensor data and position data acquired by other underwater vehicles. The array of underwater vehicles may function as a large aperture phased array, and phased array analysis techniques may be applied to the time-synchronized sensor data and position data.

Accordingly, apparatus and methods for changing the capabilities of an acoustic array may find utility.

There is herein described a system for acoustic testing. The system comprises a plurality of acoustic sensors mounted to a plurality of vehicles, a control system to control the plurality of vehicles, and a data acquisition system to receive data generated by the plurality of acoustic sensors in response to noise from a noise source proximate the plurality of vehicles. The control system controls the plurality of vehicles to move into a first predetermined configuration in a first predetermined location in which the acoustic sensors form a first acoustic array having a first aperture size and a first spatial resolution. The control system controls the plurality of vehicles to move from the first predetermined configuration into a second predetermined configuration in which the acoustic sensors from a second acoustic array having a second aperture size and a second spatial resolution. The control system is configured to control the plurality of vehicles to move into a configuration in which the acoustic sensors form an array having locally non-redundant spacing such that no two vector spacings are the same. The plurality of vehicles comprises a plurality of unmanned air vehicles to which the plurality of sensors are mounted. The control system is configured to control the plurality of unmanned air vehicles to collect noise data from the noise source. The noise source comprises an engine.

There is also described herein a method for acoustic testing comprising: (a) positioning a plurality of vehicles proximate a noise source, wherein the plurality of vehicles comprise a plurality of acoustic sensors mounted to the plurality of vehicles, (b) controlling the plurality of vehicles to move into a first predetermined configuration in a first predetermined location in which the acoustic sensors form a first acoustic array having a first aperture size and a first spatial resolution, (c) controlling the plurality of vehicles to move into a second predetermined configuration in which the acoustic sensors form a second acoustic array having a second aperture size and a second spatial resolution, (d) receiving data generated by the plurality of acoustic sensors in response to noise from the noise source proximate the plurality of vehicles, and (e) controlling the plurality of vehicles to move into a configuration in which the acoustic sensors form an array having locally non-redundant spacing such that no two vector spacings are the same. The plurality of vehicles comprise a plurality of unmanned air vehicles to which the plurality of sensors are mounted. The noise source comprises an engine.

In one example, a method for acoustic testing comprises positioning a plurality of unmanned air vehicles proximate an engine, wherein the plurality of unmanned air vehicles comprise a plurality of acoustic sensors mounted to a plurality of vehicles, controlling the plurality of unmanned air vehicles to move into a first predetermined configuration in a first predetermined location in which the acoustic sensors form a first acoustic array having a first aperture size and a first spatial resolution, and receiving data generated by the plurality of acoustic sensors in response to noise from the engine.

The features, functions and advantages discussed herein can be achieved independently in various embodiments described herein or may be combined in yet other embodiments, further details of which can be seen with reference to the following description and drawings.

In the following description, numerous specific details are set forth to provide a thorough understanding of various embodiments. However, it will be understood by those skilled in the art that the various embodiments may be practiced without the specific details. In other instances, well-known methods, procedures, components, and circuits have not been illustrated or described in detail so as not to obscure the particular embodiments.

Phased array measurement capabilities are determined by both the overall size of the array (i.e., the aperture size) and by how the sensors are distributed spatially (i.e., the spatial resolution). For sensors that are fixed in space, the array measurement capabilities are likewise fixed and cannot be changed. By allowing the sensors to move to any of an infinite number of locations in space, the array measurement capabilities therefore likewise become infinite. The subject matter described herein allows for a mobile acoustic sensor that could be deployed in any scenario for which the location and/or magnitude of a noise source is desired. Such capabilities could be implemented together into a single type (i.e., operate on ground, underwater or in air), or operate in a combination of mediums (ground only; water only; air only; ground and water; ground and air; water and air). The sensors of the array could even be attached to the side of a moving vehicle such as a train, car, airplane, or boat and could have the ability to move around on the side of the object to redistribute as needed.

<FIG> is a schematic block diagram illustration of a system <NUM> for acoustic testing according to aspects. Referring to <FIG>, the system <NUM> comprises one or more vehicles which include a location system <NUM>, a communication system <NUM>, a data collection system <NUM>, a power system <NUM> and propulsion system <NUM>.

The location system <NUM> may comprise a satellite-based navigation system such as a global positioning system (GPS) system or the like. Alternatively, or in addition, the location system <NUM> may comprise an inertial positioning system, an optical positioning system or the like.

Communication system <NUM> may be a wireless communication system which operates in accordance with any number of wireless communication standards. Examples of suitable wireless communication interfaces include an IEEE <NUM>. 11a, b, or g-compliant interface (see, e.g., IEEE Standard for IT-Telecommunications and information exchange between systems LAN/MANPart II: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications Amendment <NUM>: Further Higher Data Rate Extension in the <NUM> Band, <NUM>-<NUM>). Another example of a wireless interface would be a general packet radio service (GPRS) interface (see, e.g., Guidelines on GPRS Handset Requirements, Global System for Mobile Communications/GSM Association, Ver. <NUM>, December <NUM>).

Communication system <NUM> may comprise a command and control processing module <NUM> to process commands and controls received over communication system <NUM>, a data transmission module <NUM> to transmit data over communication system <NUM>, and a wireless synchronization module <NUM> to synchronize wireless communication with other devices.

Data collection system <NUM> comprises a data collection module <NUM> and one or more sensors <NUM>. Data collection module <NUM> may be embodied as logic to manage the operations of sensors <NUM>. Examples of suitable sensors <NUM> may include microphones, hydrophones, laser sensors, seismometers, and other suitable sensors.

Power system <NUM> provides power to the vehicles <NUM> and/or to the various systems on vehicles <NUM>. In some examples power systems <NUM> may include one or more power sources such as a battery or a liquid or solid fuel source. Propulsion system <NUM> may comprise one or more engines or motors coupled to power system <NUM> and may comprise a transmission to power wheels, rotors or the like.

In various examples the vehicles <NUM> may comprise at least one of a manned vehicle, an unmanned aerial vehicle (UAV), an unmanned ground-based vehicle or an unmanned underwater-based vehicle. For example, the vehicles <NUM> may comprise UAVs such as quadrotor crafts, helicopters, blimps, or the like. Ground-based vehicles <NUM> may include remote-control (RC) vehicles <NUM> which move on wheels, tracks, or the like. Underwater-based vehicles <NUM> may include submersible vehicles which move using propellers or other appropriate underwater propulsion systems.

Acoustic testing system <NUM> further comprises a control system <NUM> to control operations of vehicles <NUM> and a data acquisition system <NUM> to receive data from the data collection system <NUM> on vehicles <NUM>. Control system <NUM> and data acquisition system <NUM> may be implemented on computer systems and may be communicatively coupled to the vehicles <NUM> via communication system <NUM>.

In operation, the acoustic testing system <NUM> may be used to detect and characterize noise from a noise source <NUM>. Examples of noise sources may include mechanical systems such as aircraft engines, industrial machinery, aircraft frames and/or control surfaces, underwater biologics and the like.

In some embodiments the acoustic testing system <NUM> may comprise a plurality of vehicles <NUM> which may be controlled by control system <NUM> to behave in a coordinated fashion. Such a group of vehicles <NUM> may be referred to as a "swarm" of vehicles <NUM>. In operation, the control system <NUM> may instruct the plurality of vehicles <NUM> to form particular configurations in particular locations proximate the noise source <NUM> to collect data from the noise source <NUM>. The particular configurations and locations may be changed during an acoustic test.

<FIG> is a schematic block diagram of a processing system <NUM> which may be used in a system for acoustic testing, according to aspects. In the example depicted in <FIG>, processing system <NUM> includes a communication fabric <NUM>, which provides a communication path between processor unit <NUM>, memory <NUM>, persistent storage <NUM>, communications unit <NUM>, input/output (I/O) unit <NUM>, and display <NUM>.

Data processing system <NUM> is an example of a data processing system that may be used to implement control system <NUM> and/or data acquisition system <NUM> depicted in <FIG>. If used to implement data acquisition system <NUM> in <FIG>, input/output unit <NUM> may be connected to communication system <NUM> on vehicles <NUM>.

Processor unit <NUM> serves to execute instructions for software that may be loaded into memory <NUM>. Processor unit <NUM> may be a set of one or more processors or may be a multi-processor core, depending on the particular implementation. Further, processor unit <NUM> may be implemented using one or more heterogeneous processor systems in which a main processor is present with secondary processors on a single chip. As another illustrative example, processor unit <NUM> may be a symmetric multi-processor system containing multiple processors of the same type.

Memory <NUM> and persistent storage <NUM> are examples of storage devices. A storage device is any piece of hardware that is capable of storing information either on a temporary basis and/or a permanent basis. Memory <NUM>, in these examples, may be, for example, a random access memory or any other suitable volatile or non-volatile storage device. Persistent storage <NUM> may take various forms depending on the particular implementation.

For example, persistent storage <NUM> may contain one or more components or devices. For example, persistent storage <NUM> may be a hard drive, a flash memory, a rewritable optical disk, a rewritable magnetic tape, or some combination of the above. The media used by persistent storage <NUM> also may be removable.

Communications unit <NUM>, in these examples, provides for communications with other data processing systems or devices. In these examples, communications unit <NUM> is a network interface card. Communications unit <NUM> may provide communications through the use of either or both physical and wireless communications links.

Input/output unit <NUM> allows for input and output of data with other devices that may be connected to data processing system <NUM>. For example, input/output unit <NUM> may provide a connection for user input through a keyboard and mouse. Further, input/output unit <NUM> may send output to a printer. Display <NUM> provides a mechanism to display information to a user.

Instructions for the operating system and applications or programs are located on persistent storage <NUM>. These instructions may be loaded into memory <NUM> for execution by processor unit <NUM>. The processes of the different embodiments may be performed by processor unit <NUM> using computer implemented instructions, which may be located in a memory, such as memory <NUM>. These instructions are referred to as program code, computer usable program code, or computer readable program code that may be read and executed by a processor in processor unit <NUM>. The program code in the different embodiments may be embodied on different physical or tangible computer readable media, such as memory <NUM> or persistent storage <NUM>.

Program code <NUM> may be located in a functional form on computer readable media <NUM> that is selectively removable and may be loaded onto or transferred to data processing system <NUM> for execution by processor unit <NUM>. Program code <NUM> and computer readable media <NUM> form computer program product <NUM> in these examples. In one example, computer readable media <NUM> may be in a tangible form, such as, for example, an optical or magnetic disc that is inserted or placed into a drive or other device that is part of persistent storage <NUM> for transfer onto a storage device, such as a hard drive that is part of persistent storage <NUM>.

In a tangible form, computer readable media <NUM> also may take the form of a persistent storage, such as a hard drive, a thumb drive, or a flash memory that is connected to data processing system <NUM>. The tangible form of computer readable media <NUM> is also referred to as computer recordable storage media. In some instances, computer readable media <NUM> may not be removable.

Alternatively, program code <NUM> may be transferred to data processing system <NUM> from computer readable media <NUM> through a communications link to communications unit <NUM> and/or through a connection to input/output unit <NUM>. The communications link and/or the connection may be physical or wireless in the illustrative examples. The computer readable media also may take the form of non-tangible media, such as communications links or wireless transmissions containing the program code.

The different components illustrated for data processing system <NUM> are not meant to provide architectural limitations to the manner in which different embodiments may be implemented. The different illustrative embodiments may be implemented in a data processing system including components in addition to or in place of those illustrated for data processing system <NUM>. Other components shown in <FIG> can be varied from the illustrative examples shown.

As one example, a storage device in data processing system <NUM> is any hardware apparatus that may store data. Memory <NUM>, persistent storage <NUM> and computer readable media <NUM> are examples of storage devices in a tangible form.

Having described structural features of a system <NUM> for acoustic testing, attention will now be turned to operations implemented in an example acoustic test environment. <FIG> are schematic illustrations of an environment <NUM> for acoustic testing according to aspects, and <FIG> is a flowchart illustrating operations in a method for acoustic testing according to aspects.

Referring first to <FIG>, in one example a noise collection environment <NUM> may include a jet engine <NUM> mounted above ground <NUM> on stand <NUM>. Jet engine <NUM> is a device under test and is an example of a noise source, such as noise source <NUM> in <FIG>, that may be analyzed using noise collection environment <NUM>.

Jet engine <NUM> has inlet <NUM> and exhaust nozzle <NUM>. Inlet <NUM> receives air flow into jet engine <NUM> as illustrated by arrow <NUM>. Exhaust flow leaves jet engine <NUM> through exhaust nozzle <NUM> as shown by arrow <NUM>. Noise generated by jet engine <NUM> may radiate from various points of jet engine axis <NUM>, as well as from other points that may be selected.

The collection of noise data may be made through noise collection environment <NUM>, which includes phased array microphones <NUM>. The microphones <NUM> may be arranged into an array having a predetermined pattern on a ground plane <NUM> located on ground <NUM>.

Noise collection environment <NUM> also includes far field microphones <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. These microphones may be located at measurement points of interest. In the example depicted in <FIG>, nineteen fixed locations are present. These microphones may be located on and/or above ground plane <NUM>. These microphones may be mounted on structures to locate the microphones above ground plane <NUM>.

In these examples, array <NUM> may be selected or configured to have a relatively consistent density of sensors over all, while having non-redundant sensor-to-sensor spacing locally. Array <NUM> has approximately or around the same number of elements in different locations of the array to provide a relatively consistent density overall. If array <NUM> has a relatively consistent density, then extracting a subarray of a given aperture size anywhere along array <NUM> results in a subarray with approximately the same number of sensors. Non-redundant sensor spacing means that the vector spacing between any two elements in the subarray will be unique. Vector spacing is the distance and direction. A non-redundant array has no two vector spacings that are the same.

In this example, phased array microphones <NUM> contain <NUM> elements at fixed locations. The different microphones within phased array microphones <NUM> may be located at a spacing of around six inches (<NUM>) from each other. Further, phased array microphones <NUM> may span over <NUM> feet (<NUM>) to cover the range of required emission angles at the minimum required distance from jet engine <NUM>.

Array <NUM> has a pattern in the form of an arc, in these examples. In particular, phased array microphones <NUM> are arranged in the arc containing three curves, curve <NUM>, curve <NUM>, and curve <NUM>.

The half-wavelength criteria for array design to prevent spatial aliasing (i.e., false images) when using equally spaced sensors limits the usefulness of an equally spaced array to about <NUM> when six inch (<NUM>) spacing is used. In other words, the spacing between adjacent sound sensors in the array must be less than or equal to the half wavelength criteria for equally spaced sound sensors to avoid false images when performing noise source location operations.

The different advantageous embodiments recognize that currently an array may be designed for frequencies exceeding this half-wavelength criteria by using a design approach that insures non-redundant spacing between microphone pairs. Such an array may eliminate false images and suppress array side lobes to the point where the array is useful over a broad range of frequencies. The advantageous embodiments also recognize that an array can be formed using a strategy, such as geometrically increased spacing between successive microphones.

However, the different advantageous embodiments recognize that these arrays are "point design" arrays. For example, these arrays are designed as a single array for a single position. The different advantageous embodiments recognize that multiple instances of these point design arrays may be deployed to cover multiple emission angles.

The different advantageous embodiments also recognize that a traversable array also will not solve the problem, again, because the need for a large number of array locations would be prohibitive from a test conduct standpoint, for example, the time to acquire data for the number of traverse positions required may be prohibitive.

Thus, the different advantageous embodiments recognize that what is needed is an array that is globally made up of a relatively consistent density of microphones. The relatively consistent density across the array enables selection of similarly performing subarrays at any point within the array. The locally non-redundant characteristic enables these subarrays to perform well across a broad range of frequencies, including frequencies that substantially exceed the half-wavelength criteria for equally spaced array elements. The array design, in the different advantageous embodiments, embraces and achieves these principles.

Phased array microphones <NUM> may be distributed as a set of concentric logarithmic spirals. As used in these examples, concentric logarithmic spirals have a common point of origin from which the spirals are formed. These spirals start with different initial radii such that when the spirals are formed, nearly parallel curves are present. A logarithmic or equiangular spiral is a well known mathematical construct.

In one embodiment, phased array microphones <NUM> include three logarithmic spiral arcs with a common origin and a small increase in initial radius for each successive spiral, thus forming three parallel curves. Parameters may be chosen for the logarithmic spirals to ensure that every point on the curve is at least <NUM> mixed nozzle diameters from every point in the candidate source region. Mixed nozzle diameter is also referred to as Dmix. Dmix is the effective diameter of the exhaust flow from the jet engine.

In this example, <NUM> mixed nozzle diameters is considered to be far enough away from the source region that noise source components detected by the phased array microphones <NUM> can be used to accurately estimate the strength of those sources at distances farther away from the sources than the phased array microphones <NUM>. The logarithmic spiral parameters include, for example, origin location, spiral angle, and initial radius. The logarithmic spirals are sampled to determine sensor locations, each using different base spacings between successive sensors.

In the illustrative examples, the curve with the smallest radius uses a base spacing of <NUM>" (<NUM>), the curve with the next larger radius uses a base spacing of <NUM>" (<NUM>), and the curve with the largest radius uses a base spacing of <NUM>" (<NUM>). Within each log spiral curve, the actual spacing may be varied from the base spacing according to the sequence {-<NUM>", -<NUM>", -<NUM>", <NUM>", <NUM>", <NUM>", <NUM>"} ({-<NUM>, -<NUM>, -<NUM>, <NUM>, <NUM>, <NUM>, <NUM>}), and the sequence is repeated until the entire spiral has been sampled.

The base spacing may be chosen to distribute the available number of sensors over the full length of the three curves. A different base spacing is used for each curve such that when the base spacing with variation is applied to each curve, no spacing is repeated until the variation sequence is recycled for a given curve. This strategy creates a locally non-redundant array while preserving a relatively constant density of sensors along the full length of the array. The spatially separated curves, along with the log spiral arc, contribute to additional non-redundancy both locally and globally.

The array of sensors in phased array microphones <NUM> also may be more generally a set of concentric curves for which a shape of the set of curves is selected by a minimum distance of the array of sensors to the candidate source region and wherein a nearest curve in the set of curves is located at the minimum distance. As used in these examples, the minimum distance may vary in different implementations.

In these examples with jet engine <NUM>, the minimum spacing is around <NUM> mixed nozzle diameters. The set of all of the candidate source location points comprises the candidate source region. In other words, a user may define the source region and specify a minimum distance. These parameters may be used to form a boundary around the source region such that no point outside the boundary is less than the minimum distance from any point in the source region.

In the different examples, the microphones in phased array microphones <NUM> may have a shape of a continuous curve for which a tangent to the continuous curve is kept substantially close to perpendicular to lines of sight to the candidate noise source locations to be assessed using the sensor array. Also, the phased array microphones <NUM> may be located substantially perpendicular to lines of sight from the potential noise source region of interest to the measurement points of interest.

The above example array design is not intended to restrict the array design parameters that may be implemented in the different advantageous embodiments. The array may be composed from a single curve or multiple curves. Various other strategies could be used within each curve. The one feature, in these different designs, is globally consistent array density, with locally non-redundant sensor spacing. The location of the array relative to the device under test is application dependent, but the array design principles still apply.

Increased density of microphones will typically improve subarray performance since, for a non-redundant array, the number of sensors in an array for a given aperture size generally improves sensor array performance both in terms of array dynamic range and maximum frequency at which the array provides useful information.

Thus, the design strategy provides an approach for making optimal use of a restricted number of sound sensors for broad coverage of emission angles and frequency range.

In the different advantageous embodiments, the different far field microphones <NUM>-<NUM> are arranged in locations with respect to jet engine axis <NUM>. These different locations have different angles. Line <NUM> is directly below and parallel to jet engine axis <NUM> on ground plane <NUM>. The angles for far field microphones <NUM>-<NUM> may be determined from line <NUM> on the ground, as shown by line <NUM> and angle <NUM>, which is also referred to as θ.

For example, far field microphone <NUM> is located at <NUM> degrees (<NUM> radians) relative to jet engine axis <NUM>. Far field microphone <NUM> is located at <NUM> degrees (<NUM> radians) relative to jet engine axis <NUM>. As another example, far field microphone <NUM> is located at <NUM> degrees (<NUM> radians).

In the different advantageous embodiments, noise generated by jet engine <NUM> may be detected by phased array microphones <NUM> and far field microphones <NUM>-<NUM>. These different microphones transduce noise into noise data which may be analyzed to identify different noise source component locations due to operation of jet engine <NUM>. In these examples, the analysis may be made for candidate noise source locations and for different measurement points of interest. In these examples, the candidate noise source locations may lie along jet engine axis <NUM> and the measurement points of interest may correspond to the locations of the far field microphones <NUM>-<NUM>.

A similar setup may be made for other devices or noise sources. For example, for a highway with traffic, a laterally distributed region of potential noise sources is present. For the highway, various characteristics such as, for example, overpasses, intersections, and differing road surfaces, and other suitable features may be present. The measurement points of interest may be locations such as, for example, residences, city parks, businesses, and other suitable locations.

Microphones are present at the measurement points of interest to measure the overall noise at those locations. An array may be deployed between the candidate source region, the highway, and the points of interest to determine component breakdown of sources contributing to the overall noise at the points of interest.

In some embodiments the acoustic test system <NUM> may be introduced into the test environment <NUM> to control a plurality of vehicles <NUM>, each of which may comprise one or more sensors <NUM>. Referring to <FIG>, at operation <NUM> a plurality of vehicles <NUM> are positioned proximate a noise source, e.g., jet engine <NUM>. At operation <NUM>, the plurality of vehicles <NUM> are moved into a first configuration in a first location. By way of example, referring to <FIG>, in some embodiments control system <NUM> may control the plurality of vehicles <NUM> to move into a first predetermined configuration in a first predetermined location in which the acoustic sensors <NUM> form a first acoustic array having a first aperture size and a first spatial resolution. In the first predetermined configuration the plurality of sensors may be positioned in a first plane which may be different than the ground plane <NUM>.

At operation <NUM> the sensors <NUM> on the plurality of vehicles <NUM> collect noise data from the jet engine <NUM>. The noise data may be stored locally by the data collection system <NUM> and/or forwarded to the data acquisition system <NUM> via the communication system <NUM>.

At operation <NUM> the plurality of vehicles <NUM> are moved into a different configuration and/or location. By way of example, referring to <FIG>, the control system <NUM> may control the plurality of vehicles <NUM> to move from the first predetermined configuration into a second predetermined configuration in which the acoustic sensors <NUM> form a second acoustic array having a second aperture size and a second spatial resolution.

In some examples the control system <NUM> controls the plurality of vehicles <NUM> to move to a predetermined location in response to a signal, e.g., a signal from the control system <NUM>, or in response to an environmental condition such as rain, wind, a light condition, or the like. In some examples, the second predetermined configuration positions the plurality of sensors <NUM> in a plurality of planes such that the aperture is three-dimensional.

At operation <NUM> the sensors <NUM> on the plurality of vehicles <NUM> collect noise data from the jet engine <NUM> in the second configuration and/or location. The noise data may be stored locally by the data collection system <NUM> and/or forwarded to the data acquisition system <NUM> via the communication system <NUM>.

If, at operation <NUM> the acoustic test is not finished then control may pass back to operation <NUM> and the controller again moves the plurality of vehicles <NUM> into a different configuration and/or location. By way of example, referring to <FIG>, the control system <NUM> may control the plurality of vehicles <NUM> to move from the second predetermined configuration into a third predetermined configuration in which the acoustic sensors <NUM> form a third acoustic array having a third aperture size and a second spatial resolution and the data collection process continues.

By contrast, if at operation <NUM> the acoustic test is finished then control passes to operation <NUM> and the test is finished. Thus, the operations depicted in <FIG> allow the controller <NUM> to position the plurality of vehicles <NUM> in a variety of different positions and locations during an acoustic test. Reference in the specification to "one embodiment" or "some embodiments" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least an implementation. The appearances of the phrase "in one embodiment" in various places in the specification may or may not be all referring to the same embodiment.

Claim 1:
A system (<NUM>) for acoustic testing, comprising:
a plurality of acoustic sensors (<NUM>; <NUM>) mounted to a plurality of vehicles (<NUM>);
a control system configured to control the plurality of vehicles (<NUM>); and
a data acquisition system (<NUM>) configured to receive data generated by the plurality of acoustic sensors in response to noise from a noise source (<NUM>; <NUM>) proximate the plurality of vehicles;
wherein the control system is configured to control the plurality of vehicles to move (<NUM>) into a first predetermined configuration in a first predetermined location in which the acoustic sensors form a first acoustic array (<NUM>) having a first aperture size and a first spatial resolution; and
the control system is configured to control the plurality of vehicles to move (<NUM>) from the first predetermined configuration into a second predetermined configuration in which the acoustic sensors form a second acoustic array having a second aperture size and a second spatial resolution,
wherein the control system is configured to control the plurality of vehicles to move into a configuration in which the acoustic sensors form an array having locally non-redundant spacing such that no two vector spacings are the same,
wherein the plurality of vehicles (<NUM>) comprises a plurality of unmanned air vehicles to which the plurality of sensors are mounted, wherein the control system is configured to control the plurality of unmanned air vehicles to collect noise data from the noise source, wherein the noise source comprises an engine.