Systems, methods and apparatuses for detecting turbulence and wake-vortices and mangagement of flight navigation

Abstract

An apparatus is provided that includes an infrasound microphone for positioning in a soundscape containing turbulence such as may be caused by an aircraft within a radius of the microphone. The apparatus also includes a processor configured to receive an input waveform from the microphone and to perform a signature analysis on the input waveform. The processor is configured to configured to isolate features from the waveform. The isolated features can represent the turbulence. The apparatus may include an output device, such as an aircraft navigation system which can be controlled to update flight paths of other aircraft, based on the isolated features. Various other apparatuses, systems and methods are proposed.

Description

SYSTEMS, METHODS AND APPARATUSES FOR DETECTING TURBULENCE AND WAKE-VORTICES AND MANGAGEMENT OF FLIGHT NAVIGATIONBACKGROUND

[0001] Flight operations, whether in the proximity of airports or in high altitude cruising flight, can expose aircraft to wake turbulence, a potentially hazardous condition caused by vortices that trail behind an aircraft as it cuts through the air. Vortices can linger in the airspace for several minutes, posing significant risk to following aircraft, especially lighter ones. These wake-vortices can induce high-g forces, negative-g forces, rolling motions or cause sudden altitude changes, which can pose severe challenges to pilot control and compromise safety, particularly during critical phases of flight such as take-off and landing. Furthermore, turbulence encountered during cruising altitude can also be caused by a myriad of atmospheric conditions or jet streams and can impact passenger comfort and well-being, fuel efficiency, and flight safety. Hence, wake turbulence and airborne turbulence remain substantial obstacles in maintaining optimal aviation safety and operational efficiency.SUMMARY

[0002] An aspect of the specification provides an apparatus for turbulence detection including: an infrasound microphone for positioning in a soundscape containing turbulence within a radius of the microphone; a processor configured to receive an input waveform from the microphone and to perform a signature analysis on the input waveform; the processor further configured to isolate features from the waveform; the isolated features representing the turbulence; and, an output device connected the processor; the processor further configured to control the output device based on the isolated features.

[0003] An aspect of the specification provides an apparatus, wherein the processor is further configured to: obtain a Power Spectral Density (PSD) representation from the input waveform; convert the PSD representation into infrasound energy (E); generate a plot of the inverse power index (i) of the infrasound energy (E) against a progressive air distance flown; where the power index (i) is between about zero and about one. generate a linear regression based on the plot; and determine a zero-crossing point of the mean line obtained from the linear regression to indicate the distance to the turbulence.

[0004] An aspect of the specification provides an apparatus wherein the power index (i) is about 1 / 2.

[0005] An aspect of the specification provides an apparatus wherein the power index (i) is about 1 / 3.

[0006] An aspect of the specification provides an apparatus wherein the processor is further configured to estimate a value of the radius of the turbulence from the microphone.

[0007] An aspect of the specification provides an apparatus wherein the infrasound microphone is sensitive to a radius that is above, behind, on top, or underneath the turbulence, and further including an analog-to-digital converter for converting the input waveform into a digital waveform for the processor.

[0008] An aspect of the specification provides an apparatus wherein the processor is configured to isolate features, at least in part, based on determining sensed infrasound energy using a log-linear regressive fit that correlates turbulence with the regressive fit.

[0009] An aspect of the specification provides an apparatus wherein the processor is further configured to isolate features, at least in part, based on determining unsteady wind derived from an Eddy Dissipation Rate (EDR) and a radial distance from an origin of the turbulence.

[0010] An aspect of the specification provides an apparatus wherein the sensed infrasound energy is divided by the EDR to generate a first type of patches of data points that represent vortex turbulence that are larger than a second type of patches of datapoints that represent background atmospheric turbulence.

[0011] An aspect of the specification provides an apparatus wherein the controlling includes sending the features over an air traffic control (ATC) network that causes changes to flight navigation of aircraft with a predefined range of the turbulence.

[0012] An aspect of the specification provides an apparatus wherein the microphone includes a windshield.

[0013] An aspect of the specification provides an apparatus wherein the microphone and the windshield are disposed at one end of a tube, the tube having a tip opposite from the microphone, that protrudes from the nose-bay of an aircraft.

[0014] An aspect of the specification provides a method of controlling a navigation of an aircraft including: positioning in infrasound microphone in a soundscape containing turbulence; collecting infrasound sound waveforms from the soundscape at the microphone; converting the waveforms into an electronic waveform; analyzing, at a processor, the electronic waveform; isolating, at the processor, features from the electronic waveform representing the turbulence, including a location of the turbulence; and, controlling an output device based on the location.

[0015] An aspect of the specification provides a method wherein the output device is an aircraft flight control system and the controlling includes: receiving a flightpath for the aircraft; comparing the flightpath to the location of the turbulence; modifying the flightpath of the aircraft to avoid the turbulence; and, communicating the modified flightpath to the aircraft flight control system.

[0016] An aspect of the specification provides a method wherein the location is based on an estimate of the value of the radius of the turbulence from the microphone.

[0017] An aspect of the specification provides a method wherein the infrasound microphone is sensitive to a radius that is above, behind, on top, or underneath the turbulence.

[0018] An aspect of the specification provides a method further including an analog-to-digital conversion for converting the input waveform into a digital waveform.

[0019] An aspect of the specification provides a method wherein the isolating is, at least in part, based on determining sensed infrasound energy using a log-linear regressive fit that correlates turbulence with the regressive fit.

[0020] An aspect of the specification provides a method wherein the isolation is at least in part, based on determining unsteady wind derived from an Eddy Dissipation Rate (EDR) and a radial distance from an origin of the turbulence.

[0021] An aspect of the specification provides a method wherein the sensed infrasound energy is divided by the EDR to generate a first type of patches of data points that represent vortex turbulence that are larger than a second type of patches of datapoint that represent background atmospheric turbulence.

[0022] An aspect of the specification provides a method further including sending the isolated features over an air traffic control (ATC) network that causes changes to flightpaths of all aircraft with a predefined range of the turbulence.

[0023] An aspect of the specification provides a method wherein the microphone includes a windshield.

[0024] An aspect of the specification provides a method wherein the microphone and the windshield are placed disposed at one end of a tube, the tube having a tip opposite from the microphone that protrudes from the nose-bay of the aircraft.

[0025] An aspect of the specification provides a method, wherein the analyzing includes: obtaining a Power Spectral Density (PSD) representation from the analyzing of the electronic waveform; converting the PSD representation into infrasound energy (E); plotting the inverse square-root of the infrasound energy (E) against the progressive air distance flown by the aircraft; and, generating a linear regression based on the plot of the inverse square-root of E versus distance flown.

[0026] An aspect of the specification provides a method wherein the isolating includes: determining a zero-crossing point of the mean line obtained from the linear regression to indicate the distance to the turbulence.

[0027] An aspect of the specification provides a method, further including: repeating the collecting, converting, analyzing and isolating for a plurality of different directions of flight; calculating the direction of the disturbance based on the direction with the highest infrasound energy level.

[0028] An aspect of the specification provides a method, further including: receiving multiple infrasound sound waveforms from different directions relative to the aircraft's flight path; identifying the direction with the highest infrasound energy level based on the multiple waveforms; and determining the direction of the greatest turbulence threat based on the direction with the highest infrasound energy level.

[0029] An aspect of the specification provides an apparatus, wherein the infrasound microphone operates with a sampling rate of about 0.25 to about 4 KHz and a sampling period of about 0.5 to about 4 seconds.

[0030] An aspect of the specification provides an apparatus, wherein each infrasound microphone's sampling rate is preferably about 0.5 to about 2 KHz.

[0031] An aspect of the specification provides an apparatus, wherein each infrasound microphone's sampling period is preferably about 1 to about 3.33 seconds.

[0032] An aspect of the specification provides an apparatus, wherein the datasets collected from each infrasound microphone for analysis include about 500 to about 2000 data points.

[0033] An aspect of the specification provides an apparatus, wherein the datasets collected from each infrasound microphone preferably include about 600 data points.

[0034] An aspect of the specification provides a method, wherein each infrasound microphone in the system is configured to operate with a sampling rate of about 0.25 to about 4 KHz and a sampling period of about 0.5 to about 4 seconds.

[0035] An aspect of the specification provides a method, wherein each infrasound microphone's sampling rate is preferably about 0.5 to about 2 KHz.

[0036] An aspect of the specification provides a method, wherein each infrasound microphone's sampling period is preferably about 1 to about 3.33 seconds.

[0037] An aspect of the specification provides a method, wherein the datasets collected from each infrasound microphone for analysis include about 500 to about 2000 data points.

[0038] An aspect of the specification provides a method, wherein the datasets collected from each infrasound microphone preferably include about 600 data points.

[0039] An aspect of the specification provides an apparatus, wherein the processor is further configured to compute the infrasound energy EEE using a lower bound of integration between about 0.5 Hz and about 2 Hz, and an upper bound of integration between about 20 Hz and about 40 Hz.

[0040] An aspect of the specification provides a method, wherein the analyzing includes computing the infrasound energy EEE using a lower bound of integration between about 0.5 Hz and about 2 Hz, and an upper bound of integration between about 20 Hz and about 40 Hz.

[0041] An aspect of the specification provides an apparatus wherein the processor is further configured to detect and analyze the turbulence without Doppler compensation.

[0042] An aspect of the specification provides an apparatus wherein the processor is further configured to detect and analyze the turbulence with Doppler compensation.BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Various embodiments of the present invention will now be discussed, by way of example only, with reference to the attached figures, in which:

[0044] Figure 1 shows a first airplane and a second airplane in an example schematic prior art flying formation.

[0045] Figure 2 is the schematic illustration of a novel aircraft according to an embodiment.

[0046] Figure 3, shows microphone assembly 204 in context with nose-bay 208.

[0047] Figure 4 shows schematic representations of the engine and ACU.

[0048] Figure 5 is a flowchart which represents a method for turbulence detection.

[0049] Figure 6 shows a NASA 1.5 inch infrasound microphone, plumbed into a one-quarter inch metal line, intended to sense static pressure perturbations, via flush static port sensing from the outside surface of a carrier aeroplane or aircraft.

[0050] Figure 7 shows an infrasound microphone, plumbed installation layout in the nosebay.

[0051] Figure 8 shows an NRC CT133 with sensors

[0052] Figure 9 shows an infrasound microphone time-domain output signal, initial flights of the tube-plumbed installation in the NRC CT133.

[0053] Figure 10 shows a Power Spectral Density ("PSD") graph of the infrasound microphone output signal, 150 m / s TAS, 98% RPM, 5 km height.

[0054] Figure 11, shows an elevation (top) and planform (bottom) views of B77L intercept, with vortex core crossings highlighted, together the wake vortex flight line, from generation at the B77L.

[0055] Figure 12 shows a microphone output signal time-trace (abscissa is the ith point, where 600 points = 1 second of time interval), highlighting wake vortex core traverse.

[0056] Figure 13 shows spatial (left, in flightpath displacement, m)) and temporal (right, sec) distributions of vortex core traverse parameters.

[0057] Figure 14 shows distance separation between CT133 and trailing vortex origin (B77L)

[0058] Figure 15 shows examples of frequency domain PSD of I / F microphone output signal.

[0059] Figure 16 shows a first radial plot of infrasound energy.

[0060] Figure 17 shows a second radial plot of infrasound energy.

[0061] Figure 18 is a bubble plot of infrasound energy magnitude.

[0062] Figure 19 shows examples of infrasound interference patterns for about 2.5 Hz and about 5 Hz.

[0063] Figure 20 shows examples of infrasound interference patterns for about 10 and about 20 Hz, for two acoustic sources, namely port and starboard line vortices, invariant axially.

[0064] Figure 21 shows a timetrace of microphone output signal (mV, ordinate) for an A333 wake vortex infrasound sensing with no windscreen foam inserted and about 10,000 mV was signal saturation.

[0065] Figure 22 shows A333 wake vortex infrasound sensing for the same flight as Figure 21.

[0066] Figure 23 shows a crossplane [x y] (metres) position 'bubble' plot of infrasound energy of about 2 to about 10 Hz.

[0067] Figure 24 shows a vortex distance plot of sensed infrasound energy, illustrating a high maximum value, concurrent with CT133 maneuvering.

[0068] Figure 25 shows a CT133 maneuver effect (bank angle in level flight) upon microphone signal power PSD DC component value.

[0069] Figure 26 shows an I / F signal and associated state parameters during a B77W wakevortices 112 intercept.

[0070] Figure 27, I / F signal expanded timetrace during a B77W wake vortex survey.

[0071] Figure 28 shows typical PSD of the I / F output signal, when following a B77W, about 2,000 feet below its trailing vortex pair.

[0072] Figure 29 shows infrasound energy obtained by integrated PSD from about 1 to about 36 Hz (plenum sensing).

[0073] Figure 30 shows a Table summarizing certain intercepts.

[0074] Figure 31 shows, background atmospheric conditions in the form of wind.

[0075] Figure 32 shows, background atmospheric conditions in the form of stratification (left) and eddy dissipation rate (right).

[0076] Figure 33 shows, background atmospheric conditions in the form of air temperature sounding (met balloon and CT 133).

[0077] Figure 34 shows intercept geometry.

[0078] Figure 35 shows a B789 vortex distance plot of infrasound energy (with CT133 estimated maneuver effect removed), with log-linear mean lines of regression included.

[0079] Figure 36 shows A333 (DLH426) intercept geometry (with B777-300ER (flight KAL082) flying cross-track.

[0080] Figure 37 shows A333 (DLH426) infrasound energy

[0081] Figure 38 shows CT133 intercept of the B77W.

[0082] Figure 39 shows background atmospheric conditions during B77W intercept.

[0083] Figure 40 shows a trailing wake vortex core crossing.

[0084] Figure 41 shows a 3 inch microphone output signal PSD during a vortex core interaction.

[0085] Figure 42 shows sequential PSDs, radial distance of each from the trailing wake vortex pair centreline: red, B77W (minimum approach distance about 9 km), blue, CT133.

[0086] Figure 43 shows, (left) infrasound energy (PSD integrand 0.6-46 Hz) plot via vortex separation distance; (right) EDR magnitude by wake vortex separation distance.

[0087] Figure 44 shows B744 intercept: left top, vertical flight profile, CT133, left bottom, I / F mic.

[0088] Figure 45 shows background atmosphere.

[0089] Figure 46 shows a microphone output signal PSD.

[0090] Figure 47 shows a timetrace of sensed infrasound energy, B744 wake vortex generator.

[0091] Figure 48 shows sensed FF energy, by radial distance from the trailing vortex pair centreline.

[0092] Figure 49 shows sensed FF energy, log-linear, by radial distance from the trailing vortex pair centreline.

[0093] Figure 50 shows an unsteady wind derived EDR from in-situ turbulence.

[0094] Figure 51 shows a ratio of I / F ENERGY (microphone output PSD integrand) to the in situ EDR.

[0095] Figure 52 shows a B789 and CT133 intercepts flights.

[0096] Figure 53 shows a B789 and CT133 intercepts flights.

[0097] Figure 54 shows a B789 wake vortex infrasound survey - typical microphone output signal PSD.

[0098] Figure 55 shows a B789 and CT133 survey.

[0099] Figure 56 shows a B789 survey - infrasound energy (PSD integrand, 1-46 Hz) by vortex-centreline or origin.

[0100] Figure 57 shows a B789 survey - infrasound energy (PSD integrand, 1-46 Hz) by vortex wake length.

[0101] Figure 58 shows a flowchart depicting a method of turbulence detectionDETAILED DESCRIPTION

[0102] Referring now to Figure 1, a first airplane 100-1 and a second airplane 100-2 are shown in an example schematic prior art flying formation. (Note that first airplane 100-1and second airplane 100-2 are referred to, collectively, as airplanes 100 and generically, as airplane 100. This nomenclature is used elsewhere herein.)

[0103] Airplane 100-1 is shown flying behind the wake 104 of airplane 100-2. Airplane 100-2 is shown generating turbulence 108 within wake 104. Wake turbulence 108 creates wake-vortices 112 which are a risk to the safe operation of airplane 100-1 during passage through wake-vortices 112. The strength of the wake turbulence 108 and wake-vortices 112 are influenced by the weight and speed of the airplane 100-2. Thus, where airplane 100-2 larger and heavier relative to airplane 100-1, then airplane 100-1 may experience the effects of stronger wake turbulence 108.

[0104] Referring now to Figure 2, the schematic illustration presents a novel aircraft 200 according to an embodiment. In Figure 2, aircraft 200 is an airplane, but in other embodiments, aircraft may be a helicopter, drone, glider, dirigible, ultra-light, weather balloon or the like. As will be explained in further detail below, aircraft 200 is configured to avoid wake-vortices 112. In Figure 2, aircraft 200 is shown with a microphone assembly 204 mounted to the nose-bay 208. Microphone assembly 204 is shown connected to a computing engine 212 disposed within an avionics compartment 216 of aircraft 200 that can be located anywhere within aircraft 200 that is suitable for any other aeronautical engineering parameters of aircraft 200, but is typically under the cockpit 220 and behind nose-bay 208 and co-located with an ACU 224, which can include engine controls, flight control systems, navigation, communications, flight recorders, lighting systems, threat detection, fuel systems, electro-optic (EO / IR) systems, weather radar, performance, and other functions. (ACU 224 is short for “avionics control unit”). Accordingly, computing engine 212 is in communication with ACU 224 and may be incorporated directly into ACU 224.

[0105] Referring now to Figure 3, microphone assembly 204 is shown in greater detail as a schematic representation in context with nose-bay 208. Microphone assembly 204 includes a tube 304 whose tip 306 can protrude from nose-bay 208 towards the front of aircraft 200. Tube 304, can be about two inches in length. A presently preferred protrusion distance from nose-bay 208 is about one inch. Tube 304 has a rear-facing snape at an angle of about forty- five degrees. The amount tip 306 protrudes can be a function of balancing aerodynamic performance, risks of damage to tube 304, and the ability of microphone assembly 204 to collect data about turbulence 108. . In general, tip 306 can protrude from any reasonablelocation at any reasonable length on aircraft 200 that permits collection data about turbulence 108, but the front of nose-bay 208 is presently preferred.

[0106] A microphone 308 is disposed at the end of tube 304 that is opposite from tip 306. Microphone 308 includes a transducer 312 covered with a windshield 316. Windshield 316 can be made of foam or any other material that can absorb or filter unwanted sound, such as sound that is merely generated as a result of air coming into contact with tip 306 or tube 304 itself. In a present embodiment, microphone 308 is sensitive to infrasound, meaning that it can be called an infrasound microphone 308 that has a transducer 312 capable of detecting extremely low frequency sound waves, generally below the threshold of human hearing, typically less than about twenty hertz (about 20 Hz). Transducer 312, in turn, connects to computing engine 212.

[0107] Transducer 312 can be based on infrasonic microphones produced by PCB Piezotronics, 425 Walden Avenue, Depew, NY 14043-2495, which when used on aircraft 200 as part of microphone assembly 204, can have a diameter of about four centimeters. Larger diameters can also be used such as those about eight centimeters. Diameters will be discussed in greater detail below.

[0108] Tube 304 thus collects sound waveforms 320 from the soundscape 324 in front of nose-bay 208. Waveforms 320 are presented to transducer 312 and converted into analog infrasound electronic signals 326 for processing by computing engine 212.

[0109] As shown in Figure 3, the waveforms 320 of soundscape 324 may include leading-edge waveforms 328 from the wavefront of turbulence 108. It can be noted that leading-edge waveforms 328 may not be noticeable to a human or otherwise impact operation of aircraft 200, but can be a precursor to turbulence 108 and associated wake- vortices 112 which can seriously impact the aircraft 200. To elaborate, leading-edge waveforms 328 may be present when, for example, another airplane 100 (such as airplane 100-2, but not shown in Figure 3) is in front of aircraft 200 and, as previously discussed, generating turbulence 108.

[0110] Figure 4 shows schematic representations of engine 212 and ACU 224. Engine212 includes at least one input device which in a present embodiment includes an analog-to- digital converter 404. (In variants, other input devices are contemplated, such as a keyboard local to engine 212 within avionics compartment 216 for local configuration of computingengine 212.) Input from analog-to-digital converter 404 is received at a processor 408. In variations, processor 408 can be implemented as a plurality of processors.

[0111] Processor 408 can be configured to execute different programing instructions that can be responsive to the input received via the one or more input devices. To fulfill its programming functions, processor 408 is configured to communicate with at least one nonvolatile storage unit 412 (e.g., Erasable Electronic Programmable Read Only Memory (“EEPROM”), Flash Memory, Hard-disk) and at least one volatile storage unit 416 (e.g., random access memory (RAM)). Programming instructions (e.g. applications 420) that implement the functional teachings of engine 212 as described herein are typically maintained, persistently, in non-volatile storage unit 412 and used by processor 408 which makes appropriate utilization of volatile storage unit 416 during the execution of such programming instructions. Non-volatile storage unit 412 and volatile storage unit 416 may be considered non-limiting examples of computer readable media configured to store programming instructions for execution by a processor 408.

[0112] Processor 408 in turn is also configured to control an output device 428 and any other output devices (not shown) that may be provided in engine 212, also in accordance with different programming instructions and responsive to different input received from the input devices. For example, output device 428 could be a display local to engine 212 within avionics compartment 216 for local configuration of computing engine 212.

[0113] Processor 408 also connects to a network interface 432 for connecting to network 436. Network interface 432 can thus be generalized as a further input / output device that can be utilized by processor 408 to fulfill various programming instructions.

[0114] Network 436 can be a bus that connects to other electronics and devices within aircraft 200 and avionics compartment 216. Network 436 can also include wireless connection to another communication network 438 such as the Internet and / or air traffic control (ATC) that interconnects aircraft 200 with other aircraft (of all types, including airplanes) to manage safe and efficient movement of aircraft around the globe.

[0115] In a present embodiment, engine 212 is configured to maintain, within nonvolatile storage unit 412, datasets 424 and applications 420. Datasets 424 and applications 420 can be pre-stored in non-volatile storage unit 412 or downloaded via network interface 432 and saved on non-volatile storage unit 412. Processor 408 is configured to execute applications420, which accesses datasets 424, accessing non-volatile storage unit 412 and volatile storage unit 416 as needed. As noted above, and as will be discussed in greater detail below, processor 408, when executing applications 420,

[0116] ACU 224 includes a general architecture that is similar to engine 212, although ACU 224 would include significantly more computing resources (e.g. more memory, faster processor). Thus, ACU 224 also includes a processor 440 that interconnects one or more input devices 444 for controlling one or more output devices 446. At least one non-volatile storage unit 452 and at least one volatile storage unit 456 are available to processor 440. Applications 458 and tables 462 support the functions of processor 440. Network interface 466 connects processor 440 to network 436. ACU 224 can thus connect to, and effect control over, various aircraft systems 448 including flight control aircraft system 448-1, landing gear aircraft system 448-2, fuel aircraft system 448-3 and a plurality of other possible aircraft systems 448-n. Certain applications 458 and / or tables 462 can be respective to each system 448.

[0117] Referring now to Figure 5, a flowchart is provided which represents a method 500 for turbulence detection. Method 500 can be performed using engine 212 combined with assembly 204. It is to be understood, however, that method 500 can be performed on variants of engine 212 and / or assembly 204, even though the following discussion will make specific reference to engine 212 and microphone assembly 204. Furthermore, method 500 itself can be modified, in that according to desired implantation certain blocks may be omitted, or performed in parallel, or the order of performance may vary.

[0118] Block 504 comprises positioning a transducer in a soundscape. In general terms, block 504 comprises finding a location where it is desired to determine the presence of turbulence and / or wake-vortices. In the context of our specific (but non-limiting) example, aircraft 200, as equipped with microphone assembly 204 and engine 212, is flown into an airspace where turbulence 108 or wake-vortices 112 may be present. As shown in Figure 3, tube 304 is thus immersed in soundscape 324 during the flight of aircraft 200 and waveforms 320 can be collected. Aircraft 200 may be flown in various directions relative to turbulence 108, including, head-on towards, above, behind, or underneath turbulence 108 and the actual aircraft (such as airplane 100-2 that generated turbulence 108) that left wake 104 that caused turbulence 108.

[0119] Block 508 comprises obtaining an analogue sound sample from the soundscape. Continuing with our specific example in Figure 3, waveforms 320 are collected within tube304, which come into contact with transducer 312 as filtered by windshield 316 to mitigate pure wind noise. Transducer 312 in turn, converts waveforms 320 into analog electronic signals 326 for delivery to engine 212. It is presently preferred that transducer 312 captures infrasound electronic signals. Again, block 508 can be varied according to the structure of microphone assembly 204, and a person of skill the in art will appreciate such variations.

[0120] Block 512 comprises converting the analogue signal into a digital signal. In general terms, the analogue signal captured at block 508 is sampled. In a present embodiment, the conversion is of the infrasound analogue signal into a digital format. Also in a present embodiment, the format is a frequency domain format rather than a time domain format. Where analog infrasound electronic signals 326 are infrasound signals, the sampling rate will typically be according to a desired level of fidelity as will occur to those skilled in the art, such as about twice the rate of the highest infrasound signal, typically about twenty hertz, such that the sample rate will be about forty hertz. In variations, time domain analysis may be contemplated.

[0121] Block 516 comprises analyzing the digital signal. The means for such analysis are not particularly limited, and further in this specification several examples of specific tests and results are produced. However, in very general terms, block 516 can comprise determining the infrasound energy within the signal from block 512. The infrasound energy can be expressed in terms of a power spectral density (PSD) integrand. Spatial plots can also be determined by ascertaining non-monotonic rises in the sensed infrasound energy.

[0122] As noted microphone assembly 204 may be positioned anywhere radially proximal to turbulence 108, including in front, above, behind or underneath. Furthermore, since aircraft 200 is moving, the signals analyzed at block 516 can be varying according to the movement and maneuvering of aircraft 200. Thus, the analysis at block 516 can vary according to the positioning and movement of the transducer at block 504.

[0123] Block 520 comprises identifying vortices. Block 520 can be based on thresholds or other types of feature extractions within the data analyzed at block 516. Where leading-edge waveforms 328 of turbulence 108 have been received at block 508 as part of waveforms 320, then infrasound energy of leading-edge waveforms 328 will can be used to identify wake-vortices 112. Furthermore, the nature of leading-edge waveforms 328 can be used to a infer a distance between aircraft 200 and turbulence 108.

[0124] The identification at block 520 can also include detection of infrasound interference patterns, which can rise and fall in relation to the spatial position between aircraft 200 and turbulence 108.

[0125] Block 516 and Block 520 and certain possible variants will be discussed in greater detail below.

[0126] Block 528 comprises controlling an output device. The type of control at block 528 is not particularly limited and can be based on the analysis at block 516 and / or the identification of at block 520. As one example, block 528 can comprise making adjustments to one or more of the aircraft system 448 in order to reduce the likelihood of aircraft 200 coming into contact with turbulence 108. Indeed, flight control system 448-1 can have signals directed thereto to adjust the course for aircraft 200 to avoid the turbulence 108. In addition, or in the alternative, block 528 can comprise having engine 212 or ACU 224 send a communication message over communication network 438 such that the broader ATC can be informed of the location of turbulence 108 and to cause a course adjustments for a plurality of aircraft that are in the vicinity of turbulence 108. In addition, or in the alternative, warnings can be presented to pilots or air traffic controllers on their display screens to prompt manual intervention.

[0127] It should also be noted that all of the data collected by engine 212 can be aggregated with other engines that collect and analyze similar data. In this fashion, broader patterns of aircraft navigation and turbulence 108 can be understood, leading to generation of modern flight paths that inherently reduce the likelihood of one aircraft experiencing the turbulence 108 of another. Machine learning techniques can be used by comparing flight paths that have fewer interactions involving turbulence 108 than those flight paths that have greater interactions involving turbulence 108. Such a machine learning technique can be used to assist in generating flights paths with reduced risks of interactions involving turbulence 108 between aircraft.

[0128] Block 532 thus comprises determining if further analysis is required, in which case method 500 reverts back to block 504 and the process continues to loop. A No determination at block 532 leads to the end of method 500.

[0129] Referring again to block 516 and block 520, as discussed below, the inventors have conducted extensive research into wake-vortices 112 using equipment based on engine212 and microphone assembly 204. Such research can be used by persons of skill in the art to effect programming instructions to fulfill block 516 and block 520.

[0130] Indeed, certain teachings herein, especially applicable to block 516 and block 520, were based on a National Research Council (NRC) flight research project in collaboration with the National Aeronautics and Space Administration (“NASA”) and, separately, Air Canada, to investigate and measure the sensing of transport aircraft wake vortex flow-fields, using NASA Infrasound (I / F) sensing Microphones. These teachings also encompass many variants to the specific embodiments described herein, as will be appreciated by persons skilled in the art.

[0131] The project involved the installation of 1.5-inch and 3-inch infrasound microphones in the nose-bay of the NRC CT133 research jet. In turn, they were plumbed to static port lines, and left open, for nose-bay plenum sensing.

[0132] Microphone signals were obtained and recorded, during flight against the trailing wake vortices from air transport jets, under a variety of encounter geometries. Signals were mostly analysed in the frequency domain, although time domain modelling was used to identify infrasound wave interference patterns.

[0133] Certain flight data and analyses are presented herein.

[0134] Under a collaborative research, the NRC installed NASA miniature infrasound microphones upon the NRC CT133 research jet and flew them against a variety of Heavy Jet transport wake vortex flowfield and encounter geometries.

[0135] The measured infrasound microphone signals were analysed, notably in the frequency domain, against the principal parameter of distance from wake vortices.

[0136] Since early tower flyby flight studies of trailing wake vortices from jet transport aircraft, wake turbulence separation standards have become a necessary and integral part of air transport operations, departure, enroute and arrival / landing. Nevertheless, occasional wake vortex encounters (WVE) have occurred, at times resulting in injuries or aircraft damage and occasionally being part of catastrophic accident sequences.

[0137] Although advances in the modelling of wake vortex behaviour have been made, WVE avoidance requires remote sensing of wake vortex positions. LiDAR, SODAR and RADAR have been variously applied, in research projects, to the sensing of wake vortices,with mixed success. There has not emerged a particular sensing technology, with a clear development path through to transport aircraft deployment.

[0138] Further context is found in Hardin, J. C. and Wang, F. Y., “Sound Generation by Aircraft Wake Vortices”, NASA / CR-2003-212674 December 2003, Hardin and Wang reopened the suggestion that the tracking of infrasonic emissions would serve as a means of tracking the life span of a shed wake vortex. See also Shams, Q., Zuckerwar, A. J., Burkett, C. G., Weistroffer, G. R., “Experimental investigation into infrasonic emissions from atmospheric turbulence,” The Journal of the Acoustical Society of America 133, 1269 (2013); https: / / doi.Org / 10.1121 / l.4776180.

[0139] Figure 6 shows a NASA 1.5 inch infrasound microphone, plumbed into a one- quarter inch metal line, intended to sense static pressure perturbations, via flush static port sensing from the outside surface of a carrier aeroplane or aircraft. (Again, the example of microphone 308 in Figure 6 is an example and other microphones are contemplated.) As part of the research, they were installed upon the National Research Council (“NRC”) CT133 research jet, for acquiring infrasound flight data, emitted by the wake vortices of large transport jet, flying in the upper troposphere. Using the CT133, the NRC has undertaken wake vortex characterisation flight research since 2006. (See Brown, A. P., “Flight data of axial flows in wake vortex instability,” 8th AIAA Atmospheric and Space Environments Conference, AIAA AVIATION Forum, 13-17 June 2016, Washington, D.C., https: / / doi.org / 10.2514 / 6-2016- 3435; and Brown, A. P., Ovenden, M., Bastian, M., “ A Flight Study of Unsteady Aerodynamic Loading Induced by Wake Vortex Encounter,” 2018 Atmospheric and Space Environments Conference, AIAA AVIATION Forum, June 25-29, 2018, Atlanta, Georgia, https: / / doi.org / 10.2514 / 6-2018-3023 and Brown A.P., “ Unsteady Aerodynamic Loading from Parallel-vortex Interaction with a Lifting Wing,” AIAA Aviation 2019 Forum, 17-21 June 2019, Dallas, Texas, https: / / doi.org / 10.2514 / 6-2019-3181)

[0140] A variant of the microphone in Figure 6 is a three inch microphone, of approximately twice the diaphragm sensitivity as the microphone of Figure 6, in the infrasound regime (with an integrated signal processor, accommodated in the base of the microphone housing).

[0141] Microphone 308 can be installed in two ways:

[0142] (i) Plumbed to a nominal one-quarter inch diameter stainless steel tube, connected either side, to the brass mating tube, shown in Figure 6; the tube was the exhaust sample flow line to the Licor CO2 and water vapour sensor; the line terminated at a flush static port on the left side of the aircraft nosebay; and

[0143] (ii) Open plenum sensing in the unpressurised nosebay

[0144] Figure 7 shows an infrasound microphone, plumbed installation layout in the nosebay 208 of an NRC CT133 aircraft 200, bracket mounted to the top of the Licor analyser enclosure. The plumbed installation in the nosebay of the CT133 is depicted in Figure 7.

[0145] The output of the microphone 308 installations was a +5 volts DC analogue signal, which was connected serially to analog-to-digital converter 404 on the airdata Data Recorder Processor (DRP). The digitised signal was sampled and recorded at about 600 Hz, the same sampling frequency as the inertial and airdata for the aircraft.

[0146] Infrasound frequency range of interest was about 0 to about 20 Hz. However, WVE geometries, at times, included substantial Doppler shift, to a shifted frequency range of about 0 to about 60 Hz. The about 600 Hz sampling adequately covered the ranges of interest,

[0147] the microphones experienced saturation, principally from higher frequency boundary layer acoustics and engine airflow acoustics. To mitigate saturation, 1-2 cm lengths of microphone windshield 316 open-cell foam were inserted in the tube, at the coupling between brass tee and the stainless steel tube, connecting the flush static port. The windshield 316 foam pieces, being open-cell, enabled pressure equalisation from the static port to the microphone sensing chamber near transducer 312.

[0148] The NRC CT133 aircraft 200 is shown with sensors, in the HAARC Civil Aviation Wake Turbulence Sensing Flight Research (“CAWTSFR”) configuration, in Figure 8. In particular, the underwing pods were installed for all CAWTSFR flights.

[0149] For the analysis of microphone infrasound data, aircraft position, orientation, angular displacement, rates and linear velocities, were measured and recorded by the aircraft inertial system. Airdata was used to derive instantaneous wind and determine wake vortex location. From this, the radial / longitudinal distance from the wake vortex pair and vortex origin, respectively, was derived. The distance separation, whether in the longitudinal or vortexcrossplane, was used as the principal correlative parameter for infrasound analysis. For Doppler determination, crossplane velocity, with respect to the wake vortex centre, was used.

[0150] CT133 HAARC sensors are described in Table 1. The Cabin PressureController (“CPC”) was coupled with a denuder for non-volatile classification of ultrafine particles. By valve switching, the denuder could be bypassed (providing a measure of total ultra-fines) or it could be switched in-line, upstream of the CPC and thus enabling a measure of non- volatiles. Typically, the denuder was sequentially operated in bypass for two minutes, thence in-line for approximately the same period.

[0151] Table 1 - NRC CT133 emissions and contrails measurement instrumentation

[0152] The list of CAWTSFR flights is presented in Table 2. As seen below, the flights were divided as follows:

[0153] (i) 1.5 in.Microphone functional flight assessments - output signal saturation (full scale outputs of +10,000 mV, with sensitivity to engine RPM (airflow noise) and to nosebay boundary layer noise (TAS effect);

[0154] (ii) 1.5 in. Mic with in-tube attenuating microphone windshield foam, attenuated by 90%, still retaining good sensitivity;

[0155] (iii) 1.5 in. Mic, open to nosebay plenum (not plumbed to the flush static port); and

[0156] (iv) 3.0 in. Mic with in-tube attenuating microphone windshield foam.

[0157] A variety of intercepts was conducted, including stern conversions, head-on passes, slow overtakes, and orthogonal crossings, with both climbs and descents into the wake vortex cores.

[0158] Table 2 - CAWTSFR flight details00159] Initial investigatory flights were three in number. The first did not include flight through any wake vortex cores. The second and third flights included vortex core traverses.

[0160] Figure 9 shows an infrasound microphone time-domain output signal, initial flights of the tube-plumbed installation in the NRC CT 133. Microphone output signal sensitivity to engine RPM and flight TAS in particular was observed. A typical timetrace response of the microphone is shown in Figure 9, on this occasion takeoff ground and flight phases, followed by low / mid-altitude climb. In this case, the effect of engine RPM (advancingto takeoff thrust, 99.5%, followed by cut-back to climb thrust, 98%), was mostly responsible for saturating the microphone output signal.

[0161] Figure 10 shows a Power Spectral Density (“PSD”) graph of the infrasound microphone output signal, 150 m / s TAS, 98% RPM, 5 km height. The output signal PSD in climb at 98% RPM and 150 m / s TAS is shown in Figure 10. The signal had essentially constant acoustic modal power between de and about 70 Hz, beyond which roll-off in frequency response is observed.

[0162] The saturation was attenuated, by the insertion of a windshield 316 microphone windscreen foam in the signal input tube 304, adjacent to the microphone 308. About a one cm length of rolled and helically inserted into the tube 304, adjacent to the microphone connection tee. The foam was standard microphone windscreen open-cell foam (generally fitted in a spherical sheath over the grills of outdoor microphones, in order to reduce the acoustic hiss or howl from the passage of the wind over the microphone 308)).

[0163] With foam installed, flight included an intercept of a B77L (B777-200LR) and several wake vortex core traverses. The intercept was conducted as a stern conversion from below. The elevation and planform plots of the intercept are shown in Figure 11. Figure 11 , shows an elevation (top) and planform (bottom) vies of B77L intercept, with vortex core crossings highlighted, together the wake vortex flight line, from generation at the B77L.

[0164] With a data acquisition rate of about 600 Hz and an opening distance rate of about 3 nautical miles per minute, the decaying vortices had a mean descent rate of about 15 m / min (wake length approximately about 10 to about 23 nautical miles).

[0165] Figure 12 shows microphone output signal 326 time-trace (abscissa is the ith point, where 600 points = 1 second of time interval), highlighting wake vortex core traverse. The windscreen foam-dampened 3 in. microphone timetrace response is shown in Figure 12. It is seen that the windshield 316 foam attenuated the microphone output by approximately one decade of magnitude.

[0166] Figure 13 shows spatial (left, in flightpath displacement, m)) and temporal (right, sec) distributions of vortex core traverse parameters: wC, wA and wZ crossplane, axial and vertical vortex-wind components (m / s), PS unsteady air pressure (hPa), I / F microphone (mV / 100). Full-scale output was almost achieved during a wake vortex core crossing as can be seen in Figure 13. It is seen that the response of the microphone mirrors, hence correlates with,the magnitude of the vortex-induced wind components. However, no optimization of the windscreen dampening foam was undertaken. Thus, it was possible that the foam windshield 316, whilst mitigating saturation, may also have diminished microphone 308 sensitivity in the infrasound range.

[0167] Figure 14 shows distance separation between CT133 and trailing vortex origin (B77L) when ahead of the B77L, or radial distance separation between CT33 and trailing line vortices (centreline of the vortex pair) when following the B77L, after being overtaken by it.

[0168] Figure 14 shows the re-constructed distance of the CT133 from the lateral centreline of the trailing wake vortex pair. It is seen that the intercept started with the CT 133 about 70 km ahead of the B77L. Following the base turn and overtake of the B77L, the separation distance was that between the CT133 and the trailing vortices (which were line vortices) centreline, with the closest point being 10 m from the centreline (i.e. when the CT133 traversed through either the port or starboard trailing vortex core, of about lateral separation 20 m between them).

[0169] Figure 15 shows examples of frequency domain PSD of PF microphone output signal. Figure 15 presented frequency-domain examples of the I / F microphone output signal PSD. It is seen that spectral power was reasonably flat from about 0 to about 100 Hz, beyond which it rolled-off at an approximate rate of about 2 to about 4 decades of power per frequency decade.

[0170] The Figure 12 timetrace example illustrated that microphone output signal altered dramatically, only near the locations of wake vortex core traverses. Therefore, in order to analyse a distance-from-vortex microphone response relationship, frequency domain analysis of the output signal was conducted.

[0171] Examples of frequency domain PSD are shown in Figure 15, for various radial distances from the trailing vortex pair centreline. The integrand of the curves, with respect to frequency, f (abscissa), is the sensed acoustic energy. Therefore, integrating from a lower bound of the minimum frequency applicable to data sampling rate, to an upper infrasound boundary of about 20 Hz for example (adjusted upwards, where appropriate, to account for the Doppler effect whilst radial velocity towards the vortex centreline was greater than about zero), resulted in an integrand that represented the total infrasound energy sensed by the microphone.

[0172] Figure 16 shows a first radial plot of infrasound energy (i.e. PSD integrand) plots for lower frequency bound of about 0.6 Hz, and upper frequency bounds of about 28 Hz in a B77L aircraft.

[0173] Figure 17 shows a second radial plos of infrasound energy (i.e. PSD integrand) plots for lower frequency bound of about 0.6 Hz, and upper frequency bounds of about 48 Hz in a B77L aircraft.

[0174] An example (for the B77L wake vortex intercept and survey - including core crossings - of Figure 12), with a lower frequency bound of about 0.6 Hz, and two different upper frequency bounds of about 28 Hz and about 48 Hz, respectively, is shown in Figure 16 and Figure 17.

[0175] Firstly, for this wake vortex sensing survey, for the higher upper bound of frequency, about 48 Hz, c.f. (carrier frequency) 28 Hz, the integrand was approximately about 15 to about 20% greater, in spite of the near-doubling in frequency upper bound. This implies the majority of energy is infrasound, i.e. low frequency.

[0176] In magnitude, the sensed infrasound energy increased with reducing radial distance from the trailing vortex pair centreline. Note that, ahead of the B77L, radial distance is hemispherical; once overtaken by the B77L, the radial distance is cylindrical. The expected acoustic propagations would be similar - ahead of the B77L, rounded conical (accounting for the B77L TAS effect), behind the B77L, cylindrical. Ahead of the B77L

[0177] In shape, the infrasound energy maxima were non-monotonic, i.e., there were several peaks, with valleys between, as radial distance decreased - seen to have been, about 3 km, about 1 km, about 600 m, about 100 m and about 50 m.

[0178] Figure 18 is a bubble plot of infrasound energy magnitude. In the vortex crossplane (i.e., plane orthogonal to the trailing vortex pair axis); abscissa is lateral distance from vortex pair centreline (m); ordinate is vertical distance from vortex pair height (m). Expressed in other words, in Figure 18, in the plane orthogonal to the vortex centreline, a bubble plot of infrasound energy is shown. This plot accentuated the non-monotonic rise in sensed infrasound energy (i.e., locally larger ‘bubbles’). It highlighted that the largest sensed infrasound energy was in the immediate vicinity of the trailing vortex pair. In searching for an explanation for the non-monotonic behaviour of sensed infrasound energy with radial distance, acoustic propagation patterns were simulated.

[0179] Inflight, a trailing pair of vortices initially develop from the shedding of bound vorticity that constitutes the aerodynamic lift generated on the aircraft. The sheet of vorticity, shed at the wing trailing edge, rapidly rolls-up into such a pair of trailing vortices, with opposite signs of vortex strength, T (m2 / s). However, formation occurs in an adverse axial pressure gradient. Furthermore, mutual elliptical induction and down-draughting occurs immediately upon line vortex formation (within several wingspans behind the generating aircraft).

[0180] The effects of these phenomena upon vortex core state and hence tangential, radial and axial velocity distributions is first order and complex. For example, NRC research flights have regularly captured core radii variations (contractions and expansions), core venting (resulting in annular vorticity concentration), circumferential discretization of vorticity.

[0181] The result of these phenomena is that the nature of acoustic generation would also be axially-varied and complex. For example, for a vortex separation of about 20 m, it could be expected that elliptical instability, by varying tangential velocity about +17%, with possibly a similar variation in about IP frequency of acoustic generation.

[0182] Nevertheless, for the purposes of examining acoustic interference between the port and starboard trailing vortices, simple two-dimensional radial propagation are initially investigated.

[0183] Figure 19 shows examples of infrasound interference patterns for about 2.5 Hz and about 5 Hz. Figure 20 shows examples of infrasound interference patterns for about 10 and about 20 Hz, for two acoustic sources, namely port and starboard line vortices, invariant axially. In the upper troposphere, at an air temperature of about -55°C, the propagation speed of sound is about 296 m / s. Thus, under the assumption of two identical, constant discrete frequencies, for example about 2.5, about 5, about 10 and about 20 Hz, as presented in Figure 19 and Figure 20.

[0184] In Figure 19 and Figure 20, vortex separation has been varied (about 36 m or about 48 m) to exemplify the range of acoustic interference patterns. It should be noted that vortex separation also regularly varies, under the action of long-wave instability, a mutual instability mode of vortex attraction and repulsion, which can spatiotemporally grow to the point of port and starboard vortex linking.

[0185] For about 2.5 Hz, and about 36 m source (vortex) separation, the radial distribution of acoustic waves largely combine, so that the ‘clocking’ variation is relativelyminor (i.e., the superimposed waveforms have peaks and troughs, varying somewhat in magnitude, but propagating circularly.

[0186] For the other frequencies, the ‘clocking’ variations are substantial. For about 5 Hz, there is negligible wave amplitude propagated at about 3 and about 9 o’clock, and doubleamplitude propagated at about 6 and about 12 o’clock. For about 10 Hz, about 3, about 6, about 9 and about 12 o’clock have double amplitude propagation, but for about 3 and about 6 o’clock, the interference-beat spatial period was very large, so that the spatial variation rate would be very low; about 5 and about 7 o’clock have substantially zero infrasound amplitude at this frequency. For about 20 Hz, there was substantially zero infrasound amplitude, except between about 5 to about 7 and about 11 to about 1 o’clock.

[0187] Therefore, these interference patterns, for at least some acoustic propagation models, being circular, from a pair of axially-invariant trailing line vortices, provides insight into why the infrasound energy, as measured, is non-monotonic with radial distance from vortex centreline (such as in Figure 16 and Figure 17).

[0188] As another example, we consider an A333 interception and survey. Figure 21 shows a timetrace of microphone output signal (mV, ordinate) for an A333 wake vortex infrasound sensing with no windscreen foam inserted and about 10,000 mV was signal saturation. Windscreen foam for windshield 316 was not yet inserted in the static port tube 304. Nevertheless, saturation was somewhat limited on this wake vortex survey, as shown in Figure 21.

[0189] Figure 22 shows A333 wake vortex infrasound sensing for the same flight as Figure 21. In Figure 22, no windscreen foam for windshield 316 is inserted, with infrasound energy from about 2 to about 10 Hz PSD integrand. Figure 23 shows a crossplane [x y] (metres) position ‘bubble’ plot of infrasound energy of about 2 to about 10 Hz. The top of Figure 23 shows the full plot from Figure 22. The bottom of Figure 23 is a zoomed-in plot for about + 2 km laterally. In sum, the infrasound energy derived from output signal PSD of Figure 21, is shown in Figure 22, and a bubble crossplane plot thereof is presented in Figure 23.

[0190] Although, by simulation, acoustic interference patterns have been shown to be a potential source of non-monotonic infrasound energy behaviour with distance from vortices, there could be other effects. Increasing boundary / shear layer noise sensing has been shown tooccur with increasing True Airspeed (“TAS”). Therefore, it is also likely to have occurred with increasing a (angle of attack).

[0191] This possibility was evident in a B789 survey, when tactile buffet was experienced during the base-turn manoeuvre away from the trailing wake- vortices 112. Figure 24 shows a vortex distance plot of sensed infrasound energy, illustrating a high maximum value, concurrent with CT133 manoeuvring. The vortex distance plot of infrasound energy in Figure 24, shows a particularly high maximum concurrent with the CT133 turning (higher pitch rate, a).

[0192] Figure 25 shows a CT133 maneuver effect (bank angle in level flight) upon microphone signal power PSD DC component value. The maneuver effect upon infrasound signal has been estimated by assessing and noting the 0 Hz frequency magnitude of the PSDs. When plotted against level flight bank angle, <|), as shown in Figure 25, an interference noise effect is noted for the PSD DC component, for bank angles greater than about 15°. This is used as a scale effect to reduce the magnitude of the integrated infrasound energy.

[0193] One flight was conducted in this configuration. Figure 26 shows an I / F signal and associated state parameters during a B77W wake-vortices 112 intercept. As shown in Figure 26, the microphone output signal was much reduced, negligible saturation occurred (windshield 316 windscreen foam having been removed with the attachment tube 304). Open plenum sensing resulted in greater microphone signal sensitivity to nose-bay boundary / shear layer noise (i.e., TAS dependency).

[0194] The output signal timetrace is shown in Figure 27. Figure 27, I / F signal expanded timetrace during a B77W wake vortex survey. A beating effect of about period 50 seconds is observed and the signal level is about l / 20th of saturation, in comparison to the piped installation discussed earlier.

[0195] Figure 28 shows typical PSD of the I / F output signal, when following a B77W, about 2,000 feet below its trailing vortex pair. The PSD indicated a constant response with increasing frequency, up to about 180 Hz, beyond which microphone response rolls-off at a high rate of approximately four decades per decade.

[0196] Figure 29 shows infrasound energy obtained by integrated PSD from about 1 to about 36 Hz (plenum sensing). A signal to noise ratio (SNR) envelope (i.e., the maximum value) of about 3 at about 25 km, to about 10 at about 1 km radial distance from the trailingvortex pair centreline, is implied from this plot. This can be compared to the plumbed pipe configuration without windscreen foam, Figure 22, for which at about 20 km separation, the maximum SNR was about 10, about three-times that for open nosebay plenum acoustic sensing.

[0197] Another flight expanded the range of trailing wake vortex intercept geometries, for the 1.5 inch microphone 308, with windshield 316 windscreen foam inserted in the acoustic sensing tube 304 (as on another flight, analysed previously). Six intercepts were flown, some with passes close to trailing wake vortex cores. The flight was conducted in dry air, without any vortex condensate. The intercepts are summarised in Table 3 shown in Figure 30.

[0198] Acoustic propagation can be effected in a complex manner, by atmospheric conditions, principally stratification, winds and background turbulence. All flights were conducted in the upper troposphere lower stratosphere. Typical conditions tended to be light, locally moderate turbulence, nil or light stratification. Of these atmospheric effects, stratification can conceivably negate acoustic propagation, through refraction.

[0199] An example can be illustrated from a B789 flight. Figure 31 shows, background atmospheric conditions in the form of wind. Figure 32 shows, background atmospheric conditions in the form of stratification (left) and eddy dissipation rate (right). Figure 33 shows, background atmospheric conditions in the form of air temperature sounding (met balloon and CT133).

[0200] Thus, winds, stratification and background turbulence are presented in Figure 31, Figure 32, and Figure 33. The north and east components to the background winds exhibited variation over the survey time of aboutl7 minutes, indicative of background vorticity inducing mesoscale wind curvature. Consequently, some level of background turbulence can be expected - layered light turbulence is evident in the flight sounding data. Being layered, a level of stratification can be expected, NBV2 > 0, which it was, but very low magnitude and non-stratified (NB V2 < 0) in the patches of light turbulence.

[0201] The stratification can also be seen in the large number of small temperature inversions, in the flight sounding in Figure 31, Figure 32, and Figure 33. The Maniwaki (CYMW) meteorological balloon data exhibited two inversions, at about 10 and about 11 km height, whilst the CT133 data captured six inversions (evidence of stratification) between 9.8 and about 10.6 km height.

[0202] Figure 34 shows intercept geometry: on the top, planform (open circles are the start of intercept, an oblique opposing pass (head-on); in the middle, aircraft height against B789 wake length (maximum 200 km, at which point, with a wake age of 12 minutes, the trailing wake vortices had diminished to small-scale turbulence); on the bottom, radial distance from B789 or trailing wake vortex centreline. The intercept geometry is thus depicted in Figure 34, which includes a plot of the vortex separation of each sequential PSD of the microphone output signal. As before, the PSD were integrated between lower and upper bounds of infrasound (+Doppler) frequency, in order to derive the total sensed infrasound energy.

[0203] Figure 35 shows a B789 vortex distance plot of infrasound energy (with CT133 estimated manoeuvre effect removed), with log-linear mean lines of regression included. The infrasound energy is presented in Figure 35 (for which the manoeuvre effect has been a priori removed). Ahead of the B789 (about 38 to about 9 km, as the CT133 approached the B789 oblique head-on, about 2,000 feet below), for which acoustic propagation was conical- hemispherical, the regression line did not exhibit any significant distance effect.

[0204] Behind the B789, in cylindrical acoustic propagation, the regression line showed a definite trend with vortex separation radial distance; sensed energy magnitude halved between about 3 km and about 60 km. However the scatter was significant, as shown by the + 1 a lines in Figure 25. -i-lo scatter amounted to about 40% of mean value at short range, which is about half the increase in sensed infrasound energy between about 58 and about 2.6 km.

[0205] (Figure 36 shows A333 (DLH426) intercept geometry (with B777-300ER (flight KAL082) flying cross-track. Figure 37 shows A333 (DLH426) infrasound energy (NOTE: possible sensing of a B777-300ER flying cross- track at a similar time).)

[0206] However, in the case of the first A333 (intercept geometry shown in Figure 36), a slight mean regression effect was observed ahead of the A333 per Figure 37, once again with significant non-monotonic variation about the mean line of log-linear regression.

[0207] Furthermore, it is possible that the microphone sensed transmissions generated by the B777-300ER flying cross-track at a similar time to the A333 survey.

[0208] Figure 38 shows CT133 intercept of the B77W: top left, overall intercept; top right, .in-trail segment, showing the locations and flightpaths of the trailing wake vortex encounters; bottom, vertical view, along the trailing wake vortex axis.

[0209] The installation of the 3inch NASA I / F microphone included a doubling of microphone windshield foam. The attenuation was successfully. 10000 mV output was achieved only in the immediate vicinity of wake vortices, as illustrated in Figure 38. Background atmospheric conditions were generally wide patches of light chop.

[0210] The flight with the 3 inch microphone included intercepts of B77W, B744 and A359 Heavy jets. The B77W intercept consisted of an oblique side-on approach ahead of the B77W, followed by a turn to-follow, with several vortex core flybys / through. The intercept planform geometry is shown in the views of Figure 38, together with vortex core encounters, and a vertical view along the trailing wake vortex axial direction.

[0211] Figure 39 shows background atmospheric conditions during B77W intercept and survey.: top left, BV frequency (NBV2), top right, EDR, bottom, winds. The atmospheric state is shown in Figure 39, which includes stratification (NBV2) and EDR plots. A layer of turbulence was prevalent higher above the B77W, whilst layers of significant stratification occurred immediately above B77W level (about 33,000 feet PA), and below the trailing wake vortex turbulence (about 32,250 feet). Possibly this could reduce acoustic transmissions downwards. The winds during this vortex interaction are also shown in Figure 39. Background winds were a significant north-westerly wind of about 90 knots, hence the significant northerly and westerly components, and the background shear, resulting in generally-patchy light chop, as seen by the high spatial frequency waviness in the wind waveform, particularly northwind

[0212] Figure 40 shows a trailing wake vortex core crossing, unsteady vortex wind components, static pressure (line extending from about -293, -2 up to about 0, 302) and 3 inch I / F mic response (complex waveform)).

[0213] The 3 inch I / F microphone dynamic response was validated in a trailing wake vortex pair crossing, as shown in Figure 40. The microphone response closely followed that of the unsteady winds. In addition, the microphone output signal had a significant amplitude of a very high frequency component throughout the perturbations associated with the vortex core traverse. This could have been the greater sensitivity of the 3 inch microphone (double that of the 1.5 inch microphone) to external boundary / shear layer turbulence.

[0214] Figure 41, shows a 3 inch microphone output signal PSD during a vortex core interaction.

[0215] The frequency response of the 3 inch microphone during a vortex core interaction is shown in Figure 41. At high frequency (100-300 Hz), there is no roll-off of response, whereas the 1.5 inch microphone had a high roll-off gradient beyond 200 Hz. There would undoubtedly have been boundary / shear layer noise generation and transmission in this frequency range, to which the 3 inch microphone was more responsive than the 1.5 inch microphone

[0216] Figure 42 shows sequential PSDs, radial distance of each from the trailing wake vortex pair centreline: red, B77W (minimum approach distance about 9 km), blue, CT133. The radial distances of the sequential PSDs from the trailing wake vortex pair centreline (midpoint between the port and starboard vortices), are depicted in Figure 42.

[0217] Figure 43, shows, (left) infrasound energy (PSD integrand 0.6-46 Hz) plot via vortex separation distance; (right) EDR magnitude by wake vortex separation distance. Note that the blue circles (left most) denote measurements made initially behind / below the B77W, then behind / at the B77W level. The CT133 was about 600m below the vortices initially, then climbed to vortex height, and weaved laterally anout +2 km. ‘

[0218] As before the microphone output signal (mV) PSDs (500 point or 0.87 seconds of flight time, processed in 1024 point, i.e. 50% zero-padded, Hanning window) were integrated over frequency for the infrasound range. An examination of the integrand association with radial distance from wake vortex pair centreline is shown in Figure 43. The microphone responded to background atmospheric turbulence during the intercept approach, as evidenced by the paired plot of in-situ EDR magnitude. Smooth air is then encountered, as the CT133 turned-in ahead, then abeam, and then behind the B77W.

[0219] There was progressive rise in infrasound energy response during this sequence. In- trail, at about 5 Nm, the CT133 climbed to the afore-discussed vortex encounter, then weaved either side, about +2 km displacement, opening out at about 2.8 Nm per minute, to about 37 Nm (four minutes age, by which the high vortex strength of the trailing pair was largely dissipated), then broke-away in a left turn. The wake vortex progressively decayed over this period. By breakaway, infrasound energy response had dropped to background levels, which were then maintained.

[0220] By comparing the microphone output-derived energy and EDR magnitudes (Figure 43), it is seen that the 3 inch microphone was sensitive to both wake vortices andbackground atmospheric turbulence (which was light). The microphone response at vortex distances 6-8 kn was very likely background atmospheric turbulence.

[0221] Noting that, at 37 Nm (the start of the mauve points), that trailing wake vortex strength would have likely decayed to background turbulence level, it would be expected that there was no elevated signal in the continued lateral weave through vortex height, at that time. Therefore it leaves the blue points of infrasound energy magnitude, to observe a wake vortex noise generation. Such is observed in Figure 33 <1.8 km, but not above about 1.8 km.

[0222] However, as discussed in Figure 39, a significant level of atmospheric stratification was measured about 300 m below the wake generator, between it and the CT 133, which could have introduced acoustic reflection effects, negating the transmission of some or most of the infrasound energy to the microphone.

[0223] Figure 44 shows B744 intercept: left top, vertical flight profile, CT133, left bottom, FF mic. output signal timetrace; right, planform flightpaths, showing wake vortex proximities.

[0224] The B744 intercept was the singular quad-engined transport jet encountered on the CAWTSFR project. For this intercept, the CT133 was about 5 Nm abeam and about 2,000 feet above; at 5 Nm behind, the CT133 descended and followed the B744 as per Figure 44.

[0225] No vortex core traverses were achieved in blue-sky conditions; however, vortex core proximity passages were achieved, evident in the infrasound microphone time-domain output signal shown in Figure 44. The highest signal level was in the vicinity of the B744 trailing vortices.

[0226] Figure 45 shows background atmosphere. The left side shows stratification. The right side shows, Eddy Dissipation Rate (EDR).

[0227] Figure 46 shows a microphone output signal PSD.

[0228] The background atmosphere, per Figure 55, was lightly stratified and lightly turbulent. The PSD of the microphone output, Figure 56howed similar shape to the B77W generated signal; in particular, the relatively high power between about 100-200 Hz was evident.

[0229] Figure 47 shows a timetrace of sensed infrasound energy, B744 wake vortex generator.

[0230] The sequential infrasound energy (mV2 / Hz PSD integrand, about 1.1-22 Hz) distribution, in the time domain, is shown in Figure 47. It is seen that the sensed energy increased during the CT133 base-turn, as the offset head-on approach was converted into intrail following of the B744, by the CT133. Beyond about 5 Nm wake length, as the CT133 undertook lateral weaves (Figure 44) through vortex proximity on each traverse, the sensed energy reached maxima, thereafter reducing once again. This would agree with the nature of wake vortex strength (and acoustic transmissions, therefrom, in the audible range, in the airport environment), which decays initially, relatively slowly (about 10% per minute elapsed time), followed by rapid decay at approximate wake age of 2.5 to 4 minutes).

[0231] Figure 48 shows sensed PF energy, by radial distance from the trailing vortex pair centreline.

[0232] Figure 49 shows sensed PF energy, log-linear, by radial distance from the trailing vortex pair centreline.

[0233] Figure 50 shows unsteady wind derived EDR from in-situ turbulence.

[0234] Figure 51 shows ratio of PF ENERGY (microphone output PSD integrand) to the insitu EDR

[0235] When plotted against radial distance from the centreline of the trailing vortex pair, the I / F energy distribution was that shown in Figure 48, in linear depiction, and in Figure 49 in log-linear depiction - the latter with first and higher order regression analyses.

[0236] Log-linear, first order, and 3rd power, regressive fits are included in Figure 49. However, there is seen to have been no practical difference between first and third order regressions. The 3rd power log-linear regression was used, in order to capture the highest infrasound energy, at closest point (about 10 m) to the vortex pair centreline. However, close distances like this are the least useful application of infrasound sensing, rather large distances of greater than about 104 m are of greatest interest for vortex avoidance sensing.

[0237] For r greater than about 100 m, both regressions showed reductions in I / F energy with vortex radial distance, logarithmic decrements of about 10% per decade radialdistance. However, the scatter about the mean line was also substantial, with standard deviation of similar magnitude as the logarithmic decrement.

[0238] To be clear that this quantified microphone response represented remotely- sensed wake vortex infrasound, rather than in-situ sensed turbulence-generated acoustic fields, the latter has been studied, as previously, using the in-situ EDR turbulence parameter, Figure 40. EDR was formulated from the unsteady wind, which has been derived from air and inertial sensors, hence completely separate from the infrasound microphone. As seen in Figure 40, the in-situ turbulence rose in close proximity to the trailing wake vortex pair.

[0239] The effects can be separated by formulating the ratio of [I / F_ENERGY] to EDR, essentially Figure 49 divided by Figure 50. The distribution of this quotient by vortex radial distance is seen in Figure 51. Where the ratio was comparatively low, 410, it would appear to imply that the microphone sensed the infrasound acoustics generated by in-situ turbulence, mostly light background atmospheric turbulence. This included patches at about 50-60 m and about 200- 300 m radial distances. However, for r < about 8 km, the ratio maxima was markedly greater, greater than or equal to 710, implying the remote sensing of wake vortex generated infrasound.

[0240] The logarithmic decrement, discussed above, was much lower on the 3-inch microphone than that for the 1.5 inch microphone measuring against B789 wake vortices, an approximate 50% reduction per decade increase in distance. However, the different logarithmic decrements might not only be due to differing microphone response characteristics. They might also reflect differing wake vortex characteristics from the two jet transport Types. As measured by the NRC, B789 wake vortices were invariably dominated by secondary helical vorticity circulating around the primary core vorticity and axial discretisation (with possible circumferential discretisation).

[0241] The helical vorticity is strongly influential upon destabilising the primary core vorticity, perhaps via Taylor instability processes, but certainly short-wave instability effects. The effects are multi-wavelength axial discretization of the vortex cores, including vortex funnel features. Although there is some level of long-wave excitation, the shortwave axial discretization is the observed means of vortex destruction.

[0242] In the case of B744- wake vortices, through the years of NRC wake vortex research, there has never significant condensate evidence of secondary helical vorticity. Rather,although vortex core funnel features are regularly observed, the primary instability mode is long-wave instability, which generally develops to vortex linking, followed eventually by vortex ring destruction.

[0243] It is conceivable, if not likely, that generated acoustic fields, including infrasound, could be likewise be quite different, between the two Types. Certainly landing configuration wake vortex acoustic fields differ between jet aircraft Types. For example the CRJ series, a 60 Hz tone is dominant, that is not at all prevalent amongst many other Types.

[0244] In further illustration of the veracity of microphone response to wake vortex generated infrasound has been examined, in the case of sensing by the 3 inch microphone, during a B789 wake vortex survey, conducted on another flight.

[0245] Figure 52 shows B789 and CT133 intercepts flights: left, planform, right elevation. Wake vortex encounters are shown with discrete square symbols.

[0246] The intercept flightpaths are depicted in Figure 52, together with wake vortex encounters experienced during the intercept. Following in-trail (greater than about 5 Nm) climb to vortex height, the lateral weave was maintained less than about 500 m from the vortex pair centreline.

[0247] Figure 53 shows B789 and CT133 intercepts flights: Top, unsteady and steady (polynomial regression) winds; Middle, stratification (Brunt-Vaisala frequency NV); Bottom, eddy dissipation rate, a.

[0248] The in-situ winds, unsteady (including wake vortex encounters) and steady (i.e., polynomial-fit mean-line), are shown in Figure 53. Also presented therein, is the background atmospheric stratification and turbulence. Background turbulence at the wake vortex and generator heights, about 37,000-38,000 feet pressure altitude (PA) was negligible, although there was light turbulence about 34,000-36,000 feet PA. At vortex height, stratification was negligible, although the atmosphere was stratified between about 34,000-37,000 feet.

[0249] Figure 54 shows B789 wake vortex infrasound survey - typical microphone output signal PSD.

[0250] A typical microphone output signal PSD is presented in Figure 54. The PSD level between about 1-60 Hz was quite flat (constant power over that frequency range), followed by a power roll-off of about 4 decades per decade.

[0251] Figure 55 shows B789 and CT133 distance separation (in the top straight line, approximate wake length) and (in the lower, irregular line), orthogonal distance of the CT133 from the wake vortex centreline

[0252] The intercept geometry and airspeed resulted in the distance separation, aircraft to aircraft (approximately, the wake length), and the distance separation between the wake vortex axis and the CT133, for the sub-set where the CT133 was overtaken and behind the B 789, are shown in Figure 55. Vortex encounters are marked with arrows, the radial distances of which were about 10 to about 100 m from the vortex -pair centreline. For the vortex encounters, the CT133 was flown in a shallow weave, so that maximum separation from vortexpair centreline was about 200 m. It was only after turn-away that separation increased greatly, to about 30 km

[0253] Figure 56 shows B789 survey - infrasound energy (PSD integrand, 1-46 Hz) by vortex-centreline or origin (whether CT133 was behind or ahead of the B789, respectively).

[0254] Figure 57 shows B789 survey - infrasound energy (PSD integrand, 1-46 Hz) by vortex wake length. Maxima sensed infrasound energy reflected the greatest vortex velocity magnitudes encountered in-situ.

[0255] Therefore, confirmation is provided, when comparing Figure 57 with the unsteady wind plot of Figure 53, that the level of sensed infrasound was maximized in the presence of wake vortices. The rate of fall with radial distance was significant, to the point that the sensed infrasound energy magnitude had reduced to background levels by 2-5 km radial distance.

[0256] The static sensing tube used for 1.5 and 3 inch microphone plumbed installations, was part of an existing sensor installation in the NRC CT133. Although NASA undertook laboratory tests into the transmission characteristics of infrasound energy through such a tube, no optimization investigation was undertaken into the effect upon sensing performance, of varying tube diameter.

[0257] Likewise, the extent of in-tube microphone windshield material, used in order to prevent microphone signal output levels from saturating, was empirically chosen, by trial- and-error. It was not the subject of optimization studies, in order to explore the acoustic filtering of higher frequencies (which contributed to saturation), whilst preventing any or negligible attenuation, over the infrasound range of acoustic frequencies.

[0258] CONCLUSIONS

[0259] Initial wake vortex sensing flights using the NASA small-size infrasound microphone, have been conducted in the NRC CT133 research jet. Two microphone designs were flown: a 1.5 inch diameter diaphragm microphone with external signal conditioning, and a 3.0 inch diameter diaphragm microphone with integrated, internal signal conditioning.

[0260] The microphones were sequentially installed, one at a time, in the unpressurised nosebay of the aircraft, connected to a nom. *4 inch stainless steel line, connected to a port in the nosebay port door. The port sensed approximate, static atmospheric pressure. In addition, the 1.5 inch microphone was flown, disconnected from the static port tube, sensing plenum air pressure fluctuations in the nosebay.

[0261] Microphone output signals (analogue mV signal, digitised and sampled at 600 Hz) were successfully measured and recorded by the CT133 data acquisition system. Full- scale deflection (i.e. saturation) of the output signal was +10,000 mV. Signal saturation occurred readily inflight. Standard microphone windshield foam (open call, lightweight foam), when inserted as a 1-inch length of twirled foam, within the stainless steel tube, adjacent to the microphone connection, successfully, eliminated signal saturation for the 1.5 inch microphone; for the 3 inch microphone, a 2 inch length of twirled foam likewise, successfully eliminated saturation. In these configurations, FSD was achieved during wake vortex core traverses, i.e. was successfully scaled for maximum sensitivity. However, the degree of attenuation across different acoustic frequency ranges, was not investigated; i.e., the acoustic dampening was not optimised, nor investigated for non-linear damping across different acoustic frequencies.

[0262] Likewise, the optimisation of the *4 inch sensing tube, to the external surface static port, was not investigated; i.e., the effects upon infrasound sensing levels, of tube diameter variations were not investigated.

[0263] With these installation non-optimisations in mind, the research flights were an initial measurement of the microphone responses to the acoustic transmissions from wake vortices generated by Heavy Category jet transports in high altitude cruising flight (about 32,000-38,000 feet altitude) flying at Mach numbers in the range about 0.80-0.86.

[0264] Following scrutiny, the preferred method of infrasound response analysis was frequency domain analysis. In particular, sequential PSD spectra were integrated over the infrasound frequency ranges of approximately about 0.5-20 Hz, except in the cases of highDoppler shift (high radial velocities of the CT133 towards the wake vortex pairs), wherefore the upper bound was raised as high as about 50 or 60 Hz. Integrating the PSD curves resulted in a total infrasound energy magnitude, as sensed by the microphone.

[0265] Concerning in-situ response characteristics, both the 1.5 and 3 inch microphones were temporally shown to be correctly sensitive to flight through wake vortex cores, events of duration about 0.5-1 second (1-2 Hz, hence within the infrasound range of microphone response). Similarly, the microphones were responsive to background atmospheric turbulence, when the microphone activity was compared to the magnitude of EDR, derived from entirely different sensors.

[0266] Concerning remote sensing during approach and recession from a trailing wake vortex pair, the infrasound energy levels, as sensed, were non-monotonic. Spatially- consecutive peaks and troughs were observed in the derived infrasound energy magnitudes. Infrasound acoustic wave interference patterns in the vortex crossplane, were shown by steady 2D modelling, to be a viable explanation of this sensing phenomenon. Therefore, it was concluded that the microphones likely sensed realistic spatial variations in infrasound energy levels in the vortex crossplane.

[0267] Nevertheless, it is noted that, with the complexity of wake vortex flowfields measured during earlier NRC flight research campaigns, infrasound transmission fields are likely to be axially variant, three dimensional and highly complex, possibly increasing the spatial variations of high and low infrasound energy magnitudes.

[0268] Remotely from a wake vortex pair, the 1.5 inch microphone sensed higher infrasound energy levels at greater radial distances from the vortex cores, c.f. the 3 inch microphone. Although, for the 1.5 inch microphone, energy level lapse rates, when extrapolated outwards from small distances, discerned vortex-induced infrasound levels at high distances, about 50-80 km, without the a priori knowledge of vortex location, it was not possible to identify an approach to wake vortices from such distances, for two principal reasons:

[0269] The standard deviation of unsteadiness in derived infrasound energy levels was approximately the same order of magnitude as the distance lapse rate of energy level; and

[0270] In-situ patches of background turbulence were accompanied by sudden rises in sensed infrasound, that were greater in magnitude than the distance lapse rates of sensed infrasound energy.

[0271] The distance lapse rate of sensed infrasound energy ahead of the acoustic generator (for which acoustic propagation was spherical) and the sensed energy magnitude were lower than behind acoustic generators (for which acoustic propagation was cylindrical).

[0272] As can be seen in Figure 16 and Figure 17 and Figure 18 and Figure 29 and Figure 51 other Figures herein, a vicinity of wake-vortices 112 can be determined and used as part of block 516 and block 520.

[0273] Referring now to Figure 58, a flowchart is provided which represents method 5800 for turbulence detection. Method 5800 can be performed using the engine and microphone assembly described above. It is to be understood that method 5800 itself can be modified, omitting certain blocks or performing them in parallel, or varying the order of performance according to desired implementation. Method 5800 can be incorporated into method 500 to implement block 516.

[0274] Block 5804 comprises converting the representation of PSD into energy. The can involve capturing infrasound signals as the aircraft flies towards the disturbance, as previously discussed. The PSD values are integrated over the infrasound frequency range to obtain the total infrasound energy (E).

[0275] Block 5808 comprises plotting the inverse square-root of the infrasound energy (E) against the progressive air distance flown. This step involves calculating the inverse squareroot of E and plotting it against the distance flown by the aircraft. The plotted data points provide a visual representation of the inverse of the square-root of energy rise as the aircraft approaches the turbulence source.

[0276] Block 5812 comprises generating a linear regression based on the plot of inverse square-root of E versus distance flown. Statistical methods are used to fit a linear regression model to the plotted data points. This model helps in determining the mean line which represents the trend in the data, providing insights into the energy distribution across the distance.

[0277] (While the present embodiment for block 5808 and block 5812 contemplates the use of the inverse square root of E, other embodiments may choose an inverse cube root of E or another power index. The power index, i, can range from about 0 to about 1, where the value of i indicates the root being taken, and a negative of i indicates the inverse operation. This can allow for flexibility in the formulation and accommodates both cylindrical and spherical transmission of infrasound generated by vortex features. For example, an inverse square root corresponds to i= 1 / 2, yielding E-l / 2, and an inverse cube root corresponds to i= 1 / 3, yielding E-l / 3.)

[0278] Block 5816 comprises determining the zero-crossing point of the mean line obtained from the linear regression. The zero-crossing point indicates the distance to the high- magnitude infrasound source, which is crucial for identifying the location of the vortex. This information is used to alert the flight navigation system of the potential disturbance ahead.

[0279] When method 5800 is used to implement block 516, then the results of block 5816 can be passed to block 520 for vortex identification.

[0280] To elaborate on method 5800, as the aircraft approaches a disturbance, the intensity of the infrasound energy increases, and this variation is captured in the PSD values. By plotting the inverse square-root of the infrasound energy against the distance flown, a relationship between energy intensity and distance is established. This relationship, despite potential non-monotonic variations due to wave interference patterns, provides a clear trend that can be analyzed using linear regression techniques.

[0281] The linear regression analysis helps in identifying the mean trend line within the data points, and the point where this line crosses the zero value is indicative of the distance to the disturbance source. This zero-crossing point is a critical parameter as it denotes the proximity of the aircraft to the high-magnitude infrasound source, allowing for timely navigational adjustments.

[0282] Method 5800 leverages the directional sensitivity of microphone 308, which has been demonstrated to capture infrasound energy effectively from within a specific angle relative to the direction of flight. This directional sensitivity, combined with the linear regression analysis of the infrasound energy, forms the basis for reliable vortex identification and therefore opportunity for avoidance. It can be noted then that method 5800 as described presumes an ideal case for the algorithm where the aircraft 200 is flying in the direction of thevortex. In some embodiments, accordingly, method 5800 is effected only when the aircraft 200 and / or instruments take various readings from multiple directions until the direction with the highest energy level is identified, indicating the direction of the disturbance. Once the direction is confirmed, the aircraft can then perform method 5800, flying towards the disturbance to accurately determine the distance to the vortex using the steps outlined in blocks 5804, 5808, 5812, and 5816. This process ensures that the aircraft is heading directly towards the source of the infrasound energy, allowing for precise measurements and effective turbulence detection.

[0283] In some embodiments, even when the aircraft 200 is not flying directly towards the disturbance, performance of method 5800 may still be possible provided the direction of the disturbance is still known, with a vector normalization calculation being performed on the output at block 5816 to ascertain both the non-normal direction and distance to the disturbance. As noted, infrasound energy readings from multiple directions may be taken initially to ensure accurate direction determination, but then aircraft 200 may be flown in another direction, even away from the disturbance, if the direction of the disturbance is known and there are a sufficient number of meaningful energy readings for the plotting at block 5808 to provide a meaningful result at block 5816 based on the linear regression at block 5812. By taking these readings, the system can analyze the energy levels from various angles and identify the direction with the highest infrasound energy, which indicates the direction of the disturbance. This approach can help in triangulating the exact location of the vortex even when the aircraft is not a direct path towards it.

[0284] One of ordinary skill in the art will now appreciate that variations, modifications, subsets and / or combinations of the foregoing embodiments are contemplated.

[0285] Furthermore, according to these specific example embodiments Doppler compensation can be obviated and / or minimal. The inventor has determined that Doppler shift accounting does not enhance the ranging detection of source distance ahead along the line-of- flight in the new formulation using E, the total infrasound energy.

[0286] The present embodiments can benefit from the use of low-cost, reliable electronics. The present embodiments can operate effectively with a single infrasound microphone 308 with lower timing requirements. Embodiments herein can therefore operate with a microphone 308 sampling rate of about 0.25 to about 4 KHz, preferably about 0.5 to about 2 KHz, over a sampling period of about 0.5 to about 4 seconds, preferably about 1 toabout 3.33 seconds, and datasets comprising about 500 to about 2000 data points, with about 600 points being utilized in certain present embodiments.

[0287] As another example, it is contemplated that the teachings herein may extend to a plurality of types of disturbances. Accordingly, it should be noted that in general terms, wake 104 and turbulence 108 and wake-vortices 112 can be placed under the umbrella term “disturbance”, such as:

[0288] Atmospheric Turbulence includes other types of irregular air motion characterized by eddies and vertical currents, which can cause abrupt changes in altitude and attitude of the aircraft. Detecting atmospheric turbulence helps in maintaining passenger comfort and preventing structural damage to the aircraft.

[0289] Towering Cumulus (TCu) Cloud are clouds indicative of strong updrafts and severe weather conditions as approaching that of thunderstorms. Early detection of TCu clouds can allow the aircraft to navigate around potentially dangerous weather systems.

[0290] In-Flight Weather Anomalies include sudden changes in wind speed and direction, temperature gradients, and pressure variations. Identifying such anomalies can aid in optimizing flight paths and fuel efficiency, as well as ensuring overall flight safety.

[0291] Other types of disturbances will occur to those of skill in the art.

[0292] As another example, it is to be understood that engine 212 can be implemented with different configurations than described, omitting certain input devices, or including extra input devices, and likewise omitting certain output devices or including extra output devices. For example, output device 428 can be omitted where configuration and other control over engine 212 occurs via another computing device connected to network 436. Furthermore, engine 212 can also be incorporated directly into ACU 224, implemented as another application 458 with an appropriate corresponding set of tables 462. The detection of turbulence 108 via engine 212 can be used by ACU 224 to determine different navigation options and, for example, result output control over flight control system 448-1 to cause aircraft 200 to navigate around and / or away from turbulence 108 and avoid wake-vortices 112.

[0293] It is also to be understood that, where network 436 and network 438 are fast enough or otherwise have sufficient resources, the computational functions of processor 408 may be performed by a computer system similar to engine 212 located on the ground or inanother aircraft, or by a computer system located on a near-earth satellite within effective range of aircraft 200. Accordingly, engine 212 need not, necessarily, be located within aircraft 200 depending on the need for detection of turbulence 108. Furthermore, data determined by engine 212 based on microphone assembly 204 may be utilized by an ATC to control navigation of other airplanes, such as airplane 100-1 that are navigationally near aircraft 200, that may not be not equipped with microphone assembly 204 or engine 212. By the same token, where engine 212 can be remote to aircraft 200, then other airplanes 100 or other aircraft can be equipped with microphone assembly 204 with collected data being sent to a remote version of engine 212, thus providing the benefits of detection of turbulence 108 with a less-complex and / or costly set of capital equipment for the airplane 100 or other aircraft.

[0294] It is also to be understood that microphone assembly 204 need not be installed in an aircraft, and can suitably modified for installation on ground stations where aircraft fly overhead or nearby, and / or in other locations that are frequented by aircraft in order to detect turbulence 108 and formations of wake-vortices 112. On the ground, a plurality of microphone assembly 204 may be provided, such as three, in order to triangulate originating directions of turbulence 108 and / or wake-vortices 112.

[0295] The present specification is based on wake vortex (such as wake-vortices 112) characteristics and their understanding of these characteristics within the frequency domain based on spectral analysis of an infrasound microphone signal. The microphone assembly 204 supplied the data for analysis. Specifically, frequency domain analysis of analog infrasound electronic signals 326 was carried out.

[0296] The present specification can also be used to track and follow aircraft, such as airplane 100-2, by determining wake 104 and turbulence 108 thereof.

[0297] The present specification can be used to detect regular atmospheric turbulence in addition to turbulence from other aircraft.

[0298] In the foregoing specification, various embodiments have been described, however, the scope of the invention contemplates variations and equivalencies, as set forth in the claims below, properly construed in relation to the teachings in this entire specification.

Claims

Claims1. An apparatus for turbulence detection comprising: an infrasound microphone for positioning in a soundscape containing turbulence within a radius of the microphone; a processor configured to receive an input waveform from the microphone and to perform a signature analysis on the input waveform; the processor further configured to isolate features from the waveform; the isolated features representing the turbulence; and, an output device connected the processor; the processor further configured to control the output device based on the isolated features.

2. The apparatus of claim 1 , wherein the processor is further configured to: obtain a Power Spectral Density (PSD) representation from the input waveform; convert the PSD representation into infrasound energy (E); generate a plot of the inverse power index (i) of the infrasound energy (E) against a progressive air distance flown; where the power index (i) is between about zero and about one. generate a linear regression based on the plot; and determine a zero-crossing point of the mean line obtained from the linear regression to indicate the distance to the turbulence.

3. The apparatus of claim 2 wherein the power index (i) is about 1 / 2.

4. The apparatus of claim 2 wherein the power index (i) is about 1 / 3.

5. The apparatus of claim 1 wherein the processor is further configured to estimate a value of the radius of the turbulence from the microphone.

6. The apparatus of claim 1 wherein the infrasound microphone is sensitive to a radius that is above, behind, on top, or underneath the turbulence, and further including an analog-to-digital converter for converting the input waveform into a digital waveform for the processor.

7. The apparatus of claim 4 wherein the processor is configured isolate features, at least in part, based on determining sensed infrasound energy using a log-linear regressive fit that correlates turbulence with the regressive fit.

8. The apparatus of claim 5 wherein the processor is further configured to isolate features, at least in part, based on determining unsteady wind derived from an Eddy Dissipation Rate (EDR) and a radial distance from an origin of the turbulence.

9. The apparatus of claim 6 wherein the sensed infrasound energy is divided by the EDR to generate a first type of patches of data points that represent vortex turbulence that are larger than a second type of patches of datapoints that represent background atmospheric turbulence.

10. The apparatus of claim 1 wherein the controlling comprises sending the features over an air traffic control (ATC) network that causes changes to flight navigation of aircraft with a predefined range of the turbulence.

11. The apparatus of claim 1 wherein the microphone includes a windshield.

12. The apparatus of claim 9 wherein the microphone and the windshield are disposed at one end of a tube, the tube having a tip opposite from the microphone, that protrudes from the nose-bay of an aircraft.

13. A method of controlling a navigation of an aircraft comprising: positioning in infrasound microphone in a soundscape containing turbulence; collecting infrasound sound waveforms from the soundscape at the microphone; converting the waveforms into an electronic waveform; analyzing, at a processor, the electronic waveform;isolating, at the processor, features from the electronic waveform representing the turbulence, including a location of the turbulence; and, controlling an output device based on the location.

14. The method of claim 11 wherein the output device is an aircraft flight control system and the controlling comprises: receiving a flightpath for the aircraft; comparing the flightpath to the location of the turbulence; modifying the flightpath of the aircraft to avoid the turbulence; and, communicating the modified flightpath to the aircraft flight control system.

15. The method of claim 11 wherein the location is based on an estimate a value of the radius of the turbulence from the microphone.

16. The method of claim 11 wherein the infrasound microphone is sensitive to a radius that is above, behind, on top, or underneath the turbulence.

17. The method of claim 11 further comprising an analog-to-digital conversion for converting the input waveform into a digital waveform.

18. The method of claim 15 wherein the isolating is, at least in part, based on determining sensed infrasound energy using a log-linear regressive fit that correlates turbulence with the regressive fit.

19. The method of claim 16 wherein the isolation is at least in part, based on determining unsteady wind derived from an Eddy Dissipation Rate (EDR) and a radial distance from an origin of the turbulence.

20. The method of claim 17 wherein the sensed infrasound energy is divided by the EDR to generate a first type of patches of data points that represent vortex turbulence that are larger than a second type of patches of datapoint that represent background atmospheric turbulence.

21. The method of claim 11 further comprising sending the isolated features over an air traffic control (ATC) network that causes changes to flightpaths of all aircraft with a predefined range of the turbulence.

22. The method of claim 11 wherein the microphone includes a windshield.

23. The method of claim 20 wherein the microphone and the windshield are placed disposed at one end of a tube, the tube having a tip opposite from the microphone that protrudes from the nose-bay of the aircraft.

24. The method of claim 11, wherein the analyzing comprises: obtaining a Power Spectral Density (PSD) representation from the analyzing of the electronic waveform; converting the PSD representation into infrasound energy (E); plotting the inverse square-root of the infrasound energy (E) against the progressive air distance flown by the aircraft; and, generating a linear regression based on the plot of the inverse square -root of E versus distance flown.

25. The method of claim 22 wherein the isolating comprises: determining a zero-crossing point of the mean line obtained from the linear regression to indicate the distance to the turbulence.

26. The method of claim 22, further comprising:repeating the collecting, converting, analyzing and isolating for a plurality of different directions of flight; calculating the direction of the disturbance based on the direction with the highest infrasound energy level.

27. The method of claim 11, further comprising: receiving multiple infrasound sound waveforms from different directions relative to the aircraft's flight path; identifying the direction with the highest infrasound energy level based on the multiple waveforms; and determining the direction of the greatest turbulence threat based on the direction with the highest infrasound energy level.

28. The apparatus of claim 1, wherein the infrasound microphone operates with a sampling rate of about 0.25 to about 4 KHz and a sampling period of about 0.5 to about 4 seconds.

29. The apparatus of claim 27, wherein each infrasound microphone's sampling rate is preferably about 0.5 to about 2 KHz.

30. The apparatus of claim 27, wherein each infrasound microphone's sampling period is preferably about 1 to about 3.33 seconds.

31. The apparatus of claim 1, wherein the datasets collected from each infrasound microphone for analysis comprise about 500 to about 2000 data points.

32. The apparatus of claim 30, wherein the datasets collected from each infrasound microphone preferably comprise about 600 data points.

33. The method of claim 12, wherein each infrasound microphone in the system is configured to operate with a sampling rate of about 0.25 to about 4 KHz and a sampling period of about 0.5 to about 4 seconds.

34. The method of claim 32, wherein each infrasound microphone's sampling rate is preferably about 0.5 to about 2 KHz.

35. The method of claim 32, wherein each infrasound microphone's sampling period is preferably about 1 to about 3.33 seconds.

36. The method of claim 12, wherein the datasets collected from each infrasound microphone for analysis comprise about 500 to about 2000 data points.

37. The method of claim 35, wherein the datasets collected from each infrasound microphone preferably comprise about 600 data points.

38. The apparatus of claim 1, wherein the processor is further configured to compute the infrasound energy EEE using a lower bound of integration between about 0.5 Hz and about 2 Hz, and an upper bound of integration between about 20 Hz and about 40 Hz.

39. The method of claim 12, wherein the analyzing comprises computing the infrasound energy EEE using a lower bound of integration between about 0.5 Hz and about 2 Hz, and an upper bound of integration between about 20 Hz and about 40 Hz.

40. The apparatus of claim 1 wherein the processor is further configured to detect and analyze the turbulence without Doppler compensation.

41. The apparatus of claim 1 wherein the processor is further configured to detect and analyze the turbulence with Doppler compensation.

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