(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2014/0142838A1
`(43) Pub. Date:
`May 22, 2014
`Durand
`
`US 2014O142838A1
`
`(54)
`
`COLLISIONAVOIDANCE SYSTEM FOR
`AIRCRAFT GROUND OPERATIONS
`
`(71)
`
`Applicant:
`
`(72)
`
`Inventor:
`
`ROSEMOUNTAEROSPACE INC.,
`BURNSVILLE, MN (US)
`William Durand, Edina, MN (US)
`
`(21)
`
`Appl. No.:
`
`14/084,409
`
`(22)
`
`Filed:
`
`Nov. 19, 2013
`
`(60)
`
`Related U.S. Application Data
`Provisional application No. 61/728,005, filed on Nov.
`19, 2012.
`
`Publication Classification
`
`(2006.01)
`
`(51) Int. Cl.
`G08G 5/04
`(52) U.S. Cl.
`CPC ........................................ G08G5/04 (2013.01)
`USPC .......................................................... 701/301
`ABSTRACT
`(57)
`A ground collision avoidance system (GCAS) for an aircraft
`is disclosed. A radio frequency (RF) sensor senses a location
`of an obstacle with respect to the aircraft moving along the
`ground. An expected location of the obstacle with respect to
`the aircraft is determined from the sensed location and a
`trajectory of the aircraft. An alarm signal is generated when
`the expected location of the obstacle is less than a selected
`criterion.
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`500
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`M
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`504
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`506
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`Obtain an RF signal from scanning an
`obstacle in a volume of space near
`the aircraft.
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`Determine the obstacle’s location or
`distance with respect to the aircraft.
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`Calculate an expected obstacle
`location or distance with respect to
`aircraft.
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`Generate an alarm signal when the
`expected obstacle location or distance
`is within a selected threshold,
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`Patent Application Publication May 22, 2014 Sheet 5 of 5
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`500
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`502
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`504
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`506
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`508
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`Obtain an RF signal from scanning an
`obstacle in a volume of space near
`the aircraft.
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`Determine the obstacle's location or
`distance with respect to the aircraft.
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`Calculate an expected obstacle
`location or distance with respect to
`aircraft.
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`Generate an alarm signal when the
`expected obstacle location or distance
`is within a selected threshold.
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`FIG. 5
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`US 2014/0142838 A1
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`May 22, 2014
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`COLLISIONAVOIDANCE SYSTEM FOR
`AIRCRAFT GROUND OPERATIONS
`
`BACKGROUND
`0001. The present disclosure claims priority from United
`States Provisional Patent Application Ser. No. 61/728,005,
`filed on Nov. 19, 2012.
`0002 The present disclosure relates to aircrafts and, more
`specifically, to systems and methods to aid flight crews in
`avoiding obstacles while the aircraft is moving on the ground.
`0003 Aircraft are required to operate in two different
`environments, on the ground and in the air. While on the
`ground (e.g., while at an airport) aircraft need to be moved
`around to position them for takeoff as well as for other reasons
`Such as maintenance, storage, passenger loading/unloading
`and the like. However, aircraft are designed, primarily, to
`optimize their flight, not their ground based operations. This
`can lead to cases on the ground, especially with wide body
`aircraft, where the aircraft crews have poor situational aware
`ness of the aircraft and its dimensions due to limited visibility.
`Thus, the crew is limited in their ability to judge clearance of
`the aircraft with respect to obstacles on the ground, which
`may be numerous at unimproved airports in some countries.
`
`SUMMARY
`0004. According to one embodiment of the present disclo
`Sure, a ground collision avoidance system (GCAS) for an
`aircraft is includes a radio frequency (RF) sensor for sensing
`a location of an obstacle with respect to the aircraft moving
`along the ground; and a processor configured to: determine an
`expected location of the obstacle with respect to the aircraft
`from the sensed location and a trajectory of the aircraft, and
`generate an alarm signal when the expected location of the
`obstacle is less than a selected criterion, thus posing a colli
`sion threat to the aircraft.
`0005. In another embodiment of the present disclosure, a
`method of preventing a collision of an aircraft includes: sens
`ing, using a radio frequency (RF) sensor, a location of an
`obstacle with respect to the aircraft moving along the ground;
`determining an expected location of the obstacle with respect
`to the aircraft from the sensed location and a trajectory of the
`aircraft, and generating an alarm signal when the expected
`location of the obstacle is less than a selected criterion.
`0006 Additional features and advantages are realized
`through the techniques of the present disclosure. Other
`embodiments and aspects of the disclosure are described in
`detail herein and are considered a part of the claimed disclo
`sure. For a better understanding of the disclosure with the
`advantages and the features, refer to the description and to the
`drawings.
`
`BRIEF DESCRIPTION OF THE SEVERAL
`VIEWS OF THE DRAWINGS
`0007. The subject matter which is regarded as the disclo
`Sure is particularly pointed out and distinctly claimed in the
`claims at the conclusion of the specification. The forgoing and
`other features, and advantages of the disclosure are apparent
`from the following detailed description taken in conjunction
`with the accompanying drawings in which:
`0008 FIG. 1 shows an aircraft having a ground collision
`avoidance system (GCAS) in one embodiment of the present
`disclosure;
`
`0009 FIG. 2 shows an aircraft having a GCAS in another
`embodiment of the present disclosure;
`0010 FIG. 3 shows an aircraft having a GCAS in yet
`another embodiment of the present disclosure;
`0011
`FIG. 4 shows an illustrative GCAS system accord
`ing to one embodiment; and
`0012 FIG. 5 shows a flowchart illustrating a method of
`avoiding a ground collision according to an embodiment.
`
`DETAILED DESCRIPTION
`0013. On large airplanes (such as the Boeing 747, 757,
`767, and 777; the Airbus A380; and the McDonnell Douglas
`MD-10 and MD-11), the pilot cannot accurately judge posi
`tions of the airplane's wingtips from the cockpit unless the
`pilot opens the cockpit window and extends his or her head
`out the window, which is often impractical. One approach to
`avoiding such a problem is to include a ground collision
`avoidance system (GCAS). However, in some cases obstacles
`that are collision threats may go undetected by the GCAS.
`Also, if a GCAS provides too many false alarms (“false
`positives') when evaluating the threat of collision with an
`obstacle, the crew may begin to ignore or disable the system.
`0014 Embodiments disclosed herein integrate electro
`magnetic obstacle sensing with effective signal processing to
`detect a threat of collision of an object, Such as an airplane,
`with an obstacle with a high probability of collision, or in
`other words, with a low incidence of false alarms (“false
`positives'). Detected collision threats trigger an alert to an
`autonomous crew with sufficient lead time for the crew to take
`avoidance actions safely. The system is effective in both day
`and night conditions and in degraded environmental condi
`tions. The system is safe to operate in an airport environment
`and does not impact either onboard or ground electronic
`systems.
`(0015 FIG. 1 shows an aircraft 100 having a GCAS in one
`embodiment of the present disclosure. The aircraft includes
`sensors 110a, 110b and 112 disposed on a tail 102 of the
`aircraft 100. In one embodiment, the tail 102 may include a
`sensor 110a on a left side of the aircraft 100 that has a left
`wingtip view 104a, or in other words, a field-of-view that
`covers a volume of space near a wingtip 115a of the left wing
`108a of the aircraft 100. Similarly, sensor 110b on a right side
`of the aircraft 100 has a right wingtip view 104b or a field
`of-view that covers a volume of space near the wingtip 115b
`of the right wing 108b of the aircraft 100. The tail 102 may
`further include a sensor 112 that includes a view along a
`fuselage of the aircraft 100. In various embodiments, the left
`side sensor 110a and the right side sensor 110b may include
`a radio frequency (RF) sensor Such as a transducer for trans
`mitting and receiving radar signals at one or more frequen
`cies. Sensor 112 may be a camera or other device for record
`ing optical images. However, sensor 112 may also be an RF
`frequency sensor in various embodiments.
`(0016 FIG. 2 shows an aircraft 200 having a GCAS in
`another embodiment of the present disclosure. Sensors 210a
`and 210b are provided in wings 208a and 208b, respectively,
`of the aircraft200. Sensors 210a and 201b may be RF sensors
`Such as transducers for obtaining radar signals. The field-of
`view for sensors 210a, 210b show the volumes of space in
`front of wingtips 215a and 215b, respectively. A sensor for
`displaying a front view such as the front view 106 of FIG. 1 is
`not shown for clarity but may be provided, for example, by a
`sensor located in the tail 102 as in FIG. 1.
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`0017 FIG.3 shows an aircraft 300 having a GCAS in yet
`another embodiment of the present disclosure. Sensors 310a
`and 310b are mounted on a fuselage 305 of the aircraft 300.
`Sensors 310a and 301b may be RF sensors such as transduc
`ers for obtaining radar signals. Sensor 310a may be oriented
`to have a field-of-view that shows the volume of space in front
`of wingtip 315a. Sensor 310b may be oriented to have a
`field-of-view that shows the volume of space in front of
`wingtip 315b. Although not shown, a sensor for displaying a
`front view of the aircraft 300 may be provided, such as the
`front view 106 of FIG. 1. Sensor fields of view may be
`widened to include a forward view along the fuselage to
`detect objects in the taxi direction as well.
`0018. In prior GCAS’s, only a single type of sensor (e.g.,
`Video cameras, imaging infrared (IIR) or ultrasonic cameras)
`were provided. In embodiments disclosed herein, a GCAS is
`provided that includes not only prior sensor types but also
`radar sensors to increase the breadth of data available for
`processing and collision alarm decision making. Data fusion
`across multiple sensors may increase decision quality under
`many conditions. Also, multiple radar technologies may be
`included. For instance, Ultra Wideband (UWB) radars may be
`integrated with Frequency Modulated Continuous Wave
`(FMCW) units to improve obstacle detection performance at
`both short and long ranges.
`0019. The radar sensors described herein may be low
`power, high performance radio frequency devices. If an
`obstacle is present within the radar field of view, the reflection
`of the transmitted signal from the obstacle is received by the
`sensor. In one embodiment, a monostatic radar configuration
`uses the same antennas for transmitting and receiving signal
`energy. In another embodiment, a multistatic configuration
`may use multiple antennas to characterize obstacle geom
`etries. Both configurations may be employed in a single sys
`tem
`0020 Transmitted radar energies need to be safe for
`humans nearby the sensor, but sufficient to detect distant
`obstacles. The maximum range required will be determined
`by aircraft taxi speed, crew response time and safe aircraft
`stopping distances. In one embodiment, the radars can Sup
`port taxi speeds up to 30 knots.
`0021. According to one embodiment, the radar sensors are
`capable of detecting obstacles greater than 4 centimeters in
`size. Obstacles of particular collision risk in airport taxi envi
`ronments include: airfield fence posts/poles; airfield lighting:
`taxiway markings; housing structures; other aircraft; ground
`vehicles; and ground personnel to name but a few. As dis
`cussed briefly above, the sensors (e.g., radar antennas/mod
`ules) may be mounted at various locations on the aircraft
`including the wingtip(s), fuselage, and radome (aft of weather
`radar antenna). The radar employs a beam width suitable for
`detecting obstacle collision threats, while ignoring obstruc
`tions that are not a threat to the aircraft.
`0022 FIG. 4 shows an illustrative GCAS system 400
`according to one embodiment. The system 400 includes sen
`sors 401, 403 and 405. The sensors 401 and 403 may repre
`sent RF sensors such as the RF sensors shown in FIGS. 1-3.
`Sensor 403 may be a camera or visual sensor. Sensors 401,
`403 and 405 are coupled to a Signal Processing Unit (SPU)
`410 and provide information regarding obstacle range and
`position to the Signal Processing Unit (SPU) 410. The sensors
`401, 403 and 405 may provide the information either wire
`lessly or via a wired connection. The SPU 410 includes a
`processor 412 and a memory device 414. The memory device
`
`414 may be a non-transitory memory device, such as a RAM
`or ROM device or other suitable memory device. The
`memory device 414 may be Suitable for storing various data
`that may be used in the GCAS system 400 as well as various
`data that is obtained from the sensors 401, 403 and 405 or
`from calculations performed at processor 412. In addition, the
`memory device 414 may include one or more programs 416
`or set of instructions that are accessible to the processor 412.
`When accessed by the processor 412, the one or more pro
`grams 416 enable the processor 412 to perform the methods
`disclosed herein for avoiding collision with an obstacle while
`on the ground.
`0023 The processor 412 performs various calculations in
`order to determine a presence of an obstacle and to perform a
`decision-making algorithm to determine a probability of col
`lision with the obstacle. In one embodiment, the processor
`412 may match radar signals to obstacle shape templates
`through a correlation process in order to identify an obstacle
`presence, type, shape, etc. The processor may apply adaptive
`noise filters which characterize noise energy and attenuate the
`noise energy accordingly, and then normalize a noise floor in
`order to establish an effective obstacle detection threshold.
`The processor 412 may further employ threshold filters which
`identify radar return signals sufficiently above the noise floor
`and report these signals as representing obstacles that are
`potential collision threats. Multiple radar signals or scans
`may be stacked in order to enhance a signal-to-noise ratio of
`the obstacle. The potential collision threat may be mapped to
`a range and azimuth location around the aircraft and to their
`motion relative to the aircraft.
`0024. The processor 412 may also group radar signals
`meeting predetermined obstacle criteria and enter them as
`“objects’ into tracking files. Each tracking file can be repeat
`edly tested for temporal persistence, intensity, rate of change
`of intensity and trajectory to help differentiate objects as
`obstacles that are collision threats, other obstacles, false
`alarms or background clutter. Once a persistent obstacle col
`lision track has been established, the processor determines
`distance to the aircraft and issues an appropriate alarm or
`warning signal. If the tracks persist and grow as range
`decreases, the process performs a decision-making program
`to declare the tracks a probable collision and issues an alarm
`or warning.
`(0025. The SPU 410 therefore executes data fusion algo
`rithms, processes obstacle information, together with critical
`aircraft dynamics Such as groundspeed, heading, and aircraft
`position to compute obstacle closing Velocity and predict if a
`collision is probable. If a collision is predicted, the SPU 410
`sends a signal to the GCAS Crew Alerting Unit (GCAU) 420
`which then alerts the pilot to the potential collision.
`0026 Various data may be sent to a GCAU 420 which may
`be an interface in a cockpit of the aircraft or which is other
`wise accessible to crew of the aircraft. The various data may
`then be presented at the GCAU 420 to the crew in order to
`inform the crew of any obstacles that may be within a vicinity
`of the aircraft and capable of causing mechanical or structural
`damage to the aircraft.
`0027. In one embodiment, the GCAU 420 may include a
`screen or display 422 for providing a visual image to the crew.
`The visual image may include a representative image of an
`obstacle in relation to a part of the aircraft such as a wingtip.
`The display 422 may also show other data relevant to a dis
`tance between the aircraft and the obstacle and/or to an action
`for avoiding or preventing a collision. The GCAU 420 may
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`May 22, 2014
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`further include an audio alarm 424 that may provide an
`audible signal in order to alert the crew to the possibility of
`colliding with an obstacle. Additionally, a visual cue Such as
`a flashing light at the display 422 may be used to alert the crew
`of the possibility of collision. The GCAU 420 may provide
`system health information and indicates the operational status
`of the system. The GCAU 420 may also provide a means for
`the fight crew to disable the system. In one embodiment, the
`GCAU 420 is mounted in the cockpit, in the field of view of
`both the pilot and the first officer, and provides flight crew
`interface with the GCAS.
`0028. In operation, the GCAS disclosed herein may oper
`ate as follows: while taxiing, the flight crew identifies an
`obstacle approaching but can’t visually determine if it will
`clear the aircraft (frequently the wingtip) (alternately, the
`crew may not identify an obstacle due to decreased visibility
`conditions or high workload situation); the pilot slows the
`aircraft while approaching the obstacle and monitors the
`GCAU 320 mounted in the cockpit; the GCAS continually
`monitors distance to the obstacle; if the GCAS predicts the
`aircraft will collide with the obstacle, it issues an alert and the
`pilot stops the aircraft or implements other evasive action
`preventing the collision; if stopped, the pilot determines the
`appropriate maneuver before continuing to taxi the aircraft;
`and if the GCAS predicts the aircraft will not collide with the
`obstacle, then no alert is issued and the crew continues taxi
`ing.
`0029 FIG. 5 shows a flowchart 500 illustrating a method
`of avoiding a ground collision according to an embodiment.
`In block 502, one or more signals are obtained from the RF
`sensors, wherein the signals are indicative of obstacles and
`their location with respect to the aircraft. In block 504, the one
`or more signals are used to determine a location or distance of
`the obstacle with respect to the aircraft or a part of the aircraft
`such as a wingtip. In block 506, the determined location of the
`obstacle is used to determine an expected location or distance
`of the obstacle with respect the aircraft. In various embodi
`ments, the one or more signals may be signals taken over a
`selected time period. Therefore, the location of the obstacle
`may be determined at several times during the selected time
`period and a trend of the obstacle's location over time may be
`used to determine a trajectory and/or velocity of the obstacle
`with respect to the aircraft. The determined trajectory and/or
`velocity of the obstacle may then be used to determine the
`expected location of the obstacle at a selected later time.
`0030. In block 508, the expected location of the obstacle at
`the later time is compared to a selected threshold and if the
`expected location is within the selected threshold, an alarm
`may be generated to alert the crew. A suitable threshold may
`be 10 meters or 20 meters, so that if the obstacle is forecast to
`come within this distance of the aircraft or a wingtip of the
`aircraft, the alarm is generated. The threshold is adjusted with
`respect to aircraft taxiing speeds to allow for a safe decelera
`tion and stopping distance. The threshold may also be
`selected so that a possibility of false positive collision fore
`casting is reduced or minimized.
`0031. Also, a probability of collision with the obstacle
`may be determined based on current trajectory of the aircraft,
`current trajectory of the obstacle, etc. If the determined prob
`ability of collision is greater than a selected probability
`threshold, the alarm may be generated. The level of the prob
`ability threshold may be selected so as to reduce of minimize
`the occurrence of a false alarm. When an alarm is generated,
`the alarm may continued to be heard or displayed until either
`
`the aircraft has stopped or the threat of collision is no longer
`imminent or the system is deactivated. To minimize the poten
`tial for false positive alarms, the system may be used only
`when the aircraft is on the ground and/or taxiing.
`0032. In various embodiments, the obstacle may be
`tracked by the control unit and the tracking of the obstacle
`may be displayed at the screen of the user interface 420. The
`tracking may employ a loop between blocks 502 and 504 in
`order to obtain the obstacle's location at various times. In
`various embodiments, an obstacle that is being tracked and/or
`monitored using one sensor, Such as sensor 112 of FIG.1 may
`be "handed off to another sensor, such as sensor 110b of FIG.
`1 as the obstacle passes out of the field-of-view of the sensor
`112 and into the field-of-view of sensor 110b.
`0033. In one embodiment, Ultra Wideband (UWB) radars
`may be integrated with Frequency Modulated Continuous
`Wave (FMCW) units to improve GCAS performance at both
`short and long obstacle detection ranges. Sensor units can
`have both radar types included therein, although either radar
`may be used alone or with other sensors to construct a GCAS.
`Signal processing methods and algorithms will differ
`between radar types and methods of fusing data between the
`radars and other sensors will add complexity. Radar signal
`processing methods may include, but are not limited to, wave
`let correlation which searches for signals characteristic of
`obstacle reflections and amplifies them while attenuating ran
`dom noise, matching radar signals to obstacle shape tem
`plates through a correlation process, where high correlation
`helps rapidly identify obstacle presence and type/shape (e.g.,
`light poles, etc.), adaptive noise filters which characterize
`noise energy and attenuate signals accordingly, then normal
`ize the noise floor and help establish an effective obstacle
`detection threshold, threshold filters which identify radar
`return signals sufficiently above the noise floor and report
`these signals as representing obstacles that are potential col
`lision threats, tracking of obstacles by their motion relative to
`the aircraft and combining adjacent signals with similar
`tracks into clusters for continued observation and Subsequent
`mapping, and mapping potential collision threats to range and
`azimuth around the aircraft and to their motion relative to the
`aircraft for further understanding of collision potential.
`0034. In one embodiment, FMCW (e.g., 77 GHz) radar
`sensor alone with Such advanced signal processing Supports
`an effective GCAS capability. Many 77 GHz FMCW radars
`include integral scanning capability, enabling obstacle loca
`tion mapping in both range and azimuth relative to the aircraft
`and they can track multiple obstacles simultaneously with
`rapid response to aircraft and obstacle motion (measurements
`repeated in milliseconds).
`0035. In other embodiments, the RF sensor(s) may operate
`within a short-wave infrared range (from about 0.9 microme
`ters (Lm) to about 1.7 um), mid-wave/long-wave infrared
`range: (from about 3 um to about 14 um), a millimeter wave
`range (from about 1 millimeter (mm) to about 1 centimeter
`(cm)), an ultra-wide band range (from about 1 mm to about 1
`cm), and any other Suitable frequency range of the electro
`magnetic spectrum.
`0036 While the systems and methods disclosed herein has
`been discussed with respect to an aircraft, it is understood that
`the systems and methods may apply also to any object or
`vehicle moving along the ground.
`0037. The terminology used herein is for the purpose of
`describing particular embodiments only and is not intended to
`be limiting of the disclosure. As used herein, the singular
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`forms “a”, “an and “the are intended to include the plural
`forms as well, unless the context clearly indicates otherwise.
`It will be further understood that the terms “comprises” and/
`or “comprising, when used in this specification, specify the
`presence of stated features, integers, steps, operations, ele
`ments, and/or components, but do not preclude the presence
`or addition of one more other features, integers, steps, opera
`tions, element components, and/or groups thereof.
`0038. The corresponding structures, materials, acts, and
`equivalents of all means or step plus function elements in the
`claims below are intended to include any structure, material,
`or act for performing the function in combination with other
`claimed elements as specifically claimed. The description of
`the present disclosure has been presented for purposes of
`illustration and description, but is not intended to be exhaus
`tive or limited to the disclosure in the form disclosed. Many
`modifications and variations will be apparent to those of
`ordinary skill in the art without departing from the scope and
`spirit of the disclosure. The embodiment was chosen and
`described in order to best explain the principles of the disclo
`Sure and the practical application, and to enable others of
`ordinary skill in the art to understand the disclosure for vari
`ous embodiments with various modifications as are Suited to
`the particular use contemplated.
`0039 While the exemplary embodiment to the disclosure
`has been described, it will be understood that those skilled in
`the art, both now and in the future, may make various
`improvements and enhancements which fall within the scope
`of the claims which follow. These claims should be construed
`to maintain the proper protection for the disclosure first
`described.
`What is claimed is:
`1. A ground collision avoidance system (GCAS) for an
`object, the system comprising:
`a radio frequency (RF) sensor for sensing a location of an
`obstacle with respect to the object moving along the
`ground; and
`a processor that, in operation:
`determines an expected location of the obstacle with
`respect to the object from the sensed location and a
`trajectory of the object; and
`generates an alarm signal when the expected location of
`the obstacle with respect to the object is less than a
`selected criterion.
`2. The system of claim 1, wherein the obstacle has a veloc
`ity and trajectory, and the processor is further:
`determines the velocity and trajectory of the obstacle; and
`determines the expected location of the obstacle using a
`determined velocity and trajectory of the obstacle.
`3. The system of claim 1, wherein the object is an aircraft
`and the RF sensor is located on the aircraft at at least one of:
`(i) a tail of the aircraft; (ii) a wing of the aircraft;
`and (iii) fuselage of the aircraft
`4. The system of claim 1, wherein the RF sensor is a radar
`transducer.
`
`5. The system of claim 1, wherein the RF sensor operates in
`at least one of: (i) a short-wave infrared range; (ii) a mid-wave
`infrared range; (iii) a long wave infrared range; (iv) a milli
`meter wave range, (v) an ultra-wide band range; and (vi) a
`frequency modulated continuous wave.
`6. The system of claim 1, further comprising a camera
`configured to provide an image to the processor, wherein the
`processor is configured to use signals from both the camera
`and the RF sensor to determine the expected location of the
`obstacle.
`7. The system of claim 1, wherein the processor also tracks
`the location of the obstacle with respect to the object.
`8. The system of claim 1, wherein the processor determines
`probability of collision between the object and the obstacle,
`and generates the alarm signal when the determined probabil
`ity is greater than a selected threshold value.
`9. A method of preventing a collision of an object, the
`system comprising:
`sensing, using a radio frequency (RF) sensor, a location of
`an obstacle with respect to the object moving along the
`ground;
`determining an expected location of the obstacle with
`respect to the object from the sensed location and a
`trajectory of the aircraft, and
`generating an alarm signal when the expected location of
`the obstacle with respect to the object is less than a
`selected criterion.
`10. The method of claim 9, wherein the obstacle has a
`Velocity and trajectory, the method further comprising:
`determining the Velocity and trajectory of the obstacle and
`determining the expected location of the obstacle using
`a determined velocity and trajectory of the obstacle.
`11. The method of claim 9, wherein the object is an aircraft
`and the RF sensor is located on the aircraft at at least one of:
`(i) a tail of the aircraft; (ii) a wing of the aircraft; and (iii)
`fuselage of the aircraft
`12. The method of claim 9, wherein the RF sensor operates
`in at least one of: (i) a short-wave infrared range; (ii) a mid
`wave infrared range; (iii) a long wave infrared range; (iv) a
`millimeter wave range; (V) an ultra-wide band range; and (vi)
`a frequency modulated continuous wave.
`13. The method of claim 9, further comprising:
`providing a visual image from a camera disposed on the
`object and determining the expected location of the
`obstacle using both the image from the camera and a
`signal from the RF sensor.
`14. The method of claim 9, wherein further comprising
`tracking the location of the obstacle with respect to the object.
`15. The method of claim 9, further comprising:
`determining a probability of collision between the object
`and the obstacle, and generating the alarm signal when
`the determined probability is greater than a selected
`threshold value.
`
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