Modulated lighting infrastructure for improved low visibility detection

A modulated lighting infrastructure for a runway approach lighting system includes a network of LED emitters, emitting primarily in the visible spectral band, driven by control logic to emit brief high-frequency pulses of energy at peak brightness for a fraction of their duty cycle while emitting no energy for the remainder of the duty cycle. While the pulsed emissions of the approach lighting system are so brief as to appear normal to pilots (as the average intensity is unchanged), an onboard detection system can integrate a camera for short bursts at a high frame rate to detect images of the emitted high-frequency pulses against competing atmospheric and background illumination and display the detected images to the pilot. The emitter network may include additional emitters configured to emit energy in infrared and other spectral ranges for detection by onboard enhanced vision systems.

BACKGROUND

Aircraft-based Enhanced Vision Systems (EVS) may experience difficulty detecting approach lighting systems (ALS), airport markings, and other important indicators of an airport environment. For example, EVS systems rely on the detection of radiation in spectral ranges outside the visible band. Conventional approaches to ALS incorporate incandescent lighting which emits significant portions of energy in the short-wave infrared (SWIR) band. EVS detection in the SWIR band is advantageous due to the relative advantage of atmospheric penetration of SWIR radiation (relative to both atmospheric penetration of visible-band radiation and background illumination due to solar radiation). Both visible-band and background atmospheric radiation compete with desirable ALS emissions for detection by onboard cameras or image sensors.

The background illumination competing with desirable signals for detection can be especially problematic in daylight conditions. For example, bright sunlight may illuminate a water-laden atmosphere (e.g., fog) resulting in a bright “airtight” background that easily saturates many modern image sensors, complicating or preventing the detection of less intense point sources (e.g., desirable ALS emissions) within this background illumination. Furthermore, modern ALS and other airfield lighting systems may incorporate light emitting diode (LED) based illumination in order to save energy and maintenance costs compared to conventional incandescent lighting systems. However, LED-based illumination systems often do not emit significant amounts of radiation outside the visible band, rendering ALS detection in alternative and advantageous spectral bands near impossible in daylight or “airtight” conditions.

A potential solution involves overwhelming background illumination by increasing the brightness of visible-band ALS emissions far beyond regulatory requirements (generally 5,000-30,000 cd) in order to drown out competing background illumination. However, the energy required for this approach may render it cost-prohibitive and result in brightness inappropriate for pilots.

SUMMARY

In one aspect, embodiments of the inventive concepts disclosed herein are directed to a modulated lighting infrastructure for low visibility detection of approach lighting. The infrastructure may include a network of emitters, each emitter of the network having a power input and generating, via light emitting diodes (LED), luminous output (e.g., radiation) having an average intensity of L over a cycle of d milliseconds (where L is at most 30,000 cd, or at an appropriate level prescribed for the particular function of that lighting system). The infrastructure may include control logic linked to the power input of each emitter of the network. The control logic may modulate the emitter network for each duty cycle by driving each emitter to generate pulsed radiation at a peak brightness far beyond regulatory requirements and at high frequencies (e.g., pulses at a peak intensity of n*L for at most d/n milliseconds), while maintaining average emitted power as prescribed by regulations.

In a further aspect, embodiments of the inventive concepts herein are directed to an aircraft-based detection and display system optimized to detect emissions of the modulated lighting infrastructure. The system may include a camera for capturing a frame sequence of individual frames, each frame associated with an integration period (e.g., the time required for the camera to capture the frame) and a ratio between the luminous intensity of the infrastructure emissions and the luminous intensity of atmospheric and background illumination. The system may include an image processor for receiving the captured frame sequence and detecting captured frames within the frame sequence wherein the intensity of the infrastructure emissions is greater than the intensity of the background illumination, and therefore detectable against the background illumination. The image processor may store the detected frames in sequence to an image buffer, discarding any remaining frames. The system may include a display unit for retrieving and displaying the sequence of detected frames.

In a still further aspect, embodiments of the inventive concepts disclosed herein are directed to a method for detection and display of an approach lighting system. The method may include capturing, via a camera or image sensor, a frame sequence including frames associated with a ratio of the luminous intensity of the approach lighting system to the luminous intensity of atmospheric or background illumination. The method may include detecting, via an image processor, one or more frames within the frame sequence wherein the intensity of the lighting system is greater than the intensity of the background illumination. The method may include sequentially storing the detected frames to an image buffer, discarding the remaining frames, and sequentially displaying the detected frames via a display unit.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Broadly, embodiments of the inventive concepts disclosed herein are directed to a modulated lighting infrastructure optimized for detection by aircraft under adverse conditions where normal lighting emissions may be overwhelmed by background illumination, rendering it difficult for cameras and image sensors to accurately detect an approach lighting system. The modulated lighting infrastructure may include a network of emitters configured to emit energy at a significant multiple of its normal intensity for a fraction of its normal duty cycle. The average intensity over the full duty cycle is unchanged, so the system appears normal to the eye; however, optimized image sensors may distinguish the pulsed emission from background light and display the corresponding images of the lighting infrastructure, enhancing situational awareness.

Referring now toFIG. 1A, an exemplary embodiment of a modulated lighting infrastructure system100according to the inventive concepts disclosed herein includes an approach lighting system102comprising a network of emitters104which may be grouped into lighting assemblies106, a control processor108for modulating the network of emitters104(which may be housed in a control tower110or similar ground-based facility), and a receiver112. The control processor108may house control logic for energizing the network of emitters104, or the control logic may be embodied in each emitter104. The emitters104may be LED emitters configured to emit energy primarily in the visible spectral band for detection by a visible-band camera or image sensors aboard an aircraft114. The approach lighting system102may guide the aircraft114toward a landing on a runway116; the arrangement of individual lighting assemblies106and/or decision bars106amay help the pilot to gauge the distance between the aircraft114and the runway116, align the aircraft114with the runway116in anticipation of a landing, or assess visibility in the vicinity of the runway116. In addition to the approach lighting system102, the system100may be embodied in runway or airfield lighting systems of various configurations and installation sites, e.g., along the centerline or edges of the runway116; at a threshold or touchdown zone of the runway116; or along taxiways adjacent to the runway116. The system100may include a dual-band or multi-band infrastructure, including visible-band emitters as well as LED sources configured to emit in other spectral bands, such as 850 nm near-infrared (NIR) emitters; eye-safe emitters configured for short-wave infrared (SWIR) frequencies (e.g., 1500 nm); or medium-wave IR (MWIR) and long-wave IR (LWIR) emitters detectable by an enhanced vision system (EVS). Emitters104of a given non-visible frequency or spectral range may be configured to operate in parallel with, or may be collocated with, a visible-band LED emitter system or conventional incandescent lighting system. The control logic may drive the emitters104to emit brief high-frequency pulses118at a peak brightness far above the average luminous intensity of the normal emissions of the emitters104. Furthermore, the high-frequency pulses118may be so brief as to be indistinguishable by the pilot's eye, yet detectable by a properly configured image sensor (128,FIG. 1B) having an integration period (148,FIG. 3A) longer than the duration (142a,FIG. 3A) of the high-frequency pulse118. For example, a network of emitters104may have an average luminous intensity (e.g., brightness) L over a duty cycle of time d; L may be anywhere in the range of 50 cd (for, e.g., taxiway lighting) to 30,000 cd (for an approach lighting system102). The control processor108may pulse the emitters104for a fraction of the duty cycle d of the emitters (142,FIG. 3A), e.g., for d/N ms, at a peak brightness N*L, or N times the average intensity L (where N is a positive integer). The peak brightness of the high-frequency pulses118need not be proportional to the duration142aof the high-frequency pulses; for example, the emitters104may be driven to pulse for d/N ms at a peak brightness M*L (where M, N are positive integers and M≠N). The emitters104may be driven to emit no radiation for the remainder of the duty cycle d; the duration142aof the high-frequency pulses118is too brief for detection by the pilot's eye and the average luminous intensity over the duty cycle d remains at L. However, a properly configured image sensor may detect the high-frequency pulse118compared to competing background illumination (120,FIG. 3A).

Referring toFIG. 1B, an exemplary embodiment of the approach lighting system102ofFIG. 1A(incorporating the modulated lighting infrastructure system100ofFIG. 1A) may incorporate a configuration of lighting assemblies106. Each lighting assembly106may include a group of emitters104mounted to a superstructure122. Each emitter104may include a power input122aconnecting the emitters104to a central power supply124. The control processor108(or control logic) may drive each emitter104via the central power supply124, pulsing the network of emitters104on command to save energy. For example, the control processor108may control the distribution of power from the central power supply124to each individual emitter104. The control processor108may be manually activated to pulse the emitters104of each lighting assembly106by the crew of an airport control tower or similar ground control facility110, upon request by the pilot or crew of the approaching aircraft114. If the system100is implemented at a smaller, non-towered airfield, the system100may be a pilot-controlled system including a receiver112configured to receive a key-in message or similar signal from a pilot or crewmember of the aircraft114, e.g., by keying a transmit switch at a particular aircraft radio control of aerodrome lighting (ARCAL) frequency in a particular sequence to activate or deactivate the system100. Where the lighting assembly106or approach lighting system102includes multiple sets of emitters104, e.g., a set of emitters104configured for a visible spectral band and an alternate set of emitters104in parallel to the first set and configured for an infrared or other non-visible spectral band, the control processor108may separately energize only the set of visible-band emitters104, only the alternate set of nonvisible-band emitters104, or both sets simultaneously as needed.

Referring now toFIG. 2, a detection and display system126optimized to detect the approach lighting system102ofFIGS. 1A-Bmay include a camera (e.g., image sensor)128, an image processor130, an image buffer132, and a display unit134. The detection and display system126may include a transmitter136. The detection and display system126may be incorporated into an EVS of the aircraft114. The image sensor128may capture a stream of images of the runway116(FIG. 1A) including the approach lighting system102by free-running, or integrating for short intervals at high frame rates to capture a series of short subframes138for each duty cycle (the duty cycle of the image sensor128corresponding to the time required for to capture a standard image or frame). The image sensor128may be tuned to detect emissions in a visible spectral range or in an infrared or other nonvisible spectral range (e.g., NIR, SWIR). The image sensor128may be a multispectral image sensor. For example, the image sensor128may have a standard frame rate of 30 Hz (equivalent to a display cycle of 1/30 s≈33.3 ms, or about 33 frames per second (fps)). The image sensor128may free-run by integrating at 300 Hz, capturing a stream of 10 subframes138for each≈33 ms display cycle, which subframes may be processed by the image processor130for detection and display. If the frequency of the high-frequency pulses118generated by the emitters104is higher than the integration frequency of the image sensor (e.g., 1000 Hz pulses and 300 Hz subframe integration) the probability is increased that one or more captured subframes138will correspond to a full high-frequency pulse.

The captured subframes138may be analyzed by the image processor130to identify images corresponding to high-frequency pulses, or images in which the intensity of the energy emitted by the emitters104(FIGS. 1A-B) is significantly greater than the intensity of atmospheric and background illumination, e.g., images in which the approach lighting system102can be detected with a high degree of confidence. Any such subframes138identified by the image processor130may be stacked into an image superset stored in an image buffer132for retrieval by the display unit134. The image processor130may discard any captured frames not corresponding to high-frequency pulses118. The transceiver136may be configured to automatically signal the approach lighting system102(via the receiver112(FIG. 1A-B)) to energize the emitters104of the approach lighting system102when prompted by the image processor130. The transceiver136may signal the approach lighting system102via the receiver112by transmitting a signal generated by a pilot or crewmember aboard the aircraft114, e.g., an ARCAL frequency or similar pilot control signal.

Referring toFIG. 3A, graph140illustrates the improved detectability of the modulated lighting infrastructure system100ofFIG. 1Aaccording to the inventive concepts disclosed herein. For example, the emitters104(FIG. 1A-B) of the system100may generate radiation having an average luminous intensity L1over a normal duty cycle142(of time d; e.g., 5 ms). Under normal daylight conditions, the normal emissions118aof the emitters104may be overwhelmed by the greater luminous intensity B1of background illumination120. The emitters104may be driven to emit a high-frequency pulse118having a duration (142a) only a fraction (d/N; e.g., 0.5 ms) of the normal duty cycle142but having a far higher peak brightness L2(e.g., 10 times the average brightness L1) that overwhelms the luminous intensity B1of background illumination120, providing for easier detection by a properly configured image sensor (128,FIG. 2).

Referring toFIG. 3B, graphs144a-billustrate the detection of the modulated lighting infrastructure system100ofFIG. 1Aby a synchronous image sensor128of an exemplary embodiment of the detection and display system126ofFIG. 2according to the inventive concepts disclosed herein. Referring to graph144a, the image sensor128may be synchronized to the network of emitters104(FIG. 1A-B) of the system100. For example, the image sensor128may be synchronized to capture subframes (138,FIG. 2) at high speed and at regular intervals (e.g., integration periods146) corresponding to the frequency of the high-frequency pulses118generated by the emitters118. Referring also to graph144b, the luminous intensity of background illumination120may remain consistent through each subframe138, resulting in many subframes (138a) wherein the emitters104emit no radiation and therefore the system100may not be detectable over background illumination120, and which the image processor130(FIG. 1B) may discard. However, the integration period146of some subframes (138b) may coincide with a high-frequency pulse118; therefore the high-frequency pulse118may be detectable against background illumination120within the subframe138b. Furthermore, due to the short duration of the integration period146, the luminous intensity B1may never reach the point of saturation S1(i.e., where background illumination120saturates the image sensor128). The image processor130may sequentially save subframes138bin which the high-frequency pulses118are detectable to the image buffer134for display.

Referring toFIG. 3C, an exemplary embodiment of the detection and display system126ofFIG. 2may operate similarly to the system described byFIG. 3B, except that the image sensor128(FIG. 2) may free-run asynchronously with respect to the emitters104(FIGS. 1A-B) of the system100. For example, referring to graphs148a-b, the high-frequency pulses118generated by the emitters104may be 1000 Hz pulses approximately 1 ms in duration, similarly toFIG. 3B. The integration period146aof the image sensor128may not be precisely synchronized with the high-frequency pulses118, but an integration period146aof greater duration than the high-frequency pulses118(e.g., ≈2-2.5 ms) may fully or partially capture a high-frequency pulse118within a subframe138b-c. The image processor130may sequentially save for further display subframes138b-c, in which the high-frequency pulses118may respectively be fully or partially detectable, while discarding subframes138ain which no high-frequency pulses118are detectable.

Referring toFIG. 3D, an exemplary embodiment of the detection and display system126ofFIG. 2may operate similarly to the system described byFIG. 3C, except that the image sensor128(FIG. 2) may be self-synchronizing. For example, referring to graphs150a-bthe integration periods146aof the image sensor128may not synchronize precisely with the duration (142a) of the high-frequency pulses118generated by the emitters104. However, the image sensor128may detect the start time152of the high-frequency pulses118and adjust the start time154of the integration period146ato match the start time152of the high-frequency pulses118so that each subsequent integration period146acoincides with a high-frequency pulse118, resulting in a sequence of subframes138bwherein the high-frequency pulse118is more easily detectable against background illumination120. The image sensor128may adjust the integration period (146b) to match the duration (142a) of the high-frequency pulses118, resulting in subframes (138d) in which the high-frequency pulses are optimally detectable against background illumination120.

Referring now toFIG. 4, an exemplary embodiment of a method200for detecting a modulated lighting infrastructure system100according to the inventive concepts disclosed herein may include one or more of the following steps. At a step202, an image sensor128of the detection and display system126captures a sequence of subframes138corresponding to a duty cycle of the image sensor128, the sequence of subframes138including at least one subframe138bassociated with 1) a high-frequency pulse118of the approach lighting system102and having an intensity L2and 2) background illumination120having an intensity B1. For example, the image sensor128may capture a sequence of subframes138corresponding to the inverse of a frame rate of the image sensor128, each subframe138associated with an integration period146,146aof the image sensor128that may or may not synchronize with the high-frequency pulse118generated by the emitters104of the system100. The image sensor128may be a visible-band image sensor; an infrared image sensor tuned to emissions in the NIR, SWIR, or LWIR spectral bands; or a multispectral image sensor.

At a step204, an image processor130of the detection and display system126detects a subframe138bwithin the sequence of subframes138wherein the intensity L2of the high-frequency pulse118is greater than the intensity B1of the background illumination120.

At a step206, the image processor130sequentially stores the at least one detected subframe138bin an image buffer132of the detection and display system126.

At a step208, the image processor130discards the one or more subframes138anot associated with a detectable high-frequency pulse118.

At a step210, a display unit134of the detection and display system126sequentially displays the at least one stored subframe138b.

The method200may include additional steps212and214. At the step212, the image sensor128detects the start time152of the high-frequency pulse118.

At the step214, the image sensor128adjusts one or more of a) the start time154of the integration period146aof the image sensor128to match the detected start time152of the high-frequency pulses118and b) the duration of the integration period146bto match the duration142aof the high-frequency pulses118.

As will be appreciated from the above, systems and methods according to embodiments of the inventive concepts disclosed herein may enhance situational awareness by optimizing the visibility of runway lighting systems to approaching aircraft, especially under adverse conditions (e.g., humid atmosphere, bright sunlight) where visible-band LED emissions may be overwhelmed by background illumination, rendering it difficult for cameras and image sensors to accurately detect or locate the approach lighting system. The modulated lighting infrastructure system allows airport facilities to use lower-energy (and thus lower-cost) LED-based approach lighting systems. At the same time, efficient use can be made of the energy deployed to LED-based lighting systems by maximizing visibility by onboard enhanced vision systems while preserving compliance with brightness specifications for pilot visibility.