Patent Description:
The Federal Aviation Administration (FAA) has approved Visual Flight Rules (VFR) for Urban Air Mobility (UAM) Operations. Precision landings are fundamental to all aircrafts including UAM/Drones/electric vertical take-off and landing (eVTOL) vehicles. Autonomous precision landings guided by marker-based landings (MBLs) for UAM/drones/eVTOL vehicles under VFR require clear day light conditions. With MBLs, markers with unique patterns are used to identify a landing site and provide guidance references for the vehicle to land. An example of a unique pattern is an Augmented Reality University of Cordoba (ArUco) pattern.

Typically, printed landing markers of different dimensions and patterns are positioned in relation to each other at a landing site. Once a camera of a vehicle, capturing images in real time, captures an image of landing markers, and the identity is verified, a MBL algorithm is used by the vehicle to start and control decent to the landing site or landing pad. The MBL algorithm provides real-time position estimates used by the vehicle to control the decent. For example, based on images of the landing markers, the MBL algorithm may use Euler angles in a north-east-down (NED) coordinate system and a global positioning attitude heading reference system (GPAHRS) sensor fusion system to enable vertical and horizontal correction of the vehicle in achieving a precision landing of the vehicle.

Precision landings are fundamental to all aircrafts including UAM/Drones/eVTOL vehicles. With these types of unmanned vehicles, not having the ability to clearly detect the landing markers hinders the ability to perform precise landings at a designated landing site. Not being able to clearly detect the landing markers may be due to environmental conditions such as dusk, dawn, night, smog, fog, snow, rain, etc..

Further, it is anticipated that UAM Operations will be required to also be operated with digital flight rules (DFR) which include the VFR and instrument flight rules (IFR). The objective of DFR is to provide safe and unfettered access to the airspace to all participating vehicle operators under all visibility, all-weather conditions without incurring the limitations in operational flexibility inherent to IFR and even VFR.

For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need for a landing marker that can be used during varying environmental conditions.

<CIT> relates to systems and methods for flexibly or selectively managing aerial drone parcel transfers. According to its abstract, an aerial drone parcel delivery / transfer management server (ADPTMS) is configured for facilitating flexible management of aerial drone parcel deliveries to or transfers between aerial drone landing pads (ADLPs). Each ADLP has a corresponding ADLP address that includes a unique ADLP identifier; current or most-recently known ADLP geolocation data; and possibly current or most-recently known ADLP elevation data. The ADPTMS can communicate with order management / fulfillment servers associated with online stores, which can communicate with aerial drone parcel delivery / transfer services for dispatching aerial drones to particular ADLP addresses as part of fulfilling online orders. An ADLP can present a machine readable code such as a quick response (QR) code thereon (e.g., on a landing mat) that can be captured by an aerial drone and processed to verify the ADLP's identity. An ADLP can output local RF guiding signals and/or local optical guiding signals (e.g., infrared signals) to aid aerial drone navigation to the ADLP.

<CIT> relates to an electronic marker that may provide an approach notification to enable people to understand and interpret actions by a UAV, such as an intention to land or deposit a package at a particular location. According to its abstract, the marker may communicate a specific intention of the UAV and/or communicate a request to a person. The marker may monitor the person or data signals for a response from the person, such as movement of the person that indicates a response. The marker may be equipped with hardware and/or software configured to provide notifications and/or exchange information with a person or the UAV at or near a destination. The marker may include a display, lights, a speaker, and one or more sensors to enable the UAV to provide information, barcodes, and text. The marker can provide final landing authority and can "wave-off" the UAV if an obstacle or person exists in the landing zone.

<CIT> relates to a delivery robot that may provide an approach notification to enable people to understand and interpret actions by an unmanned aerial vehicle (UAV), such as an intention to land or deposit a package at a particular location. According to its abstract, the delivery robot may include a display, lights, a speaker, and one or more sensors to enable the robot to provide information, barcodes, and text to the UAV and/or bystanders. The robot can provide final landing authority, and can "wave-off" the UAV, if an obstacle or person exists in the landing zone.

<CIT> relates to a method of providing a smart helipad configured to support landing of a vertical takeoff and landing aircraft. According to its abstract, the method includes adaptively displaying an imaged marker recognizable by a camera mounted to the vertical takeoff and landing aircraft; obtaining tilting information about a ground surface and a sea surface using a gyro sensor; and adjusting a landing pad connected to a display unit on which the marker is displayed to be in parallel with a horizontal line based on the tilting information, using a motion platform having change responsiveness to all of the directions.

The present disclosure concerns an active landing marker as defined in claim <NUM> and a method of generating an active landing marker as defined in claim <NUM>. Dependent claims define preferred embodiments.

The following summary is made by way of example and not by way of limitation. It is merely provided to aid the reader in understanding some of the aspects of the subject matter described. Embodiments provides an active landing marker that generates a unique pattern that can be clearly identified during different environmental conditions.

In one embodiment, an active landing marker including a housing, a cover panel, a marker panel and energy sources is provided. The cover panel is coupled to the housing, the cover panel made of polarized translucent material. The marker panel is positioned within the housing. The marker panel includes a plurality of selectively positioned energy absorbing sections and a plurality of energy transmission sections. The energy sources are contained within the housing. The marker panel being positioned between the energy sources and the cover panel. Energy radiated from the energy sources passing through the plurality of energy transmission sections of the marker panel and through the cover panel generating an active signal marker having a unique marker pattern. The active signal marker aiding in the landing of vehicles during varying environmental conditions by using a sensor configured to sense an environmental condition and a controller to selectively provide power to the energy sources and configured to switch between energy sources based on the current environmental condition.

In still another embodiment, a method of generating an active landing marker is provided. The method including determining a current environmental condition by at least one sensor, forming a unique pattern in a marker panel with a plurality of energy absorbing sections and a plurality of energy transmission sections; selectively providing power to a plurality of energy sources to generate energy that is absorbed by the energy absorbing sections and transmitted from the energy transmission sections; polarizing the transmitted energy to define the unique pattern with the transmitted energy that aids in the landing of vehicles during varying environmental conditions, and switching between energy sources based on the current environmental condition.

The present invention can be more easily understood and further advantages and uses thereof will be more readily apparent, when considered in view of the detailed description and the following figures in which:.

In accordance with common practice, the various described features are not drawn to scale but are drawn to emphasize specific features relevant to the present invention. Reference characters denote like elements throughout Figures and text.

In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the inventions may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the claims.

As discussed above, some current landing markers use printed markers. Printed landing markers are passive markers because they rely on ambient light that is reflected off of the markers to provide the identification of a unique identifier of the landing marker. Hence, passive landing markers typically can only be used during daylight landing operations when sufficient ambient light is present.

Embodiments provide self-contained active landing markers. The active landing markers enable use of a vehicle's MBL system in all visibility conditions without incurring the limitations in operational flexibility inherent to IFR and even VFR. In embodiments, radiated energy from an energy source is used to form a unique marker pattern that is used by a vehicle to identify and perform a precision landing of the vehicle in varying environmental conditions.

In one example, the unique marking pattern is made with a marker panel that includes absorbing sections that absorb the energy from the energy source and energy transmission sections that radiate the energy from the active landing marker. The radiated energy is detected by the systems on the vehicle. The pattern made by the energy identifies an associated landing site and provides a reference for a vehicle's MBL system to aid in accomplishing a precision landing at the landing site.

<FIG> illustrates a block diagram of an active landing marker <NUM> of an example embodiment. The active landing marker <NUM> includes a housing <NUM>. A cover panel <NUM> is used to form an enclosed cavity <NUM> with the housing <NUM>. In one example, the cover panel <NUM> is made of a translucent material that radiates energy <NUM> from an energy source that is located within the cavity <NUM> of an active landing marker <NUM>. In one example, the cover panel <NUM> is made of a polarizing material to radiate energy in only one select direction to help define and identify the unique pattern generated by the active landing marker <NUM>. Further in an example, the cover panel <NUM> is made from a translucent white polarized material. In yet another example, the cover panel <NUM> is made from a translucent amber polarized material. In still another embodiment, the cover panel <NUM> is made from a translucent polarized material with near infrared (NIR) properties that emits NIR light in response to the NIR radiated energy from the energy source.

As discussed above, the cover panel may include polarizing material. Undesired reflections captured in a field of view of an image sensor (camera) on vehicles can cause issues when trying to identify a landing marker and implement a MBL system. This may occur, for example, as a result of bright sunlight reflecting off of bright regions or light sections of the active landing marker <NUM>. The polarized material in the cover panel addresses this issue. In one example, the polarized material includes a liner polarizing film <NUM> such as, but not limited to, a Dichroic thin film. In another example wire-grid polarizers may be used. The polarizing material absorb incident light oscillating in all but one plane, its polarizing axis, yielding linear polarization. Liner polarization of a randomly polarized light source further may reduce the intensity of the source by fifty to sixty five percent. This makes the polarization material effective in evening out illumination levels within the filed of illumination region of the active landing marker <NUM>. The cover panel <NUM> may further include one of an anti-glare coating <NUM> and a scratch-resistant covering <NUM>.

The energy source in the example illustrated in <FIG> are energy producing elements such as, but not limited to, a plurality of light emitting diodes (LEDs) <NUM>, <NUM> and <NUM>. The LEDS <NUM>, <NUM> and <NUM>, in this example, are positioned within the cavity <NUM> of the housing <NUM>. In the LED example, the LEDS <NUM>, <NUM> and <NUM> are coupled to an LED driver <NUM> to regulate power to one or more strings of LEDs <NUM>, <NUM> and <NUM> from a power source <NUM>.

In one example, different LEDS <NUM>, <NUM> and <NUM> transmit different color light. For example, LEDS <NUM> may be configured to transmit white light, LEDS <NUM> may be configured to transmit amber light and LEDS <NUM> may be configured to transmit RED light or GREEN light or BLUE light or may be a combination of the RGB light. Further in an example, the cover panel <NUM> may be made of a translucent white or amber polycarbonate, or other material like hardened glass.

Also illustrated in <FIG> is a marker panel <NUM> that is received within the cavity <NUM> of the housing <NUM> adjacent the cover panel <NUM> in this example. The marker panel <NUM>, as best illustrated in <FIG>, defines the unique pattern <NUM> of the active landing marker <NUM> that is used by the vehicle to identify a location, such as a landing site, and provide a reference for precision landings. The unique pattern <NUM> is made from a plurality of energy transmission sections <NUM> and a plurality of energy absorbing sections <NUM>. In the Example of <FIG>, the energy transmission sections <NUM> are translucent sections that allow energy generated from the LEDS <NUM>, <NUM> and <NUM> to pass through and the energy absorbing sections <NUM> are made from a plurality of opaque sections that blocks light from the LEDS <NUM>, <NUM> and <NUM> from passing through. The energy transmitted through the energy transmission sections <NUM> passes through the cover panel <NUM> that includes polarized material.

In one example, the unique pattern <NUM> is an ArUco pattern. The energy absorbing sections <NUM> of the marker panel <NUM> provide a binary zero of the ArUco pattern while the energy transmission sections <NUM> provide a binary one of the ArUco pattern. In an example, a landing identification site system in a vehicle, identifies a desired landing sited based on a detected ArUco pattern and a MBL system of a vehicle uses the unique ArUco pattern of one or more active landing markers <NUM> to accomplish a precision landing of the vehicle.

In an example, the unique pattern <NUM> of the marker panel <NUM> of the active landing marker <NUM> is designed to be changed. In one example, a different marker panel <NUM> with a different unique pattern <NUM> is used to just replace a current marker panel <NUM>. In another example, the marker panel <NUM> may be designed to selectively reconfigure its unique pattern. For example, the marker panel may be made from a plurality of dimmable glass sections or liquid crystal plates that selectively block or allow the transmission of light. In a dimmable glass section example, suspended particle devices (SPDs) that include rod like nano-scale particles are suspended in a liquid between pieces of glass or plastic. The suspended particles are randomly organized in the absence of a voltage. The randomly organized particles block and absorb energy making the section opaque. When a voltage is applied, the suspended particles align letting the energy to pass through. In another example a mechanical energy absorbing shutter system may be used to modify select sections of the marker panel to achieve a desired unique pattern <NUM>.

In examples that include changeable sections in a marker panel, a controller <NUM> may be used to selectively apply voltage from the power source <NUM> to select sections to create a desired unique pattern in the marker panel <NUM>. The controller <NUM> may be in communication with a memory <NUM> that stores operating instructions implemented by the controller <NUM>. Further, the controller <NUM> may be in communication with a wireless communication unit <NUM>. The wireless communication unit <NUM> may be used to receive remote operating signals relating to a desired unique pattern in the marker panel <NUM> or broadcast a current unique pattern to a remote location such as a vehicle seeking the landing site or a ground station.

In general, the controller <NUM> may include any one or more of a processor, microprocessor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field program gate array (FPGA), or equivalent discrete or integrated logic circuitry. In some example embodiments, controller <NUM> may include multiple components, such as any combination of one or more microprocessors, one or more controllers, one or more DSPs, one or more ASICs, one or more FPGAs, as well as other discrete or integrated logic circuitry. The functions attributed to the controller <NUM> herein may be embodied as software, firmware, hardware or any combination thereof. The controller <NUM> may be part of a system controller or a component controller. The memory <NUM> may include computer-readable operating instructions that, when executed by the controller <NUM> provides functions of creating desired unique patterns in the marker panel <NUM>. The computer readable instructions may be encoded within the memory <NUM>. Memory <NUM> is an appropriate non-transitory storage medium or media including any volatile, nonvolatile, magnetic, optical, or electrical media, such as, but not limited to, a random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), electrically-erasable programmable ROM (EEPROM), flash memory, or any other storage medium.

It may further be desired to change the wavelength of the energy transmitted from the active landing marker. This may be due to the changing of environmental conditions. The controller <NUM> acts as a switch, switching between LEDs <NUM> or LEDS <NUM> or LEDs <NUM> to achieve a desired radiated energy of a select wavelength. Other systems to change the wavelength of the radiated energy may be used including but not limited to, filtering through a shutter system. The radiated energy <NUM> from the active landing marker <NUM> may be set at a select wavelength for a given environmental condition. The given environmental condition is determined by at least one sensor <NUM> and may in addition be determined through a remote communication signal received through the wireless communication unit <NUM>. An example of types of sensors <NUM> that may be used includes, but is not limited to, light sensors, temperature sensor, moisture sensors, and smoke sensors etc..

Further, the luminosity of the radiated energy from the active landing marker <NUM> may be electronically controlled in an example taking into consideration the current ambient light available and glare. This may be accomplished by the controller <NUM> with luminous flux sensor signals from the at least one sensor <NUM>.

In an example, an active landing marker <NUM> may be configured to radiate white light based on a luminous flux sensor input from the at least one sensor <NUM>. Each energy transmission section <NUM> of the unique pattern <NUM> in this example is optically illuminated with white light. The energy absorbing sections <NUM> may include non-reflective black sections. The luminosity of the light may be electronically controlled with respect to the ambient light and glare with the luminous flux sensors input. White light may be used for day and night landings during clear visibility environmental conditions or clear visual meteorological conditions (VMC). The vehicle may use a low light electro-optical camera for the MBL system.

In another example, yellow light may be used with active landing marker <NUM>. In one example, filtering techniques may be used on generated white and amber light to radiate yellow light of <NUM> wavelength. Yellow light may be used during day and night landings in low visibility landing conditions under instrument meteorological conditions (IMC).

In another example, more than one color of light maybe used in generating the unique pattern. In one example, RED color LEDS, BLUE color LEDS, GREEN color LEDS or a combination of the RGB color LEDS are used. For example, the marker panel <NUM> may form a chroma-tag code with the sections of the marker panel <NUM> optically illuminated with specific color light sources which may be accomplished with filtering and/or polarization techniques or different LEDS <NUM>, <NUM> and <NUM>. This configuration may be used for both day and night landings in clear and low visibility landing conditions under VMC. A color code of the active landing marker or a group of active landing markers also provides more options for encoded data which provides an enhanced security element.

In still another example, the active landing marker <NUM> is designed to radiate energy in the NIR spectrum. In one example, energy transmission sections <NUM>, of the unique pattern, are optically illuminated with NIR light greater than <NUM> wavelength using filters and/or coatings and polarization techniques. This configuration works well for night landings in very low visibility landing conditions under instrument meteorological conditions (IMC). The vehicle would use a near infrared camera in capturing the unique pattern from the active landing marker.

Other types of energy sources beside LEDs may be used to create a desired unique pattern with the marker panel <NUM>. For example, heating sources may be used to generate far infrared energy, such as hot surface far infrared (FIR) energy, that are used in generating the desired unique pattern. This type of active marker-based landing system may be useful when used in inclement weather conditions where visible light is hard to detect.

An example of an active landing marker <NUM> that include heat sources <NUM> to generate FIR energy is illustrated in <FIG>. The active landing marker <NUM> includes a housing <NUM>. A cover panel <NUM> is used to form an enclosed cavity <NUM> with the housing <NUM>. In one example, the cover panel <NUM> is made of thermal conducting material that radiates thermal energy <NUM> from the heat sources <NUM> that is located within the cavity <NUM> of active landing marker <NUM>. The cover panel <NUM> may further include a scratch-resistant covering <NUM>.

In one example, the heat sources <NUM> are ceramic cartridge heaters. A controller <NUM>, such as a thermal controller, may control energy from an energy source <NUM> to regulate the generated FIR energy from the heat sources <NUM>. This example further includes thermoelectric cooling pads <NUM> that are spaced a distance from the heat sources <NUM>. The thermoelectric cooling pads <NUM> transfers heat out of the cavity <NUM> to a frame of the housing <NUM> to regulate the temperature within the cavity <NUM> therein preventing the overheating of components and a consistent unique pattern. A controller <NUM>, such as a thermal controller <NUM> may control energy from an energy source <NUM> to regulate the heat transfer provided by the thermal controller <NUM>.

In one example, a marker panel <NUM> is used that includes energy transmission sections <NUM> of thermally conductive material and energy absorbing sections <NUM> of thermal absorbing materials to generate the unique pattern provided by the active landing marker <NUM>. In another example, the heat sources <NUM> themselves are arranged in a desired unique pattern and are positioned adjacent the cover panel <NUM> to generate the unique pattern through the cover panel <NUM>.

Another example of an active landing marker <NUM> is illustrated in <FIG>. In this example, the unique pattern is made in the marker panel <NUM> with cold sections. The unique pattern can be read with thermal image capturing device in a vehicle. Active landing marker <NUM> includes thermoelectric cooling pads <NUM> used to cool material in select energy transmission sections <NUM> of the marker panel <NUM>. The active landing marker <NUM> includes a housing <NUM>. A cover panel <NUM> is used to form an enclosed cavity <NUM> with the housing <NUM>. In one example, the cover panel <NUM> is made of thermal conducting material. The thermoelectric cooling pads <NUM> are located within the cavity <NUM> of the active landing marker <NUM>. The cover panel <NUM> may further include a scratch-resistant covering <NUM>.

The marker panel <NUM> includes the energy transmission sections <NUM> of thermally conductive material that are cooled by the thermoelectric cooling pads <NUM> and energy absorbing sections <NUM> of thermal absorbing materials that thermally insolates the thermoelectric cooling pads to generate the unique pattern provided by the active landing marker <NUM>.

In one example, heat sources <NUM> are included in the cavity <NUM> of active landing marker <NUM> to regulate the temperature within the cavity <NUM> when needed. A controller <NUM>, such as a thermal controller, may control energy from an energy source <NUM> to regulate the heat generated by the heat sources <NUM>. Further controller <NUM>, such as a thermal controller may control energy from the energy source <NUM> to regulate the cooling of the thermoelectric cooling pads <NUM>. In another example, a single controller may be used to control both the thermoelectric cooling pads <NUM> and the heat sources <NUM>.

Examples of <FIG> and <FIG> discussed above, provide active landing markers <NUM> and <NUM> that provide far infrared/thermal radiated energy signals. Each section <NUM>, <NUM>, <NUM>, and <NUM> of respective marker panels <NUM> and <NUM> of the active landing markers <NUM> and <NUM> are thermally controlled. The thermal absorbing materials in the energy absorbing sections <NUM> and <NUM> are highly efficient thermal barriers designated considering the environmental temperature and other variations. The active landing markers <NUM> and <NUM> may be used in very low visibility conditions in either day or night. The vehicle would include thermal camera for the MBL.

Another example the active landing marker <NUM> is shown in <FIG>. In this example, within a housing <NUM> is a power source <NUM> and a controller <NUM>. The controller <NUM> in an example, is a simple switch that selectively provides power to energy generating sources <NUM>. The radiated energy from the energy generating sources <NUM> is projected or directed to a marker panel <NUM> with a unique pattern is configured of energy absorbing sections <NUM> and energy reflection sections <NUM>. The energy absorbing sections <NUM> absorb the radiated energy <NUM> and while the energy reflection sections <NUM> reflect the radiated energy <NUM>. The cover <NUM>, made from a polarizing material, directs the reflected radiated energy <NUM> from the energy reflection section <NUM> to define the unique pattern to be detected by a camera imaging system in a vehicle. In one example, the external energy generating sources <NUM> are positioned at corners of the active landing marker <NUM>. This type of active landing marker <NUM> provides good visibility of the unique pattern at night and during low visibility conditions.

Referring to <FIG>, an active landing marker flow diagram <NUM> is illustrated. The flow diagram <NUM> is provided as a series of sequential blocks. The sequence may occur in a different order or even in parallel in other embodiments. Hence, embodiments are not limited to the sequential order of the blocks as set out in <FIG>.

Flow diagram <NUM> starts at block <NUM> where a unique pattern is formed in a marker panel. As discussed above, the unique pattern is made of with a plurality of energy absorbing sections and a plurality of energy transmission sections. The material that the sections are made is dependent on the type of energy signal used to generate the active unique pattern. The unique pattern is a pattern recognized by a landing identification system of a vehicle and a MBL system of the vehicle uses one or more of the unique patterns as references to accomplish a precision landing of the vehicle.

The active landing marker may include a function that changes the energy signals generated based on current environmental conditions. In this example, the environmental conditions are monitored at block <NUM>. This may be done with the use of one or more sensors and a controller that selects the energy signals based on signals from the one or more sensors. In another embodiment, the current environmental conditions are provided from a remote source through a wireless communication unit.

Energy is generated at block <NUM>. The type of energy depends on the environmental conditions in an example. The type of energy may be selected based on wavelength best suited to convey the unique pattern for the current environmental conditions. This may be done, for example, by switching between energy sources or switching between different LEDs or by filtering techniques as discussed above. As also discussed above the energy is either passed through or reflected off of the energy transmission sections and through a cover of polarizing material at block (<NUM>) to radiate the energy in the unique pattern.

At block <NUM> it is determined if a new unique pattern is needed. This may come based on remote instructions received at the controller via the wireless communication unit. If a new pattern is not needed, the process continues at block <NUM> monitoring for environmental conditions. If new pattern is needed, a new unique pattern is formed in the marker panel at block <NUM>.

Claim 1:
An active landing marker (<NUM>, <NUM>, <NUM>, <NUM>) comprising:
a housing (<NUM>, <NUM>, <NUM>, <NUM>):
a cover panel (<NUM>, <NUM>, <NUM>, <NUM>) coupled to the housing, the cover panel made of polarized translucent material;
a marker panel (<NUM>, <NUM>, <NUM>, <NUM>) including a plurality of selectively positioned energy absorbing sections (<NUM>, <NUM>, <NUM>, <NUM>) and a plurality of energy transmission sections (<NUM>, <NUM>, <NUM>, <NUM>);
energy sources (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) positioned to direct energy to the marker panel (<NUM>, <NUM>, <NUM>, <NUM>), energy radiated from the energy sources (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) being absorbed by the energy absorbing sections (<NUM>, <NUM>, <NUM>, <NUM>) of the marker panel (<NUM>, <NUM>, <NUM>, <NUM>) and directed out of the cover panel (<NUM>, <NUM>, <NUM>, <NUM>) by the energy transmission sections (<NUM>, <NUM>, <NUM>, <NUM>) to generate an active signal marker having a unique marker pattern, the active signal marker aiding in the landing of vehicles;
a sensor configured to sense an environmental condition; and
a controller to selectively provide power to the energy sources,
wherein the controller is configured to switch between energy sources based on the current environmental condition.