Lei feng's Web Editor's Note: author Top Liu, Aerial Robotics Ph.D, this article without permission, and may not be reproduced
1 status and challenges
Hazards include mid-air collision caused by drones and ground impacts, including unmanned aerial vehicles and manned aircraft mid-air collision between objects is our primary concern, and to ensure flight safety at present, countries on the operation of the drone commonly used management limit the drones in the specific airspace isolated with the machine running. But with the drones in reconnaissance, search and rescue, transport, widely used in military and other fields, activity continues to increase its flight on the space environment in the other vehicle and third parties on the surface a great security risk. Isolated operating mode in the future will be difficult to meet the growing demand for application of UAV, drones share airspace with manned aircraft is the trend of the future, thus collision problem has become the one of the key challenges of UAVs. United States national airspace system (National Airspace System, and NAS) next generation airspace system plan that "next generation airspace will focus on the use of satellite air traffic controllers, pilots, passengers, unmanned aerial vehicles, and other stakeholders to share airspace in real time. "The United States Department of Defense developed a spatial integration plans, planning gradually to integrate UAVs into the shared air space. Hermes iPhone cover
The spatial integration of UAV, unmanned flying into non-isolated share airspace with manned aircraft. Characteristics for different types of use, United States defines 6 types of airspace: class a, 6000-20000m, strictly in accordance with the ATC flight b, mainly around the airport, less than the 3000m;C class, next to b's busy airport, lower than the 1200m;D class, the airport tower, below the 800m;E class, ground start, A-D outer space; the g-class, non-controlled airspace.
2 current testing technology
Object detection is the basis for avoiding, unmanned aerial vehicle detection technology there are a variety of solutions, depending on how the perception detection can be divided into cooperative and non-cooperative-type: cooperation, means that all vehicles share information through a common communication link. Non-cooperative, said aircraft in the sky without communication with each other and, therefore, means that only active detection methods. Cooperative detection equipment such as answering machine TCAS and ads-b automatic dependent surveillance-broadcast system is able to get the target aircraft loading device directly and accurately comprehensive status information, but must rely on the communications link and the target is limited. Non-cooperative detection equipment, such as radar Visual EOIR cooperation such as electro-optic infrared sensors to detect detect all objects within the field of view, including aircraft and terrain, birds and other non-cooperative target.
3 cooperative sensing probe
Air traffic alert and collision avoidance system (TCAS) and automatic dependent surveillance-broadcast (ads-b) belonging to the cooperative sensing detection equipment, it can directly access to accurate and comprehensive loading device status information on the target aircraft, but must rely on the communications link and the target is limited. Visual and radar belongs to the non-cooperative sensors to detect detect all objects within the field of view, including airplanes, birds and terrain, but the detection capability of UAV attitude and thus there are blind spots.
3.1 air traffic alert and collision avoidance system (TCAS)
TCAS is to reduce the incidence of air-to-air collision, so as to improve the flight safety of the system. TCAS was originally designed for manned space flight; however, the same can be used for unmanned flight, however, the current price (25,000-$ 150,000) may prevent the TCAS in the field of UAVs is widely used.
3.2 automatic dependent surveillance-broadcast (ads-b)
ADS-B is a relatively new technology, it provides great potential for collision. ADS-B is not limited to air-air surveillance, which uses air to ground communications and has the potential to replace the secondary surveillance radar. Used aircraft near similar to TCAS uses radio signals to send and receive information, but ADS-B one of the most important and obvious difference between the types of information exchanged. Each plane should share information including three-dimensional position, speed, heading, time and intent. This information is for collision avoidance system is very valuable.
4 non-cooperative sensing probe
Non-cooperative detection equipment, such as radar Visual EOIR cooperation such as electro-optic infrared sensors to detect detect all objects within the field of view, including aircraft and terrain, birds and other non-cooperative target.
4.1 vision-based collision detection
Passivity and robustness against non-cooperative targets are the key advantages of optoelectronic sensors, make them avoid very attractive sensor type in the application. In contrast, the traffic alert and collision avoidance system (TCAS) are more dependent on cooperation from other aircraft and method for forwarding their flight information.
Photoelectric sensors in sensor technology is relatively mature, suitable for UAV applications sense and avoid. Advanced electro-optical sensors tend to be compact, low weight, low power, so that they can be applied to relatively small unmanned platforms. In addition, it is very easy to get support for high speed IEEE1394 and IEEE802.3-2008 (Gigabit Ethernet) communications interfaces of commercial off-the-shelf (COTS) products, which can be easily realized image data real-time acquisition and high resolution transmission solutions. At present, available from the camera to the image processing computer or workstation bus standard used by digital video signals: FireWire (IEEE1394), USB2.0, CameraLink and Gigabit Ethernet.
Photoelectric Sensors provide information not just for images in the plane of the target detection and orientation. By the target location in the image plane to infer the relative course information can be used to assess the risk of collision (constant relative heading corresponds to high risk, large changes in relative freedom corresponds to the low risk). In addition, it also can be used to control information and to maneuver.
Studies have shown that, based on the photoelectric sensor perception and circumvent the system approved by the regulator most likely. However, optical sensing methods still faces many problems. The most significant challenge lies in the air environment of unpredictable and ever-changing nature. In particular, visible spectra of a photoelectric sensor, detection algorithm must be able to handle a variety of backgrounds (from the blue sky clouds to ground clutter), a variety of lighting conditions, and possible image artifacts (such as lens flare).
There is another problem with optical sensing method is image dithering noise. Due to the unpredictable aerodynamic maneuvering and drones, adding image jitter camera sensor. Detection algorithm for image planes, image dithering introduce unwanted noise, and have a significant impact on performance. Based on aircraft status information and its jitter compensation techniques have been proposed, image dithering effects can be reduced, but not completely eliminated.
Finally, the implementation of opto-electronic sensor image data in real time is a challenge. However, with the development of parallel processing hardware (such as a graphics processing unit (GPU), field-programmable gate array (FPGA) and proprietary digital signal processor (DSP), the problem is improving. Hermes iPhone 5
In the past decade, Government, University and commercial research group has demonstrated maturity based on photoelectric sensor and circumvention technologies. One of the most mature based on photoelectric sensor and evasion technique has been developed by the Defense Research Institute Limited (DefenseResearchAssociates,Inc. (DRA)) and air force research laboratory (AFRL) and the aeronautical systems Center (ASC) jointly. AEROSTAR UAV has been verified in a distance of approximately 7 miles to detect and track non-cooperative airborne equipment for general aviation. The objective of the scheme is to achieve cooperative and non-cooperative target collision avoidance capability.
Australia's Center for Aerospace Automation (ARCAA) has been undertaking cost-effective for civil UAV awareness and avoidance systems [6,8]. Closed-loop flight tests have been carried out, showing a prototype system to automatically detect the aircraft capacity for evasive action and ordered the aircraft autopilot. In the past decade, a similar study on photoelectric sensor parameters (such as vision) and system performance (such as detection range and probability of detection and false alarm rate) balance between awareness. For example, many studies have shown that, in normal circumstances, increase the field of vision will reduce the detection range, and vice versa.
4.2 radar-based collision detection
Aircraft collision of radar as a mature technology, its detection, scanning speed, and signal quality are relatively high update rate. Kwag applies to flying drones are studied, such as anti-collision radar critical design parameters. Its major technical defect size limit. Radar weight consume large amounts of power, and need a big antenna to find smaller objects, smaller antenna, you lower the precision, so that the radar is limited to large unmanned platforms. In terms of miniaturization, unmanned systems Institute of the University of Denver researchers developed a UAV to carry of phased array radar system weighs only 12 ounces, the volume is similar to one's hand.
5 conclusion
Due to the small unmanned aerial vehicles be limited by cost, weight and power consumption, is no traditional collision-avoidance systems and sensor systems, such as high-accuracy inertial navigation, radar, electro-optical pod. Achieve the small drones of perception and avoid the need to face more challenges.
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