曝光台 注意防骗
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The passive cooperative scenario, like the active cooperative one, relies on everyone having a transponder, but with everyone's transponder broadcasting position, altitude and velocity data. Its advantages are its lower relative cost (no onboard interrogator required to activate transponders) and its ability to provide S&A information in both VMC and IMC. Its disadvantage is its dependence on all traffic carrying and continuously operating transponders. In this scenario, UA should have the capability to change transponder settings while in flight.
The passive non-cooperative scenario is the most demanding one. It is also the most analogous to the human eye. A S&A system in this scenario relies on a sensor to detect and provide azimuth and elevation to the oncoming traffic. Its advantages are its moderate relative cost and ability to detect non-transponder equipped traffic. Its disadvantages are its lack of direct range or closure rate information, potentially high bandwidth requirement (if not autonomous), and its probable inability to penetrate weather. The gimbaled EO/IR sensors currently carried by reconnaissance UA are examples of such systems, but if they are looking at the ground for reconnaissance then they are not available to perform S&A. An emerging approach that would negate the high bandwidth requirement of any active system is optical flow technology, which reports only when it detects an object showing a lack of movement against the sky, instead of sending a continuous video stream to the ground controller. Imagery from one or more inexpensive optical sensors on the UA is continuously compared to the last image by an onboard processor to detect minute changes in pixels, indicating traffic of potential interest. Only when such objects are detected is their bearing relayed to the ground.
Once the "see" portion of S&A is satisfied, the UA must use this information to execute an avoidance maneuver. The latency between seeing and avoiding for the pilot of a manned aircraft ranges from 10 to
12.5 seconds according to FAA and DoD studies5. If relying on a ground operator to S&A, the UA incurs the same human latency, but adds the latency of the data link bringing the image to the ground for a
5 Tyndall Air Force Base Mid-Air Collision Avoidance Study; FAA P-8740-51; see also Krause, Avoiding Mid-Air Collisions, p. 13
APPENDIX F – AIRSPACE
Page F-8
decision and the avoidance command back to the UA. This added latency can range from less than a second for line-of-sight links to more for satellite links.
An alternative is to empower the UA to autonomously decide whether and which way to react to avoid a collision once it detects oncoming traffic, thereby removing the latency imposed by data links. This approach has been considered for implementation on TCAS II-equipped manned aircraft, since TCAS II already recommends a vertical direction to the pilot; but simulations have found the automated maneuver worsens the situation in a fraction of the scenarios. For this reason, the FAA has not certified automated collision avoidance algorithms based on TCAS resolution advisories; doing so would set a significant precedent for UA S&A capabilities.
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无人机系统路线图 Unmanned Aircraft Systems Roadmap(173)
