Publications

Probabilistic alerting systems for airborne collision avoidance often depend upon accurate estimates of the probability of conflict. Analytical, numerical approximation, and Monte Carlo methods have been applied to conflict probability estimation. The advantage of a Monte Carlo approach is the greater flexibility afforded in modeling the stochastic behavior of aircraft encounters, but typically many samples are required to provide an adequate conflict probability estimate. One approach to improve accuracy with fewer samples is to use importance sampling, where trajectories are sampled according to a proposal distribution that is different from the one specified by the model. This paper suggests several different sample proposal distributions and demonstrates how they result in significantly improved estimates.

This study, performed from May 2006 to January 2007 by MIT Lincoln Laboratory, investigated the feasibility of providing ground-sensor-based traffic data directly to Global Hawk operators at Beale AFB. The system concept involves detecting and producing tracks for all cooperative (transponder-equipped) and non-cooperative aircraft from the surface to 18,000 ft MSL, extending from the Beale AFB Class C airspace cylinder northward to the China Military Operations Area (MOA). Data from multiple sensors can be fused together to create a comprehensive air surveillance picture, with the altitudes of non-cooperative targets estimated by fusing returns from all available sensor data. Such a capability, if accepted by the FAA, could mitigate the need for Temporary Flight Restrictions (TFR) to satisfy Certificate of Waiver or Authorization (COA) requirements. There are no existing specifications for ground-sensor-based Unmanned Aerial Systems (UAS) traffic avoidance procedures, nor is it yet known how precisely altitude needs to be estimated. It may be possible to avoid traffic laterally, in which case traffic altitude need not be known accurately. If, however, it is necessary to also avoid traffic vertically, then altitudes will need to be estimated to some (as yet undefined) level of accuracy.