The probability of near midair collisions using level-crossings

We consider probabilistic methods to compute the near midair collision risk using state estimate and covariance from a target tracking filter based on angle-only sensors such as digital video cameras. Existing work is only concerned with risk estimation at a certain time instant, while the focus here is to compute the integrated risk over the critical time horizon. This novel formulation leads to evaluating the probability for level-crossing. The analytic expression for this involves a multi-dimensional integral which is hardly tractable in practice. Further, a huge number of Monte Carlo simulations would be needed to get sufficient reliability for the small risks that the applications require. Instead, we propose a sound numerical approximation that leads to a one-dimensional integral which is suitable for real-time implementations.