An Advanced Sense and Collision Avoidance Strategy for Unmanned Aerial Vehicles in Landing Phase Figure 17. Habitat modification of BBO. Figure 16. The procedure of the proposed approach. Figure 18. Habitat mutation of BBO. ing wind and aircraft modeling errors. These factors affecting the performance of the proposed collision-free trajectory should be studied in the future. Moreover, a possible future direction is to integrate BBO with other artificial heuristic approaches to improve the global exploration capability and to verify the proposed algorithm in a real UAV testbed. (A-3) where and are the velocity along x-axis and z-axis, The parameters of MX,u, satisfy: APPENDIX BBO-BASED MIGRATION AND MUTATION PROCEDURE Related Coefficients and are the Rayleigh terms deter- mined by the force equations, and are indicated as: (A-1) IMPLEMENTAION OF PROPOSED BBO WITH DIFFERENTIAL FLATNESS TO AVOID COLLISIONS The detailed procedure of BBO with differential flatness approach is introduced to generate a feasible trajectory for guiding a landing UAV to avoid multiple threats. As can be seen in Figure 16, eight steps are included in the overall procedure. C (A-2) 50 Step 1: Initialize the environment and orderly gridding coordinate. A flight range with 10,000 m × 1,000 m is decomposed into a grid array by dividing the flight environment as 500 m × 50 m squared grids. The initial point of grid is the IEEE A&E SYSTEMS MAGAZINE SEPTEMBER 2016