1. A method of monitoring airspace at least partially surrounding an unmanned aerial vehicle (UAV), the method comprising: establishing an object detection zone within the airspace extending from the UAV to a first boundary; establishing an active monitoring zone within the airspace extending from the UAV to a second boundary that is closer to the UAV than the first boundary; generating first signals representative of the airspace by at least a sensor of the UAV; detecting an aircraft within the object detection zone based at least in part on the first generated signals indicating that the aircraft is within the first boundary and outside of the second boundary; generating second signals representative of the airspace by at least the sensor of the UAV; detecting the aircraft within the active monitoring zone based at least in part on the second generated signals indicating that the aircraft is within the second boundary; determining at least an operating characteristic of the aircraft based at least in part on the detecting the aircraft within the active monitoring zone; and determining a trajectory envelope of the aircraft based at least in part on the determining the operating characteristic of the aircraft, wherein the trajectory envelope includes a range of possible trajectories of the aircraft from a given location.