Can an ultrasonic sensor mounted on a drone pick up another drone strongly enough to sense and avoid? I am asking this question to see if mid-air collisions of drones can be prevented using simple analog sensors. Can an ultrasonic sensor mounted on a drone pick up another drone strongly enough to sense and avoid it? 

I know that the sensor is range limited so the aircraft cannot be flying towards each other very fast, but to even do any sense and avoiding, can this sensor work? Or does the drone not provide enough of a return? 

Also, could the range of sensor be increased if both drones emitted ultrasonic energy to be picked up on the sensor more strongly at a distance?
The range of the ultrasonic sensors ends up at somewhere 5 meters (here is the pre-configured search). However a simple sensor would only measure the distance, by the signal travel time. It does not provide the angular co-ordinates or exact location. Same problem as with the simple radar. 

May make more sense to fit the drones with transponders so that they could actively broadcast they own location, speed, orientation and intentions to other members of the flock.