Altitude estimator for rotary-wing drone with multiple rotors

The drone has a telemetric sensor (154) that is ready to consider a distance relative to separation of the drone from a surface from echoes returning from ultrasonic impulses emitted by the drone. An altitude determination unit (134) includes a barometric sensor (156), and an estimator (152). An obstacle detecting unit analyzes the echoes to deduce presence of configuration of an obstacle and applies a corrective action to compensate the effect of the obstacle at the relative distance estimated by the telemetric sensor.