Autonomous Landing of an Unmanned Aerial System on Water in an Unknown Sea State

Abstract

Unmanned aerial systems (UAS) are used in the marine and oceans environment for a variety of purposes. In this thesis, an approach is taken to enable safe and reliable autonomous landing of a UAS on the water's surface in an unknown sea state. With a UAS capable of landing on the water's surface under a range of sea state wave conditions, the types of mission that a UAS can undertake in marine and oceans environments will be expanded. In this work, it is assumed the UAS has no prior information of the water surface wave characteristics at the landing spot. Therefore, algorithms were developed to enable the UAS to determine the dominant wave period, significant wave height, and mean wave propagation direction in-situ using range measurements with onboard range sensors. With the desired ocean wave characteristics identified, a method was devised to identify persistent low wave-height segments in the wave field, over a spot, using onboard range sensor measurements. These persistent low wave-height segments provide safe landing windows for the UAS. A staged landing algorithm was then developed to ensure safe and timely autonomous landing of the UAS on the water surface. In addition, an investigation was conducted to determine the efficacy of ultrasonic sensors to measure wave heights when the sensors are in motion and mounted at oblique angles on the UAS. The contributions of this work are: a timely method to identify water surface wave characteristics in situ using range sensor measurements, a means to classify and identify low wave-height segments of a wave field using range sensor measurements, a staged landing algorithm for safe and reliable landing on the water's surface in a sea state, and the analysis of the efficacy of an ultrasonic sensor when mounted at oblique angles to measure water wave heights.