In recent years, there has been an increasing interest in developing and using Uninhabited Air Vehicles (UAVs) as tools for ocean surface data acquisition. However, the use of UAVs for ocean applications is still limited to a few scientific institutions scattered worldwide, and most vehicles have been designed to conduct simple survey missions that in general do not require close interaction between the operator and the environment. It is by now felt that the effective use of UAVs in demanding marine science applications must be clearly demonstrated, namely by evaluating the system in terms of adaptability to different missions scenarios, maritime launch and recovery, survivability, autonomy, endurance, payload performance and usability, and system integration with the existent marine science instrumentation. Meeting these stringent requirements poses considerable challenges to marine scientists, system designers, and developers.

This project represents a step towards meeting those goals. Specifically, it aims at developing a versatile UAV prototype that can take-off and land either on an opportunity airstrip (using the landing gear) or on a bay or harbor (as a seaplane). The aircraft will be designed for marine science applications with special emphasis on the location and tracking of marine mammals and commercially important or threatened pelagic species such as the Atlantic Tuna. Further applications include sea surface temperature measurement and specialized data acquisition for faster identification and better understanding of features like eddies and air sea interaction. The use of UAVs in marine science applications can be foreseen as tool for directing research vessels to new areas of interest, enabling a more efficient use of ship time.

The main focus of this proposal is on the design and construction of the aircraft itself, and on the development and integration of advanced systems for vehicle navigation, guidance and control, payload command, telemetry, and mission control. In preparation for future operation scenarios that can involve multiple air vehicles, additional research effort will be placed on the areas of flight formation and cooperative control of multiple UAVs.

System design, implementation and test will be guided by the requirements of a number of realistic mission scenarios, including those of two scientific missions devoted to tuna fish schools detection and cetacean location and tracking, to be undertaken in the Azores during the second and third years of the project. Laboratory pre-testing of the systems developed using hardware-in-the-loop simulation and flight testing of the complete UAV prototype in an airfield will precede the actual missions at sea. A predefined set of operational modes, which range from remotely operated to fully autonomous, will illustrate the capability of the aircraft and systems developed to perform the sequence of steps that are required to program and execute scientific missions in the ocean.

The avionic system for the UAV builds on similar systems that have been fully developed by members of the proponing team over the past few years. The degree of miniaturization achieved will make it possible to install the avionics in a small water proof container that can be easily mounted on and removed from the aircraft for inspection. To implement the avionics, a DSP based computer architecture is used, allowing for easy interfacing with the data acquisition hardware through a distributed architecture built around the CAN Bus and Ethernet. The Navigation System to be developed and installed onboard the UAV uses advanced aiding techniques to enhance error estimation in low-cost strap-down inertial navigation systems. New sensor-based control techniques resorting to a radar altimeter will be explored to implement terrain following controllers, thus enabling the vehicle to fly at a constant desired distance from the ocean surface or ground. Applications to automatic takeoff and landing maneuvers will be developed, implemented, and tested in the platform.

The UAV will also be instrumented with an image acquisition module, which consists of a digital video camera mounted on a pan-tilt unit. To deal with low frequency oscillations, a closed loop control system is used for stabilizing the image by commanding the pan and tilt motions of the camera based on inertial information available from the aircraft navigation system. It is then possible to ensure that the acquired images present a smooth behavior so that a steady image of the ocean surface can be kept at all times, regardless of the pose assumed by the airplane while maneuvering or even under wind induced disturbances.