Augmented Reality (AR) is a groundbreaking technology which enhances the real world by virtual objects in order to create a new mixed reality environment. Typically Augmented Reality systems consist of an output device displaying the virtual information, a tracking system for determining position and orientation of the user, a computer processing the necessary data and arbitrary input devices for navigation and interaction.

Nevertheless water as a totally different environment adds some different, not yet quite managed challenges to the realization of AR applications. Beside leak tightness, water also requires new and innovative extensions to tracking and visualization as data transmission, lighting conditions and human perception are significantly altered under water.

One of the key challenges for Augmented Reality applications is the tracking of the user’s viewing position and orientation in real-time, in order to obtain precise alignment between real and virtual objects. Many different approaches have been developed in recent years but not all tracking technologies used in Augmented Reality systems on shore are suitable for underwater use. In Fraunhofer FIT’s first prototype, which used a regular Windows XP based ultra-mobile PC, a hybrid approach of optical marker-based tracking and inertial-magnetic-field-based tracking has been used. In AREEF the target
devices are mobile phones and tablet PCs with an application-based operating system such as Android and with far less computing power than the PC used in Fraunhofer FITs approach. Therefore in AREEF we will investigate appropriate tracking mechanisms for these devices.

Sophisticated usability is another crucial aspect for an underwater Augmented Reality
application: Water is not the natural environment for human beings and exposes the user to specific conditions. The user can e.g. only slowly move due to the water resistance and is barely able to locate sounds due to the more than four times faster sonic velocity. In AREEF we will explore adequate interaction techniques for under water use.

In summary, AREEF project will investigate to develop an affordable and advanced underwater AR system using mass-market mobile devices such as smart phones and tablets (see figure below), while the basic idea and the concept for the system are based on the original system. The technological innovations of the goal system include:

• Hybrid tracking for mobile phones / tablets for swimming pool use
• Adequate underwater interaction techniques
• Rendering of the virtual objects on the waterproof sealed mobile devices
• Multi-user interaction environment