Requirement of underwater archaeology to UUV

Because of the particularity of the environment and objects of underwater archaeology, there are some special demands for the robot and the equipment, which are described as follows:

The disturbance and destruction to the environment should be as little as possible. It is hard to avoid shuttling in the site back and forth when the underwater robot is working and the result would be serious if the cultural relic was shattered. The silt aroused by disturbance can also affect the collecting of image information. The robofish, adopted the bionic propulsion, has its own advantages compared to the traditional screw propeller. In addition, the electric cable of ROV is a potential trouble, and the crawling robot and daggling robot do not adapt to the archaeology.

Convenient equipments should be prepared for the task. The exploration apparatus and other equipments must be equipped for the underwater robot for archaeology, and they must not do harm to the cultural relic. Generally the underwater TV and sonars are used. But the working depth of underwater TV is limited, and it must work with headlamp when the depth is more than 15 meters. Sonar is the dominant equipment for underwater exploration[3]. Figure1 (a) and (b) are the images returned from underwater TV and side-scan sonar, both of which have their advantages and disadvantages respectively. The sight depth of the underwater TV is short and the eyeshot is small but the image is legible; and the image of the side-scan sonar is blurry but the sight depth is long and the eyeshot is wide. If the underwater robot was applied to the third phase of underwater archaeology, the equipments, such as machinery arm, manipulator and special tools must be equipped with it.

Fig. 1. Images from underwater archaeology

Fig. 1. Images from underwater archaeology

The Dynamic Positioning should be accurate. How to guide the underwater robot to the known target (accuracy) and how to hang around the target by propeller control in order to perform further step task after finding out target (repeatability), all of which need the support of underwater acoustical position system with high accuracy.

High maneuverability. It contains the maneuverability in horizontal (turning radius and turning rate) and vertical (rising and submergence). Usually the shipwreck site is rough and complex, so the robot maneuverability can guarantee the success of the archaeology task. The robot should have local intelligence. It could track the sea-bottom landform and avoid obstacles (independently) autonomously. Generally, the stable depth of the underwater robot is relative to the sea level. But the archaeology exploration task needs to follow the contour line relative to the sea-bottom, which involves tracking of sea-bottom landform. In addition, for the sake of safety, the robot ought to have the capability to avoid obstacles independently. The robot should have small size, light weight and low cost, which are considered from application and popularization. Robot with large size and heavy weight could bring trouble when putting and retrieving. In order to enhance the maneuverability, the underwater robot with traditional screw propeller usually need more than one thruster to produce the propulsion of vector, which makes not only the large size structure, complex control system, but also the high cost. Nevertheless the robofish has certain advantage because it produces the propulsion of vector directly by tail fin and is easier to integrate into a small size. The control should be convenient and flexible. Generally, the operators do not know about the situation of sea-bottom when the underwater robot is carrying out the archaeology task, which are navigated by the images and information returned from underwater robot. As a result it needs the underwater robots have good maneuverability, which is also for security. Moreover, there are many common problems such as the real-time exchanging of information between the mother ship and underwater robot (underwater communication), the dynamic hermeticzation with high compression resistance, the ability of resisting ocean current and so on.

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