Table 2. Comparison between the results of different methods

Table 2. Comparison between the results of different methods

It is obvious that although the helical scan wasted less time than out and home scan, but the information of the image returned was little, which was the result of area omitting, and which was almost unavoidable in the condition of manual operating. Moreover, exploring the bottom could find more questionable objects than searching in certain depth, but the cost was that it raised the benthal deposit and influenced the quality of images. Once the robot was equipped with underwater positioning system and side sonar, it would achieve the autonomous swimming of the foregone trace and the tracking of benthal landform, which would improve the exploration efficiency and quality.

Figure 7 shows a questionable picture returned from SPC-II. Since the seawater is turbid and the target is too close to the lens, its field is very blurry.

Fig. 7. One returned image from robofish 1.4 Conclusion

Underwater archaeology experiments have validated the performance of SPC-II. Meanwhile, some problems have been exposed, which referred to Dynamic Positioning, maneuverability (vertical), communication, configuration of functional devices and diving depth, etc. All these problems supply references to future researchers. To serve the underwater archaeology better, and build basis for the future complicated applications, the robofish SPC-II should be improved properly. The details are described as follows.

1. Add an underwater positioning system. Influenced by ocean current and stormy waves, the existing dead reckoning error is unacceptable. It makes the acoustic positioning system necessary. This system is also strongly required for dynamic positioning.

2. Improve the maneuverability of vertical plane. One of the diving methods is changing its own weight, but it is difficult to respond dynamically; and the other is changing the incidence angle of pectoral fins, but it requires a certain speed. In order to dive faster and vertically, it is considered to replace the pectoral fins with two vertical screw propellers.

3. Add high-performance functional devices such as high accuracy and wide-eyeshot CCD cameras, side-scan sonar, robot arms, manipulators, etc.

4. The diving depth. The target depth is set to 100 meters. Most of sites under water are within this range.

5. Optimize local intelligence. This needs to upgrade the corresponding sensors and improve algorithms.

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