Page 639 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

22.3 Putting it all together 639
Target
Anchor
FIGURE 22.15
ROV-mounted sonar.
that viewed from the submersible. From the side scan sonar perspective (i.e., from above), a drown- ing victim will give the shape and appearance of a human form. From the submersible’s perspec- tive, the body may look like a log, a pipe, a rock, or any of a number of items depending upon the viewing angle.
22.3.8 Sonar/ROV interaction
A technique for gaining an orientation on the bottom is to find either a flat rock or a solid location on the bottom to plant the submersible to gain a good vantage point to image all around. A mud bottom makes this planting a bit more permanent, since it may require an excess amount of thrust to unstick the submersible.
Once a location is found, put the submersible on the bottom so that it becomes a stable platform from which to build an image of the surrounding area. The image is generated as the sonar head scans around the vehicle, isolating the target from the surrounding terrain. To better identify the tar- get, it may be required to move the vehicle to another location to rescan the area.
The target is then brought to zero bearing (i.e., directly ahead of the vehicle) and is maintained in view while the vehicle is navigated to the target. Once the target is located and positively identi- fied, the vehicle can remain on location for as long as necessary. If the vehicle is equipped with a manipulator or some form of physical attachment device, it is best to hook on to the target to main- tain visual contact until the next step in the process is initiated.