Originally Posted by
luckypierre
I presume the Bluefin generates a finely detailed map of the bottom. From a search perspective, what are the benefits of such detail at this point rather than use a more powerful transmitter aboard a ship, such as the survey vessel Echo. At 4K meters, can a surface ship image a structure like a 777 debris field on the bottom? If so, seems to me that the sweep area would be significantly larger with a surface vessel and allow a much more rapid search. Is there any difference in the return signal after pinging off an aluminum and steel surface? Once committed to a particular search alternative (ie Bluefin), is it possible to "tune" other sonars to avoid increased noise in the search area?
Good questions. The problem is the depth, specifically the range. The 4500 m depth creates two problems that make an AUV much more effective for "mapping" than a vessel on the surface. Two key parameters of any sonar are the resolution and the range. This is oversimplified, but a typical hydrographic sonar will have around 0.5 to 1.0 degree resolution. By the time a 1 degree beam reaches the bottom (from a surface vessel), it will have spread out to almost 80 m, meaning it will only detect very large strong targets and even then, there will be very little detail. Not good if you're trying to locate a debris field with unknown target size. Also, for a sonar to have 4500 m range, it must be very high power and very low frequency. The lower the frequency, the lower the resolution. That's why it's impractical to survey the area from the surface and conversely why an AUV works so well. Unfortunately, an AUV can cover only a relatively small area, but at least if there are reasonable sized targets, it's more likely that they will be more visible than they would be from the surface. Of course, all of that depends on the conditions of the bottom. If the bottom is very soft and the debris sinks into it, the debris will be difficult to detect. If the bottom is very rocky, it will be difficult to distinguish debris from rocks. There isn't much difference between the return from different types of metals. They tend to be good acoustic reflectors, which makes aircraft wreckage relatively easy to detect.