AF 447 Search to resume

[auv-ee]

dazdaz1:

The location of an oil drum was performed by the side-scan sonar. The use of any acoustic imaging, such as side-scan, requires a trade-off between resolution and range. At the frequency used for the long range search now in progress (600m either side of track), an oil drum would be an easy detection, but not necessarily an easy identification. The goal of the initial search is to find the debris field, which should be evident from numerous targets in the same vicinity. Certainly the crew are now familiar with the variability of the background in this area..

Once the general area of the debris is located, the AUVs have two other capabilities:

1. Higher frequency side-scan. I'm not sure of the exact frequencies in use, but it would be something like 150kHz for the low frequency, longer range, and 400kHz for the high frequency, shorter range, and higher resolution. This will allow better mapping of the debris field and possible identification of larger shapes.

2. Down-looking still image camera with strobe lighting. Flown at 5-20m off the bottom (depending on water clarity and how rough the terrain is at the site), many parts should be identifiable on camera, certainly anything as large as the recorders, or the section of fuselage to which they are perhaps still attached.

These AUVs do not intentionally touch the bottom and are incapable of manipulation or recovery of objects. They are the best available tool for wide area search and survey in deep water. 10,000 square km is a lot of area to search. Hopefully they won't have to search it all.

If the debris field is located, BEA is prepared to quickly begin Phase 5 of the search, with a different ship and crew. This phase will use a remotely operated vehicle (ROV). An ROV is tethered, hover capable, and equipped with manipulators and tools for any cutting and recovery. An ROV's tether (usually) delivers the high power required for maneuvering and manipulation; and it also provides the instant imaging, data and control required for interactive use. However, the tether restricts the speed of an ROV in deep water, making it a poor wide-area search tool.