What else is there to search for MH370 wreckage underwater?

The MH370 air search has officially ended and Australia's lead in the south Indian Ocean to search for the wreckage of the MH370 airliner has entered a new phase of underwater search. Of course, the stop of the aerial search does not mean that the search is stopped, but the focus of the search work into the water. Searchers will be ready in a matter of weeks to launch search-intensive, more detailed underwater searches. So what is the change in the new phase of underwater search? First, increase the breadth of underwater search it is learned that the new phase of underwater search is significantly higher than before, plans to search 60,000 square kilometers of the region. In the previous search, the Australian side delineated the underwater range is the April 8 found Sonar pulse signal as the center, radius of about 10 kilometers of the area, an area of about 300 square kilometers. According to the reports of the previous period, we all know that the black box sonar signal effective distance is only a few kilometers, why to expand to such a large area? When the sonar signal from the black box passes through the deep water channel layer, it can produce refraction phenomenon, so that the signal spreads very far. This is because there is a special layer of seawater beneath the surface of the ocean, where sound waves travel the slowest. When sound waves pass through the water layer, refraction will occur, and even some sound waves will be imprisoned, spread thousands of of kilometers along its attenuation is very little, this layer of seawater is called the Deep Sea Channel, was discovered during World War II by scientists, it is usually located in the ocean below the depth of about 1-kilometer. When the sonar signal from the black box passes through the seawater, the refraction is shown, even farther along the deep channel. If you hear the sonar signal is precisely because of this effect only to receive, then means that the black box real location distance signal received from the place is still very far! therefore, the previously searched area is likely to be too small to further expand the search distance is very necessary. Second, to increase the depth of underwater search Remus-6000 submersible can dive 6000 meters deep, much more than the Blue fin-21 depth limit. According to reports, the search team is already preparing to dive deeper than the blue Fin-21 new submersible: Two Remus-6000 submersible may be flown to Perth, Australia. Compared with the Blue Fin-21, the dive depth and actual combat experience of Remus-6000 autonomous underwater vehicle are more noticeable. The Remus-6000 autonomous unmanned submersible is allowed to perform tasks under 6000 m-depth under submerged depths, endurance and payload (in contrast, the Blue fin-21 maximum dive depth is only 4500 meters). The submersible is a modular structure capable of installing various sensors, and has been used for hydrographic surveys, port security missions, scientific sampling and mapping, as well as basic research and applied research, funded by the U.S. Naval Research Office, the U.S. Department of Defense Advanced Research Program (DARPA) and the UK Department of Defense. In search of Air France Flight 447, which crashed into the Atlantic in 2009, experts at the Woods Hole Oceanographic Institute guided 3 Remus in the fourth round of searches, and opened probes at a depth of about 4000 metres,Eventually, in 2011, most of the wreckage of the flight was found. When using sonar to carry out systematic exploration of the seabed, it is very careful that all the information measured is part of the important evidence. Ideally, it would be best to use both Remus and bluefin tuna. It is reported that the future underwater long-term search may eventually rely on private companies. The question of the cost of continued salvage is likely to require consultation between Malaysia, the United States and China.