Finding the black box remains challenging

Up to 14 planes have continued to search the southern Indian Ocean for floating debris from the lost Malaysian Airlines jet. As the search moves underwater, the investigators are left with little choice but to send an unmanned submersible vehicle into the depths of the Indian ocean. Our correspondent Andy Saputra examines the science of this scan and the challenges they're facing 4.5 kilometers under the sea.  [Special coverage]

The bluefin 21 is the best hope for the investigators to finally locate MH 370. The autonomous underwater vehicle will scan the seabed using side sonar scan, essentially painting a rough picture of the ocean floor.

But at 4500 meters under the surface of the Indian ocean, it is a huge challenge Already, the first 2 missions of the bluefin 21 ended prematurely, one due to the unexpected terrain of the uncharted seabed of the Indian ocean and the other because of technical issues. The enormity of the task is described by Chris, who analyse sonar images as a profession.

"if you at a football field or even an area that's larger than that, much larger than that a paddock and it's completely dark and you have a spotlight where all you can do is walk around looking down with a spotlight to try and find your keys and you couldn't even get to image you were looking at until 12 hours later." Sonar Scan analyst Chris Sorgiovanni said.

That images, hours and hours of them, will then have to be analysed.

Just to give you an idea on how difficult the task the investigators are facing, this here is an image of a 1 cubic meter of concrete block and it is this small in a side sonar scan.

This scan result though is taken in a flat seabed while the Indian ocean floor will have underwater mountains and valleys that can block sonar scans from detecting the wreckage.

The challenges don't end there.. this is Rodney Thompson, he's been involved in locating and recovering underwater objects across Australia. And he describes on how precise the investigators will have to be when and if they find any signs of MH 370.

"We have situations where in 50 meters of water, it's still light, we know where something is within 1 meter and we sent down an ROV and it took us 4 hours to find it and that's a much simpler task." Thompson, said.

For now, the bluefin 21 will painstakingly map the uncharted seabed of the massive search area and the investigators and the families of the passengers are hoping that flight MH 370 is not forever lost in the bottom of the Indian ocean.