Without the signal of the aircraft's transmitter, finding the wreckage of missing Malaysia Airlines flight MH370 is a momentous task and a slow process, says maritime expert David Jardine-Smith.
DW: Objects have been spotted by various aircraft in the new search area, how difficult is it to ascertain what these objects are?
David Jardine-Smith: These things are spotted fairly regularly over a wide area - too wide an area. It's because there is so much rubbish out there in the ocean.
Unless the search aircraft can fly in low enough and slowly enough to get visual identification, like in this tragic case, an Air Malaysia logo on a piece of wreckage, then all we've got is bits, and pieces that could be from anywhere.
You have to get pretty close to the object to identify what it is, and the only way you can really do that is with a surface unit - a boat or a ship.
It would have to be fairly big pieces of garbage to confuse with plane wreckage, in this case?
Yes, a lot of shipping containers fall off ships in bad weather - plenty of those floating around. There is an awful lot of stuff out there.
I know it's difficult for laypeople to understand - but it is actually very difficult to identify things that are possibly wreckage but, frankly, more likely to be garbage that's been thrown overboard.
Most of the sightings so far have come from satellite images. Why is it so hard to identify objects seen on these images?
It takes a couple of days for the information to be collected by the satellite, downloaded to earth stations, routed through various processes, analyzed and then sent on to the search coordinators.
But is it really that hard to make out whether the image shows a whale, say, or a piece of wreckage, as it's presumably quite big?
I would have thought with the quality of imagery that they get that you could identify a whale. But what we're talking about here are things that, in a sense, cannot be identified readily - a square of white material - well that could be from almost anywhere.
What happens now that they have found objects that may belong to the plane in the new search area?
That area is that much closer to land and, therefore, search aircraft can stay on scene for longer. Obviously, you can only fly for a certain number of hours, but you want to spend as much time in the area as possible.
Ideally you get more aircraft in and try and get more information that way. There is one ship in this new area, last I heard, that ship will be moving to the location of the most recent sighted objects and, first of all, try to find them again, and then determine whether they are wreckage from MH370. Other ships are also being rerouted into the new area.
Aircraft can look for wreckage longer as it's thought to be closer to shore than previously estimated
How is this being organized internationally?
The world is divided into what we call search and rescue regions - an area of water for which a particular state takes responsibility for search and rescue actions. It has nothing to do with territorial waters, it's much bigger, generally speaking.
In this case, this whole area in the south-eastern corner of the Indian Ocean falls into the Australian search and rescue region and that is run by a rescue coordination center in Canberra, Australia, which is run by the Australian Maritime Safety Authority (AMSA).
Australia is leading this because of the likely positions based on Inmarsat's [a global satellite operator - eds.] initial analysis of the engine management data, plus the likely distance the aircraft might have flown, the speed it was last recognized as being flying by radar imagery.
But this is an international effort - the Malaysians, the Chinese, many other states are involved in the effort.
In 2011, so-called Abyss unmanned submarines helped locate the wreckage of Air France flight 447. Will they be able to help in this case again?
What you need to do first is find identifiable wreckage from MH370. The next stage is to find the black box, the data recorder which will be the primary source of evidence for finding out what has happened to MH370.
That box transmits a signal for about 30 days. If you can't get a receiving device in the water in the right general area, fairly close to that box, you're not going to pick up the signal.
The use of these deep-sea submarines will only come in once they've pinned down the right general area for the box. We're one or even two steps back from that.
These three units [there are only three Abyss submarines for civilian use in the world - the ed.] are for work in the abysses - the deep seas. And if the water is really deep, you need a submarine that goes deep - but it's only one option.
There has been a lot of criticism of the authorities in this search, many people, including passengers' relatives, have questioned why it is taking so long to find the wreckage. Is this an unusual case?
If we think of a normal emergency, if there is such a thing ... all the systems are based on the idea that someone in trouble will shout for help. That hasn't happened in this case. It's not surprising that they are having such difficulty when you don't have those systems operating. If we think back just a few days, a huge portion of the earth's surface was a potential search area, practically impossible to search.
But now they've narrowed that area down...
It's still very difficult when you haven't got anything pinging down there, sending off a beacon signal. In a big modern aircraft, these days, you'd expect the emergency locator transmitters would survive any crash. This is a very difficult case.
We have to remember - we know more about the surface of the moon than we know about the beds of our oceans. We're all so used to the idea that we, the human race, can do anything very quickly. I'm afraid that's really not true.
David Jardine-Smith is secretary of the International Maritime Rescue Federation (IMRF), based in Southampton, UK. The federation represents maritime search and rescue organizations worldwide. It is a registered charity that also aims to improve maritime search and rescue operations.