Search should be in small radius - expert
Dr Jamie Pringle, who is a reader in forensic geosciences at Keele University, says the ocean floor is a lot more rugged than on land - and there are different stratified levels of water.
“A typical land search for a missing person or vehicle would move outwards radially from the last known position. This is how this search is also likely being conducted.
“Techniques vary, but in that water depth, a sonar search system would need to be specialised to a very narrow beam but high enough frequency in order to resolve a small submersible”.
Malaysian Airlines flight MH370, which was lost in 2014 over the South China Sea, had a very large search radius and what happened to it still remains a mystery, Dr Pringle adds.
“This search should be a much smaller search radius, as the submersible was reportedly on a relatively simple down and up dive.”
We don't know where the submersible is - expert
Robert Blasiak - an ocean researcher with the Stockholm Resilience Centre - outlined the tough conditions facing the search teams.
"The ocean on average is about four kilometres deep so this [submersible] is at great depth," Blasiak told the BBC.
He added that light only penetrates up to about one kilometre into the ocean's surface, so that's in 'pitch black and water pressures of about 400 atmospheres'.
Blasiak described the challenges for OceanGate's Titan submersible craft in reaching the wreck of the Titanic:
Quote Message: We know where the Titanic is, but we don't know where the submersible is. So it could be that it's nowhere near that depth and that's what we should all hope for at this time."
We know where the Titanic is, but we don't know where the submersible is. So it could be that it's nowhere near that depth and that's what we should all hope for at this time."
US Coast Guard confirms five on submarine missing for more than a day
The US Coast Guard has confirmed
there were five people onboard the submarine vessel, which it says has been missing since Sunday morning local time.
In a series of
Twitter posts, the Coast Guard described the submarine as being 21 feet (6.4m) in length.
It went missing
more than 24 hours ago, on Sunday morning, about one hour and 45 minutes into its dive.
Both US and Canadian naval surveillance aircraft
are currently searching for it, including a highly-sophisticated
P8 Poseidon aircraft with underwater detection capabilities.