KUALA LUMPUR, April 9 — Thick siltation at the bottom of the Indian Ocean could keep the wreckage of flight MH370 well out of sight, Australian officials said today, as efforts intensify to narrow down the search area prior to deployment of a deep sea submersible to find the missing plane.

Retired Air Marshal Angus Houston, who helms the Joint Agency Coordination Centre (JACC) in charge of the search, said experts believe the siltation could be “tens of metres thick”, adding to the difficulty of the search that could reach over 4 kilometres deep.

“The silt will complicate that search... it is a very difficult environment. The more effort we put in location, the more certainty we will have to find something at the bottom,” he told a press conference broadcast live out of Perth, Australia by CNN.

Australian Navy commodore Peter Leavy explained that few details are known of the actual topography of the ocean floor in the current search area.

If true that there is significant siltation at the bottom of the search area, visual search efforts could be greatly impaired as the wreckage or any debris could easily end up sinking into the muck, he said.

The Australian navy chief added that siltation could diffuse any signal transmitted by a black box, making it weaker and more difficult to detect compared to a rockbed ocean floor which would reflect the transmission.

Leavy, however, noted that evidence of siltation at the floor of the southern Indian Ocean was based on research carried out at a location some 180 kilometres off the current search area.

“It has been said that we know more about the surface of the moon than we do about the bottom of the ocean, and in this case that rings true,” he said.

Houston said the siltation only emphasises the need for the Ocean Shield, from which a towed ping locater is deployed, to continue to scour the area where four transmissions believed to be from the black box were received from deep in the southern Indian Ocean.

“It looks like the signals we picked up recently are much weaker, so probably we are either a long way away from it, or more likely in my view, the batteries are fading and the signals are weaker.

“We need to make hay while the sun shines. We need to get all the data we can, and with all that data we can compress the search area where we will do the very difficult search with the underwater autonomous vehicle,” he said, referring to the Bluefin-21 submersible, which came along with the towed pinger locator.

Earlier at the press conference, Houston confirmed that Ocean Shield successfully reacquired two more electronic pulse signals from the Indian Ocean in their hunt for MH370, and said the latest breakthrough means they are “searching in the right area”.

Retired air marshal Angus Houston, who is leading the search Down Under, said the two signals were picked up by Australia's Ocean Shield hours apart yesterday with the first at 4.45pm, lasting all of five minutes and 32 seconds, and a second time at 10.17pm, lasting seven minutes.

“I believe we are searching in the right area but we need to visually identify aircraft wreckages before we can confirm with certainty that this is the final resting place of MH370,” he said.

Houston said data analysis of the previous two signal detections have returned “promising” results, showing the pulses were registered at a 33.331 kHz frequency, which is consistent with transmissions that would come from the aircraft's recorders.

They were “distinct and clear”, he added, and had consistently pulsed at a 1.106 second interval.

Expert analysis by Australia's Joint Acoustic Analysis Centre also showed that the transmission was not of natural original and was likely sourced from specific electronic equipment, Houston said.

“They believe this is consistent with the specifications of a flight data recorder,” he added.

MH370 went missing shortly after departing Kuala Lumpur International Airport for Beijing on March 8 and remains missing despite an international search involving over two dozen countries.

The Beijing-bound plane was ferrying 239 people on board.

Just a month in, it has already become the most expensive search operation in the history of the world, already eclipsing the US$50 million (RM162 million) spent on the nearly two years it took to locate Air France flight AF447 that crashed in 2009.