Black-Box Search Tricky Without Ocean Map

Search teams have started to prepare for the possibility of scouring a remote patch of the southern Indian Ocean floor amid a flurry of recent sightings of potential debris from Malaysia Airlines Flight 370.

The trouble is, they would have little more than guesswork on which to rely.

On Monday, the U.S. military started to bring in specialist equipment to help locate the two black-box recorders, which contain digital flight data and recordings of cockpit conversation. Each box is designed to withstand crashes and intense undersea pressure.

But if the search operation has so far been tricky, the retrieval of the two black boxes brings its own set of challenges. The U.S. military would be working in an unmapped area of seabed, covered by anything from deep ravines to hilly terrain arising from muddy plains.

The digital flight information and two final hours of cockpit voice recordings the boxes contain are critical to shedding light on what happened to the Boeing 777-200, which disappeared on March 8 carrying 239 people en route to Beijing from Kuala Lumpur.

“This movement is simply a prudent effort to preposition equipment and trained personnel closer to the search area so that if debris is found we will be able to respond as quickly as possible, since the battery life of the black box’s pinger is limited,” said Commander Chris Budde, operations officer of the U.S. Seventh Fleet. The black-box batteries have 14 days left before expiring.

The latest sighting was announced by Australia’s prime minister, Tony Abbott, Monday night. Mr. Abbott said an Australian plane had spotted two objects that search teams were now looking to retrieve.

An earlier sighting by a Chinese aircraft that joined the Australian-led operation for the first time on Monday failed to turn up anything. China’s official Xinhua news agency had described the plane as having seen two large, white items with several smaller objects floating several kilometers away from them.

Multinational search teams have sprung to action several times after receiving a string of satellite images supplied separately by China, France and DigitalGlobe Inc., a company that works closely with the Pentagon’s geospatial agency.

The lack of survey data about the ocean floor in the search areas makes it near-impossible for the operators of remote-controlled and autonomous submersibles to know precisely the terrain they have to navigate.

Robin Beaman, a marine geologist at James Cook University in Queensland state, said the search area was hundreds of miles south of the South East Indian Ridge, a region mapped out almost two decades ago by U.S. survey teams. He said nobody had a clear idea of the geography of the ocean floor anywhere south of that zone.

Iain Parnum, a scientist at Curtin University in Western Australia, said a surprising amount of Australia’s remote southern territorial waters had never been surveyed. Ocean maps have largely been extrapolations based on sonar readings from vessels engaged in Antarctic research, and crude data from satellites capable of estimating seafloor depth.

Mr. Parnum said Australian researchers often joked that contemporary maps of the region seemed to rely on survey data from the voyages of Captain Matthew Flinders, who used heavy lead weights tied to long ropes to measure parts of the country’s southern waters in the 18th and 19th centuries.

U.S. involvement, while expected, demonstrates a pinch point for Australia’s ability to contribute to the resource-heavy search.

Ocean floor surveys require a deep-water ship equipped with multibeam sonar capacity to first establish the terrain. The only Australian government vessel capable of doing this was recently decommissioned and sold. A replacement, the RV Investigator, is still undergoing ocean trials.

Australia could hire private contractors to help do the job, but that is costly. Adam Hamilton, a business manager in Perth for Fugro NV, a Netherlands-based marine surveying company, said hiring commercial survey vessels used in the offshore oil-and-gas industry could cost between 75,000 Australian dollars (US$68,000) and A$160,000 a day.

Mapping the area to help search for wreckage is likely to take weeks or even months, which means using private companies could easily clock up a multimillion-dollar bill.

Government survey vessels from Malaysia or Singapore could be used, but they are frequently tied up with oil-and-gas activities and could take more than 10 days to reach the search area, Mr. Hamilton said.

Write to Daniel Stacey at daniel.stacey@wsj.com

Black-Box Search Tricky Without Ocean Map