A commercial vessel under contract from the Australian government has begun mapping the floor of the southern Indian Ocean in preparation for a renewed search for Malaysia Airlines’ missing Flight 370, but that search has been complicated by a complete lack of satellite images of the new search area from the week after the plane disappeared, the New York Times reports.

The Fugro Equator, a commercial survey ship on a three-month lease, is moving slowly around an area 500 miles southwest of the region where the ocean floor was searched in April and early May, according to commercially available data from a satellite locator beacon aboard the vessel. The new search area is 960 miles northwest of Perth, Australia.

Martin Dolan, the chief commissioner of the Australian Transport Safety Bureau, Wednesday, June 25, that “Fugro Equator has been assigned to an area consistent with the provisional results of our search area analysis.”

Tim Farrar, a satellite communications consultant in Menlo Park, Calif., one of a group of satellite experts who have been independently analyzing clues on Flight 370, expressed surprise that the search area had not been moved even farther southwest.

The plane disappeared on March 8 with 239 people aboard during a flight from Kuala Lumpur, Malaysia, to Beijing.

The new location is consistent with the plane having traveled south at a speed of about 380 knots after it disappeared from Malaysian radar while over the northern end of the Strait of Malacca, Farrar said. The area that was checked in April and May, after United States Navy contractors thought they had heard acoustic pings from the aircraft’s “black boxes,” was consistent with a plane limping along at 325 knots.

But Farrar said that the group of independent experts with whom he was working had assumed a speed of 460 to 470 knots. “We are unclear about why they are driving to a relatively slower solution,” he said.

Two possible explanations are that the authorities believe that the plane went farther west before turning south, or that the plane did not follow a straight path on its trip south, Farrar said. The international search effort and the group in which Farrar participates are relying on data from a series of electronic “handshakes” between the plane and a satellite over the Indian Ocean, operated by the company Inmarsat, to calculate arcs for the plane’s final location, according to the NYT.

Australia’s government has said that it will announce the new search area by the end of June. It is in the process of seeking a commercial operator to tow up to three deep-sea submersibles over the ocean floor for as long as a year, using sonar in the murky depths to scan for debris.

The Fugro Equator is mapping the seafloor first, with particular attention to finding any previously undetected mountains and hills at the bottom of the ocean that a deep-sea submersible might hit while being towed, which could wreck it.