Australian officials said Thursday that they are confident they are searching in the right area for the missing Malaysia Airlines jet after more signals were detected in a 17-mile area in the south Indian Ocean.

Angus Houston, the head of a joint agency coordinating the search, said that the Australian Navy's Ocean Shield had picked up two more underwater signals. However, the newly detected signals did not narrow the search area enough to dispatch a submersible vehicle to search for wreckage.

"I think that we're looking in the right area, but I'm not prepared to say, to confirm, anything until such time as somebody lays eyes on the wreckage," he said. "I'm now optimistic that we will find the aircraft, or what is left of the aircraft, in the not-too-distant future. We need to visually identify aircraft wreckage before we can confirm with certainty that this is the final resting place of MH370."

The signals detected 1,020 miles northwest of Perth are the strongest indication yet that the plane crashed and is now lying at the bottom of the ocean in the area where the search is now focused.

Finding the black boxes quickly is a matter of urgency because their locator beacons have a battery life of only about a month, and Tuesday marked exactly one month since the plane vanished on March 8 with 239 people on board.

If the beacons blink off before the black boxes' location can be determined, finding them in such deep water -- about 4,500 meters, or 15,000 feet -- would be an immensely difficult, if not impossible, task.

The Ocean Shield first detected the sounds late Saturday and early Sunday before losing them, and Houston said the ship relocated the signals twice on Tuesday.

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The ship is equipped with a U.S. Navy towed pinger locator that is designed to pick up signals from a plane's black boxes.

To assist the Ocean Shield, the Australian Navy on Wednesday began using parachutes to drop a series of buoys in a pattern near where the signals were last heard.

Royal Australian Navy Commodore Peter Leavy said each buoy will dangle an underwater listening device called a hydrophone about 1,000 feet below the surface. The hope, he said, is the buoys will help better pinpoint the location of the signals.

Houston acknowledged searchers were running out of time, and noted that the signals picked up on Tuesday were weaker and briefer than the ones heard over the weekend, suggesting that the batteries might be dying. The two signals detected on Saturday lasted 2 hours, 20 minutes and 13 minutes, respectively. The two sounds heard Tuesday lasted just 5 minutes, 30 seconds and 7 minutes.

"So we need to, as we say in Australia, `make hay while the sun shines,"' Houston said.

Picking up the sound again is crucial to narrowing the search area so a small, unmanned submarine can be deployed to create a sonar map of a potential debris field on the seafloor. The sub, dubbed Bluefin 21, takes six times longer to cover the same area as the pinger locator, which is pulled behind the boat at a depth of 3,000 meters.

U.S. Navy Capt. Mark Matthews said the detections indicate the device emitting the pings is somewhere within about a 12-mile radius. Still, he said, that equates to a 500-square-mile chunk of the ocean floor.

That amounts to trying to find a desktop computer in a city the size of Los Angeles, and would take the sub about six weeks to two months to canvass. So it makes more sense to continue using the towed pinger locator to zero in on a more precise location, Matthews said.

"It's certainly a man-made device emitting that signal," he said. "And I have no explanation for what other component could be there."

The disappearance of Malaysia Airlines Flight 370 on a trip from Kuala Lumpur to Beijing has sparked one of aviation's biggest mysteries. The search has shifted from waters off of Vietnam, to the Strait of Malacca and then to waters in the southern Indian Ocean as data from radar and satellites was further analyzed.

The weakening of the signals could indicate that the batteries were reaching the end of their life, or that the device was farther away, Matthews said. Temperature, water pressure or the saltiness of the sea could also be factors.

Houston said a decision had not yet been made on how long searchers would wait after the final sound was heard before the sub was deployed, saying only that time was "not far away."

"Hopefully in a matter of days, we will be able to find something on the bottom that might confirm that this is the last resting place of MH370," he said.

The Bluefin sub's sonar can scan only about 100 meters and it can "see" with lights and cameras only a few meters. The maximum depth it can dive is 4,500 meters, and some areas of the search zone are deeper.

Search crews are also contending with a thick layer of silt on the seafloor that can both hide any possible wreckage and distort the sounds emanating from the black boxes that may be resting there, said Leavy, who is helping to lead the search.

Despite the challenges still facing search crews, those involved in the hunt were buoyed by the Ocean Shield's findings.

"I'm an engineer, so I don't talk emotions too much," Matthews said. "But certainly when I received word that they had another detection, you feel elated. You're hopeful that you can locate the final resting place of the aircraft and bring closure to all the families involved."

The multinational search for the plane began shortly after it vanished with 239 people on board in the early hours of March 8 while en route from Kuala Lumpur, Malaysia, to Beijing. The search began off the coast of Vietnam, near where civilian air traffic controllers last had contact with the flight, before shifting to the coast of western Malaysia, before finally settling in the southern Indian Ocean, approximately 1,000 miles off the coast of Western Australia.

Malaysian authorities have previously said that satellite data appears to indicate that the plane did go down near the present search area, raising speculation as to what happened to drive the plane so far from its intended flight path.

The Associated Press contributed to this report.