Story highlights Thursday's search area is scaled back to cover about 22,400 square miles

Four signals total are detected in the same general area

Previous signals are "consistent" with that of a flight data recorder

The signals are getting weaker

In a sea of uncertainty, two bits of good news emerged Wednesday.

Searchers picked up fresh signals that officials hope came from locator beacons attached to the so-called black boxes in the tail of Malaysia Airlines Flight 370, which disappeared more than a month ago while carrying 239 people from Kuala Lumpur to Beijing.

The Australian ship Ocean Shield first picked up two sets of underwater pulses Saturday. It heard nothing more until Tuesday, when it reacquired the signals twice. The four signals were within 17 miles of one another.

"I believe we are searching in the right area, but we need to visually identify wreckage before we can confirm with certainty that this is the final resting place of MH370," said retired Air Chief Marshal Angus Houston, who's coordinating the Australian operation.

The second piece of good news? Authorities analyzed the signals picked up over the weekend and concluded that they probably came from specific electronic equipment rather than from marine life, which can make similar sounds.

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Photos: The search for MH370 Photos: The search for MH370 Two years after Malaysia Airlines Flight 370 went missing, a relative of one of the passengers burns incense in Beijing on March 8, 2016. Flight 370 vanished on March 8, 2014, as it flew from Kuala Lumpur, Malaysia, to Beijing. There were 239 people on board. Hide Caption 1 of 43 Photos: The search for MH370 On July 29, police carry a piece of debris on Reunion Island, a French territory in the Indian Ocean. A week later, authorities confirmed that the debris was from the missing flight. Hide Caption 2 of 43 Photos: The search for MH370 Staff members with the Australian Transport Safety Bureau examine a piece of aircraft debris at their laboratory in Canberra, Australia, on July 20. The flap was found in June by residents on Pemba Island off the coast of Tanzania, and officials had said it was highly likely to have come from Flight 370. Experts at the Australian Transport Safety Bureau, which is heading up the search for the plane, confirmed that the part was indeed from the missing aircraft. Hide Caption 3 of 43 Photos: The search for MH370 In late February, American tourist Blaine Gibson found a piece of plane debris off Mozambique, a discovery that renewed hope of solving the mystery of the missing flight. The piece measured 35 inches by 22 inches. A U.S. official said it was likely the wreckage came from a Boeing 777, which MH370 was. Hide Caption 4 of 43 Photos: The search for MH370 Relatives of the flight's passengers console each other outside the Malaysia Airlines office in Subang, Malaysia, on February 12, 2015. Protesters had demanded that the airline withdraw the statement that all 239 people aboard the plane were dead. Hide Caption 5 of 43 Photos: The search for MH370 A police officer watches a couple cry outside the airline's office building in Beijing after officials refused to meet with them on June 11, 2014. The couple's son was on the plane. Hide Caption 6 of 43 Photos: The search for MH370 Members of the media scramble to speak with Azharuddin Abdul Rahman, director general of Malaysia's Civil Aviation Department, at a hotel in Kuala Lumpur, Malaysia, on May 27, 2014. Data from communications between satellites and the missing flight was released the day before, more than two months after relatives of passengers said they requested it be made public. Hide Caption 7 of 43 Photos: The search for MH370 Operators aboard the Australian ship Ocean Shield move Bluefin-21, the U.S. Navy's autonomous underwater vehicle, into position to search for the jet on April 14, 2014. Hide Caption 8 of 43 Photos: The search for MH370 A member of the Royal New Zealand Air Force looks out of a window while searching for debris off the coast of western Australia on April 13, 2014. Hide Caption 9 of 43 Photos: The search for MH370 The HMS Echo, a vessel with the British Roya; Navy, moves through the waters of the southern Indian Ocean on April 12, 2014. Hide Caption 10 of 43 Photos: The search for MH370 A Royal Australian Air Force AP-3C Orion, on a mission to drop sonar buoys to assist in the search, flies past the Australian vessel Ocean Shield on April 9, 2014. Hide Caption 11 of 43 Photos: The search for MH370 A relative of a missing passenger cries at a vigil in Beijing on April 8, 2014. Hide Caption 12 of 43 Photos: The search for MH370 Australian Defense Force divers scan the water for debris in the southern Indian Ocean on April 7, 2014. Hide Caption 13 of 43 Photos: The search for MH370 A towed pinger locator is readied to be deployed off the deck of the Australian vessel Ocean Shield on April 7, 2014. Hide Caption 14 of 43 Photos: The search for MH370 A member of the Royal New Zealand Air Force looks at a flare in the Indian Ocean during search operations on April 4, 2014. Hide Caption 15 of 43 Photos: The search for MH370 On March 30, 2014, a woman in Kuala Lumpur prepares for an event in honor of those aboard Flight 370. Hide Caption 16 of 43 Photos: The search for MH370 The sole representative for the families of Flight 370 passengers leaves a conference at a Beijing hotel on March 28, 2014, after other relatives left en masse to protest the Malaysian government's response to their questions. Hide Caption 17 of 43 Photos: The search for MH370 A member of the Royal Australian Air Force is silhouetted against the southern Indian Ocean during the search for the missing jet on March 27, 2014. Hide Caption 18 of 43 Photos: The search for MH370 Flight Lt. Jayson Nichols looks at a map aboard a Royal Australian Air Force aircraft during a search on March 27, 2014. Hide Caption 19 of 43 Photos: The search for MH370 People in Kuala Lumpur light candles during a ceremony held for the missing flight's passengers on March 27, 2014. Hide Caption 20 of 43 Photos: The search for MH370 Malaysian Prime Minister Najib Razak, center, delivers a statement about the flight on March 24, 2014. Razak's announcement came after the airline sent a text message to relatives saying it "deeply regrets that we have to assume beyond any reasonable doubt that MH 370 has been lost and that none of those onboard survived." Hide Caption 21 of 43 Photos: The search for MH370 Grieving relatives of missing passengers leave a hotel in Beijing on March 24, 2014. Hide Caption 22 of 43 Photos: The search for MH370 A passenger views a weather map in the departures terminal of Kuala Lumpur International Airport on March 22, 2014. Hide Caption 23 of 43 Photos: The search for MH370 A Chinese satellite captured this image, released on March 22, 2014, of a floating object in the Indian Ocean, according to China's State Administration of Science. It was a possible lead in the search for the missing plane. Surveillance planes were looking for two objects spotted by satellite imagery in remote, treacherous waters more than 1,400 miles from the west coast of Australia. Hide Caption 24 of 43 Photos: The search for MH370 Satellite imagery provided by the Australian Maritime Safety Authority on March 20, 2014, showed debris in the southern Indian Ocean that could have been from Flight 370. The announcement by Australian officials raised hopes of a breakthrough in the frustrating search. Hide Caption 25 of 43 Photos: The search for MH370 Another satellite shot provided by the Australian Maritime Safety Authority shows possible debris from the flight. Hide Caption 26 of 43 Photos: The search for MH370 A distraught relative of a missing passenger breaks down while talking to reporters at Kuala Lumpur International Airport on March 19, 2014. Hide Caption 27 of 43 Photos: The search for MH370 On March 18, 2014, a relative of a missing passenger tells reporters in Beijing about a hunger strike to protest authorities' handling of information about the missing jet. Hide Caption 28 of 43 Photos: The search for MH370 U.S. Navy crew members assist in search-and-rescue operations in the Indian Ocean on March 16, 2014. Hide Caption 29 of 43 Photos: The search for MH370 Members of the Chinese navy continue search operations on March 13, 2014. After starting in the sea between Malaysia and Vietnam, the plane's last confirmed location, search efforts expanded west into the Indian Ocean. Hide Caption 30 of 43 Photos: The search for MH370 A Vietnamese military official looks out an aircraft window during search operations March 13, 2014. Hide Caption 31 of 43 Photos: The search for MH370 Malaysian air force members look for debris near Kuala Lumpur on March 13, 2014. Hide Caption 32 of 43 Photos: The search for MH370 Relatives of missing passengers wait for the latest news at a hotel in Beijing on March 12, 2014. Hide Caption 33 of 43 Photos: The search for MH370 A member of the Vietnamese air force checks a map while searching for the missing plane on March 11, 2014. Hide Caption 34 of 43 Photos: The search for MH370 A Vietnamese air force plane found traces of oil that authorities had suspected to be from the missing Malaysia Airlines plane, the Vietnamese government online newspaper reported on March 8, 2014. However, a sample from the slick showed it was bunker oil, typically used to power large cargo ships, Malaysia's state news agency, Bernama, reported on March 10, 2014. Hide Caption 35 of 43 Photos: The search for MH370 A U.S. Navy Seahawk helicopter lands aboard the USS Pinckney to change crews on March 9, 2014, before returning to search for the missing plane in the Gulf of Thailand. Hide Caption 36 of 43 Photos: The search for MH370 Buddhist monks at Kuala Lumpur International Airport offer a special prayer for the missing passengers on March 9, 2014. Hide Caption 37 of 43 Photos: The search for MH370 Members of a Chinese emergency response team board a rescue vessel at the port of Sanya in China's Hainan province on March 9, 2014. Hide Caption 38 of 43 Photos: The search for MH370 The rescue vessel sets out from Sanya in the South China Sea on March 9, 2014. Hide Caption 39 of 43 Photos: The search for MH370 Malaysian Prime Minister Najib Razak, center, arrives to meet family members of missing passengers at the reception center at Kuala Lumpur International Airport on March 8, 2014. Hide Caption 40 of 43 Photos: The search for MH370 A relative of two missing passengers reacts at their home in Kuala Lumpur on March 8, 2014. Hide Caption 41 of 43 Photos: The search for MH370 Chinese police at the Beijing airport stand beside the arrival board showing delayed Flight 370 in red on March 8, 2014. Hide Caption 42 of 43 Photos: The search for MH370 Malaysia Airlines Group CEO Ahmad Juahari Yahya, front, speaks during a news conference at a hotel in Sepang on March 8, 2014. "We deeply regret that we have lost all contacts" with the jet, he said. Hide Caption 43 of 43

"They believe the signals to be consistent with the specification and description of a flight data recorder," Houston said. "I'm now optimistic that we will find the aircraft or what's left of the aircraft in the not too distant future."

Signals getting weaker

Thursday is Day 34 in the search for Flight 370, which went missing March 8. Authorities are pinning their hopes of finding it on the pings.

Time is of the essence: The batteries powering the flight recorders' locator beacons are certified to emit high-pitched signals for 30 days after they get wet.

"The signals are getting weaker," Houston said, "which means we're either moving away from the search area or the pinger batteries are dying."

• The first signal, at 4:45 p.m. Perth time on Saturday, lasted two hours and 20 minutes, he said;

• the second, at 9:27 p.m. Saturday, lasted 13 minutes;

• the third signal was picked up Tuesday at 4:27 p.m. and lasted five minutes and 32 seconds;

• the fourth, at 10:17 p.m. Tuesday, was seven minutes long.

"It's certainly encouraging that more signals have been detected," Pentagon spokesman Adm. John Kirby told CNN. "There is still much work to do, however."

Scouring the ocean for debris

Though plenty of debris has been found, none of it has been linked to the plane, and so the search goes on.

Thursday's effort is set to include up to 10 military planes, four civil aircraft and 13 ships.

Three of them -- the Ocean Shield to the north, and the British HMS Echo and Chinese Haixun 01 to the south -- were focusing underwater.

All told, everyone involved will be scouring a 22,400-square-mile (58,000-square-kilometer) zone centered about 1,400 miles northwest of Perth.

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That's roughly the size of West Virginia.

But Thursday's search area is about three quarters of the size of the area teams combed the day before and far smaller than what it was a few weeks ago.

"I think we have got a much clearer picture around the areas that we need to concentrate on," Kevin McEvoy, a New Zealand air force commodore involved in the effort, told CNN's Erin Burnett from Auckland.

Authorities reduced that area after analyzing satellite data and concluding that Flight 370 set off from Kuala Lumpur, Malaysia, toward Beijing, turned back over the Malay Peninsula, then ended up in the southern Indian Ocean.

Why? The answer may reside in the information stored inside the cockpit voice recorder and the flight data recorder.

The ocean to contend with

Hopes were initially raised when a Chinese ship detected pulses last Friday and Saturday that may have been from the plane.

According to McEvoy, "the main focus" now centers on the site of Ocean Shield's discovery. The ship used more advanced detection gear than that aboard the Chinese vessel, whose find was about 375 miles away, leading Houston to believe they are separate signals.

Beyond the dwindling battery life, the ocean also presents challenges: The Ocean Shield signals were in water about 2.6 miles deep, meaning any number of things could literally impede or otherwise disrupt the pulses.

To limit further roiling of the waters, officials are limiting sea traffic in the area. That's one reason that there's no rush to put drones in the water to take photos.

Another reason: Drones are painfully slow. The Ocean Shield towing a pinger locator can search six times the area than can a drone equipped with sonar, Houston said.

"The better the Ocean Shield can define the area, the easier it will be for the autonomous underwater vehicle to subsequently search for aircraft wreckage," he said.

A painstaking process

The more pulses investigators detect, the more they will be able to zero in on the locator beacons, which emit signals for 5 miles in all directions, said Mary Schiavo, a former inspector general for the U.S. Department of Transportation.

Once they lose the signals, authorities will start the painstaking process of using side-scanning sonar to search the ocean floor.

Somewhat 'befuddling'

The absence of wreckage near the detected signals leaves some skeptical, worried that the Chinese and Australian ships' finds could mean more false leads in an investigation that's been full of them.

Acknowledging "a very high-speed vertical impact" could explain the lack of aircraft debris, CNN aviation analyst Miles O'Brien said. He said there's reason to be cautious.

"It's either the most extraordinary event, or those pings weren't real," he said. "It's somewhat befuddling."

In Beijing on a 10-day trip to the Asia-Pacific region, U.S. Defense Secretary Chuck Hagel appeared to be hopeful but restrained. "There has been some new evidence here that maybe these new and emerging sounds may lead to something, but it's important we don't lift anyone's hopes -- the families of these passengers -- in an unfair way," he told CNN's Jim Sciutto in an exclusive interview.

Sarah Bajc, the partner of American passenger Philip Wood, told Burnett that she isn't sure about anything.

"All of us pretty well agree that, until there's the bulk of the plane, the bulk of the bodies discovered, and a black box intact, we won't believe that it's final evidence," Bajc said Wednesday from Beijing. "I don't think the authorities have given us much confidence of their investigative skills so far."

The lack of clarity makes it hard to "grieve properly and ... move on," she said.

"I want to fight to find him, in whatever form that ends up being," said Bajc, who is coordinating with other passengers' kin to press for answers. "And I think most of the families feel the same way."

Until he gets answers, Steve Wang, whose mother was on the plane, is clinging to hope while trying to hold himself together. "We're just going through so many kinds of emotion," he said of his position and those of other relatives of passengers. "Desperate, sad and helpless -- something like that. Everything."