These limits are shaped by physics, money and practicality. Military and commercial satellites are not closely observing and amassing data about the blank places on the map in lightly traveled seas - such as remote areas of the Indian Ocean thousands of miles from where Flight MH370 vanished from radar.
There’s also a trade-off when scrutinizing the surface from space: You can go wide or you can go deep, but you can’t do both. The most sophisticated spy satellites are essentially looking down straws, trying to resolve small details in a narrow field of view.
“Imagine driving down the street at 70 miles an hour with a pair of binoculars and trying to look at every single mailbox,” said Brian Weeden, technical adviser to the Secure World Foundation, a nonprofit organization devoted to space policy. “You can’t slew your binoculars around fast enough.”
The satellites may yet prove triumphant in this baffling case. There is tantalizing imagery of possible debris from the missing plane that has been made public by Australian officials, taken by WorldView-2, a high-resolution commercial satellite circling the planet at an altitude of 470 miles.
It’s unclear what’s in the images. The primary object, if it is an object and not some trick of light, was seen on March 16 - eight days after Flight MH370 disappeared - in the southern Indian Ocean about 1,500 miles west of Perth, Australia.
Nothing has been spotted by aircraft or satellites in that location in the days since, officials have said. If the mystery object is part of the plane, it means the Boeing 777 flew from the Equator almost halfway to the South Pole.
“It looks to me like possibly just an exceptionally large patch of sun glint,” said John Amos, president of SkyTruth, which uses satellite imagery to raise awareness of environmental issues. “We’re down in the subtle and ambiguous weeds of human image analysis, where we desperately are trying to find patterns in what we’re seeing.”
The company that owns WorldView-2, Colorado-based DigitalGlobe, said the lengthy period of analysis between the day the satellite obtained the image and when the Australians released it to the public is a reflection of the daunting nature of combing through so much data.
“Our constellation of five high-resolution imaging satellites captures more than 3 million square kilometers of earth imagery each day, and this volume of imagery is far too vast to search through in real time without an idea of where to look,” the company said in a statement.
DigitalGlobe has also used a subsidiary company, Tomnod, to crowdsource the search for the plane among volunteers around the world who have looked over the company’s imagery.
“The efforts of millions of online volunteers around the world allowed us to rule out broad swaths of ocean with some certainty,” DigitalGlobe said.
WorldView-2 was launched in 2009 on a polar orbit. As the satellite goes around the planet, pole to pole, every 100 minutes, the planet turns beneath it. Over the course of a day, the spacecraft will pass over most of the surface, including the southern Indian Ocean.
DigitalGlobe calls WorldView-2 “the first high-resolution 8-band multispectral commercial satellite.” The satellite can see something as small as 20 inches across.
A satellite has also proved crucial to understanding what might have happened to the plane after it vanished from radar.
About three hours after Flight MH370 went missing, Inmarsat, a British-based satellite company, began tracking the Boeing 777 through an on-board data system called Aero Classic. Every hour, Inmarsat’s satellites would try to communicate with the aircraft, pinging it with a computerized question asking, in effect, “Are you there?”
For several hours, Flight MH370 responded “Yes, I am,” notifying engineers on the ground with a so-called handshake that the plane was still powered up.
Using that series of pings, Inmarsat engineers and other analysts were able to piece together two broad, arcing regions where the plane could have been located when it last communicated with the satellite.
“Our engineers looked at the time between the handshakes, and they realized that the object wasn’t stationary under a satellite but moving away from it,” Christopher McLaughlin, senior vice president of Inmarsat, said Thursday. “Over time, the engineers here recognized that there were a number of data points and that it had flown for several hours. We didn’t know if it was on the northern or southern corridor.”
An official close to the investigation, who requested anonymity because of the sensitive nature of the case, said American and British intelligence services checked with the governments of India, Russia and China, as well as U.S. military officials at the Bagram Air Base in Afghanistan, to determine if any objects the size of a Boeing 777 had crossed into their airspace and if any jets had been scrambled to intercept an aircraft.
With no reports of an aircraft crossing into that airspace, investigators ruled out the northern route and turned their attention to the southern axis, pointing toward the Indian Ocean west of Australia.
Many nations have tasked their satellites to help in the search. NASA is contributing data from multiple scientific satellites as well as from a camera on the International Space Station. Patrick Ventrell, a National Security Council spokesman, said Thursday, “We have put every necessary resource that we have available at the disposal of the search process.”
There are satellites in geostationary orbits that can see huge swaths of the planet, but they’re 22,000 miles above the surface, and lack the resolution of the satellites in low Earth orbit.
“Weather satellites can see the whole world, but can’t see anything much smaller than a hurricane,” said Jonathan McDowell, an astronomer at the Harvard-Smithsonian Center for Astrophysics who also runs a website tracking all the satellites currently in orbit.
Confounding the search is that no one is sure what, exactly, to look for.
“It’s very hard to find something in the middle of the ocean,” Weeden said. “We don’t know the size and shape of the object we’re looking for and there’s lots of stuff in the ocean. There’s debris from shipping - containers and other stuff blown overboard. There’s natural stuff like trees and everything else.”
And there’s a lot of ocean out there.
“The Earth is big,” said Weeden. “The Earth is really big.”
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