How can an aircraft as long as six double decker buses simply vanish without a trace? In an age when thousands of satellites are constantly scanning the Earth’s surface with a borderline intrusive level of detail, this question has been puzzling the public. However, experts explain the eyes in the sky are not always omnipresent.
Almost three weeks after the final ‘All right, good night’ was heard from the cockpit of the ill-fated Boeing 777-200ER en route from Kuala Lumpur to Beijing, the world is still waiting to find out what actually happened during that seemingly calm night.
The first credible hints of the plane’s whereabouts came from the Australian search team more than a week after the aircraft’s disappearance, when Australia’s remote sensing satellites orbiting above the southern Indian Ocean captured images showing two large floating objects in the sea several thousands of kilometres from where the plane disappeared.
But why did it take so long when three days after the plane’s disappearance China, the home country of more than 150 passengers on board the aircraft, requested the activation of the International Charter on Space and Major Disasters? This cooperative framework binds member space agencies to task its satellites to obtain images of the search area and forward them to the investigators and search and rescue organisations free of charge.
“The problem is that, despite the fact there might be maybe dozens of satellites orbiting above the area where the aircraft travelled at some point of time, the satellites are not always active,” explains John Yates, chair of the IET Satellite Systems and Applications Network.
“These satellites have limited capacity to store images on-board between downloads, they are not operating continuously. Usually, they are tasked by ground controllers to acquire images of a particular area they will be passing over. That means it would have been by pure chance if there was a satellite capturing images of this particular area when the plane was still airborne before the international community was alerted that something went wrong with that flight,” he says.
It would seem even less probable considering the fact that the rough waters of the southern Indian Ocean are not of any great interest to the paying customers who guide the satellite operator’s decisions to switch on the imaging instruments in the first place.
However, since the desperate search for flight MH370 began in earnest, the attention of the international satellite operating community has focused fully on solving the mystery. Five sets of images have already been found showing suspicious fragments floating in the waters of the southern Indian Ocean with the last set, acquired by a Thai satellite Thaichote on March 24, capturing a field of debris consisting of about 300 objects.
However, as with the ground-based search teams, the view of the eyes in space could be obscured, at least partially, when weather gets rough.
Seeing through clouds
Although modern remote-sensing satellites can provide photographs with resolution so high that it enables objects as small as 50cm to be identified, these optical instruments become powerless once the surface is hidden under thick cloud cover.
“Many satellites are equipped with the synthetic aperture radar (SAR) that can penetrate cloud cover,” says Yates. “However, SAR doesn’t provide such detailed information as the optical instruments. It may be able to pick up especially larger objects and distinguish their size but to get to any sort of detail, like colour, you would have to have optical images.”
“If there was a SAR equipped satellite orbiting above the area when the plane was still airborne, it would have been able to distinguish the plane but it has more difficulty spotting debris.”
On the other hand, unlike optical instruments, SAR can capture images regardless of whether it’s day or night. That makes the life of satellite operators a bit easier. Satellites follow pre-defined orbits and don’t pass over the same place with every orbit or even during the same time of the day. As the amount of fuel aboard these spacecraft is rather limited, the operators have little chance to adjust the orbit and make the satellite go and look at a particular area. Thus being able to acquire images with every pass, day or night, sun or rain, is a real advantage.
“Satellite operators hardly ever change satellites’ orbits,” says Yates. “It is possible but requires significant amounts of fuel. It would shorten the lifetime of the satellites considerably; it could cut down perhaps 25 per cent of the satellite’s planned life time."
Find the right haystack
Among the satellite companies employing its spacecraft in the massive search operation that involves about 25 countries is the UK-based operator DMCii, a subsidiary of satellite manufacturer SSTL.
Managing a fleet of five remote-sensing satellites comprising the Disaster Monitoring Constellations, DMCii has tasked two of its spacecraft – the UK DMC2 and the NigeriaSat-2 to assist the increasingly desperate search.
While the low resolution UK-DMC2 can cover rather large areas within one pass, NigeriaSat-2 with the resolution of up to two metres could provide very detailed information.
The satellite search, though, is a tedious process that involves not only waiting for the right pass but also elaborate analyses of vast amounts of data. Images from the wide-area low-resolution UK-DMC2 can be pre-screened using computer algorithms to identify anomalies. The high-res NigeriaSat-2 could then be programmed to have a closer look at any area of interest.
With the search zone under investigation spanning approximately 320,000 square kilometers, the haystack remains sizeable in tracking down the needle-sized remains of any aircraft.
“The most important development was when the UK telecommunication satellite operator Inmarsat managed to narrow down the search area using data from regular pings exchanged between its satellites and the aircraft,” Yates says. “At least now we know which the right haystack to look into is and where to direct the remote sensing satellites.”
Since then, advanced radar data analysis determined the aircraft could have been travelling faster than was previously thought, meaning it must have run out of fuel earlier. The search area was subsequently shifted nearer to the coast of Australia.
The hunt for the missing flight MH370 has been described as the most massive operation of its kind ever, by far exceeding the search for the wreckage of the Air France-operated Airbus 330 that crashed into the Atlantic on May 31 2009. In that case remnants of the wreckage were located within five days.
With all the available eyes in space now carefully watching, the hope remains the world will eventually learn what caused the MH370 mystery.
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