All of
us have experienced that a train's whistle changes note or the pitch
as it approaches near to us and then again when it speeds away from
us. Way back, a physicist form Salzburg, Austria; Christian Doppler (
1803-1853), was the first person to give physical explanation for
this commonly observed phenomenon. At the age of 38, Doppler gave a
lecture to the Royal Bohemian Society of Sciences titled as, "Über
das farbige Licht der Doppelsterne und einiger anderer Gestirne des
Himmels" (On the
coloured light of the binary stars and some other stars of the
heavens), In this work, Doppler explained his idea that the observed
frequency of a wave depends on the relative speed of the source and
the observer, and he tried to use this concept for explaining the
colour of binary stars. Lateron, Doppler's idea became known as
Doppler Shift or Doppler effect. His hypothesis was tested for sound
waves by Buys Ballot in 1845. He confirmed that the sound's pitch was
higher than the emitted frequency when the sound source approached
him, and lower than the emitted frequency when the sound source
receded from him. Within 3 years or in 1848, Hippolyte Fizeau
discovered independently, the same phenomenon on electromagnetic
waves. This meant that the Doppler shift held good for all kinds of
waves.
Christian Doppler (
1803-1853)
The
applications, where Doppler shift has been put to use, are spread
over a large range from simple day-to day uses like a Siren Alarm or
most complex physical measurement like measuring temperature of a
gas. Here are some more applications of this principle.
- Astronomy
- Radar
- Medical imaging and blood flow measurement
- Flow measurement
- Satellite communications
- Vibration measurement
Joining
this long list of applications of Doppler shift, is a totally new
method by which a Satellite company has tracked the last few hours of
the flight path of Malaysian Airlines, ill fated flight to Beijing,
MH 370.
Inmarsat
plc is a British satellite telecommunications company, that offers
global and mobile services. It provides telephone and data services
to users worldwide, via portable or mobile terminals which
communicate to ground stations through eleven geostationary
telecommunications satellites. Inmarsat's network provides
communications services to a range of governments, aid agencies,
media outlets and businesses with a need to communicate in remote
regions or where there is no reliable terrestrial network.
The
most formidable obstacle in tracking down flight MH370, after it went
off the radar screens at 01.30 AM on 8th
March, 2014 and when
it was flying over Gulf of Thailand, was that the the main aircraft
communications addressing and reporting system (which would usually
transmit the plane's position) got switched off mysteriously. However
whosoever or whatsoever switched off the communication systems on
board, 9 minutes earlier or at 0.1.21 AM, perhaps was not well aware
that there still was a communication terminal on board that gave a
series of automated hourly 'pings' from the plane.
About
45 minutes later or at 2.15 AM, Malaysia's military radar detected
flight MH370 in the Andaman Sea north of Indonesian island of
Sumatra, though at that time it was not aware that the dot on the
Radar screens was actually the missing MH 370. After this Radar
appearance, no further trace of the aircraft was seen anywhere again
on any Radar. Yet, one of Inmarsat’s satellites continued to pick
up a series of automated hourly 'pings' coming from a terminal on the
plane.
In a
path breaking endeavour, Inmarstat's engineers were able to establish
that MH370 continued to fly for at least five hours after the
aircraft left Malaysian airspace by analysing the pings coming from
the aircraft that were picked up by the satellite. They also
predicted that it had flown along one of two 'corridors' – one
arcing north and the other south. The plane was reportedly flying at
a cruising height above 30,000 feet.
How
did they do it? It is here, where the universally useful Doppler
shift, comes into picture. Since the satellite moved in a known fixed
orbit, the engineers were able to predict the position of the
aircraft from the change in frequency observed due to the movement of
the satellite in its orbit. Senior vice president of external affairs
at Inmarsat, Chris McLaughlin, says: "We looked at the Doppler
effect, which is the change in frequency due to the movement of a
satellite in its orbit. What that then gave us was a predicted path
for the northerly route and a predicted path the southerly route.
That’s never been done before; our engineers came up with it as a
unique contribution."
Not
satisfied with this, Inmarsat's engineers carried out further
analysis of the pings and created much more detailed Doppler effect
models for both the northern and southern paths. After this, they
compared the data received from MH 370 with other aircraft on similar
routes and were able to establish a match between MH 370's predicted
path and the readings from other planes on that route. Finally on
24th
March 2014, Inmersat engineers confirmed that MH 370 had indeed taken
a southerly route.
Inmarsat's
predictions however can not tell us, where the aircraft actually went
down because of one serious limitation. No one knows at what speed,
the aircraft was flying. This means that many questions such as
whether aircraft fuel finally ran out? or whether it was in flames
at that time? or whether planed plunged or glided? Will remain
unanswered.
The
search for the missing plane has to shift now to the southern Indian
ocean, where weather conditions remain a big challenge. We do not as
yet know for certain, whether research carried out by Inmarsat
engineers is truly on right track till we find some debris floating
on water. Finding out the black box from the aircraft would be the
top most priority then, because that is the only thing, which can
tell us what really happened in the final hours of MH 370, before it
went down.
In any
case it is impossible to console the relatives and kin of 247
unfortunate individuals, who were on board. Still, finding the black
box, may give some kind of closure to their minds and it might help
in solving some of the mysteries of MH 370 so that effective steps
can be taken up in future, to avoid or minimise such tragedies.
26th
March 2014
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