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The latest
satellite ship-tracker goes into orbit this weekend for Canada's ExactEarth
company.
The
monitoring of vessels at sea is a fast-developing space service.
It's a
market being driven presently by ExactEarth and its US competitor, Orbcomm.
Their
satellites listen in to the AIS (Automatic Identification System) signals
broadcast from vessels.
All ships
over 300 gross tons (and many passenger ships) are mandated to carry
transponders that push out data that includes not just position, course, and speed,
but also information about a ship's type, draught, cargo - even its captain.
AIS was
established in the first instance as a safety system - something maritime
agencies and ship operators themselves could use near shore to keep tabs on who
was doing what in local waters.
Its
limitation is that communication with coastal receiving stations is line of
sight, meaning it's not possible to track vessels once they've gone out into
the open ocean. Hence the enterprise of also putting receiving stations in orbit.
"It's
interesting. Before satellite AIS came along, you'd talk to people and they'd
just assume that ships were tracked wherever they went in the world. But the
reality was that there were 60,000 ships out there carrying nine trillion
dollars' worth of cargo, and when the captain went over the horizon, unless he
sent a signal, no-one knew where he went. That's all changed now," says
ExactEarth's John Allan.
The company
claims its exactView-1 satellite will be the most performant platform yet
launched.
The
spacecraft is British-built, assembled by Surrey Satellite Technology Limited
in Guildford. It AIS receiving equipment is also UK built - developed by the
European division of Com Dev (which part owns ExactEarth) at its Stoke
Mandeville base in Buckinghamshire.
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| It was apparent just from the AIS data that the Costa Allegra was in trouble |
Doing
ship-tracking from orbit is not straightforward. In some of the busiest
waterways, it can be very difficult to disentangle the signatures of the
individual vessels.
Rob
Goldsmith from Com Dev Europe explained: "One of the problems with AIS is
that it was designed as a terrestrial system - ship to ship, and ship to shore.
It's a VHF signal and it uses something called Self-Organized Time Division
Multiple Access, which means that within a communication frequency, each ship
will be allocated a slot and it will co-ordinate with all the others so there
is no interference.
"That's
fine over a 50-70-nautical-mile cell, but from space you see a lot of these
cells and they collide - you get a lot of noise. But we have a very clever
algorithm. Our satellites capture the signals and download them to the ground
where a big computer separates them."
ExactEarth
expects the next-generation receiver on the new satellite to finesse this
process even more.
There are
lots of applications for this type of data.
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| The exactView-1 spacecraft is the smaller of the three satellites mounted for launch on Sunday |
Safety at
sea is an obvious one. If a vessel gets into trouble, the maritime authorities
can see very quickly where that ship is and those that are closest to it and
might be able to offer assistance.
"In
the AIS data, you get course over ground information (the direction in which
it's moving) and heading (the direction the ship's pointing). These can tell
you a lot about what a ship is doing," says John Allan.
"You
may remember the Costa Allegra, which had a fire about two weeks after its
sister ship, the Costa Concordia, ran aground.
"The
fire knocked out the engine and the ship started drifting, and you could see
that in the AIS data. The ship went side on in the current, but its heading was
about 90 degrees different.
"Just
by looking at the AIS data, you could tell there was something wrong with the
vehicle.
"Now,
if you were a coastguard and you saw that behaviour in a supertanker, it would
certainly pique your interest."
AIS
information is being used to challenge owners whose ships take dangerous
shortcuts or fish in restricted zones.
It's also
being used in the effort to combat piracy, by enabling the authorities to
manage and monitor convoys of ships passing through high-risk waters. Nato is
using satellite AIS to monitor the situation off the Somali coast.
The killer
application in the future will be to put an AIS receiver on a radar satellite.
Radar sees
through cloud and can picture the sea surface day or night.
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| Plans are afoot to put AIS on radar satellites, which can see the ocean surface whatever the weather |
Not only
then would you have the identification data but you could tie this directly to
the imagery evidence.
This would
allow you to check the vessel was indeed the type of ship its AIS transmission
claimed it to be; or, in the opposite scenario, investigate why a big ship
picked up on radar was not broadcasting its status.
It has been
known, for example, for traffickers to turn off their AIS to try to hide their
activity.
The Spanish government's first radar satellite, Paz, due to launch next year will carry an
AIS receiver.
There is a
proposal also for the forthcoming British NovaSAR radar satellite to be fitted
with such equipment.
And the
European Space Agency recognises the benefits of joining the two technologies
and is talking about including AIS on one of its future Sentinel radar platforms.
You should
be able to watch Sunday's Soyuz rocket launch here. You can also read more
about the other satellites launching with exactView-1 here.
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