The Economist January 29th 2022 Technology Quarterly Defence technology 5again creating a battlespace in which movement becomes ex
tremely dangerous,” writes T.X. Hammes of America’s National
Defence University. “If a unit moves, it will create a signal and can
be attacked at much greater ranges than in the past.” In his book
“Eyes in the Sky”, Arthur Holland Michel quotes a defence official
describing being under widearea dronebased videosurveillance
as like “the scene in ‘Jurassic Park’ where Dr Alan Grant faces down
a T. Rex:‘Don’t move. He can’t see us if we don’t move.’”
The advantage of surprise, idiomatic since the days of Sun Tzu,
will become more difficult to achieve at scale. Coups like China’s
offensive over the Yalu river in the Korean war, or Egypt’s dazzling
strike on Israel in October 1973, will be all but impossible. Russia
has tried various tactics to confuse those observing its deploy
ments on Ukraine’s border, including removing unit markings,
shuttling convoys back and forth and shutting down trainspotting
websites. The brute fact of the buildup is impossible to hide.
Some go as far as to argue that military offensives may no lon
ger be possible against forces that have embraced all that technol
ogy now has to offer: to move will be to be seen will be to be shot.
Otherssuggestthatthechangesmaybelessmarkedthanworried
officersareimagining.StephenBiddleofColumbiaUniversity
pointsoutthatasearlyasthefirstworldwar,tacticianslearnthow
toavoidexposingtheirforcestomodernartilleryandairpower—
capabilitiesasremarkablethenasquicksensortoshooterkill
chainsaretoday.Thebasicsofconcealmentanddeceptioncan
andwillbeupdatedforthedigitalage.“TheArmeniansmadethe
mistakeofnothavingthoughthardenoughaboutthis,”saysMr
Biddle.“Nobodyelseisgoingtomakethatmistake.”n
All thetargets, all the time
T
he first time that humans observed a battlefield from a celes
tial vantage point was in June 1794, scarcely a decade after the
Montgolfier brothers had invented the hotair balloon. The French
Aerostatic Corps, a motley crew of chemists, carpenters and hang
ers on (sometimes literally), flew a tethered hydrogen balloon,
l’Entrepenant, over the battlefield at Fleurus, in what is now Belgi
um.The spotters on board informed their comrades down below
about the disposition and movements of their Austrian enemies
by semaphore. France won the battle.
The success was not in itself trendsetting. When France, Brit
ain and Prussia met 21 years later at Waterloo, 30km north of Fleu
rus, no one looked down but the birds: Napoleon had abolished
the Aerostatic Corps in 1799. Military ballooning did not really
come into its own until the American civil war, and its importance
was short lived. When war returned to the low countries in 1914 the
balloon was already beginning to give way to the aeroplane; by the
end of the war it had been completely eclipsed. By the time nato
moved its military headquarters to Mons, 40km west of Fleurus,
in the 1960s, satellites had entered the picture.
Yet even as the method of elevation changed, the means of
sensing did not. What struck the retinas of the French balloon
ists—visible light—was the same thing that struck the film of the
panoramic cameras aboard America’s first spy satellites. Film sen
sitive to the near infrared has sometimes been used to differen
tiate camouflage (which until recently tended not to reflect those
wavelengths) from foliage (which reflects them strongly). Satel
lites built to spot the launch of ballistic missiles do so by picking
out the longer infrared wavelengths associated with hot rocket ex
hausts. But most systems for looking down from orbit have relied
mostly on visible light.
This has two obvious problems when you are looking down
from orbit: night and cloud. Half the world is in darkness at any
given time. Most of it is sometimes cloudy and some of it is nearly
always cloudy. More than half of Europe is typically obscured at
any given time and in parts of South America cloudfree images
only appear every decade or so, according to Adam Maher of Ursa
Space, a startup based in Ithaca, New York, which uses satellite
pictures for business intelligence. Planet, a company which aims
to take onemetre resolution pictures of the entire land surface ev
ery day, says that about 70% of the surface is cloudy at any one
time. Soldiers, sneaky as they are, have been moving troops and
equipment under cover of inclement weather for decades.
In the past few years, though, an alternative to visible wave
lengths has been making enormous strides. The satellites from
which Ursa draws its images are built around radio antennae, not
lenses. These orbiting radars illuminate the surface using wave
lengths hundreds of thousands of times longer than those of vis
ible light. Such wavelengths pass easily through clouds, fog, smog
and, when necessary, camouflage netting before hitting the sur
face and bouncing back out into space.
The advantages long wavelengths offer in terms of penetration
come with compensating drawbacks. The resolution a sensor de
pends on the wavelength and on the size of its aperture—the mir
ror or lens in the case of a camera or a telescope, the antenna in a
radar. If you lengthen the wavelength, you increase the size of the
aperture you need in order to achieve a given resolution. To pro
duce detailed images with radar requires a very large aperture in
deed—far larger than anything a single spacecraft can offer.
Syntheticaperture radar (sar) provides a way round that pro
blem. Satellites move at quite a clip—typically, in low orbit,
around 25,000kph. By taking all the echoes a radar satellite gets
from a given target as it passes over it—and processing them into a
single image, sarproduces a result as precise as if it had been
made using a single aperture as wide across as the distance the sat
ellite travelled while gathering the data—tens of hundreds of kilo
metres (see diagram on next page).
This technology has been available since the 1960s, and used by
spy satellites since the 1980s. But it was limited, expensive and
highly classified. It was not until the late 2000s, when India and
Israel both had military sarsatellites of their own that America’s
National Reconnaissance Office, an arm of the Pentagon, declassi
fied the existence of its own such satellites, finally allowing its
employees to talk to Air Force officers about them. Civilian spaceAmong all the new ways of seeing available to generals,
one stands out
Synthetic-aperture radar