106 APRIL2020|COMPUTER SHOPPER|ISSUE386
IMAGING BEYONDTHE EARTH
Many of the same methods that are used forimaging our own
planet have also been used by NASA forcapturing spectacular
imagery of alien worlds that are just dots of light, if that, in the
night sky.
But while Earth imaging requires images to be transmitted from
just afew hundred or afew thousand kilometres away,
Mars, the planet that has been most studied by space
probes, is 57.6 million kilometres awayatits
closest. And even that is in our backyard.
Pluto, the most distant body to have
been visited by NASA’s spacecraft, was
about 4.7 billion kilometres from the
Earth when New Horizons visited it in
- At that distance,radio signals
travelling at the speed of light, which
carried the space probe’s impressive
images, took four-and-a-half hours
to reach the Earth.
What’s more,atthis distance,the radiosignal was so weak that
it could be transmitted at only 2Kbit/s, which is about 10,000 times
less than the data rateofthe UK’s average broadband connection.
This meant that it took about 15 months forall the data collected
during New Horizon’s encounter with Plutotobereturned to Earth.
Plutowas imaged during aflyby, as many other planets
have been –includingUranus and Neptune –plus
their various moons such as Io,Europa,
Ganymede,Calistoand Titan. However,other
bodies have been photographed using
orbiting satellites like those that image
the Earth, and here we can refertothe
Moon, Mercury,Venus, Mars, Jupiter
and Saturn.
Finally, on thesubjectofimaging technology,weneed to
return to the subject of multi-spectral imaging. The sensor in
most camerasrecords light in the threeprimary coloursof
red,greenand blue to allow afull-colourimage to be built up.
That might be allthat’s needed to createanimage the human
eyewillrecognise,but the Earthisilluminated by radiation in
many more wavelengths than those we cansee.What’s more,
by recording imagesusing these invisible forms of radiation,
characteristicsofthe Earth’s surface that are nototherwise
visible can be detected. These additional bands aregenerally
in thenear infrared, shortwaveinfrared, andthermal infrared
regions of thespectrum and allow,for example,imagestobe
captured throughsmoke or haze, formoisture or surface
temperatures to be recorded, the health of crops to be
appraised,and man-madematerials to be differentiated.
SATELLITE IMAGING IN PRACTICE
Thetechnologyinvolved in bringing us unprecedented images
of the Earth’s surface might be something of an eye-opener
and thephotosmay be stunning, butjustwhat benefits do
imagingsatellitesoffer? We might have introduced this
articlebyreference to the Ordnance Survey, but it’s pertinent
to askwhether it’s strictlytrue that satelliteimaging is aform
of mapping. KimPartington, CEO of satelliteand drone
imagery company Geocento, thinksso, butwithadifference.
“Satellite imageryis, in essence,mapping, but thisterm
does indeed apply very broadly,” he suggests.
So,while somenational mappingagencies rely on satellite
imagery,more generally it’s relatedtofeaturesthatare more
transientinnature and therefore never appear on paper maps.
“Itcan relatetoconditions on theoceansurface,shallow
waterdepth, surface changessuchasmovement, vegetation
health, air qualityand humanactivities. It is therefore
necessary to expand the conventional idea of a2Dmap to 3D,
less commonly mapped conditions –atmosphereand ocean
as well as land–and evolution in time,”Partington adds.
Dr JeffMasek, NASA’sLandsat9projectscientist,
elaboratedonthis themebyreferring to applicationsof
NASA’s 47-year-old Landsatprogramme of eight missions,
andparticularly howit’s used formonitoringchange.
“Ingeneral, mappingannual changes in land coverand
landuse is thebreadand butteractivity of Landsat, including
trackingthe extent of globalirrigated and rain-fed agriculture,
forestextentand type,and urban growth”, Maseksays.
Many of these applicationsrelatetothe environmental
issuesfacing us today. According to Masek, “Landsat
provides ourcore estimates forglobal forest dynamics,
includingannual rates of tropical deforestation. By tracking
movement of features on ice sheets,researchers have used it
to map ice stream velocities in Greenland and Antarctica, and
the datahas beenused to track the declineofmountain
glaciers duetoclimatewarming over the last fivedecades.
“Inaddition to scientificapplications, there are numerous
landmanagement applications. TheUSForest Service
monitors forest disturbance,including fire andinsect
outbreaks, and also usesdata productstomap wildfireburn
severityand track restorationefforts after fires.”
Impressive as the technology involved in bringing us
images of the Earthmay be,making use of these valuable
resourcesusuallyinvolves alot more than simply viewing the
LEFT:Io,one of themoons of Jupiter,isthe
most volcanic body in the Solar System, as this
image shot by the Galileo space probe reveals
ABOVE:From an
orbital altitude
of35,786km,
geostationary
satellites, like
this NOAA
satellitethat’s
used for weather
forecasting,
can image the
entire globe in a
single view
