BBC_Earth_UK_-_January_2017

Space

Climate satellite

In its short six years of life,

CryoSat has allowed scientists to

learn more about Arctic sea ice than

any previous satellite mission.

The satellite measures the sea

surface with such precision that it

can pick up on the effects of gravity

from the sea floor, and by doing this,

produce a map of the valleys and

ridges on the ocean bed.

In 2016 Cryosat recorded the

lowest growth of Arctic sea ice ever

for November, proving just how

warm the polar north is getting.

Temperatures as high as -5°C

were measured when -25°C would

traditionally be the norm.

Did you

know?

different regions, so you really don’t know what is happening

elsewhere unless you are measuring the whole of the ice. You

need a satellite for that,’ says Shepherd.

The satellite has also proved useful in other ways. In 2016

scientists from the Norwegian University of Life Sciences

used CryoSat to measure sea levels around rugged coastlines

• no mean feat given the wide-ranging topography there.
  The accuracy of the results allowed them to study the effects
  of sea-level rises on countries vulnerable to coastal erosion.
  Three years before, CryoSat was also used to measure the
  water levels of surges during a storm in northern Europe.
  ‘Oceanographers have used satellite altimeters like CryoSat
  for decades in the lower latitude orbits,’ says Shepherd. ‘But
  CryoSat is in a polar orbit that takes it much higher and closer
  to the poles than traditional ocean altimeter satellites and it

can measure the bits of the ocean that they miss. It also has

a weird orbit repeat pattern that densely samples the Earth’s

oceans that is different to the way traditional ocean altimeters

do, so it gives the oceanographers an additional degree of

information about how sea level is rising in localised areas,

particularly around coastlines of countries.’

The radar altimeter is so sensitive that it has been able

to profile lakes, rivers and tributaries and even map the

topography of the ocean floor, by picking up the tiniest of

valleys and ridges on the sea surface. Since the gravitational

pull in the ocean causes these to mirror the differing heights

of the seafloor, it has become useful for measuring the shape

of the Earth and allowed new maps to be created.

And yet, for all this, CryoSat was built to last just three

years. The original mission was an experiment to see whether

it was possible to measure sea and land ice with a degree

of certainty. Now having proven it can do this, it is living on

borrowed time and has no planned successor. Professor

Shepherd hopes that won’t be the case forever. ‘We may be

able to design and build a follow-on mission before CryoSat

runs out of steam and that would be the ideal situation.’

A thinner ice pack

is less resilient to

changes in climate

Sea ice reflects the sun’s

energy back into space,

so without it our planet

would get warmer

Words: David Crookes. Photographs: European Space Agency, NASA